CN103792465B - A kind of method of the range finding of the one-phase earthing failure in electric distribution network based on residual voltage - Google Patents

Abstract

The invention relates to a method for distance measurement of a single-phase ground fault in a distribution network based on zero-sequence voltage, which belongs to methods for distance measurement of a distribution network ground fault. The fault location method is based on the overall zero-sequence parameters of the single-ended radial medium-voltage distribution network, and considers the influence of the distributed parameter model when analyzing single-phase ground faults, and measures the steady-state zero-sequence voltage values at the busbar and at the end of each outgoing line after the fault and the zero-sequence current of each feeder, and find out the zero-sequence voltage variation characteristics of the faulty feeder and non-faulty feeder. The present invention utilizes a large number of existing devices, has low real-time requirements for data sampling, and is easy to realize; through the analysis of the simulation model established according to actual parameters, the neutral point is not grounded or the neutral point is grounded through the arc suppression coil. Realize fault distance measurement with high precision. The positioning method of the invention can be applied to medium and low voltage distribution networks.

Description

A method for single-phase-to-earth fault location in distribution network based on zero-sequence voltage

Technical field:

The invention relates to a method for distance measurement of a distribution network ground fault, in particular to a method for distance measurement of a distribution network single-phase ground fault based on zero-sequence voltage.

Background technique:

The safe operation of the distribution network provides an important guarantee for social production and life. Once a major failure occurs, the economic loss is difficult to estimate. Therefore, fast and accurate fault location is very important to the economy, safety and reliability of the power system. The single-phase-to-ground fault has the highest probability of occurrence in the distribution network.

With the development of distribution network automation technology, installing a new type of distribution switch with measurement and communication functions on the feeder can obtain a large amount of line power information, and then use the principle of electrical network graph theory to establish the adjacency matrix and node information matrix of nodes. Then the fault judgment matrix is obtained and its elements are analyzed, and the fault section can be judged. The identification of the fault section can realize rapid fault removal, but it cannot accurately realize fault distance measurement and cannot meet the requirements of follow-up work. There are two main methods for fault location: traveling wave method and impedance method. Among them, the traveling wave method has good accuracy, and the impedance method has good stability. The advantages of the two methods are combined, and the distance can be measured by using the phase relationship between the negative sequence current at the measurement point and the negative sequence voltage at the fault point. However, the structure of distribution lines is complex, there are many branches, and the line distance is short, so it is difficult to solve the problems of fault wave head identification and mixed line wave impedance changes. At the same time, multiple sets of traveling wave detection equipment are required, and the economic cost is relatively high. Therefore, the traveling wave method is difficult to apply to the distribution network. If the impedance method is used, it can not only overcome the distance measurement problem of the traveling wave method, but also can use a large number of existing equipment in operation, the hardware investment is small, and it is easy to implement. For the double-terminal impedance method, the phase compensation method can be used to eliminate the error between the zero-sequence current and voltage collected asynchronously to calculate the fault distance. However, most of the impedance methods used in the past are calculated by the lumped parameter model. Since the influence of distributed capacitance is not considered, the calculation results have large errors. The fault location method based on the distributed parameter model overcomes the disadvantage of ignoring the influence of distributed capacitance when based on the lumped parameter model, and can improve the location accuracy. Some calculation methods use fixed line parameters to calculate, and there are also large errors. my country's medium-voltage distribution network is mostly a single-ended radial grid, and single-phase ground faults often occur. The research on fault line selection and fault interval determination has achieved fruitful results and has been well applied. How to realize the medium-voltage distribution network Accurate fault location is more difficult. When a single-phase ground fault occurs, the transient energy is small, and it is difficult to measure the traveling wave signal; while the traditional ranging technology based on the impedance method is mostly used in the high-voltage power grid, and the neutral point grounding method is different from that of the medium and low-voltage distribution network. It cannot be directly applied to the medium-voltage distribution network because of the consideration of sequence parameters and more consideration of a single line.

Contents of the invention

The purpose of the present invention is to provide a single-phase ground fault distance measurement method in distribution network based on zero-sequence voltage, which can solve the problem of single-phase ground fault distance measurement caused by complex line structure, many branches and short line distance in distribution network. The problem of large errors.

The object of the present invention is achieved in this way: the fault location method starts from the overall zero-sequence parameters of the single-ended radial medium-voltage distribution network, considers the influence of the distributed parameter model when analyzing single-phase ground faults, and measures the busbar and each outgoing line The steady-state zero-sequence voltage value and the zero-sequence current of each feeder after terminal faults are used to find out the zero-sequence voltage variation characteristics of faulted feeders and non-faulted feeders.

Specific steps are as follows:

(1), distributed parameter line model

The distribution network is used for fault location measurement, and the distributed parameter model is used for fault location measurement; by calculating the line parameters, when a single-phase ground fault occurs, the conductance current to the ground is much smaller than the capacitance current, so the influence on the conductance to the ground can be ignored. The distributed parameter model of the zero-sequence equivalent circuit is simplified as the average distribution of line impedance and ground capacitance along the line;

(2), non-fault line analysis

Divide the feeder line into n subsections, take any subsection and record it as [x, x+Δx]. The ground current ΔI _C = I _C .Δx generated in this subsection, I _C is the unit length Line-to-ground capacitive current;

For non-fault lines, the current ΔI _C generated between each sub-district flows on the line from the bus to the location x of the sub-district, and then flows to the fault point through the ground; assuming that the corresponding starting position of each sub-district is x, then The voltages generated by the current action are ΔI _C .Xx, and the ground current generated in each interval acts on the voltage generated on the line: ΔU=ΔI _C .Xx, where: X is the impedance value of the line unit length;

According to the superposition theorem, the zero-sequence voltage difference at both ends of the line is the result of the zero-sequence current, and both sides of the above formula are integrated for x at the same time: ${\∫}_0^{l}d\stackrel{.}{u}={\∫}_0^l\stackrel{.}{I_C}\&Center\; Dot;x\&Center\; Dot;x\·\mathrm{dx},$ Calculated: ${\stackrel{.}{u}}_2-\stackrel{.}{u_1}=\frac{1}{2}{I}_C\·x\·l^2\left(1\right),$ l is the length of the non-fault line, Zero-sequence voltage at the beginning and end of non-fault lines respectively;

(3) Analysis of the fault line of the neutral point ungrounded system

For the fault line, the current flowing through the fault point includes the capacitive current of the non-fault line and the capacitive current of the fault line; Then flow back to the line from the fault point, which has no effect on the line before the fault point, which is equivalent to forming a circular loop between the line, the ground capacitance, the ground and the fault point; the ground capacitance current between the cells flows to the earth through the ground capacitance, and then After the fault point, it flows back to the bus through the line; therefore, the range of the voltage generated by the action of the ground current between the small areas is from the small area to the fault point, and the current from the small area to the bus section cancels each other; if the fault distance is x, then the distance from the bus The voltage variation ΔU'=ΔI _C .X.(x-x') generated by the ground current generated between the cells of x' acting on the line; same as above, the ground current acting on the line from the bus to the fault point can be obtained The amount of voltage change: ${\∫}_0^{x}d\stackrel{.}{u^{\′}}={\∫}_0^x-\stackrel{.}{I_C}\·x\·(x-x^{\′})\·{\mathrm{dx}}^{\′},$ which is $\stackrel{.}{u^{\′}}=-\frac{1}{2}{\stackrel{.}{I}}_C\·x\·x^2;$ The zero-sequence current from the fault point to the bus section also includes the ground current of the non-fault line and In the voltage change generated in this interval: $\stackrel{.}{u^{\′\′}}=\stackrel{.}{I_{C_{\mathrm{\Σ}}}}\&Center\; Dot;x\&Center\; Dot;x;$ According to the superposition theorem, we know that: $\stackrel{.}{u^{\′}}+\stackrel{.}{u^{\′\′}}=-(\frac{1}{2}{\stackrel{.}{I}}_C\&Center\; Dot;x-{\stackrel{.}{I}}_{C_{\mathrm{\Σ}}})x\·x={\stackrel{.}{u}}_f-{\stackrel{.}{u}}_1^{\′}$ (2); The voltage change of the fault line is the same as that of the non-fault line, therefore, $\frac{1}{2}{\stackrel{.}{I}}_C\&Center\; Dot;x\&Center\; Dot;{(l^{\′}-x)}^2={\stackrel{.}{u}}_2^{\′}-{\stackrel{.}{u}}_f$ (3); where: l' is the total length of the fault line, Corresponding to the zero-sequence voltage at the beginning and end of the fault line and the voltage at the fault point respectively; (2) and (3) are added together to get: ${\stackrel{.}{u}}_2^{\′}-{\stackrel{.}{u}}_1^{\′}=\frac{1}{2}{\stackrel{.}{I}}_C\&Center\; Dot;x\&Center\; Dot;(l^{\′2}-{2l}^{\′}\&Center\; Dot;x)+{\stackrel{.}{I}}_{C_{\mathrm{\Σ}}}\·x\&Center\; Dot;x---\left(4\right);$

(4) Analysis of neutral point via arc suppression coil fault line

The change of zero-sequence current and zero-sequence voltage of the non-faulted line in the neutral point through the arc suppression coil grounding system is the same as that of the neutral point ungrounded system; and the zero-sequence current of the faulty line is equivalent to the faulty line in the neutral point ungrounded system. Superimpose the inductive current flowing through the arc suppression coil at the fault point That is to say, if the system is working in the fully compensated state, the reactive current at the fault point is zero. If the active current of the system is ignored, the zero-sequence current measured from the head end of the fault branch is the capacitive current generated by the branch itself. However, in order to avoid resonance when the arc suppressing coil is running, it generally runs in the overcompensated state, that is, when a single-phase ground occurs, the zero-sequence current properties of the faulty branch are similar to those of the non-faulty branch. The difference in compensation situation is larger than the capacitive current generated by its own distribution parameters, and The size of can be obtained from the parameters when the arc suppression coil is tuned; the current generated by the zero sequence voltage acting on the arc suppression coil lags by 90°, and the capacitor current to the ground leads the zero sequence voltage by 90°, so and Phase opposite. The amount of voltage variation generated in the fault zone: Finally, the formula corresponding to the crowbar-grounded system is obtained: ${\stackrel{.}{u}}_2^{\′}-{\stackrel{.}{u}}_1^{\′}=\frac{1}{2}{\stackrel{.}{I}}_C\&Center\; Dot;x\&Center\; Dot;(l^{\′2}-{2l}^{\′}\·x)+({\stackrel{\·}{I}}_{C_{\mathrm{\Σ}}}-{\stackrel{.}{I}}_L)\&Center\; Dot;x\·x---\left(5\right).$

Beneficial effects, adopting the above-mentioned scheme, can utilize a large number of existing equipments put into operation, realize simple, have strong economy and good practical value; use distributed parameter model calculation, overcome the traditional fault location method of distribution network due to The use of the lumped parameter model causes large errors; this method is not only suitable for the neutral point ungrounded system, but also for the neutral point grounded system through the arc suppression coil, and only needs to obtain the zero point of each branch after the single-phase ground fault The sequence current, the zero-sequence voltage steady-state value at the end of the branch and the tuning of the arc suppression coil can be accurately measured on the basis of correctly selecting the fault feeder.

Description of drawings

Figure 1 Zero-sequence equivalent circuit distributed parameter model.

Figure 2 Zero-sequence current distribution diagram of non-fault lines.

Fig. 3 Characteristics of the zero-sequence current of the fault line in the neutral point ungrounded system.

Fig. 4 The characteristics of the zero-sequence current of the fault line of the neutral point arc suppressing coil grounding system.

Fig. 5 is a flow chart of a method for locating a single-phase-to-ground fault in a distribution network based on zero-sequence voltage.

Figure 6PSCAD simulation model.

detailed description:

Embodiment 1: The fault location method starts from the overall zero-sequence parameters of the single-ended radial medium-voltage distribution network, considers the influence of the distributed parameter model when analyzing single-phase ground faults, and measures the post-fault steady state of the busbar and each outgoing line terminal The zero-sequence voltage value and the zero-sequence current of each feeder are used to find out the zero-sequence voltage variation characteristics of the faulty feeder and the non-faulty feeder.

Specific steps are as follows:

1. Distributed parameter line model

Use the distributed parameter model to measure the fault location of the distribution network; by calculating the line parameters, when a single-phase ground fault occurs, the conductance current to the ground is much smaller than the capacitance current, so the influence on the conductance to the ground can be ignored, and the zero-sequence equivalent circuit The distributed parameter model is simplified as the average distribution of line impedance and ground capacitance along the line;

2. Analysis of non-fault lines

Divide the feeder line into n subsections, take any subsection and record it as [x, x+Δx]. The ground current ΔI _C = I _C .Δx generated in this subsection, I _C is the unit length Line-to-ground capacitive current;

For non-fault lines, the current ΔI _C generated between each sub-district flows on the line from the bus to the location x of the sub-district, and then flows to the fault point through the ground; assuming that the corresponding starting position of each sub-district is x, then The voltages generated by the current action are ΔI _C .Xx, and the ground current generated in each interval acts on the voltage generated on the line: ΔU=ΔI _C .Xx, where: X is the impedance value of the line unit length;

According to the superposition theorem, the zero-sequence voltage difference at both ends of the line is the result of the zero-sequence current, and both sides of the above formula are integrated for x at the same time: ${\∫}_0^{l}d\stackrel{.}{u}={\∫}_0^l\stackrel{.}{I_C}\&Center\; Dot;x\&Center\; Dot;x\·\mathrm{dx},$ Calculated: ${\stackrel{.}{u}}_2-\stackrel{.}{u_1}=\frac{1}{2}{I}_C\&Center\; Dot;x\&Center\; Dot;l^2\left(1\right),$ l is the length of the non-fault line, Zero-sequence voltage at the beginning and end of non-fault lines respectively;

3. Fault line analysis of neutral point ungrounded system

For the fault line, the current flowing through the fault point includes the capacitive current of the non-fault line and the capacitive current of the fault line; Then flow back to the line from the fault point, which has no effect on the line before the fault point, which is equivalent to forming a circular loop between the line, the ground capacitance, the ground and the fault point; the ground capacitance current between the cells flows to the earth through the ground capacitance, and then After the fault point, it flows back to the bus through the line; therefore, the range of the voltage generated by the action of the ground current between the small areas is from the small area to the fault point, and the current from the small area to the bus section cancels each other; if the fault distance is x, then the distance from the bus The voltage variation ΔU'=ΔI _C .X.(x-x') generated by the ground current generated between the cells of x' acting on the line; same as above, the ground current acting on the line from the bus to the fault point can be obtained The amount of voltage change: ${\∫}_0^{x}d\stackrel{.}{u^{\′}}={\∫}_0^x-\stackrel{.}{I_C}\&Center\; Dot;x\&Center\; Dot;(x-x^{\′})\·{\mathrm{dx}}^{\′},$ which is $\stackrel{.}{u^{\′}}=-\frac{1}{2}{\stackrel{.}{I}}_C\&Center\; Dot;x\&Center\; Dot;x^2;$ The zero-sequence current from the fault point to the bus section also includes the ground current of the non-fault line and The amount of voltage variation produced in this interval: $\stackrel{.}{u^{\′\′}}=\stackrel{.}{I_{C_{\mathrm{\Σ}}}}\&Center\; Dot;x\&Center\; Dot;x;$ According to the superposition theorem, we know that: $\stackrel{.}{u^{\′}}+\stackrel{.}{u^{\′\′}}=-(\frac{1}{2}{\stackrel{.}{I}}_C\&Center\; Dot;x-{\stackrel{.}{I}}_{C_{\mathrm{\Σ}}})x\&Center\; Dot;x={\stackrel{.}{u}}_f-{\stackrel{.}{u}}_1^{\′}$ (2); The voltage change of the fault line is the same as that of the non-fault line, therefore, (3); where: l' is the total length of the fault line, Corresponding to the zero-sequence voltage at the beginning and end of the fault line and the voltage at the fault point respectively; (2) and (3) are added together to get: ${\stackrel{.}{u}}_2^{\′}-{\stackrel{.}{u}}_1^{\′}=\frac{1}{2}{\stackrel{.}{I}}_C\&Center\; Dot;x\·(l^{\′2}-{2l}^{\′}\&Center\; Dot;x)+{\stackrel{.}{I}}_{C_{\mathrm{\Σ}}}\&Center\; Dot;x\&Center\; Dot;x---\left(4\right);$

4. Analysis of neutral point via arc suppression coil fault line

The change of zero-sequence current and zero-sequence voltage of the non-faulted line in the neutral point through the arc suppression coil grounding system is the same as that of the neutral point ungrounded system; and the zero-sequence current of the faulty line is equivalent to the faulty line in the neutral point ungrounded system. Superimpose the inductive current flowing through the arc suppression coil at the fault point That is to say, if the system is working in the fully compensated state, the reactive current at the fault point is zero. If the active current of the system is ignored, the zero-sequence current measured from the head end of the fault branch is the capacitive current generated by the branch itself. However, in order to avoid resonance when the arc suppressing coil is running, it generally runs in the overcompensated state, that is, when a single-phase ground occurs, the zero-sequence current properties of the faulty branch are similar to those of the non-faulty branch. The difference in compensation situation is larger than the capacitive current generated by its own distribution parameters, and The size of can be obtained from the parameters when the arc suppression coil is tuned; the current generated by the zero sequence voltage acting on the arc suppression coil lags by 90°, and the capacitor current to the ground leads the zero sequence voltage by 90°, so and Phase opposite. The amount of voltage variation generated in the fault zone: Finally, the formula corresponding to the crowbar-grounded system is obtained: ${\stackrel{.}{u}}_2^{\′}-{\stackrel{.}{u}}_1^{\′}=\frac{1}{2}{\stackrel{.}{I}}_C\·x\·(l^{\′2}-{2l}^{\′}\&Center\; Dot;x)+({\stackrel{\&Center\; Dot;}{I}}_{C_{\mathrm{\Σ}}}-{\stackrel{.}{I}}_L)\·x\·x---\left(5\right).$

The specific implementation flow chart of this method is shown in Figure 5, and the specific implementation steps are as follows:

Read the current flowing through the arc-suppression coil (for the neutral point through the arc-suppression coil grounding system), the bus voltage, the zero-sequence current of the first end and the zero-sequence voltage waveform data of the end after each feeder fails from the wave recording device;

Fast Fourier transform (FFT) is performed on the read data to obtain the effective value of the power frequency corresponding to each signal, and the calculation using the power frequency signal can eliminate the errors caused by signals such as harmonics;

Determine the faulty branch on the basis of the completion of line selection;

Substitute the data corresponding to the measured non-fault line into formula (1), and calculate the zero-sequence impedance value X per unit length of the line at the time of the fault online;

Determine the neutral point grounding method of the system;

For the neutral point ungrounded system, the data measured by the fault line and the zero-sequence impedance value X per unit length of the line calculated in step 4 are substituted into the formula (4) to calculate the fault distance; for the neutral point grounded system through the arc suppression coil, Substitute into formula (5) to calculate.

(1) Voltage and current distribution characteristics after a fault

After a fault, the ground-to-ground capacitive current of the feeder is distributed along the line. All the ground-to-ground capacitive current first flows to the ground, flows back to the fault line through the fault point, and finally flows to the busbar. The flow of the ground-to-ground current has an effect on the change of the zero-sequence voltage. The effective value of the zero-sequence voltage along the line is distributed according to the law of gradual increase of the oblique line from the busbar to the end of the line. The regular distribution of the slope gradually increases, that is, the effective value of the zero-sequence voltage at the fault point is the smallest.

(2) Fault location algorithm

After the fault occurs and the fault state is stable, read the bus voltage, the zero-sequence current of each feeder line and the zero-sequence voltage waveform data at the end after the fault of each feeder from the wave recording device. For the waveform data of the coil current, fast Fourier transform (FFT) is performed on the read data to obtain the effective value of the power frequency corresponding to each signal, and the calculation using the power frequency signal can eliminate the error caused by the harmonic and other signals. Step by step calculation results and determine the faulty line according to the existing mature line selection scheme, and substitute the data corresponding to the measured non-faulty line into the formula Calculate the zero-sequence impedance value X per unit length of the line at the time of the fault online, and for the neutral point ungrounded system, substitute the data measured on the fault line and the zero-sequence impedance value X per unit length of the line calculated in the previous step into the formula Calculate the fault distance, and for the neutral point through the arc suppression coil grounding system, substitute into the formula ${\stackrel{.}{u}}_2^{\′}-{\stackrel{.}{u}}_1^{\′}=\frac{1}{2}{\stackrel{.}{I}}_C\&Center\; Dot;x\·(l^{\′2}-{2l}^{\′}\&Center\; Dot;x)+{\stackrel{.}{I}}_{C_{\mathrm{\Σ}}}\·x\·x$ calculate.

Evaluation of the effect of the program:

The present invention has high positioning accuracy and high adaptability in complex distribution networks, and the present invention can satisfy different neutral point grounding modes. Now take a model as an example:

Use PSCAD/EMTDC software tool to establish the simulation model of 35kV single-ended radial grid system, as shown in Figure 6. The secondary side of the transformer is connected to the arc suppressing coil through the circuit breaker, which can simulate the neutral point ungrounded system and the arc suppressing coil grounded system; the system has three cables, the cable lengths are respectively 18km, 16km and 20km, and the cables are buried 1m underground. Three single-phase cables are laid in an inverted triangle (the distance between the axes is 30mm), and the cross-sectional area of the cables is 240mm2; the 110kV to 35kV transformer with Y-Δ connection is used on the busbar side, and the 35kV transformer with Δ-Y connection is used at the end of the line. 10kV transformer; the load is connected to a three-phase balanced load of 0.35MW+0.08MVar.

Taking the neutral point ungrounded system, metallic grounding occurs at a distance of 2km from the busbar as an example for calculation. The bus voltage is 20469.2V, the zero-sequence current at the head end of each feeder is 7.33167A, 6.51593A, 13.8476A, and the zero-sequence voltage at the end of each feeder is 20493.9V, 20488.7V, 20483.4V. Using the existing line selection scheme, such as the ratio phase comparison method, it can be judged that the faulty line is line III.

Use the line I to calculate the line-to-ground capacitive current I _C per unit length and the zero-sequence impedance value X per unit length:

${\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; C</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; C</span>}\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; /</span>{\mathrm{<span\; class="notranslate">\; l</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 0.407315</span>}\mathrm{<span\; class="notranslate">\; A</span>}<span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; km</span>}<span\; class="notranslate">\; .</span>\mathrm{<span\; class="notranslate">\; x</span>}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; )</span>}{{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; C</span>}}<span\; class="notranslate">\; \&Center\; Dot;</span>{\mathrm{<span\; class="notranslate">\; l</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 0.374327</span>}\mathrm{<span\; class="notranslate">\; \&Omega;</span>}<span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; km</span>}<span\; class="notranslate">\; .</span>$

For the neutral point ungrounded system, the capacitive current of the non-fault line to the ground is equal to the zero-sequence current measured at the head end of the fault line, that is: $I_{C3}=I_{C1}+I_{C2}=I_{C_{\mathrm{\&Sigma;}}}=13.8476A.$

Substitute the above calculation results into formula (4) to get the fault distance x = 1.9791km.

The measurement error is defined as: The error is 0.104%.

In order to verify the effectiveness of this method, Table 1 gives the distance measurement results when the single-phase ground fault of the neutral point ungrounded system occurs at different positions and is grounded through different transition resistances.

Table 1 Neutral point ungrounded single-phase ground fault location results

The distance measurement results in Table 1 show that for the neutral point ungrounded system, at different fault locations and transition resistances, the maximum distance measurement error is within 1% of the total length of the line. can achieve accurate distance measurement.

Table 2 shows the grounding system with the neutral point via the arc suppression coil. The total capacitive current to the ground of the system is about 64A when the fault occurs, and the arc suppression coil works under the overcompensation state. % or so, the distance measurement results when the single-phase ground fault occurs in different positions and grounded through different transition resistances.

Table 2 The distance measurement results of the single-phase ground fault with the neutral point grounded through the arc suppression coil

It can be seen from Table 2 that the algorithm is also applicable to the neutral point through the arc suppression coil grounding system, and it has high ranging accuracy for different detuning degrees.

Claims (1)

1. a method for the range finding of the one-phase earthing failure in electric distribution network based on residual voltage, is characterized in that: this fault distance-finding methodBe from single-ended radial medium voltage distribution network entirety Zero sequence parameter, while analyzing singlephase earth fault, consider distributed parameter modelImpact, stable state residual voltage value and each feeder line zero-sequence current after measurement bus place and each outlet end fault, find out fault feederAnd non-fault feeder residual voltage Variation Features;

Concrete steps are as follows:

(1), distributed parameter model

Power distribution network is carried out to fault localization, utilize distributed parameter model to carry out fault localization; By line parameter circuit value is calculated,When singlephase earth fault occurs, conduction current is much smaller than capacitance current, therefore can ignore the impact that electricity is led over the ground, zero sequence equivalent over the groundCircuit distributed parameter model is reduced to line impedance and direct-to-ground capacitance is evenly distributed along the line;

(2), non-fault line analysis

Feeder line is divided into n minizone, gets wherein arbitrary minizone and be denoted as [x, x+ Δ x], this minizone producesTo earth-current Δ I_C＝I_C·Δx，I_CFor the line mutual-ground capacitor electric current of unit length;

For non-fault line, the electric current Δ I that each minizone produces_CThe scope flowing through on the line by bus to minizone institutePosition x, then flow to trouble point through ground; If original position corresponding to every minizone is x, the voltage that function of current producesAmount is Δ I_CXx, the voltage that each interval function of current over the ground producing produces on circuit: Δ U=Δ I_CXx, formulaIn: X is the resistance value of circuit unit length;

Known according to superposition theorem, the residual voltage at circuit two ends is poor is the result of zero-sequence current effect, and above formula both sides are simultaneously to xIntegration obtains: ${\&Integral;}_0^{l}d\stackrel{\&CenterDot;}{U}={\&Integral;}_0^l{\stackrel{\&CenterDot;}{I}}_C\&CenterDot;X\&CenterDot;x\&CenterDot;dx,$ Calculate: ${\stackrel{\&CenterDot;}{U}}_2-{\stackrel{\&CenterDot;}{U}}_1=\frac{1}{2}{I}_C\&CenterDot;X\&CenterDot;l^2---\left(1\right),$ L is non-fault line length,Be respectively non-fault line first and end residual voltage;

(3), isolated neutral system faulty line is analyzed

For faulty line, trouble point current flowing comprises non-fault capacitive earth current and faulty line direct-to-ground capacitance electricityStream; Voltage, current distributions behind trouble point are identical with non-fault line, and minizone capacitive earth current is flowed to large by electric capacityGround, then flows back to circuit by trouble point, to the circuit before trouble point without effect, be equivalent to circuit, direct-to-ground capacitance, and trouble pointBetween form loop checking installation; Minizone capacitive earth current flows to the earth by direct-to-ground capacitance, then passes through circuit through trouble pointFlow back to bus; Therefore minizone over the ground the function of current produce the scope of voltage be by minizone to trouble point, bus is arrived in minizoneSection electric current one goes out one and enters to cancel out each other; If fault distance is x, the function of current over the ground producing apart from the minizone of bus x ' inThe voltage variety Δ U '=Δ I producing on circuit_CX (x-x '); The same, can obtain bus to trouble point line-to-ground electric currentAct on the voltage variety that circuit produces: ${\&Integral;}_0^{x}d{\stackrel{\&CenterDot;}{U}}^{\&prime;}={\&Integral;}_0^x-{\stackrel{\&CenterDot;}{I}}_C\&CenterDot;X\&CenterDot;(x-x^{\&prime;})\&CenterDot;{\mathrm{dx}}^{\&prime;},$ ? ${\stackrel{\&CenterDot;}{U}}^{\&prime;}=-\frac{1}{2}{\stackrel{\&CenterDot;}{I}}_C\&CenterDot;X\&CenterDot;x^2;$ Trouble pointAlso comprise non-fault line to earth-current to bus section, busbar section zero-sequence current and Voltage variety in this interval generation: ${\stackrel{\&CenterDot;}{U}}^{\&prime;\&prime;}={\stackrel{\&CenterDot;}{I}}_{C_{\mathrm{\&Sigma;}}}\&CenterDot;X\&CenterDot;x;$ Known according to superposition theorem: ${\stackrel{\&CenterDot;}{U}}^{\&prime;}+{\stackrel{\&CenterDot;}{U}}^{\&prime;\&prime;}=-(\frac{1}{2}{\stackrel{\&CenterDot;}{I}}_C\&CenterDot;x-{\stackrel{\&CenterDot;}{I}}_{C_{\mathrm{\&Sigma;}}})X\&CenterDot;x={\stackrel{\&CenterDot;}{U}}_f-{\stackrel{\&CenterDot;}{U}}_1^{\&prime;}---\left(2\right);$ Fault dotted lineThe voltage change on road is identical with non-fault line situation, therefore,Wherein: l ' is faultTotal line length,Corresponding faulty line first and end residual voltage and fault point voltage respectively; (2), (3) formula phaseAdd: ${\stackrel{\&CenterDot;}{U}}_2^{\&prime;}-{\stackrel{\&CenterDot;}{U}}_1^{\&prime;}=\frac{1}{2}{\stackrel{\&CenterDot;}{I}}_C\&CenterDot;X\&CenterDot;(l^{\&prime;2}-2l^{\&prime;}\&CenterDot;x)+{\stackrel{\&CenterDot;}{I}}_{C_{\mathrm{\&Sigma;}}}\&CenterDot;X\&CenterDot;x---\left(4\right);$

(4), neutral point is analyzed through arc suppression coil faulty line

The non-fault line zero-sequence current of neutral by arc extinction coil grounding system and residual voltage situation of change and neutral point are notEarthed system is identical; And faulty line zero-sequence current situation is equivalent on isolated neutral system faulty line basis in eventThe inductance current of arc suppression coil is flow through in the stack of barrier pointIf system works is when the full compensating coefficient, trouble point reactive current isZero, if ignore system watt current, the zero-sequence current recording from fault branch head end is to be produced by this branch road selfCapacitance current, application residual voltage changes and cannot find range; But for avoiding resonance to occur, generally operated in when arc suppression coil operationCompensating coefficient, also in the time there is single-phase earthing, the zero-sequence current character of fault branch is similar to non-fault branch, mends owing to crossingThe capacitance current that self distributed constant does not produce on year-on-year basis of repaying situation is larger, andLarge I when tuning by arc suppression coilGain of parameter; Residual voltage acts on after the current hysteresis that arc suppression coil produces 90 °, and the leading residual voltage of capacitive earth current90 °, thereforeWithSingle spin-echo;The voltage variety producing in fault section:Finally, draw rightShould be in the formula of compensated distribution network: ${\stackrel{\&CenterDot;}{U}}_2^{\&prime;}-{\stackrel{\&CenterDot;}{U}}_1^{\&prime;}=\frac{1}{2}{\stackrel{\&CenterDot;}{I}}_C\&CenterDot;X\&CenterDot;(l^{\&prime;2}-2l^{\&prime;}\&CenterDot;x)+({\stackrel{\&CenterDot;}{I}}_{C_{\mathrm{\&Sigma;}}}-{\stackrel{\&CenterDot;}{I}}_L)\&CenterDot;X\&CenterDot;x$ $\left(5\right).$