CN104332968A - Current differential protection method based on high voltage DC transmission line - Google Patents

Abstract

The invention discloses a current differential protection method based on a high voltage DC transmission line. Two ends of the high voltage DC transmission line are provided with current transformers for acquiring current at two ends of the high voltage DC transmission line. The protection method comprises the following steps: after electrical signals at a fault electrode of a failing DC transmission line are analyzed and processed, that is, current signals are acquired at two sides of the failing DC transmission line, and the obtained fault component current signal size is used for analyzing the actual state where the line is located; and the current differential protection calculation result and the set disturbance value are compared for building reasonable discrimination. The problem of correlation interference caused by transient response, distributed capacitance, and an operation mode in the case of fault recognition by the prior DC transmission line can be overcome.

Description

Based on the current differential protection method of HVDC (High Voltage Direct Current) transmission line

Technical field

The present invention relates to the research field of electric power system HVDC (High Voltage Direct Current) transmission line relaying protection, particularly, relate to a kind of current differential protection method based on HVDC (High Voltage Direct Current) transmission line.

Background technology

Along with the development of China's science and technology, superhigh pressure, extra-high voltage DC transmission system obtain in China and use widely, now built, many under preparation ± 800kV extra high voltage direct current transmission line, for the following power delivery of China will play the tremendous contribution that can not be substituted.Play consistently usefulness in order to ensure above-mentioned line security, corresponding reliable relaying protection must be needed to escort.

Due to history cause, by the restriction of the factor such as technology, technique, unlike ac transmission control and scheduling co-design be separated from each other, separate feature, namely the dependent failure of direct current system has to be eliminated by power flowcontrol sometimes.The operation mechanism special just because of it and control mode, cause relevant interruption of service.The relaying protection that the DC transmission system put into operation according to China is equipped with is mainly derived from the fact of ABB AB and SIEMENS company; therefore traditional involved by this relaying protection mainly comprises the main protection formed with traveling-wave protection, differential under-voltage protection etc. and the backup protection formed with current differential protection, under-voltage protection etc., forms the relatively complete relaying protection system of DC power transmission line thus.

The feature of traveling-wave protection is to efficiently utilize the capable ripple of transient fault propagated laterally from fault point when fault occurs, and reaches the object differentiating nature of trouble.The state that each company reflects when utilizing the characteristic of row ripple, by different, therefore also embodies the difference of trace in operate time, antijamming capability and failure-resilient resistance etc.But it is poor that the greatest drawback of traveling-wave protection is reliability, be easily subject to the impact of the disturbing factors such as the impact of outside electromagnetic interference, particularly thunder and lightning, often guide and false protection occurs; Secondly, also embody traveling-wave protection and there is unsurmountable principle defect in failure-resilient resistance, fault resolution sensitivity and protection seting etc.; Finally, it is proposed higher technical requirement to the acquisition rate of data and certainty of measurement.

The feature of differential under-voltage protection is that the action situation protected quantitatively is determined in the change of the differential calculation result and actual magnitude how obtaining voltage, and it is the main protection of DC power transmission line, bears again the backup protection effect of traveling-wave protection.Its responsiveness is later than traveling-wave protection slightly, particularly as differential under-voltage protection, can exit in traveling-wave protection, voltage change ratio plays dependent interaction when being not enough to starting protection.But failure-resilient resistance ability is low, fault is screened poor sensitivity and lacks the main weakness that necessary theories integration is it.

The feature of low-voltage variation is to detect to determine protection act to working voltage amplitude position, the not high and theoretical research also relative deficiency of its instream factor.Low-voltage variation mainly comprises circuit and pole controls two kinds, and the former setting value is relatively high, will start circuit reset routine after its action, the latter then after action by locking fault pole, therefore exceeded the category of route protection.It should play its defencive function when traveling-wave protection, differential under-voltage protection are not dynamic and current differential protection has little time action.But its subject matter be to adjust lack according to, do not have direction recognition function and responsiveness still slower etc.

The feature of conventional current differential protection is the topological structure regardless of DC line, can guarantee that it has absolute fault and screens selectivity.But do not consider in the algorithm extra long distance line distribution capacitance and power flowcontrol be the impact of high-frequency harmonic; also lack the balance exchanging braking amount set by differential protection, therefore can only wait for that time delay waits for that two kinds of methods guarantee the reliability of relevant protection by heightening action threshold or increasing.By heightening the impact that action threshold can avoid relevant interference to bring, but also reduce the sensitivity of fault examination simultaneously.The effect of sensitive examination fault after can obtaining interference attenuation by increase wait time delay, but the speed of protection will obviously reduce.It is many slowly that actual act speed comparatively exchanges differential protection, waits for that time delay need reach level second according to analysis.Due in the regulation process of direct current transportation, the reaction speed that power electronics controls is relatively faster, therefore repeatedly causes the action of pole control low-voltage variation and the protection of maximum Trigger Angle, causes locking fault pole, the circuit O&M accident that therefore forced outage is such; Meanwhile, this differential protection almost can not screen high resistive fault.

Except above-mentioned all protection; also according to corresponding other the protection scheme several proposed of practical experience ripe in AC system; as electric current transverse differential protection and circuit distance protection, and according in direct current transportation present the achievement in research extensively obtained in power inverted orientation phenomenon, direction component applicability etc.Because above-mentioned protection also all exists the limitation of principle, therefore can only protect in support or the miscellaneous function item of a certain protection.

Relaying protection often lacks tight qualitative analysis conclusion and believable quantitative estimation result; therefore have to rely on the analysis conclusion based on ideal model; what simulating, verifying went actual adjustment to protect by experiment adjusts; there is no clear and definite resolution boundary and screen nargin; the target simultaneously analyzed is too dull; lack relevance and comparative; once wherein the measuring state of any one electric signal change all can the overall performance of serious distortion protection, therefore relaying protection-special in direct current transportation-time delay just becomes a kind of indispensable compensatory device.

In sum; there is following defect in prior art: existing relaying protection often lacks tight qualitative analysis conclusion and believable quantitative estimation result; therefore have to rely on the analysis conclusion based on ideal model; what simulating, verifying went actual adjustment to protect by experiment adjusts; there is no clear and definite resolution boundary and screen nargin; the target simultaneously analyzed is too dull; lack relevance and comparative, once wherein the measuring state of any one electric signal change all can the overall performance of serious distortion protection.

Summary of the invention

The object of the invention is to; for the problems referred to above; a kind of current differential protection method based on HVDC (High Voltage Direct Current) transmission line is proposed, with overcome existing DC power transmission line when Fault Identification face transient response, distributed capacitance, operational mode bring the problem of relevant interference.

For achieving the above object, the technical solution used in the present invention is:

Based on a current differential protection method for HVDC (High Voltage Direct Current) transmission line, arrange current transformer at the two ends of high-voltage dc transmission electric wire, the electric current of described current transformer to high-voltage dc transmission electric wire two ends gathers, and described guard method comprises the following steps:

Step one, analyzing and processing is carried out to the direct current transmission line fault pole electric signal broken down after, the i.e. current signal of the DC power transmission line both sides collection of fault, the virtual condition at Analyzing on Size circuit of recycling gained fault component current signal;

Step 2: compare the result of current differential protection calculating and the size of set disturbance numerical value, structure reasonably differentiates.

Preferably, described step 2 compares result that current differential protection calculates and the size of set disturbance numerical value is specially:

When after grid collapses, the two ends current transformer of protected circuit is measured the data obtaining current failure component; After correspondence protection is triggered, the unsymmetrical current result corresponding to external area error will inevitably be filtered out with startup threshold by the delay cycle arranged; Troubles inside the sample space acquired results is just in time contrary, and two kinds of fault acquired results can ensure reliably to be distinguished, and can build following distinguishing rule thus:

|f(Δi _m+Δi _n)|＞I _set

In formula, Δ i _mwith Δ i _nrepresent the sampled current value at DC power transmission line two ends respectively, I _setfor line current instrument transformer secondary side measure longer integration/accumulative and period gained sampled value maximum uneven full dose current data.

Preferably, above-mentioned discrimination formula is specially:

When circuit both sides sampled value fault component calculates satisfied with the current differential of carrying out time ultrashort:

$\left|\underset{t=1}{\overset{{\mathrm{kT}}^{\′}}{\mathrm{\Σ}}}({\mathrm{\Δi}}_m\left(t\right)+{\mathrm{\Δi}}_n\left(t\right))\right|>{\mathrm{mK}}_1{I}_{\mathrm{set}}^{\′}$

In formula, I ' _setfor line current instrument transformer secondary side measure extremely short integration/accumulative and period gained sampled value maximum imbalance fault current weight data; Time of integration when T '=5ms is sampled value current differential ultrashort; MK ₁i ' _setin m be that the sampled data of corresponding current signal within the time of integration is counted; K ₁for being greater than the real number of 1, for screening the safety factor of the state of emergency; K is the time multiple of repetition integral and calculating, its be more than or equal to 1 integer.

Preferably, above-mentioned discrimination formula is specially:

When circuit both sides power frequency fault component calculates satisfied with the current differential that the time delay of power frequency multiple is carried out:

$\left|\underset{t=1}{\overset{{\mathrm{kT}}^{\′\′}}{\mathrm{\Σ}}}({\mathrm{\Δi}}_m\left(t\right)+{\mathrm{\Δi}}_n\left(t\right))\right|>{\mathrm{mK}}_2{I}_{\mathrm{set}}^{\′\′}$

In formula, I " _setfor line current instrument transformer secondary side measure normal, general integration/accumulative and period gained sampled value maximum imbalance fault current weight data; "=20ms is the time of integration of sampled value current differential power frequency period to T; MK ₂i " _setin m be that the sampled data of corresponding current signal within the time of integration is counted; K ₂for being greater than the real number of 1, for screening the safety factor of general state; K is the time multiple of repetition integral and calculating, its be not less than 1 integer.

Preferably, for the span of described k is 3 ~ 5.

Preferably, above-mentioned discrimination formula is specially: when circuit both sides sampled value fault component calculates satisfied with the current differential of carrying out during overlength:

$\left|\underset{t=1}{\overset{{\mathrm{kT}}^{\′\′\′}}{\mathrm{\Σ}}}({\mathrm{\Δi}}_m\left(t\right)+{\mathrm{\Δi}}_n\left(t\right))\right|>m{K}_3{I}_{\mathrm{set}}^{\′\′\′}$

In formula, I " ' _setfor line current instrument transformer secondary side measure longer integration/accumulative and period gained sampled value maximum imbalance fault current weight data; " '=100-1000ms is the time of integration of sampled value current differential ultra-delay to T; MK ₃i " ' _setin m be that sampled data corresponding within the time of integration is counted; K ₃for being greater than the real number of 1, for screening the safety factor of general state; K is the time multiple of repetition integral and calculating, its be more than or equal to 1 integer.

Preferably, above-mentioned discrimination formula is specially: under the operational mode that certain is special, and fault component can not guarantee stable acquisition, increases a current differential calculating formula during electric current full dose overlength:

$\left|\underset{t=1}{\overset{{\mathrm{kT}}^4}{\mathrm{\Σ}}}(i_m\left(t\right)+i_n\left(t\right))\right|>{\mathrm{mK}}_3{I^4}_{\mathrm{set}}$

In formula, I ⁴ _setfor line current instrument transformer secondary side measure longer integration/accumulative and period gained sampled value maximum uneven full dose current data; T ⁴for the time of integration differential during electric current full dose overlength, in order to the cooperation good with formula (3) protection structure, General Requirements T ⁴> T " '; MK ₃i ⁴ _setin m be that sampled data corresponding within the time of integration is counted; K ₄for being greater than the real number of 1, k is the time multiple of repetition integral and calculating, its be more than or equal to 1 integer.

Technical scheme of the present invention has following beneficial effect:

Technical scheme of the present invention, according to the current signal of circuit gained form intrinsic state variation characteristic, with reference to the electric distributed constant feature of transmission line, know the target signature and computing function of distinguishing its state.Utilize the integrated configuration improvement project constructing super high voltage direct current electricity transmission line protection based on integration/examination characteristic that is accumulative and current differential protection algorithm.With overcome existing DC power transmission line when Fault Identification face transient response, distributed capacitance, operational mode bring the problem of relevant interference.Corresponding protection seting and the threshold of action are set according to the rate request of protection act, build thus and can control with power electronics the protection seting that beat coordinates mutually, and in responsiveness, sensitivity etc., form relatively complete configuration.

Below by drawings and Examples, technical scheme of the present invention is described in further detail.

Accompanying drawing explanation

Fig. 1 a is the sampled value fault component electric state relation external fault line principle block diagram described in the embodiment of the present invention;

Fig. 1 b is the sampled value fault component electric state relation internal fault line principle block diagram described in the embodiment of the present invention;

Fig. 2 is the line principle block diagram of the sampled value full dose electric state relation described in the embodiment of the present invention;

Fig. 3 is the line principle block diagram of sampled value load component electric state relation;

Fig. 4 reflects by each differential relaying algorithm described in the embodiment of the present invention corresponding relation figure of delay time and action threshold.

Embodiment

Below in conjunction with accompanying drawing, the preferred embodiments of the present invention are described, should be appreciated that preferred embodiment described herein is only for instruction and explanation of the present invention, is not intended to limit the present invention.

Specific embodiment is:

Step one: after analyzing and processing is carried out to the direct current transmission line fault pole electric signal broken down, the virtual condition at Analyzing on Size circuit of recycling gained fault component current signal.When the amplitude of circuit gained fault component current signal is larger, the state of corresponding circuit is more serious, only has the time of delay shortening protection act, guarantees accurately and timely to identify fault, and the infringement that minimizing fault is brought.

By established for transmission line of alternation current Equivalent Physical concept and computational methods thereof, in conjunction with the actual motion feature of HVDC (High Voltage Direct Current) transmission line, obtain protected area respectively hold current integration/accumulative and time-domain calculation form.

When HVDC (High Voltage Direct Current) transmission system and relevant device thereof break down or occur disturbance, according to the feature of linear iteraction electrical network, DC line is respectively held electric current and is the obvious equivalency transform of present condition and linear iteraction relation by the situation according to reflected DC component and each harmonic component on the line, can obtain clearer and more definite differentiation conclusion thus for screening various types of fault.

Step 2: compare the result of current differential protection calculating and the size of set disturbance numerical value, structure reasonably differentiates.

When after grid collapses, on the two ends current transformer of protected circuit, total energy measures the data obtaining current failure component, and can guarantee the startup threshold that can be greater than relevant protection.After correspondence protection is triggered, the unsymmetrical current result corresponding to external area error will inevitably be filtered out with startup threshold by the delay cycle rationally arranged; Troubles inside the sample space acquired results is just in time contrary, and two kinds of fault acquired results can ensure reliably to be distinguished.Following criterion can be built thus:

|f(Δi _m+Δi _n)|＞I _set(1)

The comprehensive embodiment of the protected effect relaying configuration shown in formula (1).After the protection of setting is activated; when above-mentioned criterion meets operation condition; reliably can be judged to internal fault, the moment no longer meeting operation condition when above-mentioned criterion is exactly external area error or system disturbance, and the determination of system running state effectively can improve the overall performance of protection.

According to the conclusion that qualitative analysis is made, start the time-domain calculation method of multi-form current differential protection respectively.When transmission line impels the increment of above-mentioned phase induced current effectively to measure for some reason, corresponding temporal current differential relaying algorithm namely can be started.

When circuit both sides sampled value fault component calculates satisfied with the current differential of carrying out time ultrashort:

$\left|\underset{t=1}{\overset{{\mathrm{kT}}^{\′}}{\mathrm{\Σ}}}({\mathrm{\Δi}}_m\left(t\right)+{\mathrm{\Δi}}_n\left(t\right))\right|>{\mathrm{mK}}_1{I}_{\mathrm{set}}^{\′}---\left(2\right)$

In formula, I ' _setfor line current instrument transformer secondary side measure extremely short integration/accumulative and period gained sampled value maximum imbalance fault current weight data; Time of integration when T '=5ms is sampled value current differential ultrashort; MK ₁i ' _setin m be that the sampled data of corresponding current signal within the time of integration is counted; K ₁for being greater than the real number of 1, for screening the safety factor of the state of emergency; K is the time multiple of repetition integral and calculating, its be more than or equal to 1 integer; Integration/accumulative and formula current differential protection are.

Formula (2) algorithm compares the algorithm of Traditional DC transmission line current differential protection: | Δ i _m(t)+Δ i _n(t) | > I _set, add integration/accumulative and calculating link, there is certain filter effect, effectively can reduce the amplitude of the unsymmetrical current same period, relatively improve the sensitivity of protection.The criterion formula (2) of established protection act thus, namely goes for the HVDC (High Voltage Direct Current) transmission line demand that relaying protection is screened in state of emergency situation, mainly for the short trouble of protection exit place big current.

When circuit both sides power frequency fault component calculates satisfied with the current differential that the time delay of power frequency multiple is carried out:

$\left|\underset{t=1}{\overset{{\mathrm{kT}}^{\′\′}}{\mathrm{\Σ}}}({\mathrm{\Δi}}_m\left(t\right)+{\mathrm{\Δi}}_n\left(t\right))\right|>{\mathrm{mK}}_2{I}_{\mathrm{set}}^{\′\′}---\left(3\right)$

In formula, I " _setfor line current instrument transformer secondary side measure normal/general integration/accumulative and period gained sampled value maximum imbalance fault current weight data; "=20ms is the time of integration of sampled value current differential power frequency period to T; MK ₂i " _setin m be that the sampled data of corresponding current signal within the time of integration is counted; K ₂for being greater than the real number of 1, for screening the safety factor of general state; K is the time multiple of repetition integral and calculating, its be not less than 1 integer, the needs simultaneously time delay good with other protection structure of screening to meet state coordinates, and k value usually can be taked to be 3 ~ 5.

Formula (3) algorithm has longer integration/accumulative and computing time, and its low-pass filter effect is stronger, therefore in the sensitivity of fault examination, be obviously better than formula (2), and both forms good cooperation in protection act speed.Formula (3) algorithm compensate for the defect of Traditional DC transmission line current differential protection just, and can adapt to the transmission line demand that relaying protection is screened in general state situation completely, be also the most important foundation of innovation achievement of the present invention.

Equally, when circuit both sides sampled value fault component calculates satisfied with the current differential of carrying out during overlength:

$\left|\underset{t=1}{\overset{{\mathrm{kT}}^{\′\′\′}}{\mathrm{\Σ}}}({\mathrm{\Δi}}_m\left(t\right)+{\mathrm{\Δi}}_n\left(t\right))\right|>m{K}_3{I}_{\mathrm{set}}^{\′\′\′}---\left(4\right)$

In formula, I " ' _setfor line current instrument transformer secondary side measure longer integration/accumulative and period gained sampled value maximum imbalance fault current weight data; " '=100-1000ms is the time of integration of sampled value current differential ultra-delay to T; MK ₃i " ' _setin m be that sampled data corresponding within the time of integration is counted; K ₃for being greater than the real number of 1, for screening the safety factor of general state; K is the time multiple of repetition integral and calculating, its be more than or equal to 1 integer; Instantaneous value current differential protection is Traditional DC transmission line current differential protection algorithm, and integration/accumulative and formula current differential protection are.

Equally, formula (4) algorithm compares the algorithm of Traditional DC transmission line current differential protection: | Δ i _m(t)+Δ i _n(t) | > I _set, add integration/accumulative and calculating link.This innovatory algorithm effectively can reduce the impact that each current component amplitude attenuation and nonstoichiometric oxide bring, and not only has certain filter effect thus, equally also obviously can reduce the amplitude of the unsymmetrical current same period, relatively improve the sensitivity of protection; And protection delay time can be reduced by highly significant due to increased above-mentioned account form.The criterion formula (4) of established protection act, possesses the ability of higher fault-resistant resistance thus, goes for the HVDC (High Voltage Direct Current) transmission line demand that relaying protection is screened under microvariations state status completely.

Under the operational mode that certain is special (such as during reclosing), fault component can not guarantee stable acquisition, and the present invention increases a current differential calculating formula during electric current full dose overlength:

$\left|\underset{t=1}{\overset{{\mathrm{kT}}^4}{\mathrm{\Σ}}}(i_m\left(t\right)+i_n\left(t\right))\right|>{\mathrm{mK}}_3{I^4}_{\mathrm{set}}---\left(5\right)$

In formula, I ⁴ _setfor line current instrument transformer secondary side measure longer integration/accumulative and period gained sampled value maximum uneven full dose current data; T ⁴for the time of integration differential during electric current full dose overlength, in order to the cooperation good with formula (4) protection structure, General Requirements T ⁴> T " '; MK ₃i ⁴ _setin m be that sampled data corresponding within the time of integration is counted; K ₄for being greater than the real number of 1, for screening the safety factor of general state.

The sharpest edges of formula (4) current differential protection algorithm are the effect with load component on the formula that its current differential calculates; improve stability and the reliability of differential calculating, the demand of DC power transmission line relaying protection stable detection under mild state can be adapted to.For the feature of temporal current full dose differential protection; the integral algorithm of formula (4) eliminates from principle the various adverse effects that power electronics regulates and controls to bring; the impact etc. of less brought load component instability is exported comprising regulation and control electric energy; merge These characteristics, finally become the main feature of the present invention's innovation.In order to form good cooperation with formula (3) described protection on the protection act time limit; the shortest time interval of formula (4) integration needs the fixed time period definitely exceeding formula (3), generally can consider suitably to extend several 20mS cycle again.

The algorithm of above-mentioned four kinds of current differential protections: the fault component based differential protection protection carried out time ultrashort can isolate the serious short trouble that the state of emergency reflects fast, the fault component based differential protection protection carried out with the time delay of power frequency multiple can isolate short trouble corresponding to general state, play the effect of quick main protection, and the fault component based differential protection protection carried out during overlength can isolate microvariations state the minor failure that is suitable for, become the II segmentation unit relaying protection in band time limit, using the backup protection of the differential protection of full dose as above-mentioned all protections, form the modular relaying protection system of complete HVDC (High Voltage Direct Current) transmission line thus.This protection is specially adapted to all running environment of DC transmission system, forms seamless, round-the-clock protection component.

Under with national grid new planning from Jiuquan to Xiangtan, Hunan Province ± 800kV length more than 2000 kilometer extra-high voltage DC transmission system is the research that target carries out modular relaying protection integrated configuration.As illustrated in figs. ia and ib, m, n represent Jiuquan and Xiangtan, Hunan Province respectively, device current transformer is equipped with in both sides, line current signal through current transformer obtain after through sampling keep and A/D change after, deliver to microcomputer main system, and can directly according to sampled value fault component electric current and result determine whether occur internal fault.

(when analytical voltage distribution relation, the impact of line distribution capacitance can be ignored), with fault point virtual voltage u ' according to shown in Fig. 1 a and Fig. 1 b _ffor reference, analyzing the characteristic of DC power transmission line when district's internal and external fault, according to linear iteraction principle, the situation of DC component and relevant higher harmonic components may be occurred when occurring abnormal according to DC power transmission line, u ' _fcan be expressed as:

In formula, U ₀for involved DC Steady component; K _tthe ratio of direct current transient state component and DC Steady component; k ₀for the damping time constant of direct current transient state component; f ₁for work frequency; I is whole multiple of high order harmonic component in this fault; I ∈ Φ is the set relating to all high frequency harmonic components of this fault; U _ifor effective amplitude of i higher harmonic components; for the initial phase of i order harmonic components; k _ifor the damping time constant of i order harmonic components.

Shown in Fig. 1 a, when running into external area error, the voltage of circuit both sides can qualitative representation be:

${\mathrm{\Δu}}_m\left(t\right)\≈u_F^{\′}\left(t\right)\frac{\mathrm{lD}+L_m}{L_F^{\′}+\mathrm{lD}+L_m};{\mathrm{\Δu}}_n\left(t\right)\≈u_F^{\′}\left(t\right)\frac{L_m}{L_F^{\′}+\mathrm{lD}+L_m}---\left(7\right)$

Parameter in formula (7) as shown in Figure 1a.LD represents length.Consider the impact of extra long distance DC power transmission line distributed capacitance, if capacitance per unit length is c, like this for external area error, the result of calculation of current differential protection is exactly the capacitance current of circuit, estimates according to lumped parameter model:

Bring formula (8) into formula (2) can find, due to integration/accumulative and the time interval the shortest, therefore filtering part high frequency harmonic components can only be ensured, therefore result of calculation has higher unsymmetrical current, affect the sensitivity of screening fault, this algorithm can only be applicable to the short trouble of big current.

Bring formula (8) into formula (3) can find, due to integration/accumulative and time interval proper extension, therefore all whole the high frequency harmonic components that filtering amplitude is constant can be ensured, effectively reduce unsymmetrical current, improve the sensitivity that fault is screened, go for the short trouble of normal condition.

Bring formula (8) into formula (4) can find, due to integration/accumulative and the time interval or delay time the longest, therefore can ensure to overcome due to amplitude change and nonstoichiometric oxide bring the impact of unsymmetrical current, the sensitivity that fault is screened further is promoted, and is adapted to the short trouble of weak pattern system especially.

Equally, shown in Fig. 1 b, when running into troubles inside the sample space, the voltage of circuit both sides can qualitative representation be:

${\mathrm{\Δu}}_m\left(t\right)\≈u_F^{\′}\left(t\right)\frac{{\mathrm{lL}}_m}{\mathrm{ld}+L_m};{\mathrm{\Δu}}_n\left(t\right)\≈u_F^{\′}\left(t\right)\frac{L_n}{l(D-d)+L_n}---\left(9\right)$

The result of calculation of current differential protection be exactly the capacitance current of circuit and fault current and:

Line distribution capacitance electric current is at integration/accumulative and effectively decayed in calculating, and it should be noted that fault current.Transient fault current ratio is comparatively difficult to analyze, and stable fault currents can use DC line rated voltage U _edescribe with related resistors:

$i_F=\frac{U_F}{R_F+\frac{(R_m+\mathrm{rd})(R_n+(D-d)r)}{R_m+\mathrm{Dr}+R_n}}---\left(11\right)$

When ignoring line distribution capacitance electric current, the result of calculation of current differential protection is with the fault resstance value of formula (11) and abort situation and respective change, and relevant with system operation mode.Like this, can determine by corresponding current differential protection algorithm starting tripping after contrasting according to the result of formula (11) and the shutter threshold value of formula (2)-formula (4).

For the current differential protection algorithm of full dose Fig. 2, Fig. 3 and Shi (5) Suo Shi, fault component and load component two parts can be divided into according to linear iterative method.For DC power transmission line, the current differential protection of load component can be defined as:

i _mL(t)+i _nL(t)≈0 (12)

Therefore, the characteristic of full dose current differential protection algorithm can describe with the current differential protection of fault component completely.

As shown in Figure 4, the failure removal sequential of transmission line, t ₁moment is that transmission line breaks down, t ₂moment be fault component ultrashort time carry out the action setting time of current differential calculating, t ₃moment is the action setting time that current differential calculating is carried out in the time delay of fault component power frequency multiple, t ₄the action setting time of current differential calculating is carried out, t when moment is fault component overlength ₅the action setting time that when moment is full dose overlength, current differential calculates.When transmission line malfunction, (the generation moment is t=t ₁) after generation, i.e. t ₁< t < t ₂time; now the threshold value of the equivalent action obtained that converts the highest, the examination of the lower fault that is in a state of emergency mainly for transmission line, the relevant action delay time determines to take 5mS as benchmark; after having judged and determine to protect whether action, terminate relevant calculating.Work as t ₂< t < t ₃time, now determine that the foundation of action threshold value depends primarily on the minimum unsymmetrical current requirement guaranteed required for power frequency multiple delaying current differential protection, also be the reference object of other protection contrast, be in the examination of fault under general state mainly for transmission line; The same, the relevant action delay time determines to take 20mS as benchmark, and after having judged and determine to protect whether action, situation is the same.Work as t ₃< t < t ₄time, now the equivalent action threshold value obtained that converts will be starkly lower than the former, be in the examination of fault under microvariations state mainly for transmission line, the relevant action delay time is determined obviously much larger than 20mS.Work as t ₄< t < t ₅time, now the equivalent action threshold value obtained that converts will be minimum, be in the examination of fault under mild state mainly for transmission line, as full dose current differential protection bring the relevant action delay time the longest.The qualitative analysis according to above-mentioned operating characteristics can be known; under system cloud gray model is in any one mode; all at least ensure more than one specific protected modes can adapt to; and guarantee the impact overcoming unsymmetrical current to greatest extent in actual applications; guarantee reliability and the sensitivity of protection, form the improvement project the modular protection integrated configuration of a kind of HVDC (High Voltage Direct Current) transmission line thus.

The inventive method is super, in the actual motion of extra high voltage direct current transmission line, the periodicity electric variation characteristic intrinsic according to the fault component electric current of fault generation, analyze numerical value conversion and the physical link feature of current model essence, a kind of transmission line malfunction character discriminating method based on integration/accumulative and current differential protection is proposed, the action threshold of current differential protection and the time delays of protection closely related, in this approach by the impact of the outer other factors of state, the control method of this method and existing DC power transmission line can be got along amiably and peacefully simultaneously, complementary use, effectively can improve reliability and the sensitivity of protection.Be expected to the effective means as the modular nature of trouble identification of superhigh pressure long distance DC power transmission line Novel intelligent.On the basis that high-performance computer protection, wide frequency domain digital communication and intelligent electronic mutual inductance treatment technology are increasingly mature, the method has a good application prospect.

Last it is noted that the foregoing is only the preferred embodiments of the present invention, be not limited to the present invention, although with reference to previous embodiment to invention has been detailed description, for a person skilled in the art, it still can be modified to the technical scheme described in foregoing embodiments, or carries out equivalent replacement to wherein portion of techniques feature.Within the spirit and principles in the present invention all, any amendment done, equivalent replacement, improvement etc., all should be included within protection scope of the present invention.

Claims (7)

1. the current differential protection method based on HVDC (High Voltage Direct Current) transmission line; at the two ends of high-voltage dc transmission electric wire, current transformer is set; the electric current of described current transformer to high-voltage dc transmission electric wire two ends gathers, and it is characterized in that, described guard method comprises the following steps:

Step one, analyzing and processing is carried out to the direct current transmission line fault pole electric signal broken down after, the i.e. current signal of the DC power transmission line both sides collection of fault, the virtual condition at Analyzing on Size circuit of recycling gained fault component current signal;

Step 2: compare the result of current differential protection calculating and the size of set disturbance numerical value, structure reasonably differentiates.

2. the current differential protection method based on HVDC (High Voltage Direct Current) transmission line according to claim 1, is characterized in that, the size of result and set disturbance numerical value that described step 2 compares current differential protection calculating is specially:

When after grid collapses, the two ends current transformer of protected circuit is measured the data obtaining current failure component; After correspondence protection is triggered, the unsymmetrical current result corresponding to external area error will inevitably be filtered out with startup threshold by the delay cycle arranged; Troubles inside the sample space acquired results is just in time contrary, and two kinds of fault acquired results can ensure reliably to be distinguished, and can build following distinguishing rule thus:

|f(Δi _m+Δi _n)|＞I _set

In formula, Δ i _mwith Δ i _nrepresent the sampled current value at DC power transmission line two ends respectively, I _setfor line current instrument transformer secondary side measure longer integration/accumulative and period gained sampled value maximum uneven full dose current data.

3. the current differential protection method based on HVDC (High Voltage Direct Current) transmission line according to claim 2, is characterized in that, above-mentioned discrimination formula is specially:

When circuit both sides sampled value fault component calculates satisfied with the current differential of carrying out time ultrashort:

$\left|\underset{t=1}{\overset{{\mathrm{kT}}^{\&prime;}}{\mathrm{\&Sigma;}}}({\mathrm{\&Delta;i}}_m\left(t\right)+{\mathrm{\&Delta;i}}_n\left(t\right))\right|>{\mathrm{mK}}_1{I}_{\mathrm{set}}^{\&prime;}$

In formula, I ' _setfor line current instrument transformer secondary side measure extremely short integration/accumulative and period gained sampled value maximum imbalance fault current weight data; Time of integration when T '=5ms is sampled value current differential ultrashort; MK ₁i ' _setin m be that the sampled data of corresponding current signal within the time of integration is counted; K ₁for being greater than the real number of 1, for screening the safety factor of the state of emergency; K is the time multiple of repetition integral and calculating, its be more than or equal to 1 integer.

4. the current differential protection method based on HVDC (High Voltage Direct Current) transmission line according to claim 2, is characterized in that, above-mentioned discrimination formula is specially:

When circuit both sides power frequency fault component calculates satisfied with the current differential that the time delay of power frequency multiple is carried out:

$\left|\underset{t=1}{\overset{{\mathrm{kT}}^{\&prime;\&prime;}}{\mathrm{\&Sigma;}}}({\mathrm{\&Delta;i}}_m\left(t\right)+{\mathrm{\&Delta;i}}_n\left(t\right))\right|>{\mathrm{mK}}_2{I}_{\mathrm{set}}^{\&prime;\&prime;}$

In formula, I " _setfor line current instrument transformer secondary side measure normal, general integration/accumulative and period gained sampled value maximum imbalance fault current weight data; "=20ms is the time of integration of sampled value current differential power frequency period to T; MK ₂i " _setin m be that the sampled data of corresponding current signal within the time of integration is counted; K ₂for being greater than the real number of 1, for screening the safety factor of general state; K is the time multiple of repetition integral and calculating, its be not less than 1 integer.

5. the current differential protection method based on HVDC (High Voltage Direct Current) transmission line according to claim 4, is characterized in that, the span for described k is 3 ~ 5.

6. the current differential protection method based on HVDC (High Voltage Direct Current) transmission line according to claim 2, is characterized in that, above-mentioned discrimination formula is specially: when circuit both sides sampled value fault component calculates satisfied with the current differential of carrying out during overlength:

$\left|\underset{t=1}{\overset{{\mathrm{kT}}^{\&prime;\&prime;\&prime;}}{\mathrm{\&Sigma;}}}({\mathrm{\&Delta;i}}_m\left(t\right)+{\mathrm{\&Delta;i}}_n\left(t\right))\right|>{\mathrm{mK}}_3{I}_{\mathrm{set}}^{\&prime;\&prime;\&prime;}$

In formula, I " ' _setfor line current instrument transformer secondary side measure longer integration/accumulative and period gained sampled value maximum imbalance fault current weight data; " '=100-1000ms is the time of integration of sampled value current differential ultra-delay to T; MK ₃i " ' _setin m be that sampled data corresponding within the time of integration is counted; K ₃for being greater than the real number of 1, for screening the safety factor of general state; K is the time multiple of repetition integral and calculating, its be more than or equal to 1 integer.

7. the current differential protection method based on HVDC (High Voltage Direct Current) transmission line according to claim 2; it is characterized in that; above-mentioned discrimination formula is specially: under the operational mode that certain is special, and fault component can not guarantee stable acquisition, increases a current differential calculating formula during electric current full dose overlength:

$\left|\underset{t=1}{\overset{{\mathrm{kT}}^4}{\mathrm{\&Sigma;}}}(i_m\left(t\right)+i_n\left(t\right))\right|>m{K}_3{I^4}_{\mathrm{set}}$

In formula, I ⁴ _setfor line current instrument transformer secondary side measure longer integration/accumulative and period gained sampled value maximum uneven full dose current data; T ⁴for the time of integration differential during electric current full dose overlength, mK ₃i ⁴ _setin m be that sampled data corresponding within the time of integration is counted; K ₄for being greater than the real number of 1, for screening the safety factor of general state; K is the time multiple of repetition integral and calculating, its be more than or equal to 1 integer.