CN105518958A - DC power grid current differential protection method and system thereof - Google Patents

Abstract

The invention discloses a DC power grid current differential protection method and a system thereof. The method comprises the steps of obtaining sampling values, obtaining pole voltage sampling values and pole current sampling values of a local terminal and a remote terminal of a DC line, extracting fault components, respectively calculating fault component pole voltage values according to the pole voltage sampling values of the local terminal and the remote terminal, respectively calculating the fault component pole current values according to the pole current sampling values of the local terminal and the remote terminal, conducting Bergeron model calculation, obtaining a fault component pole current value at a chosen point of the DC line between the local terminal and the remote terminal through the fault component pole voltage value and the fault component pole current value of the local terminal and the remote terminal calculated in a fault component extracting step in Bergeron model calculation, determining current differential protection; and if the fault component pole current value at the chosen point of the local terminal and the remote terminal and obtained in the Bergeron model calculation step satisfies a preset current differential protection criterion, the fault is determined to be internal. According to the invention, the Bergeron model is employed, distributed charging current interferences do not need to be eliminated through a long time delay so as to greatly the calculating speed of the method and the system of the invention.

Description

DC power network current differential protecting method and system thereof

Technical field

The application relates to DC power network current differential protecting method and system thereof.

Background technology

In existing HVDC system, the protection usually based on the row wavefront of local measurements is used as main protection, and classical current differential protection is used as stand-by protection.But their shortcoming is: main protection, and may malfunction in LCCDC electrical network to the poor sensitivity of high resistance failure; And stand-by protection has responsiveness slowly.

In existing two terminal HVDC systems, for the main protection of power transmission line mainly based on rate of change and the amplitude of direction row wavefront.This kind of protection has obvious advantage, is exactly that its only uses local measurements and has responsiveness quickly to metallic fault.

But this kind of protection shortcoming is that it is to the sensitivity of high resistance failure very low (poor).The fault resstance of usual >200Ohm may cause baulk, because the amplitude of wavefront depends on fault resstance to a great extent.Therefore, high resistance failure have to by its responsiveness slowly (such as >0.5s) standby current differential protection remove.This is obviously irrational.

In addition, this protection is based on the physical features of the smoothing reactor in HVDC system, and smoothing reactor can slow down curent change.In the DC network system (such as, the series connection MTDC system of some types) of some types, the row ripple that external fault causes can not flow through smoothing reactor, and the above-mentioned protection of the HVDC based on row ripple can not action or malfunction.In the worst case, have on the circuit of higher voltage level if outside DC fault occurs in, so its row wavefront even can be greater than the row wavefront caused by internal fault.This can bring burden to the existing protection of the HVDC based on row ripple.

Fig. 1 is the chart of the row wavefront of the inside and outside DC fault illustrated in LCCDC electrical network.

As shown in Figure 1, the rate of change from internal fault and the wavefront of external fault is definitely identical when starting.Meanwhile, the row wavefront of external fault is even much bigger than the row wavefront of internal fault, because the voltage levvl of outside line is higher.

In traditional traveling-wave protection device, as shown in Figure 2, three different measured values determine whether to have enough amplitudes in this ripple at the appointed time by starting.Ripple between first measured value calculates just in time before wavefront and just in time after 10 samplings (0.2ms) is poor.Ripple between second and the 3rd measured value calculate just in time before wavefront and just in time after (0.5ms and 0.7ms) is sampled in 25 times and 35 times is poor.If three measured values are all greater than threshold value, then line fault detected.

Wavefront in view of the external fault in Fig. 1 is even greater than the wavefront of internal fault, and outside has identical speed with the rate of change of internal fault, and therefore existing HVDC main protection will malfunction in LCCDC electrical network in this case.In other words, existing HVDC traveling-wave protection can not be directly used in LCCDC electrical network.

In existing HVDC system, the stand-by protection being generally used for power transmission line is Line Current Differential Protection.Classical current differential protection algorithm is used in this kind of protection.This kind of protection is (such as high resistance failure) action when main protection (traveling-wave protection) can not work.

The following shows the typical criterion of current differential protection,

|I _DL-I _{DL_FOS}|＞max(120A,0.1×|I _DL+I _{DL_FOS}|/2)

Wherein I _dLthe electric current of local side, I _{dL_FOS}it is the electric current of remote side.

The following shows another typical criterion of current differential protection,

||I _DL|-|I _{DL_FOS}||＞90A

Usually, if setting is appropriate, the sensitivity of current differential protection can be fairly good.But its responsiveness is too slow.Be generally its operate time hundreds of millisecond or even several seconds.Main cause is that failure transient and charging current will greatly affect this protection algorism.Therefore, long delay is necessary to guarantee reliability.

Main protection and stand-by protection all may be affected by high impedance fault.

1) on the impact of traveling-wave protection

Existing row ripple criterion is:

|W _COMM|＝|Z _COMI _COM-U _COM|＞350kV

|W _POLE|＝|Z _DIFI _DIF-U _DIF|＞210kV

Wherein, Z _cOMcommon mode wave impedance, Z _dIFdifferential mode wave impedance, W _pOLEpole ripple, W _cOMMit is earthwave.

I _cOMcommon mode current, U _cOMcommon-mode voltage, I _dIFdifferential-mode current, U _dIFit is differential mode voltage.

This protection uses the rate of change of earthwave to detect wave head.

|dW _COMM/dt|＞396kV/ms

When circuit is by large impedance access the earth, DC voltage declines with little rate of change, causes the misoperation of the existing protection based on row ripple.

If traveling-wave protection misoperation, control and protection system will postpone to eliminate fault.

2) on the impact of voltage changing rate and low-voltage variation

The criterion of voltage changing rate is:

D _uT=dU _dl/ dt <-396kV/ms & U _dl< 200kV, wherein U _dlline voltage distribution, D _uTit is corresponding rate of change.

When circuit is by large impedance access the earth, under little DC voltage, general who has surrendered causes voltage changing rate protection misoperation.

3) on the impact of current differential protection

The following shows the typical criterion of current differential protection:

|I _DL-I _{DL_FOS}|＞max(I _SET,k×|I _DL+I _{DL_FOS}|/2)

Wherein I _sETbe fixing current setting value, be usually set to 120A, k is the coefficient of ratio, is usually set to 0.1.

In order to ensure the action under the condition of large impedance fault, set point I _sETusually a little value is set to k.Therefore must set time of delay long enough to avoid the misoperation caused by capacitance charging current.

If protection (traveling-wave protection) misoperation fast, backup protection will postpone work.And time of delay is oversize and can not ensure the stable operation of electric power system.

Summary of the invention

Therefore, an aspect of of the present present invention provides a kind of DC power network current differential protecting method, comprises the following steps:

Sampled value obtains step: obtain the local terminal of DC circuit and the pole tension sampled value of remote terminal and electrode current sampled value;

Fault component extraction step: the pole tension sampled value according to local terminal and remote terminal calculates fault component pole tension value respectively; And calculate fault component electrode current value respectively according to the electrode current sampled value of local terminal and remote terminal;

Bei Jielong model calculation procedure: by calculating fault component pole tension value and the fault component electrode current value of local terminal and the remote terminal calculated in fault component extraction step based on Bei Jielong model, obtains the fault component electrode current value at the Chosen Point place on the DC circuit between local terminal and remote terminal;

Current differential protection determination step: if the fault component electrode current value at the Chosen Point place of the local terminal obtained in Bei Jielong model calculation procedure and remote terminal meets predetermined current differential protection criterion, then judge internal fault.

Preferably, DC electrical network is bipolar, and DC circuit comprises positive pole DC circuit and negative pole DC circuit, local terminal comprises positive pole local terminal and positive pole remote terminal, remote terminal comprises negative pole local terminal and negative pole remote terminal, positive pole DC line electricity connects positive pole local terminal and positive pole remote terminal, and negative pole DC line electricity connects negative pole local terminal and negative pole remote terminal, distance from Chosen Point to the Distance geometry of positive pole local terminal from Chosen Point to negative pole local terminal is identical, and the distance from Chosen Point to the Distance geometry of positive pole remote terminal from Chosen Point to negative pole remote terminal is identical, also comprise:

Pole modular transformation step: by carrying out pole modular transformation to each described fault component pole tension value in positive pole local terminal, positive pole remote terminal, negative pole local terminal and negative pole remote terminal, obtains the fault component mode voltage value of each modulus of local terminal and remote terminal; And by carrying out pole modular transformation to each described fault component electrode current value in positive pole local terminal, positive pole remote terminal, negative pole local terminal and negative pole remote terminal, obtain the fault component mould current value of each modulus of local terminal and remote terminal;

Bei Jielong model calculation procedure also comprises:

By calculating fault component mode voltage value and the fault component mould current value of each modulus of local terminal and remote terminal based on Bei Jielong model, obtain the fault component line wave voltage value of each modulus of local terminal and remote terminal respectively;

Respectively the fault component line wave voltage value of local terminal and remote terminal is converted to the fault component line ripple current value of local terminal and remote terminal;

The local terminal at the Chosen Point place on DC circuit and the fault component mould current value of remote terminal is determined respectively according to the fault component line ripple current value of local terminal and remote terminal;

Mould pole-change is carried out by the fault component mould current value of each modulus to the local terminal at Chosen Point place, obtain each fault component electrode current value in the positive pole local terminal at Chosen Point place on DC circuit and negative pole local terminal, and carry out mould pole-change by the fault component mould current value of each modulus to the remote terminal at Chosen Point place, obtain the fault component electrode current value of positive pole remote terminal at Chosen Point place and negative pole remote terminal.

Easily, pole tension sampled value comprises: u _lP(t), i.e. the voltage sample value of positive pole local terminal; u _lN(t), i.e. the voltage sample value of negative pole local terminal; u _rP(t), i.e. the voltage sample value of positive pole remote terminal; u _rN(t), i.e. the voltage sample value of negative pole remote terminal; Wherein t refers to the time;

Electrode current sampled value comprises: i _lP(t), the i.e. current sampling data of positive pole local terminal; i _lN(t), the i.e. current sampling data of negative pole local terminal; i _rP(t), the i.e. current sampling data of positive pole remote terminal; i _rN(t), the i.e. current sampling data of negative pole remote terminal;

Fault component pole tension value comprises: Δ u _lP(t), namely and u _lPthe fault component magnitude of voltage of t positive pole local terminal that () is corresponding; Δ u _lN(t), namely and u _lNthe fault component magnitude of voltage of t negative pole local terminal that () is corresponding; Δ u _rP(t), namely and u _rPthe fault component magnitude of voltage of t positive pole remote terminal that () is corresponding; Δ u _rN(t), namely and u _rNthe fault component magnitude of voltage of t negative pole remote terminal that () is corresponding;

Fault component electrode current value comprises: Δ i _lP(t), namely and i _lPthe fault component current value of t positive pole local terminal that () is corresponding; Δ i _lN(t), namely and i _lNthe fault component current value of t negative pole local terminal that () is corresponding; Δ i _rP(t), namely and i _rPthe fault component current value of t positive pole remote terminal that () is corresponding; Δ i _rN(t), namely and i _rNthe fault component current value of t negative pole remote terminal that () is corresponding;

Fault component mode voltage value comprises: Δ u _l0(t), i.e. the fault component common-mode voltage value of local terminal; Δ u _l1(t), i.e. the fault component differential mode voltage value of local terminal; Δ u _r0(t), i.e. the fault component common-mode voltage value of remote terminal; Δ u _r1(t), i.e. the fault component differential mode voltage value of remote terminal;

Fault component mould current value comprises: Δ i _l0(t), i.e. the fault component common-mode current value of local terminal; Δ i _l1(t), i.e. the fault component differential-mode current value of local terminal; Δ i _r0(t), i.e. the fault component common-mode current value of remote terminal; Δ i _r1(t), i.e. the fault component differential-mode current value of remote terminal;

The capable wave voltage value of fault component comprises: Δ u _l0+(t), i.e. the fault component common mode direct wave magnitude of voltage of local terminal; Δ u _l0-(t), i.e. the fault component common mode returning wave magnitude of voltage of local terminal; Δ u _l1+(t), i.e. the fault component differential mode direct wave magnitude of voltage of local terminal; △ Δ u _l0-(t), i.e. the fault component differential mode returning wave magnitude of voltage of local terminal; Δ u _r0+(t), i.e. the fault component common mode direct wave magnitude of voltage of remote terminal; Δ u _r0-(t), i.e. the fault component common mode returning wave magnitude of voltage of remote terminal; Δ u _r1+(t), the fault component differential mode direct wave magnitude of voltage of remote terminal; Δ u _r1-(t), the fault component differential mode returning wave magnitude of voltage of remote terminal;

Fault component travelling wave current value comprises: Δ i _l0+(t), i.e. the fault component common mode direct wave current value of local terminal; Δ i _l0-(t), i.e. the fault component common mode returning wave current value of local terminal; Δ i _l1+(t), i.e. the fault component differential mode direct wave current value of local terminal; Δ i _l1-(t), i.e. the fault component differential mode returning wave current value of local terminal; Δ i _r0+(t), i.e. the fault component common mode direct wave current value of remote terminal; Δ i _r0-(t), i.e. the fault component common mode returning wave current value of remote terminal; Δ i _r1+(t), i.e. the fault component differential mode direct wave current value of remote terminal; Δ i _r1-(t), i.e. the fault component differential mode returning wave current value of remote terminal;

Comprise at the fault component mould current value at Chosen Point place: Δ i _l0(x, t), i.e. the fault component common-mode current value at the Chosen Point place of local terminal; Δ i _l1(x, t), i.e. the fault component differential-mode current value at the Chosen Point place of local terminal; Δ i _r0(x, t), i.e. the fault component common-mode current value at the Chosen Point place of remote terminal; Δ i _r1(x, t), i.e. the fault component differential-mode current value at the Chosen Point place of remote terminal, wherein x is Chosen Point;

Comprise in the fault component electrode current value at Chosen Point place: Δ i _lP(x, t), i.e. the fault component electrode current value at the Chosen Point place of positive pole local terminal; Δ i _lN(x, t), i.e. the fault component electrode current value at the Chosen Point place of negative pole local terminal; Δ i _rP(x, t), i.e. the fault component electrode current value at the Chosen Point place of positive pole remote terminal; Δ i _rN(x, t), i.e. the fault component electrode current value at the Chosen Point place of negative pole remote terminal.

Easily, in fault component extraction step, calculate fault component pole tension value and fault component pole tension value in the following ways:

$\left\{\begin{array}{c}{\mathrm{\&Delta;i}}_{LP}\left(t\right)=i_{LP}\left(t\right)-i_{LP}(t-T)\\ {\mathrm{\&Delta;i}}_{LN}\left(t\right)=i_{LN}\left(t\right)-i_{LN}(t-T)\\ {\mathrm{\&Delta;u}}_{LP}\left(t\right)=u_{LP}\left(t\right)-u_{LP}(t-T)\\ {\mathrm{\&Delta;u}}_{LN}\left(t\right)=u_{LN}\left(t\right)-u_{LN}(t-T)\\ {\mathrm{\&Delta;i}}_{RP}\left(t\right)=i_{RP}\left(t\right)-i_{RP}(t-T)\\ {\mathrm{\&Delta;i}}_{RN}\left(t\right)=i_{RN}\left(t\right)-i_{RN}(t-T)\\ {\mathrm{\&Delta;u}}_{RP}\left(t\right)=u_{RP}\left(t\right)-u_{RP}(t-T)\\ {\mathrm{\&Delta;u}}_{RN}\left(t\right)=u_{RN}\left(t\right)-u_{RN}(t-T)\end{array}\right.,$

Wherein T represents predetermined time delay;

In pole modular transformation step, calculate fault component mode voltage value and fault component mould current value in the following ways:

$\left\{\begin{array}{c}\left[\begin{array}{c}{\mathrm{\&Delta;u}}_{L0}\left(t\right)\\ {\mathrm{\&Delta;u}}_{L1}\left(t\right)\end{array}\right]=\left[\begin{array}{cc}1& 1\\ 1& -1\end{array}\right]\left[\begin{array}{c}{\mathrm{\&Delta;u}}_{LP}\left(t\right)\\ {\mathrm{\&Delta;u}}_{LN}\left(t\right)\end{array}\right]\\ \left[\begin{array}{c}{\mathrm{\&Delta;i}}_{L0}\left(t\right)\\ {\mathrm{\&Delta;i}}_{L1}\left(t\right)\end{array}\right]=\left[\begin{array}{cc}1& 1\\ 1& -1\end{array}\right]\left[\begin{array}{c}{\mathrm{\&Delta;i}}_{LP}\left(t\right)\\ {\mathrm{\&Delta;i}}_{LN}\left(t\right)\end{array}\right]\\ \left[\begin{array}{c}{\mathrm{\&Delta;u}}_{R0}\left(t\right)\\ {\mathrm{\&Delta;u}}_{R1}\left(t\right)\end{array}\right]=\left[\begin{array}{cc}1& 1\\ 1& -1\end{array}\right]\left[\begin{array}{c}{\mathrm{\&Delta;u}}_{RP}\left(t\right)\\ {\mathrm{\&Delta;u}}_{RN}\left(t\right)\end{array}\right]\\ \left[\begin{array}{c}{\mathrm{\&Delta;i}}_{R0}\left(t\right)\\ {\mathrm{\&Delta;i}}_{R1}\left(t\right)\end{array}\right]=\left[\begin{array}{cc}1& 1\\ 1& -1\end{array}\right]\left[\begin{array}{c}{\mathrm{\&Delta;i}}_{RP}\left(t\right)\\ {\mathrm{\&Delta;i}}_{RN}\left(t\right)\end{array}\right]\end{array}\right.;$

Comprise in Bei Jielong model calculation procedure:

Calculate fault component line wave voltage value in the following ways:

$\left\{\begin{array}{c}{\mathrm{\&Delta;u}}_{L0+}\left(t\right)={\mathrm{\&Delta;u}}_{L0}\left(t\right)+{\mathrm{\&Delta;i}}_{L0}\left(t\right)\&times;Z_{C0}\\ {\mathrm{\&Delta;u}}_{L0-}\left(t\right)={\mathrm{\&Delta;u}}_{L0}\left(t\right)-{\mathrm{\&Delta;i}}_{L0}\left(t\right)\&times;Z_{C0}\\ {\mathrm{\&Delta;u}}_{L1+}\left(t\right)={\mathrm{\&Delta;u}}_{L1}\left(t\right)+{\mathrm{\&Delta;i}}_{L1}\left(t\right)\&times;Z_{C1}\\ {\mathrm{\&Delta;u}}_{L1-}\left(t\right)={\mathrm{\&Delta;u}}_{L1}\left(t\right)-{\mathrm{\&Delta;i}}_{L1}\left(t\right)\&times;Z_{C1}\\ {\mathrm{\&Delta;u}}_{R0+}\left(t\right)={\mathrm{\&Delta;u}}_{R0}\left(t\right)+{\mathrm{\&Delta;i}}_{R0}\left(t\right)\&times;Z_{C0}\\ {\mathrm{\&Delta;u}}_{R0-}\left(t\right)={\mathrm{\&Delta;u}}_{R0}\left(t\right)-{\mathrm{\&Delta;i}}_{R0}\left(t\right)\&times;Z_{C0}\\ {\mathrm{\&Delta;u}}_{R1+}\left(t\right)={\mathrm{\&Delta;u}}_{R1}\left(t\right)+{\mathrm{\&Delta;i}}_{R1}\left(t\right)\&times;Z_{C1}\\ {\mathrm{\&Delta;u}}_{R1-}\left(t\right)={\mathrm{\&Delta;u}}_{R1}\left(t\right)-{\mathrm{\&Delta;i}}_{R1}\left(t\right)\&times;Z_{C1}\end{array}\right.,$

Wherein Z _c0it is common mode wave impedance; Z _c1it is differential mode wave impedance;

Calculate fault component line ripple current value in the following ways:

$\left\{\begin{array}{c}{\mathrm{\&Delta;i}}_{L0+}\left(t\right)={\mathrm{\&Delta;u}}_{L0+}\left(t\right)/Z_{C0}\\ {\mathrm{\&Delta;i}}_{L0-}\left(t\right)=-{\mathrm{\&Delta;u}}_{L0-}\left(t\right)/Z_{C0}\\ {\mathrm{\&Delta;i}}_{L1+}\left(t\right)={\mathrm{\&Delta;u}}_{L1+}\left(t\right)/Z_{C1}\\ {\mathrm{\&Delta;i}}_{L1-}\left(t\right)=-{\mathrm{\&Delta;u}}_{L1-}\left(t\right)/Z_{C1}\\ {\mathrm{\&Delta;i}}_{R0+}\left(t\right)={\mathrm{\&Delta;u}}_{R0+}\left(t\right)/Z_{C0}\\ {\mathrm{\&Delta;i}}_{R0-}\left(t\right)=-{\mathrm{\&Delta;u}}_{R0-}\left(t\right)/Z_{C0}\\ {\mathrm{\&Delta;i}}_{R1+}\left(t\right)={\mathrm{\&Delta;u}}_{R1+}\left(t\right)/Z_{C1}\\ {\mathrm{\&Delta;i}}_{R1-}\left(t\right)=-{\mathrm{\&Delta;u}}_{R1-}\left(t\right)/Z_{C1}\end{array}\right.$

Calculate the fault component mould current value at Chosen Point place in the following ways:

$\left\{\begin{array}{c}{\mathrm{\&Delta;i}}_{L1}(x,t)={\mathrm{\&Delta;i}}_{L1+}(t-\frac{x}{v_1})-{\mathrm{\&Delta;i}}_{L1-}(t+\frac{x}{v_1})\\ {\mathrm{\&Delta;i}}_{L0}(x,t)={\mathrm{\&Delta;i}}_{L0+}(t-\frac{x}{v_0})-{\mathrm{\&Delta;i}}_{L0-}(t+\frac{x}{v_0})\\ {\mathrm{\&Delta;i}}_{R1}(x,t)={\mathrm{\&Delta;i}}_{R1+}(t-\frac{x}{v_1})-{\mathrm{\&Delta;i}}_{R1-}(t+\frac{x}{v_1})\\ {\mathrm{\&Delta;i}}_{R0}(x,t)={\mathrm{\&Delta;i}}_{R0+}(t-\frac{x}{v_0})-{\mathrm{\&Delta;i}}_{R0-}(t+\frac{x}{v_0})\end{array}\right.$

Wherein, v ₀the gait of march of fault component common mode row ripple, v ₁it is the gait of march of the capable ripple of fault component differential mode;

Calculate the fault component electrode current value at Chosen Point place in the following ways:

$\left\{\begin{array}{c}\left[\begin{array}{c}{\mathrm{\&Delta;i}}_{LP}(x,t)\\ {\mathrm{\&Delta;i}}_{LN}(x,t)\end{array}\right]=\frac{1}{2}\left[\begin{array}{cc}1& 1\\ 1& -1\end{array}\right]\left[\begin{array}{c}{\mathrm{\&Delta;i}}_{L0}(x,t)\\ {\mathrm{\&Delta;i}}_{L1}(x,t)\end{array}\right]\\ \left[\begin{array}{c}{i}_{RP}(x,t)\\ {\mathrm{\&Delta;i}}_{RN}(x,t)\end{array}\right]=\frac{1}{2}\left[\begin{array}{cc}1& 1\\ 1& -1\end{array}\right]\left[\begin{array}{c}{\mathrm{\&Delta;i}}_{R0}(x,t)\\ {\mathrm{\&Delta;i}}_{R1}(x,t)\end{array}\right]\end{array}\right..$

Easily, current differential protection determination step comprises:

If met | Δ i _lP(x, t)+Δ i _rP(x, t) | > I _res, then decision state is positive pole internal fault, if met | Δ i _lN(x, t)+Δ i _rN(x, t) | > I _res, then decision state is negative pole internal fault, wherein I _resit is predetermined threshold value;

Otherwise, will not differential protection be activated.

Preferably, DC electrical network is one pole:

Bei Jielong model calculation procedure also comprises:

By based on Bei Jielong model, calculate fault component pole tension value and the fault component mould current value of local terminal and remote terminal, obtain the fault component extremely row wave voltage value of local terminal and remote terminal respectively;

Respectively by the fault component of local terminal and remote terminal extremely row wave voltage value convert the fault component line ripple current value of local terminal and remote terminal to;

According to the fault component pole travelling wave current value of local terminal and remote terminal, determine the local terminal at the Chosen Point place on DC circuit and the fault component electrode current value of remote terminal.

Easily, in fault component extraction step, calculate fault component pole tension value and fault component pole tension value in the following ways:

$\left\{\begin{array}{c}{\mathrm{\&Delta;i}}_L\left(t\right)=i_L\left(t\right)-i_L(t-T)\\ {\mathrm{\&Delta;u}}_L\left(t\right)=u_L\left(t\right)-u_L(t-T)\\ {\mathrm{\&Delta;i}}_R\left(t\right)=i_R\left(t\right)-i_R(t-T)\\ {\mathrm{\&Delta;u}}_R\left(t\right)=u_R\left(t\right)-u_R(t-T)\end{array}\right.,$

Wherein, T represents predetermined time delay, Δ i _lt () is the fault component electrode current value of local terminal, Δ i _rt () is the fault component electrode current value of remote terminal, Δ u _lt () is the fault component pole tension value of local terminal, Δ u _rt () is the fault component pole tension value of remote terminal, i _lt () is the current sampling data of local terminal, i _rt () is the current sampling data of remote terminal, u _lt () is the voltage sample value of local terminal, u _rt () is the voltage sample value of remote terminal, t refers to the time;

Comprise in Bei Jielong model calculation procedure:

Calculate fault component extremely row wave voltage value in the following ways:

$\left\{\begin{array}{c}\mathrm{\&Delta;}{u}_{L+}\left(t\right)=\mathrm{\&Delta;}{u}_L\left(t\right)+\mathrm{\&Delta;}{i}_L\left(t\right)\&times;Z_C\\ {\mathrm{\&Delta;u}}_{L-}\left(t\right)={\mathrm{\&Delta;u}}_L\left(t\right)-{\mathrm{\&Delta;i}}_L\left(t\right)\&times;Z_C\\ {\mathrm{\&Delta;u}}_{R+}\left(t\right)={\mathrm{\&Delta;u}}_R\left(t\right)+{\mathrm{\&Delta;i}}_R\left(t\right)\&times;Z_C\\ \mathrm{\&Delta;}{u}_{R-}\left(t\right)=\mathrm{\&Delta;}{u}_R\left(t\right)-\mathrm{\&Delta;}{i}_R\left(t\right)\&times;Z_C\end{array}\right.,$

Wherein Z _cwave impedance, Δ u _l+t () is the fault component pole direct wave magnitude of voltage of local terminal; Δ u _l-t () is the fault component pole returning wave magnitude of voltage of local terminal; Δ u _r+t () is the fault component pole direct wave magnitude of voltage of remote terminal; Δ u _r-t () is the fault component pole returning wave magnitude of voltage of remote terminal;

Calculate fault component pole travelling wave current value in the following ways:

$\left\{\begin{array}{c}\mathrm{\&Delta;}{i}_{L+}\left(t\right)=\mathrm{\&Delta;}{u}_{L+}\left(t\right)/Z_C\\ {\mathrm{\&Delta;i}}_{L-}\left(t\right)=-{\mathrm{\&Delta;u}}_{L-}\left(t\right)/Z_C\\ {\mathrm{\&Delta;i}}_{R+}\left(t\right)={\mathrm{\&Delta;u}}_{R+}\left(t\right)/Z_C\\ \mathrm{\&Delta;}{i}_{R-}\left(t\right)=-\mathrm{\&Delta;}{u}_{R-}\left(t\right)/Z_C\end{array}\right.,$

Wherein, Δ i _l+t () is the fault component pole direct wave current value of local terminal; Δ i _l-t () is the fault component pole returning wave current value of local terminal; Δ i _r+t () is the fault component pole direct wave current value of remote terminal; Δ i _r-t () is the fault component pole returning wave current value of remote terminal;

Calculate the fault component electrode current value at select location place in the following ways:

$\{\begin{array}{c}{\mathrm{\&Delta;i}}_L(x,t)={\mathrm{\&Delta;i}}_{L+}(t-\frac{x}{v})-{\mathrm{\&Delta;i}}_{L-}(t+\frac{x}{v})\\ {\mathrm{\&Delta;i}}_R(x,t)={\mathrm{\&Delta;i}}_{R+}(t-\frac{x}{v})-{\mathrm{\&Delta;i}}_{R-}(t+\frac{x}{v})\end{array},$

Wherein Δ i _l(x, t) is the fault component electrode current value at the Chosen Point place of local terminal; Δ i _r(x, t) is the fault component electrode current value at the Chosen Point place of remote terminal, and v is the gait of march of the capable ripple of fault component.

Easily, comprise at current differential protection determination step:

If met | Δ i _l(x, t)+Δ i _r(x, t) | > I _res, then decision state is internal fault, wherein I _resit is predetermined threshold value.

Easily, current differential protection determination step also comprises:

If state is determined into internal fault, then send error protection order to activate differential protection; Otherwise, will not differential protection be activated.

Another aspect provides a kind of computer program, comprise be suitable for performing when running on computers above-mentioned either side computer program code in steps.

Another aspect of the present invention provides according to the above-mentioned computer program be recorded in computer-readable medium.

Another aspect of the present invention provides a kind of DC power network current differential protective system, comprises with lower module:

Sampled value obtains module: obtain the pole tension sampled value in the local terminal of DC circuit and remote terminal and electrode current sampled value;

Fault component extraction module: the pole tension sampled value according to local terminal and remote terminal calculates fault component pole tension value respectively; And calculate fault component electrode current value respectively according to the electrode current value of local terminal and remote terminal;

Bei Jielong model computation module: by based on Bei Jielong model, calculate fault component pole tension value and the fault component electrode current value of local terminal and the remote terminal calculated in fault component extraction step, obtain the fault component electrode current value at the Chosen Point place on the DC circuit between local terminal and remote terminal;

Current differential protection determination module: if the fault component electrode current value at the Chosen Point place of the local terminal obtained in Bei Jielong model computation module and remote terminal meets predetermined current differential protection criterion, then judge internal fault.

Preferably, DC electrical network is bipolar and DC circuit comprises positive pole DC circuit and negative pole DC circuit, local terminal comprises positive pole local terminal and positive pole remote terminal, remote terminal comprises negative pole local terminal and negative pole remote terminal, positive pole DC line electricity connects positive pole local terminal and positive pole remote terminal, negative pole DC line electricity connects negative pole local terminal and negative pole remote terminal, distance from Chosen Point to the Distance geometry of positive pole local terminal from Chosen Point to negative pole local terminal is identical, distance from Chosen Point to the Distance geometry of positive pole remote terminal from Chosen Point to negative pole remote terminal is identical, also comprise:

Pole modular transformation module: by carrying out pole modular transformation to each described fault component pole tension value in positive pole local terminal, positive pole remote terminal, negative pole local terminal and negative pole remote terminal, obtains the fault component mode voltage value of each modulus in local terminal and remote terminal; And by carrying out pole modular transformation to each described fault component electrode current value in positive pole local terminal, positive pole remote terminal, negative pole local terminal and negative pole remote terminal, obtain the fault component mould current value of each modulus of local terminal and remote terminal;

Bei Jielong model computation module also comprises:

By based on Bei Jielong model, calculate fault component mode voltage value and the fault component mould current value of each modulus of local terminal and remote terminal, obtain the fault component line wave voltage value of each modulus of local terminal and remote terminal respectively;

Respectively the fault component line wave voltage value of local terminal and remote terminal is converted to the fault component line ripple current value of local terminal and remote terminal;

The local terminal at the Chosen Point place on DC circuit and the fault component mould current value of remote terminal is determined respectively according to the fault component line ripple current value of local terminal and remote terminal;

Mould pole-change is carried out by the fault component mould current value of each modulus to the local terminal at Chosen Point place, obtain each fault component electrode current value in the positive pole local terminal at Chosen Point place on DC circuit and negative pole local terminal, and carry out mould pole-change by the fault component mould current value of each modulus to the remote terminal at Chosen Point place, obtain the fault component electrode current value of positive pole remote terminal at Chosen Point place and negative pole remote terminal.

Easily, pole tension sampled value comprises: u _lP(t), i.e. the voltage sample value of positive pole local terminal; u _lN(t), i.e. the voltage sample value of negative pole local terminal; u _rP(t), i.e. the voltage sample value of negative pole remote terminal; u _rN(t), i.e. the voltage sample value of negative pole remote terminal; Wherein t refers to the time;

Electrode current sampled value comprises: i _lP(t), the i.e. current sampling data of positive pole local terminal; i _lN(t), the i.e. current sampling data of negative pole local terminal; i _rP(t), the i.e. current sampling data of positive pole remote terminal; i _rN(t), the i.e. current sampling data of negative pole remote terminal;

Fault component pole tension value comprises: Δ u _lP(t), namely and u _lPthe fault component magnitude of voltage of t positive pole local terminal that () is corresponding; Δ u _lN(t), namely and u _lNthe fault component magnitude of voltage of t negative pole local terminal that () is corresponding; Δ u _rP(t), namely and u _rPthe fault component magnitude of voltage of t positive pole remote terminal that () is corresponding; Δ u _rN(t), namely and u _rNthe fault component magnitude of voltage of t negative pole remote terminal that () is corresponding;

Fault component electrode current value comprises: Δ i _lP(t), namely and i _lPthe fault component current value of t positive pole local terminal that () is corresponding; Δ i _lN(t), namely and i _lNthe fault component current value of t negative pole local terminal that () is corresponding; Δ i _rP(t), namely and i _rPthe fault component current value of t positive pole remote terminal that () is corresponding; Δ i _rN(t), namely and i _rNthe fault component current value of t negative pole remote terminal that () is corresponding;

Fault component mode voltage value comprises: Δ u _l0(t), i.e. the fault component common-mode voltage value of local terminal; Δ u _l1(t), i.e. the fault component differential mode voltage value of local terminal; Δ u _r0(t), i.e. the fault component common-mode voltage value of remote terminal; Δ u _r1(t), i.e. the fault component differential mode voltage value of remote terminal;

Fault component mould current value comprises: Δ i _l0(t), i.e. the fault component common-mode current value of local terminal; Δ i _l1(t), i.e. the fault component differential-mode current value of local terminal; Δ i _r0(t), i.e. the fault component common-mode current value of remote terminal; Δ i _r1(t), i.e. the fault component differential-mode current value of remote terminal;

The capable wave voltage value of fault component comprises: Δ u _l0+(t), i.e. the fault component common mode direct wave magnitude of voltage of local terminal; Δ u _l0-(t), i.e. the fault component common mode returning wave magnitude of voltage of local terminal; Δ u _l1+(t), i.e. the fault component differential mode direct wave magnitude of voltage of local terminal; Δ u _l0-(t), i.e. the fault component differential mode returning wave magnitude of voltage of local terminal; Δ u _r0+(t), i.e. the fault component common mode direct wave magnitude of voltage of remote terminal; Δ u _r0-(t), i.e. the fault component common mode returning wave magnitude of voltage of remote terminal; Δ u _r1+(t), i.e. the fault component differential mode direct wave magnitude of voltage of remote terminal; Δ u _r1-(t), i.e. the fault component differential mode returning wave magnitude of voltage of remote terminal;

Fault component travelling wave current value comprises: Δ i _l0+(t), i.e. the fault component common mode direct wave current value of local terminal; Δ i _l0-(t), i.e. the fault component common mode returning wave current value of local terminal; Δ i _l1+(t), i.e. the fault component differential mode direct wave current value of local terminal; Δ i _l1-(t), i.e. the fault component differential mode returning wave current value of local terminal; Δ i _r0+(t), i.e. the fault component common mode direct wave current value of remote terminal; Δ i _r0-(t), i.e. the fault component common mode returning wave current value of remote terminal; Δ i _r1+(t), i.e. the fault component differential mode direct wave current value of remote terminal; Δ i _r1-(t), i.e. the fault component differential mode returning wave current value of remote terminal;

Comprise at the fault component mould current value at Chosen Point place: Δ i _l0(x, t), i.e. the fault component common-mode current value at the Chosen Point place of local terminal; Δ i _l1(x, t), i.e. the fault component differential-mode current value at the Chosen Point place of local terminal; Δ i _r0(x, t), i.e. the fault component common-mode current value at the Chosen Point place of remote terminal; Δ i _r1(x, t), i.e. the fault component differential-mode current value at the Chosen Point place of remote terminal, wherein x is Chosen Point;

The fault component electrode current value at Chosen Point place comprises: Δ i _lP(x, t), i.e. the fault component electrode current value at the Chosen Point place of positive pole local terminal; Δ i _lN(x, t), i.e. the fault component electrode current value at the Chosen Point place of negative pole local terminal; Δ i _rP(x, t), i.e. the fault component electrode current value at the Chosen Point place of positive pole remote terminal; Δ i _rN(x, t), i.e. the fault component electrode current value at the Chosen Point place of negative pole remote terminal.

Easily, in fault component extraction module, calculate fault component pole tension value and fault component pole tension value in the following ways:

$\left\{\begin{array}{c}{\mathrm{\&Delta;i}}_{LP}\left(t\right)=i_{LP}\left(t\right)-i_{LP}(t-T)\\ {\mathrm{\&Delta;i}}_{LN}\left(t\right)=i_{LN}\left(t\right)-i_{LN}(t-T)\\ {\mathrm{\&Delta;u}}_{LP}\left(t\right)=u_{LP}\left(t\right)-u_{LP}(t-T)\\ {\mathrm{\&Delta;u}}_{LN}\left(t\right)=u_{LN}\left(t\right)-u_{LN}(t-T)\\ {\mathrm{\&Delta;i}}_{RP}\left(t\right)=i_{RP}\left(t\right)-i_{RP}(t-T)\\ {\mathrm{\&Delta;i}}_{RN}\left(t\right)=i_{RN}\left(t\right)-i_{RN}(t-T)\\ {\mathrm{\&Delta;u}}_{RP}\left(t\right)=u_{RP}\left(t\right)-u_{RP}(t-T)\\ {\mathrm{\&Delta;u}}_{RN}\left(t\right)=u_{RN}\left(t\right)-u_{RN}(t-T)\end{array}\right.$

Wherein, T represents predetermined time delay;

In pole modular transformation module, calculate fault component mode voltage value and fault component mould current value in the following ways:

$\left\{\begin{array}{c}\left[\begin{array}{c}{\mathrm{\&Delta;u}}_{L0}\left(t\right)\\ {\mathrm{\&Delta;u}}_{L1}\left(t\right)\end{array}\right]=\left[\begin{array}{cc}1& 1\\ 1& -1\end{array}\right]\left[\begin{array}{c}{\mathrm{\&Delta;u}}_{LP}\left(t\right)\\ {\mathrm{\&Delta;u}}_{LN}\left(t\right)\end{array}\right]\\ \left[\begin{array}{c}{\mathrm{\&Delta;i}}_{L0}\left(t\right)\\ {\mathrm{\&Delta;i}}_{L1}\left(t\right)\end{array}\right]=\left[\begin{array}{cc}1& 1\\ 1& -1\end{array}\right]\left[\begin{array}{c}{\mathrm{\&Delta;i}}_{LP}\left(t\right)\\ {\mathrm{\&Delta;i}}_{LN}\left(t\right)\end{array}\right]\\ \left[\begin{array}{c}{\mathrm{\&Delta;u}}_{R0}\left(t\right)\\ {\mathrm{\&Delta;u}}_{R1}\left(t\right)\end{array}\right]=\left[\begin{array}{cc}1& 1\\ 1& -1\end{array}\right]\left[\begin{array}{c}{\mathrm{\&Delta;u}}_{RP}\left(t\right)\\ {\mathrm{\&Delta;u}}_{RN}\left(t\right)\end{array}\right]\\ \left[\begin{array}{c}{\mathrm{\&Delta;i}}_{R0}\left(t\right)\\ {\mathrm{\&Delta;i}}_{R1}\left(t\right)\end{array}\right]=\left[\begin{array}{cc}1& 1\\ 1& -1\end{array}\right]\left[\begin{array}{c}{\mathrm{\&Delta;i}}_{RP}\left(t\right)\\ {\mathrm{\&Delta;i}}_{RN}\left(t\right)\end{array}\right]\end{array}\right.;$

Comprise in Bei Jielong model computation module:

Calculate fault component line wave voltage value in the following ways:

$\left\{\begin{array}{c}{\mathrm{\&Delta;u}}_{L0+}\left(t\right)={\mathrm{\&Delta;u}}_{L0}\left(t\right)+{\mathrm{\&Delta;i}}_{L0}\left(t\right)\&times;Z_{C0}\\ {\mathrm{\&Delta;u}}_{L0-}\left(t\right)={\mathrm{\&Delta;u}}_{L0}\left(t\right)-{\mathrm{\&Delta;i}}_{L0}\left(t\right)\&times;Z_{C0}\\ {\mathrm{\&Delta;u}}_{L0-}\left(t\right)={\mathrm{\&Delta;u}}_{L0}\left(t\right)-{\mathrm{\&Delta;i}}_{L0}\left(t\right)\&times;Z_{C0}\\ {\mathrm{\&Delta;u}}_{L1+}\left(t\right)={\mathrm{\&Delta;u}}_{L1}\left(t\right)+{\mathrm{\&Delta;i}}_{L1}\left(t\right)\&times;Z_{C1}\\ {\mathrm{\&Delta;u}}_{L1-}\left(t\right)={\mathrm{\&Delta;u}}_{L1}\left(t\right)-{\mathrm{\&Delta;i}}_{L1}\left(t\right)\&times;Z_{C1}\\ {\mathrm{\&Delta;u}}_{R0-}\left(t\right)={\mathrm{\&Delta;u}}_{R0}\left(t\right)-{\mathrm{\&Delta;i}}_{R0}\left(t\right)\&times;Z_{C0}\\ {\mathrm{\&Delta;u}}_{R1+}\left(t\right)={\mathrm{\&Delta;u}}_{R1}\left(t\right)+{\mathrm{\&Delta;i}}_{R1}\left(t\right)\&times;Z_{C1}\\ {\mathrm{\&Delta;u}}_{R1-}\left(t\right)={\mathrm{\&Delta;u}}_{R1}\left(t\right)-{\mathrm{\&Delta;i}}_{R1}\left(t\right)\&times;Z_{C1}\end{array}\right.,$

Wherein Z _c0it is common mode wave impedance; Z _c1it is differential mode wave impedance;

Calculate fault component line ripple current value in the following ways:

$\left\{\begin{array}{c}{\mathrm{\&Delta;i}}_{L0+}\left(t\right)={\mathrm{\&Delta;u}}_{L0+}\left(t\right)/Z_{C0}\\ {\mathrm{\&Delta;i}}_{L0-}\left(t\right)=-{\mathrm{\&Delta;u}}_{L0-}\left(t\right)/Z_{C0}\\ {\mathrm{\&Delta;i}}_{L1+}\left(t\right)={\mathrm{\&Delta;u}}_{L1+}\left(t\right)/Z_{C1}\\ {\mathrm{\&Delta;i}}_{L1-}\left(t\right)=-{\mathrm{\&Delta;u}}_{L1-}\left(t\right)/Z_{C1}\\ {\mathrm{\&Delta;i}}_{R0+}\left(t\right)={\mathrm{\&Delta;u}}_{R0+}\left(t\right)/Z_{C0}\\ {\mathrm{\&Delta;i}}_{R0-}\left(t\right)=-{\mathrm{\&Delta;u}}_{R0-}\left(t\right)/Z_{C0}\\ {\mathrm{\&Delta;i}}_{R1+}\left(t\right)={\mathrm{\&Delta;u}}_{R1+}\left(t\right)/Z_{C1}\\ {\mathrm{\&Delta;i}}_{R1-}\left(t\right)=-{\mathrm{\&Delta;u}}_{R1-}\left(t\right)/Z_{C1}\end{array}\right.;$

Calculate the fault component mould current value at Chosen Point place in the following ways:

$\{\begin{array}{c}{\mathrm{\&Delta;i}}_{L1}(x,t)={\mathrm{\&Delta;i}}_{L1+}(t-\frac{x}{v_1})-{\mathrm{\&Delta;i}}_{L1-}(t+\frac{x}{v_1})\\ {\mathrm{\&Delta;i}}_{L0}(x,t)={\mathrm{\&Delta;i}}_{L0+}(t-\frac{x}{v_0})-{\mathrm{\&Delta;i}}_{L0-}(t+\frac{x}{v_0})\\ {\mathrm{\&Delta;i}}_{R1}(x,t)={\mathrm{\&Delta;i}}_{R1+}(t-\frac{x}{v_1})-{\mathrm{\&Delta;i}}_{R1-}(t+\frac{x}{v_1})\\ {\mathrm{\&Delta;i}}_{R0}(x,t)={\mathrm{\&Delta;i}}_{R0+}(t-\frac{x}{v_0})-{\mathrm{\&Delta;i}}_{R0-}(t+\frac{x}{v_0})\end{array},$

Wherein, v ₀the gait of march of fault component common mode row ripple, v ₁it is the gait of march of the capable ripple of fault component differential mode;

Calculate the fault component electrode current value at Chosen Point place in the following ways:

$\left\{\begin{array}{c}\left[\begin{array}{c}{\mathrm{\&Delta;i}}_{LP}(x,t)\\ {\mathrm{\&Delta;i}}_{LN}(x,t)\end{array}\right]=\frac{1}{2}\left[\begin{array}{cc}1& 1\\ 1& -1\end{array}\right]\left[\begin{array}{c}{\mathrm{\&Delta;i}}_{L0}(x,t)\\ {\mathrm{\&Delta;i}}_{L1}(x,t)\end{array}\right]\\ \left[\begin{array}{c}{i}_{RP}(x,t)\\ {\mathrm{\&Delta;i}}_{RN}(x,t)\end{array}\right]=\frac{1}{2}\left[\begin{array}{cc}1& 1\\ 1& -1\end{array}\right]\left[\begin{array}{c}{\mathrm{\&Delta;i}}_{R0}(x,t)\\ {\mathrm{\&Delta;i}}_{R1}(x,t)\end{array}\right]\end{array}\right..$

Easily, current differential protection determination module comprises:

If met | Δ i _lP(x, t)+Δ i _rP(x, t) | > I _res, then decision state is positive pole internal fault, if met | Δ i _lN(x, t)+Δ i _rN(x, t) | > I _res, then decision state is negative pole internal fault, wherein, and I _resrepresent predetermined threshold value;

Otherwise, will not differential protection be activated.

Preferably, DC electrical network is one pole:

Bei Jielong model computation module also comprises:

By based on Bei Jielong model, calculate fault component pole tension value and the fault component mould current value of local terminal and remote terminal, obtain the fault component extremely row wave voltage value of local terminal and remote terminal respectively;

Respectively by the fault component of local terminal and remote terminal extremely row wave voltage value convert the fault component line ripple current value of local terminal and remote terminal to;

Fault component pole travelling wave current value according to local terminal and remote terminal determines the local terminal at the Chosen Point place on DC circuit and the fault component electrode current value of remote terminal.

Easily, in fault component extraction module, calculate fault component pole tension value and fault component pole tension value in the following ways:

$\left\{\begin{array}{c}{\mathrm{\&Delta;i}}_L\left(t\right)=i_L\left(t\right)-i_L(t-T)\\ {\mathrm{\&Delta;u}}_L\left(t\right)=u_L\left(t\right)-u_L(t-T)\\ {\mathrm{\&Delta;i}}_R\left(t\right)=i_R\left(t\right)-i_R(t-T)\\ {\mathrm{\&Delta;u}}_R\left(t\right)=u_R\left(t\right)-u_R(t-T)\end{array}\right.,$

Wherein T represents predetermined time delay, Δ i _lt () is the fault component electrode current value of local terminal, Δ i _rt () is the fault component electrode current value of remote terminal, Δ u _lt () is the fault component pole tension value of local terminal, Δ u _rt () is the fault component pole tension value of remote terminal, i _lt () is the current sampling data of local terminal, i _rt () is the current sampling data of remote terminal, u _lt () is the voltage sample value of local terminal, u _rt () is the voltage sample value of remote terminal, and t refers to the time;

Comprise in Bei Jielong model computation module:

Calculate fault component extremely row wave voltage value in the following ways:

$\left\{\begin{array}{c}\mathrm{\&Delta;}{u}_{L+}\left(t\right)=\mathrm{\&Delta;}{u}_L\left(t\right)+\mathrm{\&Delta;}{i}_L\left(t\right)\&times;Z_C\\ {\mathrm{\&Delta;u}}_{L-}\left(t\right)={\mathrm{\&Delta;u}}_L\left(t\right)-{\mathrm{\&Delta;i}}_L\left(t\right)\&times;Z_C\\ {\mathrm{\&Delta;u}}_{R+}\left(t\right)={\mathrm{\&Delta;u}}_R\left(t\right)+{\mathrm{\&Delta;i}}_R\left(t\right)\&times;Z_C\\ \mathrm{\&Delta;}{u}_{R-}\left(t\right)=\mathrm{\&Delta;}{u}_R\left(t\right)-\mathrm{\&Delta;}{i}_R\left(t\right)\&times;Z_C\end{array}\right.,$

Wherein, Z _cwave impedance, Δ u _l+t () is the fault component pole direct wave magnitude of voltage of local terminal; Δ u _l-t () is the fault component pole returning wave magnitude of voltage of local terminal; Δ u _r+t () is the fault component pole direct wave magnitude of voltage of remote terminal; Δ u _r-t () is the fault component pole returning wave magnitude of voltage of remote terminal;

Calculate fault component pole travelling wave current value in the following ways:

$\left\{\begin{array}{c}\mathrm{\&Delta;}{i}_{L+}\left(t\right)=\mathrm{\&Delta;}{u}_{L+}\left(t\right)/Z_C\\ {\mathrm{\&Delta;i}}_{L-}\left(t\right)=-{\mathrm{\&Delta;u}}_{L-}\left(t\right)/Z_C\\ {\mathrm{\&Delta;i}}_{R+}\left(t\right)={\mathrm{\&Delta;u}}_{R+}\left(t\right)/Z_C\\ \mathrm{\&Delta;}{i}_{R-}\left(t\right)=-\mathrm{\&Delta;}{u}_{R-}\left(t\right)/Z_C\end{array}\right.,$

Wherein, Δ i _l+t () is the fault component pole direct wave current value of local terminal; Δ i _l-t () is the fault component pole returning wave current value of local terminal; Δ i _r+t () is the fault component pole direct wave current value of remote terminal; Δ i _r-t () is the fault component pole returning wave current value of remote terminal;

Calculate the fault component electrode current value at select location place in the following ways:

$\{\begin{array}{c}{\mathrm{\&Delta;i}}_L(x,t)={\mathrm{\&Delta;i}}_{L+}(t-\frac{x}{v})-{\mathrm{\&Delta;i}}_{L-}(t+\frac{x}{v})\\ {\mathrm{\&Delta;i}}_R(x,t)={\mathrm{\&Delta;i}}_{R+}(t-\frac{x}{v})-{\mathrm{\&Delta;i}}_{R-}(t+\frac{x}{v})\end{array},$

Wherein Δ i _l(x, t) is the fault component electrode current value at the Chosen Point place of local terminal; Δ i _r(x, t) is the fault component electrode current value at the Chosen Point place of remote terminal, and v is the gait of march of the capable ripple of fault component.

Easily, comprise at current differential protection determination module:

If met | Δ i _l(x, t)+Δ i _r(x, t) | > I _res, then decision state is internal fault, wherein I _resit is predetermined threshold value.

Easily, current differential protection determination module also comprises:

If state is determined into internal fault, then sends error protection order to activate differential protection, otherwise will not differential protection be activated.

Bei Jielong model is based on distributed constant and telegraph equation (wave equation).Therefore, the present invention adopts Bei Jielong model, does not therefore need long time lengthening to eliminate the interference of the charging current of distribution, thus substantially increases computational speed of the present invention.

Meanwhile, operational failure component of the present invention removes the impact of load current on differential protection, thus improves sensitivity.

Accompanying drawing explanation

Fig. 1 shows the chart of the row wavefront of the inside and outside DC fault in LCCDC electrical network;

Fig. 2 shows the instrumentation plan of traditional traveling-wave protection device;

Fig. 3 shows the flow chart illustrated according to DC power network current differential protecting method of the present invention;

Fig. 4 schematically shows fault component distribution electrical network;

Fig. 5 shows the state when there is internal fault in circuit;

Fig. 6 shows the state when there is external fault in circuit;

Fig. 7 shows simulation model;

Fig. 8 shows analog result;

Fig. 9 shows the construction module figure of DC power network current differential protective system;

Figure 10 shows monopolar HVDC system.

Embodiment

Hereinafter, by reference to the accompanying drawings, the present invention is introduced more in detail by specific embodiment.

Fig. 3 shows the flow chart illustrated according to DC power network current differential protecting method of the present invention, and method comprises the following steps:

Step S301: obtain the pole tension sampled value in the local terminal of DC circuit and remote terminal and electrode current sampled value;

Step S302: calculate fault component pole tension value according to the pole tension sampled value of local terminal and remote terminal respectively; And calculate fault component electrode current value according to the electrode current sampled value of local terminal and remote terminal respectively;

Step S303: by based on Bei Jielong model (Bergeronmodel), the fault component pole tension value of the local terminal calculated in calculation procedure S302 and remote terminal and fault component electrode current value, obtain the fault component electrode current value of Chosen Point on the DC circuit between local terminal and remote terminal;

Step S304: if the fault component electrode current value at the Chosen Point place of the local terminal obtained in step S303 and remote terminal meets predetermined current differential protection criterion, then judge internal fault.

Bei Jielong model is based on distributed constant and telegraph equation (wave equation).Therefore the charging current that distributes during needing inherently and accurately to consider failure transient of the method in theory.

Therefore, the present invention adopts Bei Jielong model, does not so just need long time lengthening to eliminate the interference of the charging current of distribution, thus greatly improves the computational speed in the present invention.

Meanwhile, in step s 302, pole tension sampled value is converted into fault component pole tension value, and electrode current sampled value is converted into fault component electrode current value.Therefore, in this step, fault component pole tension value is separated from pole tension sampled value, and fault component electrode current value is separated from electrode current sampled value.In this case, when breaking down in electrical network, electrical network may be divided into fault-free network and fault component network, and such fault component pole tension value and fault component electrode current value are the pole tension/current values in fault component network.In step S303 subsequently and S304, fault component pole tension value and fault component electrode current value are carried out to pole modular transformation and be applied to Bei Jielong model.That is, the invention provides the current differential protection based on fault component.Therefore, operational failure component of the present invention removes the impact of load current on differential protection, thus improves sensitivity.

In preferred embodiment of the present invention, especially, DC electrical network is bipolar, and DC circuit comprises positive pole DC circuit and negative pole DC circuit, local terminal comprises positive pole local terminal and positive pole remote terminal, remote terminal comprises negative pole local terminal and negative pole remote terminal, positive pole DC line electricity connects positive pole local terminal and positive pole remote terminal, and negative pole DC line electricity connects negative pole local terminal and negative pole remote terminal, distance from Chosen Point to the Distance geometry of positive pole local terminal from Chosen Point to negative pole local terminal is identical, distance from Chosen Point to the Distance geometry of positive pole remote terminal from Chosen Point to negative pole remote terminal is identical, also comprise:

Pole modular transformation step: by carrying out pole modular transformation to each described fault component pole tension value in positive pole local terminal, positive pole remote terminal, negative pole local terminal and negative pole remote terminal, obtain the fault component mode voltage value of each modulus in local terminal and remote terminal, and by carrying out pole modular transformation to each described fault component electrode current value in positive pole local terminal, positive pole remote terminal, negative pole local terminal and negative pole remote terminal, obtain the fault component mould current value of each modulus of local terminal and remote terminal;

Step S303 also comprises:

By based on Bei Jielong model, calculate fault component mode voltage value and the fault component mould current value of each modulus of local terminal and remote terminal, obtain the fault component line wave voltage value of each modulus of local terminal and remote terminal respectively;

Respectively the fault component line wave voltage value of local terminal and remote terminal is converted to the fault component line ripple current value of local terminal and remote terminal;

The local terminal at the Chosen Point place on DC circuit and the fault component mould current value of remote terminal is determined respectively according to the fault component line ripple current value of local terminal and remote terminal;

Mould pole-change is carried out by the fault component mould current value of each modulus of the local terminal to Chosen Point place, obtain each fault component electrode current value in the positive pole local terminal at the Chosen Point place on DC circuit and negative pole local terminal, carry out mould pole-change by the fault component mould current value of each modulus of the remote terminal to Chosen Point place, obtain the positive pole remote terminal at Chosen Point place and the fault component electrode current value of negative pole remote terminal.

The fault component mode voltage and fault component mould electric current of carrying out mould pole-change are applied to Bei Jielong model by this embodiment, thus achieve particularly the Bei Jielong model of the fault component based on bipolar DC electrical network.

In one embodiment:

Pole tension sampled value comprises: u _lP(t), i.e. the voltage sample value of positive pole local terminal; u _lN(t), i.e. the voltage sample value of negative pole local terminal; u _rP(t), i.e. the voltage sample value of positive pole remote terminal; u _rN(t), i.e. the voltage sample value of negative pole remote terminal; Wherein t refers to the time;

Electrode current sampled value comprises: i _lP(t), the i.e. current sampling data of positive pole local terminal; i _lN(t), the i.e. current sampling data of negative pole local terminal; i _rP(t), the i.e. current sampling data of positive pole remote terminal; i _rN(t), the i.e. current sampling data of negative pole remote terminal;

Fault component pole tension value comprises: Δ u _lP(t), namely and u _lPthe fault component magnitude of voltage of t positive pole local terminal that () is corresponding; Δ u _lN(t), namely and u _lNthe fault component magnitude of voltage of t negative pole local terminal that () is corresponding; Δ u _rP(t), namely and u _rPthe fault component magnitude of voltage of t positive pole remote terminal that () is corresponding; Δ u _rN(t), namely and u _rNthe fault component magnitude of voltage of t negative pole remote terminal that () is corresponding;

Fault component electrode current value comprises: Δ i _lP(t), namely and i _lPthe fault component current value of t positive pole local terminal that () is corresponding; Δ i _lN(t), namely and i _lNthe fault component current value of t negative pole local terminal that () is corresponding; Δ i _rP(t), namely and i _rPthe fault component current value of t positive pole remote terminal that () is corresponding; Δ i _rN(t), namely and i _rNthe fault component current value of t negative pole remote terminal that () is corresponding;

Fault component mode voltage value comprises: Δ u _l0(t), i.e. the fault component common-mode voltage value of local terminal; Δ u _l1(t), i.e. the fault component differential mode voltage value of local terminal; Δ u _r0(t), i.e. the fault component common-mode voltage value of remote terminal; Δ u _r1(t), i.e. the fault component differential mode voltage value of remote terminal;

Fault component mould current value comprises: Δ i _l0(t), i.e. the fault component common-mode current value of local terminal; Δ i _l1(t), i.e. the fault component differential-mode current value of local terminal; Δ i _r0(t), i.e. the fault component common-mode current value of remote terminal; Δ i _r1(t), i.e. the fault component differential-mode current value of remote terminal;

The capable wave voltage value of fault component comprises: Δ u _l0+(t), i.e. the fault component common mode direct wave magnitude of voltage of local terminal; Δ u _l0-(t), i.e. the fault component common mode returning wave magnitude of voltage of local terminal; Δ u _l1+(t), i.e. the fault component differential mode direct wave magnitude of voltage of local terminal; Δ u _l0-(t), i.e. the fault component differential mode returning wave magnitude of voltage of local terminal; Δ u _r0+(t), i.e. the fault component common mode direct wave magnitude of voltage of remote terminal; Δ u _r0-(t), i.e. the fault component common mode returning wave magnitude of voltage of remote terminal; Δ u _r1+(t), i.e. the fault component differential mode direct wave magnitude of voltage of remote terminal; Δ u _r1-(t), i.e. the fault component differential mode returning wave magnitude of voltage of remote terminal;

Fault component travelling wave current value comprises: Δ i _l0+(t), i.e. the fault component common mode direct wave current value of local terminal; Δ i _l0-(t), i.e. the fault component common mode returning wave current value of local terminal; Δ i _l1+(t), i.e. the fault component differential mode direct wave current value of local terminal; Δ i _l1-(t), i.e. the fault component differential mode returning wave current value of local terminal; Δ i _r0+(t), i.e. the fault component common mode direct wave current value of remote terminal; Δ i _r0-(t), i.e. the fault component common mode returning wave current value of remote terminal; Δ i _r1+(t), i.e. the fault component differential mode direct wave current value of remote terminal; Δ i _r1-(t), i.e. the fault component differential mode returning wave current value of remote terminal;

The fault component mould current value at Chosen Point place comprises: Δ i _l0(x, t), i.e. the fault component common-mode current value at the Chosen Point place of local terminal; Δ i _l1(x, t), i.e. the fault component differential-mode current value at the Chosen Point place of local terminal; Δ i _r0(x, t), i.e. the fault component common-mode current value at the Chosen Point place of remote terminal; Δ i _r1(x, t), i.e. the fault component differential-mode current value at the Chosen Point place of remote terminal;

The fault component electrode current value at Chosen Point place comprises: Δ i _lP(x, t), i.e. the fault component electrode current value at the Chosen Point place of positive pole local terminal; Δ i _lN(x, t), i.e. the fault component electrode current value at the Chosen Point place of negative pole local terminal; Δ i _rP(x, t), i.e. the fault component electrode current value at the Chosen Point place of positive pole remote terminal; Δ i _rN(x, t), i.e. the fault component electrode current value at the Chosen Point place of negative pole remote terminal.

This embodiment calculates for positive pole and negative pole respectively, thus achieves respectively for the differential protection of two poles.

In one embodiment:

In step s 302, fault component pole tension value and fault component pole tension value is calculated in the following ways:

$\left\{\begin{array}{c}{\mathrm{\&Delta;i}}_{LP}\left(t\right)=i_{LP}\left(t\right)-i_{LP}(t-T)\\ {\mathrm{\&Delta;i}}_{LN}\left(t\right)=i_{LN}\left(t\right)-i_{LN}(t-T)\\ {\mathrm{\&Delta;u}}_{LP}\left(t\right)=u_{LP}\left(t\right)-u_{LP}(t-T)\\ {\mathrm{\&Delta;u}}_{LN}\left(t\right)=u_{LN}\left(t\right)-u_{LN}(t-T)\\ {\mathrm{\&Delta;i}}_{RP}\left(t\right)=i_{RP}\left(t\right)-i_{RP}(t-T)\\ {\mathrm{\&Delta;i}}_{RN}\left(t\right)=i_{RN}\left(t\right)-i_{RN}(t-T)\\ {\mathrm{\&Delta;u}}_{RP}\left(t\right)=u_{RP}\left(t\right)-u_{RP}(t-T)\\ {\mathrm{\&Delta;u}}_{RN}\left(t\right)=u_{RN}\left(t\right)-u_{RN}(t-T)\end{array}\right.,$

Wherein, T represents time delay;

In pole modular transformation step, calculate fault component mode voltage value and fault component mould current value in the following ways:

$\left\{\begin{array}{c}\left[\begin{array}{c}{\mathrm{\&Delta;u}}_{L0}\left(t\right)\\ {\mathrm{\&Delta;u}}_{L1}\left(t\right)\end{array}\right]=\left[\begin{array}{cc}1& 1\\ 1& -1\end{array}\right]\left[\begin{array}{c}{\mathrm{\&Delta;u}}_{LP}\left(t\right)\\ {\mathrm{\&Delta;u}}_{LN}\left(t\right)\end{array}\right]\\ \left[\begin{array}{c}{\mathrm{\&Delta;i}}_{L0}\left(t\right)\\ {\mathrm{\&Delta;i}}_{L1}\left(t\right)\end{array}\right]=\left[\begin{array}{cc}1& 1\\ 1& -1\end{array}\right]\left[\begin{array}{c}{\mathrm{\&Delta;i}}_{LP}\left(t\right)\\ {\mathrm{\&Delta;i}}_{LN}\left(t\right)\end{array}\right]\\ \left[\begin{array}{c}{\mathrm{\&Delta;u}}_{R0}\left(t\right)\\ {\mathrm{\&Delta;u}}_{R1}\left(t\right)\end{array}\right]=\left[\begin{array}{cc}1& 1\\ 1& -1\end{array}\right]\left[\begin{array}{c}{\mathrm{\&Delta;u}}_{RP}\left(t\right)\\ {\mathrm{\&Delta;u}}_{RN}\left(t\right)\end{array}\right]\\ \left[\begin{array}{c}{\mathrm{\&Delta;i}}_{R0}\left(t\right)\\ {\mathrm{\&Delta;i}}_{R1}\left(t\right)\end{array}\right]=\left[\begin{array}{cc}1& 1\\ 1& -1\end{array}\right]\left[\begin{array}{c}{\mathrm{\&Delta;i}}_{RP}\left(t\right)\\ {\mathrm{\&Delta;i}}_{RN}\left(t\right)\end{array}\right]\end{array}\right.$

Comprise in step S303:

Calculate fault component line wave voltage value in the following ways:

$\left\{\begin{array}{c}{\mathrm{\&Delta;u}}_{L0+}\left(t\right)={\mathrm{\&Delta;u}}_{L0}\left(t\right)+{\mathrm{\&Delta;i}}_{L0}\left(t\right)\&times;Z_{C0}\\ {\mathrm{\&Delta;u}}_{L0-}\left(t\right)={\mathrm{\&Delta;u}}_{L0}\left(t\right)-{\mathrm{\&Delta;i}}_{L0}\left(t\right)\&times;Z_{C0}\\ {\mathrm{\&Delta;u}}_{L0-}\left(t\right)={\mathrm{\&Delta;u}}_{L0}\left(t\right)-{\mathrm{\&Delta;i}}_{L0}\left(t\right)\&times;Z_{C0}\\ {\mathrm{\&Delta;u}}_{L1+}\left(t\right)={\mathrm{\&Delta;u}}_{L1}\left(t\right)+{\mathrm{\&Delta;i}}_{L1}\left(t\right)\&times;Z_{C1}\\ {\mathrm{\&Delta;u}}_{L1-}\left(t\right)={\mathrm{\&Delta;u}}_{L1}\left(t\right)-{\mathrm{\&Delta;i}}_{L1}\left(t\right)\&times;Z_{C1}\\ {\mathrm{\&Delta;u}}_{R0-}\left(t\right)={\mathrm{\&Delta;u}}_{R0}\left(t\right)-{\mathrm{\&Delta;i}}_{R0}\left(t\right)\&times;Z_{C0}\\ {\mathrm{\&Delta;u}}_{R1+}\left(t\right)={\mathrm{\&Delta;u}}_{R1}\left(t\right)+{\mathrm{\&Delta;i}}_{R1}\left(t\right)\&times;Z_{C1}\\ {\mathrm{\&Delta;u}}_{R1-}\left(t\right)={\mathrm{\&Delta;u}}_{R1}\left(t\right)-{\mathrm{\&Delta;i}}_{R1}\left(t\right)\&times;Z_{C1}\end{array}\right.,$

Wherein, Z _c0it is common mode wave impedance; Z _c1it is differential mode wave impedance;

Calculate fault component line ripple current value in the following ways:

$\left\{\begin{array}{c}{\mathrm{\&Delta;i}}_{L0+}\left(t\right)={\mathrm{\&Delta;u}}_{L0+}\left(t\right)/Z_{C0}\\ {\mathrm{\&Delta;i}}_{L0-}\left(t\right)=-{\mathrm{\&Delta;u}}_{L0-}\left(t\right)/Z_{C0}\\ {\mathrm{\&Delta;i}}_{L1+}\left(t\right)={\mathrm{\&Delta;u}}_{L1+}\left(t\right)/Z_{C1}\\ {\mathrm{\&Delta;i}}_{L1-}\left(t\right)=-{\mathrm{\&Delta;u}}_{L1-}\left(t\right)/Z_{C1}\\ {\mathrm{\&Delta;i}}_{R0+}\left(t\right)={\mathrm{\&Delta;u}}_{R0+}\left(t\right)/Z_{C0}\\ {\mathrm{\&Delta;i}}_{R0-}\left(t\right)=-{\mathrm{\&Delta;u}}_{R0-}\left(t\right)/Z_{C0}\\ {\mathrm{\&Delta;i}}_{R1+}\left(t\right)={\mathrm{\&Delta;u}}_{R1+}\left(t\right)/Z_{C1}\\ {\mathrm{\&Delta;i}}_{R1-}\left(t\right)=-{\mathrm{\&Delta;u}}_{R1-}\left(t\right)/Z_{C1}\end{array}\right.;$

Calculate the fault component mould current value at Chosen Point place in the following ways:

$\left\{\begin{array}{c}{\mathrm{\&Delta;i}}_{L1}(x,t)={\mathrm{\&Delta;i}}_{L1+}(t-\frac{x}{v_1})-{\mathrm{\&Delta;i}}_{L1-}(t+\frac{x}{v_1})\\ {\mathrm{\&Delta;i}}_{L0}(x,t)={\mathrm{\&Delta;i}}_{L0+}(t-\frac{x}{v_0})-{\mathrm{\&Delta;i}}_{L0-}(t+\frac{x}{v_0})\\ {\mathrm{\&Delta;i}}_{R1}(x,t)={\mathrm{\&Delta;i}}_{R1+}(t-\frac{x}{v_1})-{\mathrm{\&Delta;i}}_{R1-}(t+\frac{x}{v_1})\\ {\mathrm{\&Delta;i}}_{R0}(x,t)={\mathrm{\&Delta;i}}_{R0+}(t-\frac{x}{v_0})-{\mathrm{\&Delta;i}}_{R0-}(t+\frac{x}{v_0})\end{array}\right.$

Wherein, v ₀the gait of march of fault component common mode row ripple, v ₁it is the gait of march of the capable ripple of fault component differential mode;

Calculate the fault component electrode current value at Chosen Point place in the following ways:

$\left\{\begin{array}{c}\left[\begin{array}{c}{\mathrm{\&Delta;i}}_{LP}(x,t)\\ {\mathrm{\&Delta;i}}_{LN}(x,t)\end{array}\right]=\frac{1}{2}\left[\begin{array}{cc}1& 1\\ 1& -1\end{array}\right]\left[\begin{array}{c}{\mathrm{\&Delta;i}}_{L0}(x,t)\\ {\mathrm{\&Delta;i}}_{L1}(x,t)\end{array}\right]\\ \left[\begin{array}{c}{i}_{RP}(x,t)\\ {\mathrm{\&Delta;i}}_{RN}(x,t)\end{array}\right]=\frac{1}{2}\left[\begin{array}{cc}1& 1\\ 1& -1\end{array}\right]\left[\begin{array}{c}{\mathrm{\&Delta;i}}_{R0}(x,t)\\ {\mathrm{\&Delta;i}}_{R1}(x,t)\end{array}\right]\end{array}\right.$

In one embodiment:

Comprise in step s 304:

If met | Δ i _lP(x, t)+Δ i _rP(x, t) | > I _res, then decision state is positive pole internal fault; If met | Δ i _lN(x, t)+Δ i _rN(x, t) | > I _res, then decision state is negative pole internal fault, wherein I _resrepresent predetermined threshold value;

Otherwise, will not differential protection be activated.

In one embodiment, DC electrical network is one pole:

Step S303 also comprises:

By based on Bei Jielong model, calculate fault component pole tension value and the fault component mould current value of local terminal and remote terminal, obtain the fault component extremely row wave voltage value of local terminal and remote terminal respectively;

Respectively by the fault component of local terminal and remote terminal extremely row wave voltage value convert the fault component line ripple current value of local terminal and remote terminal to;

According to the fault component pole travelling wave current value of local terminal and remote terminal, determine the local terminal at the Chosen Point place on DC circuit and the fault component electrode current value of remote terminal.

This embodiment achieves the Bei Jielong model of the fault component based on one pole DC electrical network especially.

In one embodiment, in step s 302, fault component pole tension value and fault component electrode current value is calculated in the following ways:

$\left\{\begin{array}{c}{\mathrm{\&Delta;i}}_L\left(t\right)=i_L\left(t\right)-i_L(t-T)\\ {\mathrm{\&Delta;u}}_L\left(t\right)=u_L\left(t\right)-u_L(t-T)\\ {\mathrm{\&Delta;i}}_R\left(t\right)=i_R\left(t\right)-i_R(t-T)\\ {\mathrm{\&Delta;u}}_R\left(t\right)=u_R\left(t\right)-u_R(t-T)\end{array}\right.,$

Wherein, T represents time delay, Δ i _lt () is the fault component electrode current value of local terminal, Δ i _rt () is the fault component electrode current value of remote terminal, Δ u _lt () is the fault component pole tension value of local terminal, Δ u _rt () is the fault component pole tension value of remote terminal, i _lt () is the current sampling data of local terminal, i _rt () is the current sampling data of remote terminal, u _lt () is the voltage sample value of local terminal, u _rt () is the voltage sample value of remote terminal, and t refers to the time;

Step S303 comprises:

Calculate fault component extremely row wave voltage value in the following ways:

$\left\{\begin{array}{c}\mathrm{\&Delta;}{u}_{L+}\left(t\right)=\mathrm{\&Delta;}{u}_L\left(t\right)+\mathrm{\&Delta;}{i}_L\left(t\right)\&times;Z_C\\ {\mathrm{\&Delta;u}}_{L-}\left(t\right)={\mathrm{\&Delta;u}}_L\left(t\right)-{\mathrm{\&Delta;i}}_L\left(t\right)\&times;Z_C\\ {\mathrm{\&Delta;u}}_{R+}\left(t\right)={\mathrm{\&Delta;u}}_R\left(t\right)+{\mathrm{\&Delta;i}}_R\left(t\right)\&times;Z_C\\ \mathrm{\&Delta;}{u}_{R-}\left(t\right)=\mathrm{\&Delta;}{u}_R\left(t\right)-\mathrm{\&Delta;}{i}_R\left(t\right)\&times;Z_C\end{array}\right.$

Wherein, Z _cwave impedance, Δ u _l+t () is the fault component pole direct wave magnitude of voltage of local terminal; Δ u _l-t () is the fault component pole returning wave magnitude of voltage of local terminal; Δ u _r+t () is the fault component pole direct wave magnitude of voltage of remote terminal; Δ u _r-t () is the fault component pole returning wave magnitude of voltage of remote terminal;

Calculate fault component pole travelling wave current value in the following ways:

$\left\{\begin{array}{c}\mathrm{\&Delta;}{i}_{L+}\left(t\right)=\mathrm{\&Delta;}{u}_{L+}\left(t\right)/Z_C\\ {\mathrm{\&Delta;i}}_{L-}\left(t\right)=-{\mathrm{\&Delta;u}}_{L-}\left(t\right)/Z_C\\ {\mathrm{\&Delta;i}}_{R+}\left(t\right)={\mathrm{\&Delta;u}}_{R+}\left(t\right)/Z_C\\ {\mathrm{\&Delta;i}}_{R-}\left(t\right)=-{\mathrm{\&Delta;u}}_{R-}\left(t\right)/Z_C\end{array}\right.$

Wherein, Δ i _l+t () is the fault component pole direct wave current value of local terminal; Δ i _l-t () is the fault component pole returning wave current value of local terminal; Δ i _r+t () is the fault component pole direct wave current value of remote terminal; Δ i _r-t () is the fault component pole returning wave current value of remote terminal;

Calculate the fault component electrode current value at select location place in the following ways:

$\left\{\begin{array}{c}{\mathrm{\&Delta;i}}_L(x,t)={\mathrm{\&Delta;i}}_{L+}(t-\frac{x}{v})-{\mathrm{\&Delta;i}}_{L-}(t+\frac{x}{v})\\ {\mathrm{\&Delta;i}}_R(x,t)={\mathrm{\&Delta;i}}_{R+}(t-\frac{x}{v})-{\mathrm{\&Delta;i}}_{R-}(t+\frac{x}{v})\end{array}\right.$

Wherein Δ i _l(x, t) is the fault component electrode current value at the Chosen Point place in local terminal; Δ i _r(x, t) is the fault component electrode current value at the Chosen Point place of remote terminal, and v is the gait of march of the capable ripple of fault component.

In one embodiment, step S304 comprises:

If met | Δ i _l(x, t)+Δ i _r(x, t) | > I _res, then decision state is internal fault.

In one embodiment, step S304 also comprises:

If state is determined into internal fault, then sends error protection order to activate differential protection, otherwise will not differential protection be activated.

Bipolar DC electrical network

In preferred embodiment of the present invention, the fault component schematically illustrated distribution electrical network as shown in Figure 4, current differential protection method of the present invention manages to calculate at the Δ i of specific t at Chosen Point place _lP(x, t) and Δ i _rP(x, t), to make the judgement of positive electrode fault, and calculates at the Δ i of specific t at Chosen Point x place simultaneously _lN(x, t) and Δ i _rN(x, t), to make the judgement of negative pole fault.Local side 41 can be communicated by communication line with remote side 42, and so local side 41 can obtain whole parameter informations of local side 41 and remote side 42.Especially, Δ i can be calculated in the following ways _lP(x, t), Δ i _rP(x, t), Δ i _lN(x, t) and Δ i _rN(x, t):

Fault component electric current and voltage calculate

Fault component is calculated by following formula (1):

$\left\{\begin{array}{c}{\mathrm{\&Delta;i}}_{LP}\left(t\right)=i_{LP}\left(t\right)-i_{LP}(t-T)\\ {\mathrm{\&Delta;i}}_{LN}\left(t\right)=i_{LN}\left(t\right)-i_{LN}(t-T)\\ {\mathrm{\&Delta;u}}_{LP}\left(t\right)=u_{LP}\left(t\right)-u_{LP}(t-T)\\ {\mathrm{\&Delta;u}}_{LN}\left(t\right)=u_{LN}\left(t\right)-u_{LN}(t-T)\\ {\mathrm{\&Delta;i}}_{RP}\left(t\right)=i_{RP}\left(t\right)-i_{RP}(t-T)\\ {\mathrm{\&Delta;i}}_{RN}\left(t\right)=i_{RN}\left(t\right)-i_{RN}(t-T)\\ {\mathrm{\&Delta;u}}_{RP}\left(t\right)=u_{RP}\left(t\right)-u_{RP}(t-T)\\ {\mathrm{\&Delta;u}}_{RN}\left(t\right)=u_{RN}\left(t\right)-u_{RN}(t-T)\end{array}\right.---\left(1\right)$

Wherein, T is time delay, and according to demand, T can be set to such as 10ms or 100ms.

Pole mode conversion

Fault component current value and magnitude of voltage Δ i is being obtained by formula (1) _lP(t), Δ i _lN(t), Δ u _lP(t), Δ u _lN(t), Δ i _rP(t), Δ i _rN(t), Δ u _rP(t) and Δ u _rNt, after (), next step does pole modular transformation to convert maximum dose to modulus.The pole modular transformation matrix for voltage and current is given in formula (2).

$\left\{\begin{array}{c}\left[\begin{array}{c}{\mathrm{\&Delta;u}}_{L0}\left(t\right)\\ {\mathrm{\&Delta;u}}_{L1}\left(t\right)\end{array}\right]=\left[\begin{array}{cc}1& 1\\ 1& -1\end{array}\right]\left[\begin{array}{c}{\mathrm{\&Delta;u}}_{LP}\left(t\right)\\ {\mathrm{\&Delta;u}}_{LN}\left(t\right)\end{array}\right]\\ \left[\begin{array}{c}{\mathrm{\&Delta;i}}_{L0}\left(t\right)\\ {\mathrm{\&Delta;i}}_{L1}\left(t\right)\end{array}\right]=\left[\begin{array}{cc}1& 1\\ 1& -1\end{array}\right]\left[\begin{array}{c}{\mathrm{\&Delta;i}}_{LP}\left(t\right)\\ {\mathrm{\&Delta;i}}_{LN}\left(t\right)\end{array}\right]\\ \left[\begin{array}{c}{\mathrm{\&Delta;u}}_{R0}\left(t\right)\\ {\mathrm{\&Delta;u}}_{R1}\left(t\right)\end{array}\right]=\left[\begin{array}{cc}1& 1\\ 1& -1\end{array}\right]\left[\begin{array}{c}{\mathrm{\&Delta;u}}_{RP}\left(t\right)\\ {\mathrm{\&Delta;u}}_{RN}\left(t\right)\end{array}\right]\\ \left[\begin{array}{c}{\mathrm{\&Delta;i}}_{R0}\left(t\right)\\ {\mathrm{\&Delta;i}}_{R1}\left(t\right)\end{array}\right]=\left[\begin{array}{cc}1& 1\\ 1& -1\end{array}\right]\left[\begin{array}{c}{\mathrm{\&Delta;i}}_{RP}\left(t\right)\\ {\mathrm{\&Delta;i}}_{RN}\left(t\right)\end{array}\right]\end{array}\right.---\left(2\right)$

Differential current based on Bei Jielong model calculates

In this step, based on Bei Jielong model (row wave propagation equations), will use respectively from the measured value of two terminals, calculate the fault component capable ripple common and different mode current value at the Chosen Point x place on protected circuit.

(1) fault component pattern row wave voltage value is calculated

Formula 3 can be used for calculating the common mode forward voltage capable ripple Δ u of local side fault component _l0+with reverse voltage capable ripple Δ u _l0-, the differential mode forward voltage capable ripple Δ u of local side fault component _l1+with reverse voltage capable ripple Δ u _l1-, the common mode forward voltage capable ripple Δ u of remote side fault component _r0+with reverse voltage capable ripple Δ u _r0-, and the differential mode forward voltage capable ripple Δ u of remote side fault component _r1+with reverse voltage capable ripple Δ u _r1-.

$\left\{\begin{array}{c}{\mathrm{\&Delta;u}}_{L0+}\left(t\right)={\mathrm{\&Delta;u}}_{L0}\left(t\right)+{\mathrm{\&Delta;i}}_{L0}\left(t\right)\&times;Z_{C0}\\ {\mathrm{\&Delta;u}}_{L0-}\left(t\right)={\mathrm{\&Delta;u}}_{L0}\left(t\right)-{\mathrm{\&Delta;i}}_{L0}\left(t\right)\&times;Z_{C0}\\ {\mathrm{\&Delta;u}}_{L1+}\left(t\right)={\mathrm{\&Delta;u}}_{L1}\left(t\right)+{\mathrm{\&Delta;i}}_{L1}\left(t\right)\&times;Z_{C1}\\ {\mathrm{\&Delta;u}}_{L1-}\left(t\right)={\mathrm{\&Delta;u}}_{L1}\left(t\right)-{\mathrm{\&Delta;i}}_{L1}\left(t\right)\&times;Z_{C1}\\ {\mathrm{\&Delta;u}}_{R0+}\left(t\right)={\mathrm{\&Delta;u}}_{R0}\left(t\right)+{\mathrm{\&Delta;i}}_{R0}\left(t\right)\&times;Z_{C0}\\ {\mathrm{\&Delta;u}}_{R0-}\left(t\right)={\mathrm{\&Delta;u}}_{R0}\left(t\right)-{\mathrm{\&Delta;i}}_{R0}\left(t\right)\&times;Z_{C0}\\ {\mathrm{\&Delta;u}}_{R1+}\left(t\right)={\mathrm{\&Delta;u}}_{R1}\left(t\right)+{\mathrm{\&Delta;i}}_{R1}\left(t\right)\&times;Z_{C1}\\ {\mathrm{\&Delta;u}}_{R1-}\left(t\right)={\mathrm{\&Delta;u}}_{R1}\left(t\right)-{\mathrm{\&Delta;i}}_{R1}\left(t\right)\&times;Z_{C1}\end{array}\right.---\left(3\right)$

Wherein Z _c0common mode wave impedance, Z _c1it is differential mode wave impedance.

(2) fault component line ripple current value is calculated

Formula 4 can be used for calculating the common mode forward current capable ripple Δ i of local side fault component _l0+with reverse current capable ripple Δ i _l0-, the differential mode forward current capable ripple Δ i of local side fault component _l1+with reverse current capable ripple Δ i _l1-, the common mode forward current capable ripple Δ i of remote side fault component _r0+with reverse current capable ripple Δ i _r0-, and the differential mode forward current capable ripple Δ i of remote side fault component _r1+with reverse current capable ripple Δ i _r1-.

$\left\{\begin{array}{c}{\mathrm{\&Delta;i}}_{L0+}\left(t\right)={\mathrm{\&Delta;u}}_{L0+}\left(t\right)/Z_{C0}\\ {\mathrm{\&Delta;i}}_{L0-}\left(t\right)=-{\mathrm{\&Delta;u}}_{L0-}\left(t\right)/Z_{C0}\\ {\mathrm{\&Delta;i}}_{L1+}\left(t\right)={\mathrm{\&Delta;u}}_{L1+}\left(t\right)/Z_{C1}\\ {\mathrm{\&Delta;i}}_{L1-}\left(t\right)=-{\mathrm{\&Delta;u}}_{L1-}\left(t\right)/Z_{C1}\\ {\mathrm{\&Delta;i}}_{R0+}\left(t\right)={\mathrm{\&Delta;u}}_{R0+}\left(t\right)/Z_{C0}\\ {\mathrm{\&Delta;i}}_{R0-}\left(t\right)=-{\mathrm{\&Delta;u}}_{R0-}\left(t\right)/Z_{C0}\\ {\mathrm{\&Delta;i}}_{R1+}\left(t\right)={\mathrm{\&Delta;u}}_{R1+}\left(t\right)/Z_{C1}\\ {\mathrm{\&Delta;i}}_{R1-}\left(t\right)=-{\mathrm{\&Delta;u}}_{R1-}\left(t\right)/Z_{C1}\end{array}\right.---\left(4\right)$

(3) at the fault component mould current value at select location place

Based on row ripple principle, use following formula 5 can calculate at the local terminal at Chosen Point x place and the fault component differential mode of remote terminal and common mode current, wherein calculated fault component differential mode and the common mode current of the local terminal at Chosen Point x place by the measured value of local terminal, calculated fault component differential mode and the common mode current of the remote terminal at Chosen Point x place by the measured value of remote terminal:

$\left\{\begin{array}{c}{\mathrm{\&Delta;i}}_{L1}(x,t)={\mathrm{\&Delta;i}}_{L1+}(t-\frac{x}{v_1})-{\mathrm{\&Delta;i}}_{L1-}(t+\frac{x}{v_1})\\ {\mathrm{\&Delta;i}}_{L0}(x,t)={\mathrm{\&Delta;i}}_{L0+}(t-\frac{x}{v_0})-{\mathrm{\&Delta;i}}_{L0-}(t+\frac{x}{v_0})\\ {\mathrm{\&Delta;i}}_{R1}(x,t)={\mathrm{\&Delta;i}}_{R1+}(t-\frac{x}{v_1})-{\mathrm{\&Delta;i}}_{R1-}(t+\frac{x}{v_1})\\ {\mathrm{\&Delta;i}}_{R0}(x,t)={\mathrm{\&Delta;i}}_{R0+}(t-\frac{x}{v_0})-{\mathrm{\&Delta;i}}_{R0-}(t+\frac{x}{v_0})\end{array}\right.---\left(5\right)$

(4) mould pole-change

In this step, mould pole-change is all used to calculate positive electrode current at Chosen Point place and cathodal current for local and remote terminal.In following formula 6, transformation matrix is shown:

$\left\{\begin{array}{c}\left[\begin{array}{c}{\mathrm{\&Delta;i}}_{LP}(x,t)\\ {\mathrm{\&Delta;i}}_{LN}(x,t)\end{array}\right]=\frac{1}{2}\left[\begin{array}{cc}1& 1\\ 1& -1\end{array}\right]\left[\begin{array}{c}{\mathrm{\&Delta;i}}_{L0}(x,t)\\ {\mathrm{\&Delta;i}}_{L1}(x,t)\end{array}\right]\\ \left[\begin{array}{c}{i}_{RP}(x,t)\\ {\mathrm{\&Delta;i}}_{RN}(x,t)\end{array}\right]=\frac{1}{2}\left[\begin{array}{cc}1& 1\\ 1& -1\end{array}\right]\left[\begin{array}{c}{\mathrm{\&Delta;i}}_{R0}(x,t)\\ {\mathrm{\&Delta;i}}_{R1}(x,t)\end{array}\right]\end{array}\right.---\left(6\right)$

Criterion for activated current differential protection:

If meet following formula 7:

|Δi _LP(x,t)+Δi _RP(L-x,t)|＞I _res(7)

Then state is determined into " positive pole internal fault ", thus sends error protection order, and activates the control of differential protection.

If meet following formula (8):

|Δi _LN(x,t)+Δi _RN(L-x,t)|＞I _res(8)

Then state is determined into " negative pole internal fault ", thus sends error protection order, and activates the control of differential protection.

One pole DC electrical network:

In preferred embodiment of the present invention, as shown in Figure 10, wherein, Δ u _l(t) and Δ i _lt () is the fault component voltage and current of local terminal, Δ u _r(t) and Δ i _rt () is the fault component voltage and current of remote terminal,

Δ i _l(x, t) be adopt local measurements calculate at an electric current at x place,

Δ i _r(x, t) be adopt remote measurement value to calculate at an electric current at x place,

As shown above, will based on Bei Jielong model (telegraph equation, traveling-wave equation), the measured value of employing two terminals calculates the fault component electric current at Chosen Point " x " place respectively.

For the current component adopting local measurements to calculate, x is along the distance between any Chosen Point and local terminal of circuit.Such as, if Chosen Point is remote terminal, so distance x is the length L of circuit;

For the current component adopting remote measurement value to calculate, x is along the distance between any Chosen Point and remote terminal of circuit.Such as, if Chosen Point is remote terminal, so distance x is zero.

In following chapters and sections, calculation procedure will be introduced in detail.

Fault component electric current and voltage calculate

The method calculating fault component is:

$\left\{\begin{array}{c}\mathrm{\&Delta;}u\left(t\right)=u\left(t\right)-u(t-T)\\ \mathrm{\&Delta;}i\left(t\right)=i\left(t\right)-i(t-T)\end{array}\right.---\left(9\right)$

In formula 9, u (t) and i (t) is the pole tension and current sampling data measured.Δ u (t) and Δ i (t) are corresponding fault component voltage and current values.T is time delay, can be set to such as 10ms or 100ms as required.According to this method, the fault component magnitude of voltage at the two poles of the earth and two ends and current value can both calculate as formula 10.

$\left\{\begin{array}{c}{\mathrm{\&Delta;i}}_L\left(t\right)=i_L\left(t\right)-i_L(t-T)\\ {\mathrm{\&Delta;u}}_L\left(t\right)=u_L\left(t\right)-u_L(t-T)\\ {\mathrm{\&Delta;i}}_R\left(t\right)=i_R\left(t\right)-i_R(t-T)\\ {\mathrm{\&Delta;u}}_R\left(t\right)=u_R\left(t\right)-u_R(t-T)\end{array}\right.---\left(10\right)$

Differential current based on Bei Jielong model calculates

In this step, will, based on Bei Jielong model (row wave propagation equations), the measured value from two terminals be adopted to calculate the travelling wave current at the Chosen Point x place on protected circuit respectively.

Row wave voltage component calculates

Formula 11 can be used to calculate forward voltage capable ripple Δ u _l+with reverse voltage capable ripple Δ u _l-.

$\left\{\begin{array}{c}\mathrm{\&Delta;}{u}_{L+}\left(t\right)=\mathrm{\&Delta;}{u}_L\left(t\right)+\mathrm{\&Delta;}{i}_L\left(t\right)\&times;Z_C\\ {\mathrm{\&Delta;u}}_{L-}\left(t\right)={\mathrm{\&Delta;u}}_L\left(t\right)-{\mathrm{\&Delta;i}}_L\left(t\right)\&times;Z_C\\ {\mathrm{\&Delta;u}}_{R+}\left(t\right)={\mathrm{\&Delta;u}}_R\left(t\right)+{\mathrm{\&Delta;i}}_R\left(t\right)\&times;Z_C\\ \mathrm{\&Delta;}{u}_{R-}\left(t\right)=\mathrm{\&Delta;}{u}_R\left(t\right)-\mathrm{\&Delta;}{i}_R\left(t\right)\&times;Z_C\end{array}\right.---\left(11\right)$

Travelling wave current component calculates

Then, formula 12 can be used to calculate forward current capable ripple Δ i _l+with reverse current capable ripple Δ i _l-.

$\left\{\begin{array}{c}\mathrm{\&Delta;}{i}_{L+}\left(t\right)=\mathrm{\&Delta;}{u}_{L+}\left(t\right)/Z_C\\ {\mathrm{\&Delta;i}}_{L-}\left(t\right)=-{\mathrm{\&Delta;u}}_{L-}\left(t\right)/Z_C\\ {\mathrm{\&Delta;i}}_{R+}\left(t\right)={\mathrm{\&Delta;u}}_{R+}\left(t\right)/Z_C\\ \mathrm{\&Delta;}{i}_{R-}\left(t\right)=-\mathrm{\&Delta;}{u}_{R-}\left(t\right)/Z_C\end{array}\right.---\left(12\right)$

Travelling wave current component at Chosen Point place calculates

Based on row ripple principle, use formula 13 can calculate the electric current at Chosen Point x place.

$\left\{\begin{array}{c}{\mathrm{\&Delta;i}}_L(x,t)={\mathrm{\&Delta;i}}_{L+}(t-\frac{x}{v})-{\mathrm{\&Delta;i}}_{L-}(t+\frac{x}{v})\\ {\mathrm{\&Delta;i}}_R(x,t)={\mathrm{\&Delta;i}}_{R+}(t-\frac{x}{v})-{\mathrm{\&Delta;i}}_{R-}(t+\frac{x}{v})\end{array}\right.---\left(13\right)$

Wherein, v is the gait of march of row ripple;

T is the time;

X is any point along circuit, and it can be intermediate point, end points, starting point or other point any;

Δ i _l(x, t) is the fault component electric current at the Chosen Point x place adopting the measured value of local terminal to calculate;

Δ i _r(x, t) is the fault component electric current at the Chosen Point x place adopting the measured value of remote terminal to calculate;

Differential current calculates

As shown in Equation 14, calculate differential current by electrode current, and compare with threshold value.If differential current is greater than suppression electric current, then mean internal fault.Otherwise meaning external fault.The following shows the criterion for detecting internal fault.

|Δi _L(x,t)+Δi _R(x,t)|＞I _res(14)

Performance evaluation

Classical differential protection in HVDC circuit

The following shows the criterion of typical classical differential protection:

|I _Local+I _Remote|＞I _Set(9)

Wherein, I _locallocal terminal electric current, I _remoteit is remote terminal electric current.

Fig. 5 illustrates the state when there is internal fault in circuit.For internal fault, have

|I _Local+I _Remote|＝I _F+I _C(10)

Wherein, I _fthe fault current by fault branch as shown in Figure 5, I _cthe electric current of the electric capacity flowed through along circuit distribution, usually much higher than zero, particularly for the transmission line that length is long.Compare with formula (9), we can be observed protection philosophy and can correctly work.

But for external fault, condenser current will cause problem.Fig. 6 shows the state when there is external fault in circuit.For external fault, have

|I _Local+I _Remote|＝I _C(11)

From formula (11), we recognize the misoperation in order to avoid external fault, set point I _setmust higher than I _c.Due to I _conly temporarily exist after a failure, the another method avoiding misoperation makes I _setremain standard value, but use long time delay to wait for until transient process disappears.

Usually in actual applications, in order to not damage the sensitivity of Protection criteria under high impedance fault, second method is used, namely long time delay (0.5s-1.5s).But subsequently, response speed has slowed down.

The present invention

The present invention is based on the traveling-wave component using Bei Jielong model to calculate, wherein Bei Jielong model take into account line distribution capacitance.

Thereby, it is possible to calculate accurate differential current, accurate differential current eliminates the charging current of discrete capacitor:

-when internal fault occurs, the differential current of calculating is the fault current I flowing through fault branch _f, such as, | Δ i _lP(x, t)+Δ i _rP(x, t) |=I _f;

-when external fault occurs, the differential current that the present invention calculates is zero, such as | Δ i _lP(x, t)+Δ i _rP(x, t) |=0.

This allows the present invention not by the impact of the electric capacity along circuit distribution, thus guarantees responsiveness.

Quick acting speed

Responsiveness for protection extremely important; It is a most important requirement to protection.When an error occurs, the stability of a system and personal security are on the hazard, and isolation is highly profitable for the stability of a system and personal security fast.Important stability and sensitivity are required to include to two other of protection.Good protection philosophy must realize this three advantages: quick acting speed, stability and sensitivity.

Due to capacitance current, classical differential protection can not quick acting, and waits for before transient phases in the past, because which limit its speed.Different with classical differential protection, the present invention is not by the impact of the electric capacity along circuit distribution, and therefore it can realize responsiveness faster.And be also that therefore it can use lower current threshold and realize higher sensitivity because it is not by the impact of capacitance current.

Consider the length that depends on circuit and communication lines by call duration time, in most cases responsiveness of the present invention is less than 15ms, and the operate time of classical differential protection is 0.5s-1.5s.Algorithm of the present invention can be used as the main protection for above-mentioned LCCDC electrical network, and can be used as the stand-by protection of the DC electrical network for other type, and can obtain the responsiveness higher than classical differential protection; And it also can be used as the main protection for short-term road, wherein the call duration time of short-term road is shorter than the DC network system of other type, or point-to-point HVDC system.

To the good sensitivity of high resistance failure

The sensitivity that the present invention has had high resistance failure, because it is based on fault component, eliminate the impact of load current on differential protection, and load current decreases the sensitivity of classical differential protection.

Adaptability widely

In this joint, adaptability will be analyzed from two aspects: operation principle and responsiveness.

Operation principle relative adaptability

From the above analysis, Differential Protection Theory of the present invention is only relevant with line parameter circuit value, and it uses line parameter circuit value to carry out the electric current at calculation level " x " place, and it is to the topological structure of DC system and control not special requirement.

Responsiveness relative adaptability

Thus we understand in most cases responsiveness of the present invention be less than 15ms.

Therefore, we can select relaying configuration of the present invention to become main protection or stand-by protection according to the requirement of the responsiveness to different DC system.

Such as, for based on the point-to-point DC circuit of LCC technology or DC electrical network, and have the point-to-point DC circuit of VSC technology, the present invention can either be used as main protection can be used as stand-by protection again.

For the DC electrical network based on VSC technology, the present invention can be used as stand-by protection, because quite high to the requirement of responsiveness, usually in 5ms.If the length of transmission line is short, then can reduce the time delay communicating and cause, thus the present invention also can be used as main protection.

It should be pointed out that when being configured to stand-by protection, the existing stand-by protection based on differential current of Performance Ratio of the present invention is much better, and the operate time based on the stand-by protection of differential current is longer than hundreds of millisecond usually.

Resonant enhance

Exist along circuit distribution lines electric capacity, because HVDC circuit is very long, line capacitance is large.When an error occurs, there is large voltage and current concussion (" resonance "), will some traditional protection philosophies be had a strong impact on, such as traditional current differential protection, low-voltage variation etc.

And direction component of the present invention is based on Bei Jielong model, this model considers " resonance " inherently, and is not affected by " resonance ".

Simulation

Simulation model

Fig. 7 shows simulation model, and the 4 end series connection MTDC of ± 800kV are made up of Liang Ge converting plant (R1 and R2) and two Inverter Station (I1 and I2).The total length of transmission line is 2000km, comprises two branched lines (each 500km) and a backbone (1000km).Each Inverter Station has the configuration with 12 pulse valve groups.The nominal DC voltage that each rectifier converters will have across 400kV, the nominal DC voltage that each inversion converter will have across 373kV, and the earthed voltage of HVDC line is approximately 400kV (for R1 and I1) or is approximately 800kV (for R2 and I2).

The present invention protects, and relay 71,72 is positioned at two terminals of the power transmission line of+800kV shown in upper figure.And internal fault is in the end of+800kV circuit, external fault is on+400kV circuit.And in this case extremely to pole wave impedance Z _cbe 264 Ω.

Fig. 8 shows analog result, and internal fault occurs when 2s, and external fault occurs when 4s.In Fig. 8,

The actual current of fault branch is flowed through during-" IF ";

-" Idif Bei Jielong " is the differential current calculated by the protection philosophy based on Bei Jielong model;

-" Idif is classical " is the differential current calculated by classical differential protection.

Internal fault analysis

As shown in Figure 8, internal fault occurs when 2s, and fault resstance is 3000 ohm.

It should be noted that, when internal fault occurs, " Idif Bei Jielong " and " IF " is incomplete same, reason is to calculate differential current based on the principle operational failure component of Bei Jielong model, and only there is 50ms, therefore these two electric current differences after fault starts 50ms in the fault component in this simulation.But the time is from fault during (2s) to 2.05s, the differential current calculated according to the principle based on Bei Jielong model is enough close to physical fault electric current " IF ".

Also can obtain the differential current of classical protection calculation also close to physical fault electric current " IF " from Fig. 8, but waveform is large.

External fault is analyzed

As shown in Figure 8, external fault occurs in 4s.

When external fault occurs, fault current should not be there is in theory.But the differential current calculated according to classical differential protection (" Idif is classical ") is quite large, when internal fault when 2s occurs even higher than differential current.Therefore we can observe classical differential current protection in transient process and can not distinguish external fault and internal fault, and before transient process disappears, it must be waited for.

" Idif Bei Jielong " shows the differential current that the present invention calculates.The differential current that can be observed to calculate after external fault occurs from Fig. 8 is very little, the differential current calculated under being far smaller than internal fault.That is, it can distinguish external fault and internal fault effectively.

In short, analog result shows compares with classical differential protection, and the impact that the differential protection based on Bei Jielong model is subject to line distribution capacitance is less.

Fig. 9 shows the structural model figure of DC power network current differential protective system, comprises with lower module:

Sampled value obtains module 901, for pole tension sampled value and the electrode current sampled value of the local terminal and remote terminal that obtain DC electrical network;

Fault component extraction module 902, for calculating fault component pole tension value respectively according to the pole tension sampled value of local terminal and remote terminal; And calculate fault component electrode current value respectively according to the electrode current sampled value of local terminal and remote terminal;

Pole modular transformation module 903, for obtaining fault component mode voltage value respectively by carrying out pole modular transformation to the described fault component pole tension value in local terminal and remote terminal, and obtain fault component mould current value respectively by carrying out pole modular transformation to the described fault component electrode current magnitude of voltage in local terminal and remote terminal;

Bei Jielong model computation module 904, for passing through based on Bei Jielong model, calculate the fault component mode voltage value in local terminal and remote terminal and fault component mould current value, obtain the fault component electrode current value in local terminal and remote terminal at Chosen Point place respectively;

Current differential protection determination module 905; if the fault component electrode current value comprised in the local terminal and remote terminal at Chosen Point place meets predetermined current differential protection criterion; then judge internal fault, then send error protection order to activate differential protection, otherwise will not differential protection be activated.

Above-described embodiment is only used for describing several example of the present invention, although describe in detail these embodiments, not should be understood to and limits the scope of the invention.It should be noted that, when not exceeding technical concept of the present invention, those skilled in the art can make several amendment and/or improvement, and these all fall into protection scope of the present invention.Therefore, protection scope of the present invention depends on claims.

Claims (20)

1. a DC power network current differential protecting method, comprises the following steps:

Sampled value obtains step: obtain the pole tension sampled value in the local terminal of DC circuit and remote terminal and electrode current sampled value;

Fault component extraction step: calculate fault component pole tension value according to the described pole tension sampled value of local terminal and remote terminal respectively; And calculate fault component electrode current value according to the described electrode current sampled value of local terminal and remote terminal respectively;

Bei Jielong model calculation procedure: by calculating fault component pole tension value and the fault component electrode current value of local terminal and the remote terminal calculated in described fault component extraction step based on Bei Jielong model, obtains the fault component electrode current value at the Chosen Point place on the DC circuit between local terminal and remote terminal;

Current differential protection determination step: if the fault component electrode current value at the Chosen Point place at local terminal and remote terminal obtained in described Bei Jielong model calculation procedure meets predetermined current differential protection criterion, then judge internal fault.

2. method according to claim 1, wherein DC electrical network is bipolar, and described DC circuit comprises positive pole DC circuit and negative pole DC circuit, described local terminal comprises positive pole local terminal and positive pole remote terminal, described remote terminal comprises negative pole local terminal and negative pole remote terminal, described positive pole DC line electricity connects described positive pole local terminal and described positive pole remote terminal, and described negative pole DC line electricity connects described negative pole local terminal and described negative pole remote terminal, distance from described Chosen Point to the Distance geometry of described positive pole local terminal from described Chosen Point to described negative pole local terminal is identical, and the distance from described Chosen Point to the Distance geometry of described positive pole remote terminal from described Chosen Point to described negative pole remote terminal is identical, also comprise:

Pole modular transformation step: by carrying out pole modular transformation to each described fault component pole tension value in described positive pole local terminal, described positive pole remote terminal, described negative pole local terminal and described negative pole remote terminal, obtains the fault component mode voltage value of each modulus in local terminal and remote terminal; And by carrying out pole modular transformation to each described fault component electrode current value in described positive pole local terminal, described positive pole remote terminal, described negative pole local terminal and described negative pole remote terminal, obtain the fault component mould current value of each modulus in local terminal and remote terminal;

Described Bei Jielong model calculation procedure also comprises:

By calculating fault component mode voltage value and the fault component mould current value of each modulus of local terminal and remote terminal based on Bei Jielong model, obtain the fault component line wave voltage value of each modulus of local terminal and remote terminal respectively;

Respectively the described fault component line wave voltage value of local terminal and remote terminal is converted to the fault component line ripple current value of local terminal and remote terminal;

Respectively according to the described fault component line ripple current value of local terminal and remote terminal, determine the local terminal at the Chosen Point place on described DC circuit and the fault component mould current value of remote terminal;

Mould pole-change is carried out by the described fault component mould current value of each modulus of the local terminal to Chosen Point place, obtain each fault component electrode current value in the positive pole local terminal at the Chosen Point place on described DC circuit and negative pole local terminal, and carry out mould pole-change by the described fault component mould current value of each modulus of the remote terminal to Chosen Point place, obtain the positive pole remote terminal at Chosen Point place and the fault component electrode current value of negative pole remote terminal.

3. method according to claim 2, wherein said pole tension sampled value comprises: u _lP(t), i.e. the voltage sample value of positive pole local terminal; u _lN(t), i.e. the voltage sample value of negative pole local terminal; u _rP(t), i.e. the voltage sample value of positive pole remote terminal; u _rN(t), i.e. the voltage sample value of negative pole remote terminal; Wherein t refers to the time;

Described electrode current sampled value comprises: i _lP(t), the i.e. current sampling data of positive pole local terminal; i _lN(t), the i.e. current sampling data of negative pole local terminal; i _rP(t), the i.e. current sampling data of positive pole remote terminal; i _rN(t), the i.e. current sampling data of negative pole remote terminal;

Described fault component pole tension value comprises: Δ u _lP(t), namely and u _lPthe fault component magnitude of voltage of t positive pole local terminal that () is corresponding; Δ u _lN(t), namely and u _lNthe fault component magnitude of voltage of t negative pole local terminal that () is corresponding; Δ u _rP(t), namely and u _rPthe fault component magnitude of voltage of t positive pole remote terminal that () is corresponding; Δ u _rN(t), namely and u _rNthe fault component magnitude of voltage of t negative pole remote terminal that () is corresponding;

Described fault component electrode current value comprises: Δ i _lP(t), namely and i _lPthe fault component current value of t positive pole local terminal that () is corresponding; Δ i _lN(t), namely and i _lNthe fault component current value of t negative pole local terminal that () is corresponding; Δ i _rP(t), namely and i _rPthe fault component current value of t positive pole remote terminal that () is corresponding; Δ i _rN(t), namely and i _rNthe fault component current value of t negative pole remote terminal that () is corresponding;

Described fault component mode voltage value comprises: Δ u _l0(t), i.e. the fault component common-mode voltage value of local terminal; Δ u _l1(t), i.e. the fault component differential mode voltage value of local terminal; Δ u _r0(t), i.e. the fault component common-mode voltage value of remote terminal; Δ u _r1(t), i.e. the fault component differential mode voltage value of remote terminal;

Described fault component mould current value comprises: Δ i _l0(t), i.e. the fault component common-mode current value of local terminal; Δ i _l1(t), i.e. the fault component differential-mode current value of local terminal; Δ i _r0(t), i.e. the fault component common-mode current value of remote terminal; Δ i _r1(t), i.e. the fault component differential-mode current value of remote terminal;

The capable wave voltage value of described fault component comprises: Δ u _l0+(t), i.e. the fault component common mode direct wave magnitude of voltage of local terminal; Δ u _l0-(t), i.e. the fault component common mode returning wave magnitude of voltage of local terminal; Δ u _l1+(t), i.e. the fault component differential mode direct wave magnitude of voltage of local terminal; Δ u _l0-(t), i.e. the fault component differential mode returning wave magnitude of voltage of local terminal; Δ u _r0+(t), i.e. the fault component common mode direct wave magnitude of voltage of remote terminal; Δ u _r0-(t), i.e. the fault component common mode returning wave magnitude of voltage of remote terminal; Δ u _r1+(t), i.e. the fault component differential mode direct wave magnitude of voltage of remote terminal; Δ u _r1-(t), i.e. the fault component differential mode returning wave magnitude of voltage of remote terminal;

Described fault component travelling wave current value comprises: Δ i _l0+(t), i.e. the fault component common mode direct wave current value of local terminal; Δ i _l0-(t), i.e. the fault component common mode returning wave current value of local terminal; Δ i _l1+(t), i.e. the fault component differential mode direct wave current value of remote terminal; Δ i _l1-(t), i.e. the fault component differential mode returning wave current value of local terminal; Δ i _r0+(t), i.e. the fault component common mode direct wave current value of remote terminal; Δ i _r0-(t), i.e. the fault component common mode returning wave current value of remote terminal; Δ i _r1+(t), i.e. the fault component differential mode direct wave current value of remote terminal; Δ i _r1-(t), i.e. the fault component differential mode returning wave current value of remote terminal;

The described fault component mould current value at Chosen Point comprises: Δ i _l0(x, t), i.e. the fault component common-mode current value at the Chosen Point place of local terminal; Δ i _l1(x, t), i.e. the fault component differential-mode current value at the Chosen Point place of local terminal; Δ i _r0(x, t), i.e. the fault component common-mode current value at the Chosen Point place of remote terminal; Δ i _r1(x, t), i.e. the fault component differential-mode current value at the Chosen Point place of remote terminal, wherein x is Chosen Point;

The fault component electrode current value at described Chosen Point place comprises: Δ i _lP(x, t), namely in the fault component electrode current value at the Chosen Point place of positive pole local terminal; Δ i _lN(x, t), namely in the fault component electrode current value at the Chosen Point place of negative pole local terminal; Δ i _rP(x, t), namely in the fault component electrode current value at the Chosen Point place of positive pole remote terminal; Δ i _rN(x, t), namely in the fault component electrode current value at the Chosen Point place of negative pole remote terminal.

4. method according to claim 3, wherein, in described fault component extraction step, calculates described fault component pole tension value and described fault component pole tension value in the following ways:

$\left\{\begin{array}{c}{\mathrm{\&Delta;i}}_{LP}\left(t\right)=i_{LP}\left(t\right)-i_{LP}(t-T)\\ {\mathrm{\&Delta;i}}_{LN}\left(t\right)=i_{LN}\left(t\right)-i_{LN}(t-T)\\ {\mathrm{\&Delta;u}}_{LP}\left(t\right)=u_{LP}\left(t\right)-u_{LP}(t-T)\\ {\mathrm{\&Delta;u}}_{LN}\left(t\right)=u_{LN}\left(t\right)-u_{LN}(t-T)\\ {\mathrm{\&Delta;i}}_{RP}\left(t\right)=i_{RP}\left(t\right)-i_{RP}(t-T)\\ {\mathrm{\&Delta;i}}_{RN}\left(t\right)=i_{RN}\left(t\right)-i_{RN}(t-T)\\ {\mathrm{\&Delta;u}}_{RP}\left(t\right)=u_{RP}\left(t\right)-u_{RP}(t-T)\\ {\mathrm{\&Delta;u}}_{RN}\left(t\right)=u_{RN}\left(t\right)-u_{RN}(t-T)\end{array}\right.,$

Wherein, T is predetermined time delay;

In described pole modular transformation step, calculate described fault component mode voltage value and described fault component mould current value in the following ways:

$\left\{\begin{array}{c}\left[\begin{array}{c}{\mathrm{\&Delta;u}}_{L0}\left(t\right)\\ {\mathrm{\&Delta;u}}_{L1}\left(t\right)\end{array}\right]=\left[\begin{array}{cc}1& 1\\ 1& -1\end{array}\right]\left[\begin{array}{c}{\mathrm{\&Delta;u}}_{LP}\left(t\right)\\ {\mathrm{\&Delta;u}}_{LN}\left(t\right)\end{array}\right]\\ \left[\begin{array}{c}{\mathrm{\&Delta;i}}_{L0}\left(t\right)\\ {\mathrm{\&Delta;i}}_{L1}\left(t\right)\end{array}\right]=\left[\begin{array}{cc}1& 1\\ 1& -1\end{array}\right]\left[\begin{array}{c}{\mathrm{\&Delta;i}}_{LP}\left(t\right)\\ {\mathrm{\&Delta;i}}_{LN}\left(t\right)\end{array}\right]\\ \left[\begin{array}{c}{\mathrm{\&Delta;u}}_{R0}\left(t\right)\\ {\mathrm{\&Delta;u}}_{R1}\left(t\right)\end{array}\right]=\left[\begin{array}{cc}1& 1\\ 1& -1\end{array}\right]\left[\begin{array}{c}{\mathrm{\&Delta;u}}_{RP}\left(t\right)\\ {\mathrm{\&Delta;u}}_{RN}\left(t\right)\end{array}\right]\\ \left[\begin{array}{c}{\mathrm{\&Delta;i}}_{R0}\left(t\right)\\ {\mathrm{\&Delta;i}}_{R1}\left(t\right)\end{array}\right]=\left[\begin{array}{cc}1& 1\\ 1& -1\end{array}\right]\left[\begin{array}{c}{\mathrm{\&Delta;i}}_{RP}\left(t\right)\\ {\mathrm{\&Delta;i}}_{RN}\left(t\right)\end{array}\right]\end{array}\right.,$

Comprise in described Bei Jielong model calculation procedure:

Calculate described fault component line wave voltage value in the following ways:

$\left\{\begin{array}{c}{\mathrm{\&Delta;u}}_{L0+}\left(t\right)={\mathrm{\&Delta;u}}_{L0}\left(t\right)+{\mathrm{\&Delta;i}}_{L0}\left(t\right)\&times;Z_{C0}\\ {\mathrm{\&Delta;u}}_{L0-}\left(t\right)={\mathrm{\&Delta;u}}_{L0}\left(t\right)-{\mathrm{\&Delta;i}}_{L0}\left(t\right)\&times;Z_{C0}\\ {\mathrm{\&Delta;u}}_{L1+}\left(t\right)={\mathrm{\&Delta;u}}_{L1}\left(t\right)+{\mathrm{\&Delta;i}}_{L1}\left(t\right)\&times;Z_{C1}\\ {\mathrm{\&Delta;u}}_{L1-}\left(t\right)={\mathrm{\&Delta;u}}_{L1}\left(t\right)-{\mathrm{\&Delta;i}}_{L1}\left(t\right)\&times;Z_{C1}\\ {\mathrm{\&Delta;u}}_{R0+}\left(t\right)={\mathrm{\&Delta;u}}_{R0}\left(t\right)+{\mathrm{\&Delta;i}}_{R0}\left(t\right)\&times;Z_{C0}\\ {\mathrm{\&Delta;u}}_{R0-}\left(t\right)={\mathrm{\&Delta;u}}_{R0}\left(t\right)-{\mathrm{\&Delta;i}}_{R0}\left(t\right)\&times;Z_{C0}\\ {\mathrm{\&Delta;u}}_{R1+}\left(t\right)={\mathrm{\&Delta;u}}_{R1}\left(t\right)+{\mathrm{\&Delta;i}}_{R1}\left(t\right)\&times;Z_{C1}\\ {\mathrm{\&Delta;u}}_{R1-}\left(t\right)={\mathrm{\&Delta;u}}_{R1}\left(t\right)-{\mathrm{\&Delta;i}}_{R1}\left(t\right)\&times;Z_{C1}\end{array}\right.,$

Wherein, Z _c0it is common mode wave impedance; Z _c1it is differential mode wave impedance;

Calculate described fault component line ripple current value in the following ways:

$\left\{\begin{array}{c}{\mathrm{\&Delta;i}}_{L0+}\left(t\right)={\mathrm{\&Delta;u}}_{L0+}\left(t\right)/Z_{C0}\\ {\mathrm{\&Delta;i}}_{L0-}\left(t\right)=-{\mathrm{\&Delta;u}}_{L0-}\left(t\right)/Z_{C0}\\ {\mathrm{\&Delta;i}}_{L1+}\left(t\right)={\mathrm{\&Delta;u}}_{L1+}\left(t\right)/Z_{C1}\\ {\mathrm{\&Delta;i}}_{L1-}\left(t\right)=-{\mathrm{\&Delta;u}}_{L1-}\left(t\right)/Z_{C1}\\ {\mathrm{\&Delta;i}}_{R0+}\left(t\right)={\mathrm{\&Delta;u}}_{R0+}\left(t\right)/Z_{C0}\\ {\mathrm{\&Delta;i}}_{R0-}\left(t\right)=-{\mathrm{\&Delta;u}}_{R0-}\left(t\right)/Z_{C0}\\ {\mathrm{\&Delta;i}}_{R1+}\left(t\right)={\mathrm{\&Delta;u}}_{R1+}\left(t\right)/Z_{C1}\\ {\mathrm{\&Delta;i}}_{R1-}\left(t\right)=-{\mathrm{\&Delta;u}}_{R1-}\left(t\right)/Z_{C1}\end{array}\right.;$

Calculate the fault component mould current value at Chosen Point place in the following ways:

$\left\{\begin{array}{c}{\mathrm{\&Delta;i}}_{L1}(x,t)={\mathrm{\&Delta;i}}_{L1+}(t-\frac{x}{v_1})-{\mathrm{\&Delta;i}}_{L1-}(t+\frac{x}{v_1})\\ {\mathrm{\&Delta;i}}_{L0}(x,t)={\mathrm{\&Delta;i}}_{L0+}(t-\frac{x}{v_0})-{\mathrm{\&Delta;i}}_{L0-}(t+\frac{x}{v_0})\\ {\mathrm{\&Delta;i}}_{R1}(x,t)={\mathrm{\&Delta;i}}_{R1+}(t-\frac{x}{v_1})-{\mathrm{\&Delta;i}}_{R1-}(t+\frac{x}{v_1})\\ {\mathrm{\&Delta;i}}_{R0}(x,t)={\mathrm{\&Delta;i}}_{R0+}(t-\frac{x}{v_0})-{\mathrm{\&Delta;i}}_{R0-}(t+\frac{x}{v_0})\end{array}\right.,$

Wherein, v ₀the gait of march of fault component common mode row ripple, v ₁it is the gait of march of the capable ripple of fault component differential mode;

Calculate the fault component electrode current value at Chosen Point place in the following ways:

$\left\{\begin{array}{c}\left[\begin{array}{c}{\mathrm{\&Delta;i}}_{LP}(x,t)\\ {\mathrm{\&Delta;i}}_{LN}(x,t)\end{array}\right]=\frac{1}{2}\left[\begin{array}{cc}1& 1\\ 1& -1\end{array}\right]\left[\begin{array}{c}{\mathrm{\&Delta;i}}_{L0}(x,t)\\ {\mathrm{\&Delta;i}}_{L1}(x,t)\end{array}\right]\\ \left[\begin{array}{c}{\mathrm{\&Delta;i}}_{RP}(x,t)\\ {\mathrm{\&Delta;i}}_{RN}(x,t)\end{array}\right]=\frac{1}{2}\left[\begin{array}{cc}1& 1\\ 1& -1\end{array}\right]\left[\begin{array}{c}{\mathrm{\&Delta;i}}_{R0}(x,t)\\ {\mathrm{\&Delta;i}}_{R1}(x,t)\end{array}\right]\end{array}\right..$

5. method according to claim 3, wherein, described current differential protection determination step comprises:

If met | Δ i _lP(x, t)+Δ i _rP(x, t) | > I _res, then decision state is positive pole internal fault; If met | Δ i _lN(x, t)+Δ i _rN(x, t) | > I _res, then decision state is negative pole internal fault, wherein, and I _resrepresent predetermined threshold value;

Otherwise, will not differential protection be activated.

6. method according to claim 1, wherein said DC electrical network is one pole:

Described Bei Jielong model calculation procedure also comprises:

By based on Bei Jielong model, calculate the described fault component pole tension value of local terminal and remote terminal and described fault component mould current value, obtain the fault component extremely row wave voltage value of local terminal and remote terminal respectively;

Respectively by the described fault component of local terminal and remote terminal extremely row wave voltage value convert the fault component line ripple current value of local terminal and remote terminal to;

According to the described fault component pole travelling wave current value of local terminal and remote terminal, determine the local terminal at the Chosen Point place on described DC circuit and the fault component electrode current value of remote terminal.

7. method according to claim 6, wherein in described fault component extraction step, calculates described fault component pole tension value and fault component pole tension value in the following ways:

$\left\{\begin{array}{c}{\mathrm{\&Delta;i}}_L\left(t\right)=i_L\left(t\right)-i_L(t-T)\\ {\mathrm{\&Delta;u}}_L\left(t\right)=u_L\left(t\right)-u_L(t-T)\\ {\mathrm{\&Delta;i}}_R\left(t\right)=i_R\left(t\right)-i_R(t-T)\\ {\mathrm{\&Delta;u}}_R\left(t\right)=u_R\left(t\right)-u_R(t-T)\end{array}\right.$

Wherein T represents predetermined time delay, Δ i _lt () is the fault component electrode current value of local terminal, Δ i _rt () is the fault component electrode current value of remote terminal, Δ u _lt () is the fault component pole tension value of local terminal, Δ u _rt () is the fault component pole tension value of remote terminal, i _lt () is the current sampling data of local terminal, i _rt () is the current sampling data of remote terminal, u _lt () is the voltage sample value of local terminal, u _rt () is the voltage sample value of remote terminal, and t refers to the time;

Comprise in described Bei Jielong model calculation procedure:

Calculate fault component extremely row wave voltage value in the following ways:

$\left\{\begin{array}{c}\mathrm{\&Delta;}{u}_{L+}\left(t\right)=\mathrm{\&Delta;}{u}_L\left(t\right)+\mathrm{\&Delta;}{i}_L\left(t\right)\&times;Z_C\\ {\mathrm{\&Delta;u}}_{L-}\left(t\right)={\mathrm{\&Delta;u}}_L\left(t\right)-{\mathrm{\&Delta;i}}_L\left(t\right)\&times;Z_C\\ {\mathrm{\&Delta;u}}_{R+}\left(t\right)={\mathrm{\&Delta;u}}_R\left(t\right)+{\mathrm{\&Delta;i}}_R\left(t\right)\&times;Z_C\\ {\mathrm{\&Delta;u}}_{R-}\left(t\right)={\mathrm{\&Delta;u}}_R\left(t\right)-{\mathrm{\&Delta;i}}_R\left(t\right)\&times;Z_C\end{array}\right.$

Wherein, Z _cwave impedance, Δ u _l+t () is the fault component pole direct wave magnitude of voltage of local terminal; Δ u _l-t () is the fault component pole returning wave magnitude of voltage of local terminal; Δ u _r+t () is the fault component pole direct wave magnitude of voltage of remote terminal; Δ u _r-t () is the fault component pole returning wave magnitude of voltage of remote terminal;

Calculate described fault component pole travelling wave current value in the following ways:

$\left\{\begin{array}{c}\mathrm{\&Delta;}{i}_{L+}\left(t\right)=\mathrm{\&Delta;}{u}_{L+}\left(t\right)/Z_C\\ {\mathrm{\&Delta;i}}_{L-}\left(t\right)=-{\mathrm{\&Delta;u}}_{L-}\left(t\right)/Z_C\\ {\mathrm{\&Delta;i}}_{R+}\left(t\right)={\mathrm{\&Delta;u}}_{R+}\left(t\right)/Z_C\\ {\mathrm{\&Delta;i}}_{R-}\left(t\right)=-{\mathrm{\&Delta;u}}_{R-}\left(t\right)/Z_C\end{array}\right.$

Wherein, Δ i _l+t () is the fault component pole direct wave current value of local terminal; Δ i _l-t () is the fault component pole returning wave current value of local terminal; Δ i _r+t () is the fault component pole direct wave current value of remote terminal; Δ i _r-t () is the fault component pole returning wave current value of remote terminal;

Calculate the described fault component electrode current value at select location place in the following ways:

$\left\{\begin{array}{c}{\mathrm{\&Delta;i}}_L(x,t)={\mathrm{\&Delta;i}}_{L+}(t-\frac{x}{v})-{\mathrm{\&Delta;i}}_{L-}(t+\frac{x}{v})\\ {\mathrm{\&Delta;i}}_R(x,t)={\mathrm{\&Delta;i}}_{R+}(t-\frac{x}{v})-{\mathrm{\&Delta;i}}_{R-}(t+\frac{x}{v})\end{array}\right.,$

Wherein Δ i _l(x, t) is the fault component electrode current value at the Chosen Point place of local terminal; Δ i _r(x, t) is the fault component electrode current value at the Chosen Point place of remote terminal, and v is the gait of march of the capable ripple of fault component.

8. method according to claim 7, wherein, comprises at described current differential protection determination step:

If met | Δ i _l(x, t)+Δ i _r(x, t) | > I _res, then decision state is internal fault, wherein I _resit is predetermined threshold value.

9. the method according to any one in claim 1-8, wherein said current differential protection determination step also comprises:

If state is determined into internal fault, then sends error protection order to activate differential protection, otherwise will not differential protection be activated.

10. one kind comprise be suitable for when running on computers perform with the computer program of the computer program code of any one step upper.

11. 1 kinds of computer programs according to claim 6, described computer program recorded on a computer-readable medium.

12. 1 kinds of DC power network current differential protective systems, comprise with lower module:

Sampled value obtains module: obtain the local terminal of DC circuit and the pole tension sampled value of remote terminal and electrode current sampled value;

Fault component extraction module: calculate fault component pole tension value according to the described pole tension sampled value of local terminal and remote terminal respectively; And calculate fault component electrode current value according to the described electrode current value of local terminal and remote terminal respectively;

Bei Jielong model computation module: based on Bei Jielong model, by calculating the described fault component pole tension value of local terminal and the remote terminal calculated in described fault component extraction module and described fault component electrode current value, obtain the fault component electrode current value at the Chosen Point place on the DC circuit between local terminal and remote terminal;

Current differential protection determination module: if the described fault component electrode current value at the Chosen Point place of the local terminal obtained in Bei Jielong model computation module and remote terminal meets predetermined current differential protection criterion, then judge internal fault.

13. systems according to claim 12, wherein, described DC electrical network is that bipolar and described DC circuit comprises positive pole DC circuit and negative pole DC circuit, described local terminal comprises positive pole local terminal and positive pole remote terminal, described remote terminal comprises negative pole local terminal and negative pole remote terminal, described positive pole DC line electricity connects described positive pole local terminal and described positive pole remote terminal, and described negative pole DC line electricity connects described negative pole local terminal and described negative pole remote terminal, distance from described Chosen Point to the Distance geometry of described positive pole local terminal from described Chosen Point to described negative pole local terminal is identical, distance from described Chosen Point to the Distance geometry of described positive pole remote terminal from described Chosen Point to described negative pole remote terminal is identical, also comprise:

Pole modular transformation module: by described positive pole local terminal, described positive pole remote terminal, each described fault component pole tension value in described negative pole local terminal and described negative pole remote terminal carries out pole modular transformation, obtain the fault component mode voltage value of each modulus in local terminal and remote terminal, and pass through described positive pole local terminal, described positive pole remote terminal, each described fault component electrode current value in described negative pole local terminal and described negative pole remote terminal carries out pole modular transformation, obtain the fault component mould current value of each modulus of local terminal and remote terminal,

Described Bei Jielong model computation module also comprises:

By based on Bei Jielong model, calculate the described fault component mode voltage value of each modulus of local terminal and remote terminal and described fault component mould current value, obtain the fault component line wave voltage value of each modulus to local terminal and remote terminal respectively;

Respectively the described fault component line wave voltage value of local terminal and remote terminal is converted to the fault component line ripple current value of local terminal and remote terminal;

Respectively according to the described fault component line ripple current value of local terminal and remote terminal, determine the local terminal at the Chosen Point place on DC circuit and the fault component mould current value of remote terminal;

Mould pole-change is carried out by the described fault component mould current value of each modulus of the local terminal to Chosen Point place, obtain each fault component electrode current value in the positive pole local terminal at the Chosen Point place on DC circuit and negative pole local terminal, and carry out mould pole-change by the fault component mould current value of each modulus to the remote terminal at Chosen Point place, obtain the fault component electrode current value of positive pole remote terminal at Chosen Point place and negative pole remote terminal.

14. systems according to claim 13, wherein, described pole tension sampled value comprises: u _lP(t), i.e. the voltage sample value of positive pole local terminal; u _lN(t), i.e. the voltage sample value of negative pole local terminal; u _rP(t), i.e. the voltage sample value of positive pole remote terminal; u _rN(t), i.e. the voltage sample value of negative pole remote terminal; Wherein t refers to the time;

Described electrode current sampled value comprises: i _lP(t), the i.e. current sampling data of positive pole local terminal; i _lN(t), the i.e. current sampling data of negative pole local terminal; i _rP(t), the i.e. current sampling data of positive pole remote terminal; i _rN(t), the i.e. current sampling data of negative pole remote terminal;

Described fault component pole tension value comprises: Δ u _lP(t), namely and u _lPthe fault component magnitude of voltage of t positive pole local terminal that () is corresponding; Δ u _lN(t), namely and u _lNthe fault component magnitude of voltage of t negative pole local terminal that () is corresponding; Δ u _rP(t), namely and u _rPthe fault component magnitude of voltage of t positive pole remote terminal that () is corresponding; Δ u _rN(t), namely and u _rNthe fault component magnitude of voltage of t negative pole remote terminal that () is corresponding;

Described fault component electrode current value comprises: Δ i _lP(t), namely and i _lPthe fault component current value of t positive pole local terminal that () is corresponding; Δ i _lN(t), namely and i _lNthe fault component current value of t negative pole local terminal that () is corresponding; Δ i _rP(t), namely and i _rPthe fault component current value of t positive pole remote terminal that () is corresponding; Δ i _rN(t), namely and i _rNthe fault component current value of t negative pole remote terminal that () is corresponding;

Described fault component mode voltage value comprises: Δ u _l0(t), i.e. the fault component common-mode voltage value of local terminal; Δ u _l1(t), i.e. the fault component differential mode voltage value of local terminal; Δ u _r0(t), i.e. the fault component common-mode voltage value of remote terminal; Δ u _r1(t), i.e. the fault component differential mode voltage value of remote terminal;

Described fault component mould current value comprises: Δ i _l0(t), i.e. the fault component common-mode current value of local terminal; Δ i _l1(t), i.e. the fault component differential-mode current value of local terminal; Δ i _r0(t), i.e. the fault component common-mode current value of remote terminal; Δ i _r1(t), i.e. the fault component differential-mode current value of remote terminal;

The capable wave voltage value of described fault component comprises: Δ u _l0+(t), i.e. the fault component common mode direct wave magnitude of voltage of local terminal; Δ u _l0-(t), i.e. the fault component common mode returning wave magnitude of voltage of local terminal; Δ u _l1+(t), i.e. the fault component differential mode direct wave magnitude of voltage of local terminal; Δ u _l0-(t), i.e. the fault component differential mode returning wave magnitude of voltage of local terminal; Δ u _r0+(t), i.e. the fault component common mode direct wave magnitude of voltage of remote terminal; Δ u _r0-(t), i.e. the fault component common mode returning wave magnitude of voltage of remote terminal; Δ u _r1+(t), i.e. the fault component differential mode direct wave magnitude of voltage of remote terminal; Δ u _r1-(t), i.e. the fault component differential mode returning wave magnitude of voltage of remote terminal;

Described fault component travelling wave current value comprises: Δ i _l0+(t), i.e. the fault component common mode direct wave current value of local terminal; Δ i _l0-(t), i.e. the fault component common mode returning wave current value of local terminal; Δ i _l1+(t), i.e. the fault component differential mode direct wave current value of remote terminal; Δ i _l1-(t), i.e. the fault component differential mode returning wave current value of local terminal; Δ i _r0+(t), i.e. the fault component common mode direct wave current value of remote terminal; Δ i _r0-(t), i.e. the fault component common mode returning wave current value of remote terminal; Δ i _r1+(t), i.e. the fault component differential mode direct wave current value of remote terminal; Δ i _r1-(t), i.e. the fault component differential mode returning wave current value of remote terminal;

The described fault component mould current value at Chosen Point comprises: Δ i _l0(x, t), i.e. the fault component common-mode current value at the Chosen Point place of local terminal; Δ i _l1(x, t), i.e. the fault component differential-mode current value at the Chosen Point place of local terminal; Δ i _r0(x, t), i.e. the fault component common-mode current value at the Chosen Point place of remote terminal; Δ i _r1(x, t), i.e. the fault component differential-mode current value at the Chosen Point place of remote terminal, wherein x is Chosen Point;

The described fault component electrode current value at Chosen Point place comprises: Δ i _lP(x, t), i.e. the fault component electrode current value at the Chosen Point place of positive pole local terminal; Δ i _lN(x, t), i.e. the fault component electrode current value at the Chosen Point place of negative pole local terminal; Δ i _rP(x, t), i.e. the fault component electrode current value at the Chosen Point place of positive pole remote terminal; Δ i _rN(x, t), i.e. the fault component electrode current value at the Chosen Point place of negative pole remote terminal.

15. systems according to claim 14, wherein in described fault component extraction module, calculate described fault component pole tension value and described fault component pole tension value in the following ways:

$\left\{\begin{array}{c}{\mathrm{\&Delta;i}}_{LP}\left(t\right)=i_{LP}\left(t\right)-i_{LP}(t-T)\\ {\mathrm{\&Delta;i}}_{LN}\left(t\right)=i_{LN}\left(t\right)-i_{LN}(t-T)\\ {\mathrm{\&Delta;u}}_{LP}\left(t\right)=u_{LP}\left(t\right)-u_{LP}(t-T)\\ {\mathrm{\&Delta;u}}_{LN}\left(t\right)=u_{LN}\left(t\right)-u_{LN}(t-T)\\ {\mathrm{\&Delta;i}}_{RP}\left(t\right)=i_{RP}\left(t\right)-i_{RP}(t-T)\\ {\mathrm{\&Delta;i}}_{RN}\left(t\right)=i_{RN}\left(t\right)-i_{RN}(t-T)\\ {\mathrm{\&Delta;u}}_{RP}\left(t\right)=u_{RP}\left(t\right)-u_{RP}(t-T)\\ {\mathrm{\&Delta;u}}_{RN}\left(t\right)=u_{RN}\left(t\right)-u_{RN}(t-T)\end{array}\right.,$

Wherein, T represents predetermined time delay;

In described pole modular transformation module, calculate described fault component mode voltage value and described fault component mould current value in the following ways:

$\left\{\begin{array}{c}\left[\begin{array}{c}{\mathrm{\&Delta;u}}_{L0}\left(t\right)\\ {\mathrm{\&Delta;u}}_{L1}\left(t\right)\end{array}\right]=\left[\begin{array}{cc}1& 1\\ 1& -1\end{array}\right]\left[\begin{array}{c}{\mathrm{\&Delta;u}}_{LP}\left(t\right)\\ {\mathrm{\&Delta;u}}_{LN}\left(t\right)\end{array}\right]\\ \left[\begin{array}{c}{\mathrm{\&Delta;i}}_{L0}\left(t\right)\\ {\mathrm{\&Delta;i}}_{L1}\left(t\right)\end{array}\right]=\left[\begin{array}{cc}1& 1\\ 1& -1\end{array}\right]\left[\begin{array}{c}{\mathrm{\&Delta;i}}_{LP}\left(t\right)\\ {\mathrm{\&Delta;i}}_{LN}\left(t\right)\end{array}\right]\\ \left[\begin{array}{c}{\mathrm{\&Delta;u}}_{R0}\left(t\right)\\ {\mathrm{\&Delta;u}}_{R1}\left(t\right)\end{array}\right]=\left[\begin{array}{cc}1& 1\\ 1& -1\end{array}\right]\left[\begin{array}{c}{\mathrm{\&Delta;u}}_{RP}\left(t\right)\\ {\mathrm{\&Delta;u}}_{RN}\left(t\right)\end{array}\right]\\ \left[\begin{array}{c}{\mathrm{\&Delta;i}}_{R0}\left(t\right)\\ {\mathrm{\&Delta;i}}_{R1}\left(t\right)\end{array}\right]=\left[\begin{array}{cc}1& 1\\ 1& -1\end{array}\right]\left[\begin{array}{c}{\mathrm{\&Delta;i}}_{RP}\left(t\right)\\ {\mathrm{\&Delta;i}}_{RN}\left(t\right)\end{array}\right]\end{array}\right.;$

Comprise in described Bei Jielong model computation module:

Calculate described fault component line wave voltage value in the following ways:

$\left\{\begin{array}{c}{\mathrm{\&Delta;u}}_{L0+}\left(t\right)={\mathrm{\&Delta;u}}_{L0}\left(t\right)+{\mathrm{\&Delta;i}}_{L0}\left(t\right)\&times;Z_{C0}\\ {\mathrm{\&Delta;u}}_{L0-}\left(t\right)={\mathrm{\&Delta;u}}_{L0}\left(t\right)-{\mathrm{\&Delta;i}}_{L0}\left(t\right)\&times;Z_{C0}\\ {\mathrm{\&Delta;u}}_{L1+}\left(t\right)={\mathrm{\&Delta;u}}_{L1}\left(t\right)+{\mathrm{\&Delta;i}}_{L1}\left(t\right)\&times;Z_{C1}\\ {\mathrm{\&Delta;u}}_{L1-}\left(t\right)={\mathrm{\&Delta;u}}_{L1}\left(t\right)-{\mathrm{\&Delta;i}}_{L1}\left(t\right)\&times;Z_{C1}\\ {\mathrm{\&Delta;u}}_{R0+}\left(t\right)={\mathrm{\&Delta;u}}_{R0}\left(t\right)+{\mathrm{\&Delta;i}}_{R0}\left(t\right)\&times;Z_{C0}\\ {\mathrm{\&Delta;u}}_{R0-}\left(t\right)={\mathrm{\&Delta;u}}_{R0}\left(t\right)-{\mathrm{\&Delta;i}}_{R0}\left(t\right)\&times;Z_{C0}\\ {\mathrm{\&Delta;u}}_{R1+}\left(t\right)={\mathrm{\&Delta;u}}_{R1}\left(t\right)+{\mathrm{\&Delta;i}}_{R1}\left(t\right)\&times;Z_{C1}\\ {\mathrm{\&Delta;u}}_{R1-}\left(t\right)={\mathrm{\&Delta;u}}_{R1}\left(t\right)-{\mathrm{\&Delta;i}}_{R1}\left(t\right)\&times;Z_{C1}\end{array}\right.$

Wherein Z _c0it is common mode wave impedance; Z _c1it is differential mode wave impedance;

Calculate described fault component line ripple current value in the following ways:

$\left\{\begin{array}{c}{\mathrm{\&Delta;i}}_{L0+}\left(t\right)={\mathrm{\&Delta;u}}_{L0+}\left(t\right)/Z_{C0}\\ {\mathrm{\&Delta;i}}_{L0-}\left(t\right)=-{\mathrm{\&Delta;u}}_{L0-}\left(t\right)/Z_{C0}\\ {\mathrm{\&Delta;i}}_{L1+}\left(t\right)={\mathrm{\&Delta;u}}_{L1+}\left(t\right)/Z_{C1}\\ {\mathrm{\&Delta;i}}_{L1-}\left(t\right)=-{\mathrm{\&Delta;u}}_{L1-}\left(t\right)/Z_{C1}\\ {\mathrm{\&Delta;i}}_{R0+}\left(t\right)={\mathrm{\&Delta;u}}_{R0+}\left(t\right)/Z_{C0}\\ {\mathrm{\&Delta;i}}_{R0-}\left(t\right)=-{\mathrm{\&Delta;u}}_{R0-}\left(t\right)/Z_{C0}\\ {\mathrm{\&Delta;i}}_{R1+}\left(t\right)={\mathrm{\&Delta;u}}_{R1+}\left(t\right)/Z_{C1}\\ {\mathrm{\&Delta;i}}_{R1-}\left(t\right)=-{\mathrm{\&Delta;u}}_{R1-}\left(t\right)/Z_{C1}\end{array}\right.;$

Calculate the described fault component mould current value at Chosen Point place in the following ways:

$\left\{\begin{array}{c}{\mathrm{\&Delta;i}}_{L1}(x,t)={\mathrm{\&Delta;i}}_{L1+}(t-\frac{x}{v_1})-{\mathrm{\&Delta;i}}_{L1-}(t+\frac{x}{v_1})\\ {\mathrm{\&Delta;i}}_{L0}(x,t)={\mathrm{\&Delta;i}}_{L0+}(t-\frac{x}{v_0})-{\mathrm{\&Delta;i}}_{L0-}(t+\frac{x}{v_0})\\ {\mathrm{\&Delta;i}}_{R1}(x,t)={\mathrm{\&Delta;i}}_{R1+}(t-\frac{x}{v_1})-{\mathrm{\&Delta;i}}_{R1-}(t+\frac{x}{v_1})\\ {\mathrm{\&Delta;i}}_{R0}(x,t)={\mathrm{\&Delta;i}}_{R0+}(t-\frac{x}{v_0})-{\mathrm{\&Delta;i}}_{R0-}(t+\frac{x}{v_0})\end{array}\right.,$

Wherein, v ₀the gait of march of fault component common mode row ripple, v ₁it is the gait of march of the capable ripple of fault component differential mode;

Calculate the described fault component electrode current value at Chosen Point place in the following ways:

$\left\{\begin{array}{c}\left[\begin{array}{c}{\mathrm{\&Delta;i}}_{LP}(x,t)\\ {\mathrm{\&Delta;i}}_{LN}(x,t)\end{array}\right]=\frac{1}{2}\left[\begin{array}{cc}1& 1\\ 1& -1\end{array}\right]\left[\begin{array}{c}{\mathrm{\&Delta;i}}_{L0}(x,t)\\ {\mathrm{\&Delta;i}}_{L1}(x,t)\end{array}\right]\\ \left[\begin{array}{c}{\mathrm{\&Delta;i}}_{RP}(x,t)\\ {\mathrm{\&Delta;i}}_{RN}(x,t)\end{array}\right]=\frac{1}{2}\left[\begin{array}{cc}1& 1\\ 1& -1\end{array}\right]\left[\begin{array}{c}{\mathrm{\&Delta;i}}_{R0}(x,t)\\ {\mathrm{\&Delta;i}}_{R1}(x,t)\end{array}\right]\end{array}\right..$

16. systems according to claim 14, wherein said current differential protection determination module comprises:

If met | Δ i _lP(x, t)+Δ i _rP(x, t) | > I _res, then decision state is positive pole internal fault; If met | Δ i _lN(x, t)+Δ i _rN(x, t) | > I _res, then decision state is negative pole internal fault, wherein, and I _resrepresent predetermined threshold value;

Otherwise, will not differential protection be activated.

17. systems according to claim 12, wherein, described DC electrical network is one pole:

Described Bei Jielong model computation module also comprises:

By based on Bei Jielong model, calculate the described fault component pole tension value of local terminal and remote terminal and described fault component mould current value, obtain the fault component extremely row wave voltage value of local terminal and remote terminal respectively;

Respectively by the described fault component of local terminal and remote terminal extremely row wave voltage value convert the fault component line ripple current value of local terminal and remote terminal to;

Described fault component pole travelling wave current value according to local terminal and remote terminal determines the local terminal at the Chosen Point place on described DC circuit and the fault component electrode current value of remote terminal.

18. systems according to claim 17, wherein, in described fault component extraction model, calculate described fault component pole tension value and described fault component pole tension value in the following ways:

$\left\{\begin{array}{c}{\mathrm{\&Delta;i}}_L\left(t\right)=i_L\left(t\right)-i_L(t-T)\\ {\mathrm{\&Delta;u}}_L\left(t\right)=u_L\left(t\right)-u_L(t-T)\\ {\mathrm{\&Delta;i}}_R\left(t\right)=i_R\left(t\right)-i_R(t-T)\\ {\mathrm{\&Delta;u}}_R\left(t\right)=u_R\left(t\right)-u_R(t-T)\end{array}\right.,$

Wherein T represents predetermined time delay, Δ i _lt () is the fault component electrode current value of local terminal, Δ i _rt () is the fault component electrode current value of remote terminal, Δ u _lt () is the fault component pole tension value of local terminal, Δ u _rt () is the fault component pole tension value of remote terminal, i _lt () is the current sampling data of local terminal, i _rt () is the current sampling data of remote terminal, u _lt () is the voltage sample value of local terminal, u _rt () is the voltage sample value of remote terminal, and t refers to the time;

Comprise in described Bei Jielong model computation module:

Calculate described fault component extremely row wave voltage value in the following ways:

$\left\{\begin{array}{c}\mathrm{\&Delta;}{u}_{L+}\left(t\right)=\mathrm{\&Delta;}{u}_L\left(t\right)+\mathrm{\&Delta;}{i}_L\left(t\right)\&times;Z_C\\ {\mathrm{\&Delta;u}}_{L-}\left(t\right)={\mathrm{\&Delta;u}}_L\left(t\right)-{\mathrm{\&Delta;i}}_L\left(t\right)\&times;Z_C\\ {\mathrm{\&Delta;u}}_{R+}\left(t\right)={\mathrm{\&Delta;u}}_R\left(t\right)+{\mathrm{\&Delta;i}}_R\left(t\right)\&times;Z_C\\ {\mathrm{\&Delta;u}}_{R-}\left(t\right)={\mathrm{\&Delta;u}}_R\left(t\right)-{\mathrm{\&Delta;i}}_R\left(t\right)\&times;Z_C\end{array}\right.,$

Wherein, Z _cwave impedance, Δ u _l+t () is the fault component pole direct wave magnitude of voltage of local terminal; Δ u _l-t () is the fault component pole returning wave magnitude of voltage of local terminal; Δ u _r+t () is the fault component pole direct wave magnitude of voltage of remote terminal; Δ u _r-t () is the fault component pole returning wave magnitude of voltage of remote terminal;

Calculate described fault component pole travelling wave current value in the following ways:

$\left\{\begin{array}{c}\mathrm{\&Delta;}{i}_{L+}\left(t\right)=\mathrm{\&Delta;}{u}_{L+}\left(t\right)/Z_C\\ {\mathrm{\&Delta;i}}_{L-}\left(t\right)=-{\mathrm{\&Delta;u}}_{L-}\left(t\right)/Z_C\\ {\mathrm{\&Delta;i}}_{R+}\left(t\right)={\mathrm{\&Delta;u}}_{R+}\left(t\right)/Z_C\\ {\mathrm{\&Delta;i}}_{R-}\left(t\right)=-{\mathrm{\&Delta;u}}_{R-}\left(t\right)/Z_C\end{array}\right.,$

Wherein, Δ i _l+t () is the fault component pole direct wave current value of local terminal; Δ i _l-t () is the fault component pole returning wave current value of local terminal; Δ i _r+t () is the fault component pole direct wave current value of remote terminal; Δ i _r-t () is the fault component pole returning wave current value of remote terminal;

Calculate the described fault component electrode current value at select location place in the following ways:

$\left\{\begin{array}{c}{\mathrm{\&Delta;i}}_L(x,t)={\mathrm{\&Delta;i}}_{L+}(t-\frac{x}{v})-{\mathrm{\&Delta;i}}_{L-}(t+\frac{x}{v})\\ {\mathrm{\&Delta;i}}_R(x,t)={\mathrm{\&Delta;i}}_{R+}(t-\frac{x}{v})-{\mathrm{\&Delta;i}}_{R-}(t+\frac{x}{v})\end{array}\right.,$

Wherein Δ i _l(x, t) is the fault component electrode current value at the Chosen Point place of local terminal; Δ i _r(x, t) is the fault component electrode current value at the Chosen Point place of remote terminal, and v is the gait of march of the capable ripple of fault component.

19. systems according to claim 18, wherein, comprise at described current differential protection determination module:

If met | Δ i _l(x, t)+Δ i _r(x, t) | > I _res, then decision state is internal fault, wherein I _resit is predetermined threshold value.

20. according to the system in claim 12-19 described in any one, and wherein, described current differential protection determination module also comprises:

If state is determined into internal fault, then sends error protection order to activate differential protection, otherwise will not differential protection be activated.