CN102288872B - Small-current grounding system single-phase grounding fault distance measurement method based on signal injection method - Google Patents

Abstract

The invention relates to a small-current grounding system single-phase grounding fault distance measurement method based on a signal injection method. Under a single-phase grounding fault, a constant-frequency sine current signal is injected through a voltage transformer during secondary lateral fault phase short circuit; the current generates a corresponding voltage drop on a faulted line; relational expressions between injection signal voltage and injection signal current at the head end of the line and the injection signal voltage and the injection signal current on a faulted point can be written by adopting a distribution parameter model of the line based on a long-line equation; relational expressions between the injection signal voltage and the injection signal current on the faulted point and transitional resistance can be also written; the virtual part of the transitional resistance is set to be 0 and the plural equations are solved, so that a fault distance can be obtained. The small-current grounding system single-phase grounding fault distance measurement method based on the signal injection method has the advantages that: due to adoption of an injection signal for distance measurement, influences of a system structure, a running mode and an arc suppression coil can be avoided; due to adoption of the distribution parameter model of the line, an influence of a distribution capacitor can be avoided; therefore, a distance measurement result has higher precision, and the small-current grounding system has high anti-transitional-resistance capability.

Description

Single-phase grounded malfunction in grounded system of low current distance-finding method based on the signal injection method

Technical field

The present invention relates to the electric power system fault distance-finding method, especially a kind of single-phase grounded malfunction in grounded system of low current distance-finding method based on the signal injection method.

Background technology

China 6-35kV distribution system generally adopts the method for operation of small current neutral grounding, and the advantage of this method of operation is when singlephase earth fault takes place, because system line voltage is still symmetrical, can continue operation 2 hours by tape jam, therefore has higher power supply reliability.The shortcoming of this method of operation is that the singlephase earth fault feature is not obvious, brings big difficulty to faulty line selection and fault localization.More to single-phase grounded malfunction in grounded system of low current route selection principle and Study on Technology at present, multiple selection method has also been proposed, wherein based on the fault line selection method for single-phase-to-ground fault of signal injecting principle owing to have and be not subjected to that system operation mode and arc suppression coil influence, the route selection high accuracy for examination, obtained comparatively general application.But not deep enough for the single-phase ground fault distance measuring technical research, owing to be subjected to the influence of factors such as system architecture, the method for operation, transition resistance, fault signature be not obvious, the fault localization precision has much room for improvement.

Chinese patent application 200510016286.3 discloses a kind of distance-finding method of small current neutral grounding system transmission line one-phase earth fault, when this method adopts the zero sequence signal that collected by data acquisition unit greater than threshold value, starts the fault localization algorithm; The false voltage data or the fault current data that collect are carried out high-pass filtering processing, filtering power frequency and following low-frequency harmonics component; Calculate distance through the trouble spot after the Filtering Processing.This invention is difficult to solve the single-phase ground fault distance measuring problem of neutral by arc extinction coil grounding system, and distance accuracy is subjected to the influence of distance coefficient bigger.

Chinese patent application 200810229756.8 discloses a kind of small current neutral grounding system double-loop wire single-phase ground fault distance measuring method, and this method is numbered the double loop of diverse location and be preset in the microcomputer of ground connection transfer device; Gather, calculate phase, line voltage and residual voltage and each circuit zero-sequence current on the substation bus bar in real time by microcomputer, judgement system has or not the separate of ground connection and ground connection, when system's generation singlephase earth fault, provide the split-phase switch reclosing command of ground connection phase by microcomputer, provide the instruction of record ripple simultaneously; After the record ripple was finished, microcomputer carried out the route selection operation in conjunction with the numbering of double loop by residual voltage and the zero-sequence current of measuring; Then, calculate to the range equation between the trouble spot by measuring the double loop first line ground current branch flow valuve equation, the measurement double loop second line ground current branch flow valuve equation, measurement inflow trouble spot ground current value equation and measuring circuit end by microcomputer, the position of earth point when trying to achieve some ground connection of double loop, promptly line end is to the distance between the trouble spot.The present invention by fault take place back control neutral point in short-term the mode of ground connection artificially increase zero-sequence current, thereby reach the purpose of correct route selection and range finding, excessive zero-sequence current brings adverse effect can for the normal operation of system equipment, and needs to increase corresponding primary equipment.

Chinese patent application 201010135675.9 discloses a kind of fault distance-finding method of using three primary colours to represent travel waves of single-phase earth fault current of transmission line, the present invention represents the fault current direction row ripple of transmission line of alternation current with three primary colours, under the three primary colours color mode, realize one-end fault ranging, when guaranteeing the fault localization accuracy, make that range finding is more directly perceived.The present invention is primarily aimed at the range finding problem of transmission system singlephase earth fault, requirement to sample frequency is very high, and be applicable to situations such as line length is long, the no branch in centre, the distribution system line length is bigger, the circuit medial fascicle is numerous, the catadioptric process complexity of fault traveling wave adopts this method to have certain limitation in distribution system.

Summary of the invention

For improving the single-phase grounded malfunction in grounded system of low current distance measuring precision, the invention provides a kind of single-phase grounded malfunction in grounded system of low current distance-finding method based on the signal injection method.When singlephase earth fault takes place after, at first inject a sinusoidal current signal that frequency is constant mutually to fault, according to comparing the size of injecting the marking current amplitude in each bar outlet, select faulty line, based on the distributed parameter model of circuit, list the faulty line head end and inject the mathematic(al) representation that concerns between signal voltage, electric current and fault distance and the transition resistance then, be resistive characteristics according to transition resistance, can obtain fault distance by solving an equation, thereby reach the purpose of fault localization.

The present invention adopts following technical proposals to realize:

A kind of single-phase grounded malfunction in grounded system of low current distance-finding method based on the signal injection method may further comprise the steps:

The first step: behind the small current neutral grounding system generation singlephase earth fault, determine that according to the situation of change of phase voltage and residual voltage fault is separate, the enabling signal source by voltage transformer secondary side to the constant sinusoidal current signal of distribution system injected frequency;

Second step: the zero sequence current mutual inductor by each circuit measures the injection marking current that flows through every circuit, and these current amplitudes are compared, and the circuit of maximal value correspondence is faulty line;

The 3rd step: obtain the voltage drop that injection current forms at faulty line by voltage measuring transformer, the zero sequence current mutual inductor by faulty line measures the current amplitude that is injected in the faulty line; If voltage measurement point is that fault distance is l to the distance between the trouble spot,, lists measurement point and inject the relational expression that signal voltage, electric current inject in signal voltage, electric current and place, trouble spot based on the distributed parameter model and the long-line equation of circuit; Injection current also equals to flow through the injection current of this point and the product of transition resistance at the voltage that the place, trouble spot produces, and obtains the injection signal voltage electric current of transition resistance and measurement point and the relational expression between the fault distance l thus;

The 4th step: above-mentioned expression formula is plural equation, and is resistive because transition resistance presents, so its imaginary part is 0, finds the solution plural equation in view of the above and obtains fault distance l.

After singlephase earth fault in the described first step took place, the fault phase voltage reduced, and less than 60% of rated voltage, but not fault phase voltage and residual voltage can raise, and it is separate to find out fault in view of the above.After determining that fault is separate, control is injected signal source and is injected sinusoidal current signal by voltage transformer secondary side mutually to the system failure, so that carry out failure line selection and fault localization.For the ease of detecting, inject the frequency of signal and must distinguish the output signal frequency f of signal source mutually with the frequency of electric system intrinsic signal _sCan not be the integral multiple of 50Hz or 50Hz, i.e. n * 50Hz＜f _s＜(n+1) * and 50Hz, n=1,2,3....

Injection signal measurement in described second step is from zero sequence current mutual inductor.Be injected into current signal in each distribution line zero sequence current mutual inductor of will inevitably flowing through, therefore available zero sequence current mutual inductor is measured the current signal that injects, but zero sequence current mutual inductor also can react the power current signal of 50Hz and the harmonic current signal of 50Hz integral multiple secondary frequencies simultaneously, therefore must adopt analog filter and digital filter will inject signal extraction reliably, accurately and come out.Be connected on and all have the inflow of injection current signal in all circuits on same the bus, but flow into the injection signal maximum in the faulty line, relatively flow into the size of the injection current in each bar distribution line, the circuit of maximum current correspondence is faulty line.

Circuit distributed parameter model in described the 3rd step as shown in Figure 1.Inject at known measurement point on the basis of signal voltage, electric current, the distance of establishing between trouble spot and the measurement point is l, and the relational expression that writes out between measurement point voltage, electric current and the fault point voltage electric current by long-line equation is:

$\left[\begin{array}{c}{\stackrel{\·}{U}}_1\\ {\stackrel{\·}{I}}_1\end{array}\right]=\left[\begin{array}{cc}\cosh \mathrm{\γl}& Z_c\sinh {\mathrm{\γ}}_l\\ \frac{\sinh \mathrm{\γl}}{Z_c}& \cosh \mathrm{\γl}\end{array}\right]\left[\begin{array}{c}{\stackrel{\·}{U}}_F\\ {\stackrel{\·}{I}}_F\end{array}\right]---\left(1\right)$

Wherein,

Be the injection signal voltage and the electric current phasor of circuit head end measurement point,

Be the characteristic impedance of circuit, Be the propagation coefficient of circuit, z ₁, y ₁Be impedance of circuit unit length and admittance,

Injection signal voltage and electric current phasor for the place, trouble spot.

If transition resistance is R _g, the distribution line total length is L, the relation that the injection signal injects signal voltage, electric current at the distribution situation and the place, trouble spot of whole piece circuit can be write out the relational expression that signal voltage, electric current inject in the place, trouble spot as shown in Figure 2:

${\stackrel{\·}{U}}_F={\stackrel{\·}{I}}_g\·R_g=({\stackrel{\·}{I}}_F-{\stackrel{\·}{I}}_Y)\·R_g---\left(2\right)$

Wherein,

Be the transition resistance R that flows through _gInjection current,

Be the equivalent admittance electric current of trouble spot to line end, this value is:

${\stackrel{\&CenterDot;}{I}}_Y={\stackrel{\&CenterDot;}{U}}_F\&CenterDot;Y_E={\stackrel{\&CenterDot;}{U}}_F\&CenterDot;[{\mathrm{<figure-callout\; id="1"\; label="y"\; filenames="HDA0000072582290000011.png"\; state="\{\{state\}\}">y</figure-callout>}}_1\&CenterDot;(L-l)]---\left(3\right)$

Wherein, Y _EBe the equivalent admittance of trouble spot to line end, L is the total length of distribution line.

Can put out the transition resistance R in order by formula (1)～(3) _gExpression formula be:

$R_g=\frac{Z_c}{-\frac{\sinh \mathrm{\&gamma;l}{\stackrel{\&CenterDot;}{U}}_1-Z_c\cosh \mathrm{\&gamma;l}{\stackrel{\&CenterDot;}{I}}_1}{\cosh \mathrm{\&gamma;l}{\stackrel{\&CenterDot;}{U}}_1-Z_c\sinh \mathrm{\&gamma;l}{\stackrel{\&CenterDot;}{I}}_1}-\mathrm{\&gamma;}(L-l)}---\left(4\right)$

Following formula is plural equation, and transition resistance R _gBe resistive, so its imaginary part is 0.Find the solution formula (4) according to this condition, can obtain fault distance l.

The present invention finishes based on the signal injecting principle on the basis of single-phase earth fault line selection, inject the regularity of distribution of signal by analyzing at faulty line, can obtain describing the equation expression formula of injecting mathematical relation between signal voltage, electric current and the line parameter circuit value, just can calculate fault distance by solving equation, thereby finish the line single phase grounding failure distance measurement function.

The present invention adopts the constant frequency sinusoidal ac signal that single-phase grounded malfunction in grounded system of low current is found range, and compares with existing similar technology to have following advantage:

1. compare with the method that adopts power frequency component to carry out fault localization, adopt inject signal find range have the system architecture of not being subjected to, the characteristics of the influence of the method for operation and arc suppression coil, have applicability preferably.In addition, inject signal and only after singlephase earth fault takes place, just occur, under normal operation and other fault condition, can not occur, can guarantee the precision of fault localization;

2. compare with the distance-finding method that adopts the circuit lumped parameter model, adopt distributed parameter model can overcome the influence of distributed capacitance preferably, guaranteed distance measuring precision from circuit model;

3. taken into full account when the transition resistance eutral grounding trouble spot and further improved the precision of fault localization to the shunting action of distributed capacitance between the line end;

4. utilizing transition resistance to be resistive, imaginary part is that 0 feature is found the solution the fault distance equation, has that operand is little, soon, there are not advantages such as pseudo-root in computing velocity.

Description of drawings

Fig. 1 is a circuit distributed parameter model synoptic diagram;

Fig. 2 is that signal voltage, current relationship synoptic diagram inject in the place, trouble spot;

The single-phase grounded malfunction in grounded system of low current range measurement system that Fig. 3 is based on the signal injection method constitutes synoptic diagram

Embodiment

The present invention is further described below in conjunction with accompanying drawing and example.

1. the formation of single-phase ground fault distance measuring system

The single-phase grounded malfunction in grounded system of low current range measurement system constitutes as shown in Figure 3.This system comprises injects signal source, voltage transformer (VT), zero sequence current mutual inductor and single-phase ground fault distance measuring device.Inject signal source and can produce a sinusoidal current signal that frequency is different with the electric system natural frequency, amplitude is about 5A, inject signal source only when singlephase earth fault takes place, be connected in short-term the fault of voltage transformer secondary side separate on, injecting to faulty line can be for the signal that detects, and fault stops to inject signal after disappearing; Voltage transformer (VT) is used for each phase of measuring system, residual voltage and injection signal voltage on the one hand, will inject signal on the other hand and be coupled to primary system by secondary side; Zero sequence current mutual inductor is used for measuring the injection marking current that flow in this circuit; The single-phase ground fault distance measuring device calculates the singlephase earth fault distance by the injection signal voltage at measurement bus place and the injection marking current of faulty line head end, provides foundation for finding fast and getting rid of fault.

2. singlephase earth fault detects and failure line selection

During small current neutral grounding system generation Single Phase Metal earth fault, the fault phase voltage is 0, and non-fault phase voltage raises and is line voltage, and the residual voltage that is obtained by the zero sequential potential transformer secondary side is about 100V, according to the Changing Pattern of above-mentioned voltage, it is separate to find out fault.The current source that can produce the constant frequency sinusoidal ac signal then is connected to the secondary side of fault phase voltage mutual inductor, will inject signal by voltage transformer (VT) and be coupled to primary system.Because there is earth point in faulty line, therefore can flow through bigger injection signal, and not have earth point on the non-fault line, only can flow through very little capacitance current.No matter which breaks down mutually, injects the zero sequence current mutual inductor that signal all can current through line, and therefore the zero sequence current mutual inductor secondary side from each outlet can detect the injection signal.By the injection current amplitude that flows through each bar circuit is compared, the circuit of maximal value correspondence is faulty line, so just can determine faulty line.

3. single-phase ground fault distance measuring

Selecting on the basis of faulty line, can record the injection signal voltage of faulty line head end, can record by the zero sequence current mutual inductor on the faulty line and flow through the injection marking current that injects the circuit head end by voltage transformer (VT).Distance between assumed fault point and the circuit head end is l, based on distribution circuit parameter model shown in Figure 1, adopts long-line equation to obtain the voltage and current that the trouble spot is located by head end voltage, electric current, as shown in Equation (1)

$\left[\begin{array}{c}{\stackrel{\&CenterDot;}{U}}_1\\ {\stackrel{\&CenterDot;}{I}}_1\end{array}\right]=\left[\begin{array}{cc}\cosh \mathrm{\&gamma;l}& Z_c\sinh {\mathrm{\&gamma;}}_l\\ \frac{\sinh \mathrm{\&gamma;l}}{Z_c}& \cosh \mathrm{\&gamma;l}\end{array}\right]\left[\begin{array}{c}{\stackrel{\&CenterDot;}{U}}_F\\ {\stackrel{\&CenterDot;}{I}}_F\end{array}\right]---\left(1\right)$

Wherein, Be the injection signal voltage and the electric current phasor of circuit head end measurement point, Be the characteristic impedance of circuit,

Be the propagation coefficient of circuit, z ₁, y ₁Be impedance of circuit unit length and admittance,

Injection signal voltage and electric current phasor for the place, trouble spot.

Inject marking current as shown in Figure 2 in the distribution of faulty line.

Be the injection signal voltage and the electric current phasor of circuit head end, Be injection signal voltage and electric current phasor that the trouble spot that obtains based on the circuit distributed parameter model is located, wherein fault distance l is a unknown number.The injection marking current that flows into the trouble spot transition resistance of all not flowing through, some is shunted to the distributed capacitance of this section of line end circuit by the trouble spot.Consider that shunting is mainly caused by distributed capacitance, and distributed capacitance is bigger, calculates to simplify the analysis, the trouble spot can replace with an admittance with lumped parameter characteristic to the distributed capacitance of line end, as the Y among Fig. 2 _eShown in.Then equivalent capacity is to injecting splitting into of signal:

${\stackrel{\&CenterDot;}{I}}_Y={\stackrel{\&CenterDot;}{U}}_F\&CenterDot;Y_e---\left(5\right)$

The injection current of transition resistance of flowing through is:

${\stackrel{\&CenterDot;}{I}}_g={\stackrel{\&CenterDot;}{I}}_F-{\stackrel{\&CenterDot;}{I}}_Y={\stackrel{\&CenterDot;}{I}}_F-({\stackrel{\&CenterDot;}{U}}_F\&CenterDot;Y_e)---\left(6\right)$

And:

${\stackrel{\&CenterDot;}{U}}_F={\stackrel{\&CenterDot;}{I}}_g\&CenterDot;R_g=[{\stackrel{\&CenterDot;}{I}}_F-({\stackrel{\&CenterDot;}{U}}_F\&CenterDot;Y_e)]\&CenterDot;R_g---\left(7\right)$

So:

$R_g=\frac{{\stackrel{\&CenterDot;}{U}}_F}{{\stackrel{\&CenterDot;}{I}}_F-({\stackrel{\&CenterDot;}{U}}_F-Y_e)}---\left(8\right)$

Formula (1) is updated in the following formula, can obtains formula (4).Formula (4) comprises two unknown numbers, is respectively R _gAnd l.Because transition resistance R _gBe resistive, therefore having only real part, imaginary part is 0.Utilize this characteristics, can solve unknown number l, i.e. fault distance by through type (4).

Claims (4)

1. the single-phase grounded malfunction in grounded system of low current distance-finding method based on the signal injection method is characterized in that, may further comprise the steps:

The first step: behind the small current neutral grounding system generation singlephase earth fault, determine that according to the situation of change of phase voltage and residual voltage fault is separate, the enabling signal source, by voltage transformer secondary side to the constant sinusoidal current signal of system's injected frequency;

Second step: the zero sequence current mutual inductor by each circuit measures the injection marking current that flows through every circuit, and these current amplitudes are compared, and the circuit of maximal value correspondence is faulty line;

The 3rd step: record the voltage drop that injection current forms at faulty line by voltage transformer (VT), the zero sequence current mutual inductor by faulty line measures the electric current that is injected in the faulty line; If measurement point is fault distance l to the distance between the trouble spot,, list the injection signal voltage phasor of circuit head end measurement point based on the distributed parameter model and the long-line equation of circuit

And electric current phasor The signal voltage phasor is injected at the place with the trouble spot

Electric current phasor

Relational expression:

$\left[\begin{array}{c}{\stackrel{\&CenterDot;}{U}}_1\\ {\stackrel{\&CenterDot;}{I}}_1\end{array}\right]=\left[\begin{array}{cc}\cosh \mathrm{\&gamma;l}& Z_c\sinh \mathrm{\&gamma;l}\\ \frac{\sinh \mathrm{\&gamma;l}}{Z_c}& \cosh \mathrm{\&gamma;l}\end{array}\right]\left[\begin{array}{c}{\stackrel{\&CenterDot;}{U}}_F\\ {\stackrel{\&CenterDot;}{I}}_F\end{array}\right]---\left(1\right)$

Wherein,

Be the characteristic impedance of circuit,

Be the propagation coefficient of circuit, z ₁, y ₁Be impedance of circuit unit length and admittance;

If transition resistance is R _g, the distribution line total length is L, the injection signal voltage phasor at place, trouble spot

Electric current phasor

Relational expression:

${\stackrel{\&CenterDot;}{U}}_F={\stackrel{\&CenterDot;}{I}}_g\&CenterDot;R_g=({\stackrel{\&CenterDot;}{I}}_F-{\stackrel{\&CenterDot;}{I}}_Y)\&CenterDot;R_g---\left(2\right)$

Wherein,

Be the transition resistance R that flows through _gInjection current,

Be the equivalent admittance electric current of trouble spot to line end, this value is:

${\stackrel{\&CenterDot;}{I}}_Y={\stackrel{\&CenterDot;}{U}}_F\&CenterDot;Y_E={\stackrel{\&CenterDot;}{U}}_F\&CenterDot;[y_1\&CenterDot;(L-l)]---\left(3\right)$

Wherein, Y _EBe the equivalent admittance of trouble spot to line end;

Obtain transition resistance R by formula (1)～(3) _gInjection signal voltage phasor with circuit head end measurement point

And electric current phasor

And the relational expression between the fault distance l is:

$R_g=\frac{Z_c}{-\frac{\sinh \mathrm{\&gamma;l}{\stackrel{\&CenterDot;}{U}}_1-Z_c\cosh \mathrm{\&gamma;l}{\stackrel{\&CenterDot;}{I}}_1}{\cosh \mathrm{\&gamma;l}{\stackrel{\&CenterDot;}{U}}_1-Z_c\sinh \mathrm{\&gamma;l}{\stackrel{\&CenterDot;}{I}}_1}-\mathrm{\&gamma;}(L-l)}---\left(4\right)$

The 4th step: above-mentioned expression formula (4) is plural equation, comprises transition resistance R in this plural number equation _gWith two unknown numbers of fault distance l, but because transition resistance R _gBe resistive,, find the solution plural equation in view of the above and obtain fault distance l so its imaginary part is 0.

2. the single-phase grounded malfunction in grounded system of low current distance-finding method based on the signal injection method according to claim 1, it is characterized in that: for the ease of detecting, inject the frequency of signal and must distinguish the output signal frequency f of signal source mutually with the frequency of electric system intrinsic signal _sCan not be the integral multiple of 50Hz or 50Hz, i.e. n * 50Hz＜f _s＜(n+1) * and 50Hz, n is a positive integer.

3. the single-phase grounded malfunction in grounded system of low current distance-finding method based on the signal injection method according to claim 1, it is characterized in that: in described second step, be injected into current signal in the circuit zero sequence current mutual inductor of will inevitably flowing through, after singlephase earth fault takes place, the secondary side output of zero sequence current mutual inductor not only comprises 50Hz power frequency component and harmonic signal, also comprise the injection signal, adopt analog filter and digital filter will inject Signal Separation and come out.

4. the single-phase grounded malfunction in grounded system of low current distance-finding method based on the signal injection method according to claim 1, it is characterized in that: what circuit adopted in described the 3rd step is the influence that distributed parameter model has been considered distributed capacitance, therefore has higher precision.

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