Method for locating distribution network circuit fault based on full waveform information

Abstract

A method for detecting and locating faulty line on the distribution network circuit based on full waveform information, which uses the current data on the fault occurrence and whole-process operation of the compensation device to effectively solve such common problems as low fault current, poor reliability and low sensitivity in case of single-phase grounding fault to the low-current system through precise GPS synchronization. It improves the sensitivity and reliability of the grounding fault detection, which does not interfere with the system and is applicable to high-resistance grounding.

Claims

1. A method for locating a faulty section on a line in an electrical power distribution network having multiple measurement points along each line and protected by protection devices, comprising: measuring a three-phase current and a zero-sequence voltage on a busbar in an electrical power distribution network where a fault has occurred at a section on a line, determining a type, phase, and time of the fault based on the three-phase current and zero-sequence voltage being measured, measuring the three-phase current or a zero-sequence current and a zero-sequence voltage at initial ends of each line in the electrical power distribution network during a time period from occurrence of the fault to action by the protection device, determining a faulty line that has the faulty section thereon based on the type of the fault and the three-phase current or the zero-sequence current and the zero-sequence voltage at initial ends of each line being measured, measuring a current at each of measurement points along the faulty line, and locating the faulty section on the faulty line by the current at each of the measurement points along the faulty line, wherein the protection device is a relay protection device or an arc suppression coil; when the type of the fault is determined to be an inter-phase fault, the three-phase current at the initial ends of each line during the time period from the occurrence of the fault to the action of the relay protection device are measured to determine the faulty line, and a fault-phase current at each measurement points along the faulty line are measured to locate the faulty section; and when the type of the fault is determined to be a grounding fault, the zero-sequence current and the zero-sequence voltage at the initial ends of each line during the time period from the occurrence of the fault to action of the arc suppression coil are measured to determine the faulty lire, and zero-sequence current at each measurement points along the faulty line are measured to locate the faulty section.

2. The method as claimed in claim 1, further comprising detecting an over-current on the three-phase current on the busbar and determining the type of the fault to be an inter-phase fault; obtaining the phase of the fault; and determining the time of the fault to be a time period that the three-phase current is detected to the action of the relay protection device.

3. The method as claimed in claim 2, further comprising detecting the over-current on the three-phase current on a line on the busbar, and determining that the line having the over-current is the faulty line.

4. The method as claimed in claim 3, further comprising collecting a fault-phase current of each of the measurement points along the faulty line as characteristic current, calculating a standard deviation d.sub.p.u. of formula (7) based on the characteristic current of each of the measurement points along the faulty line: $\begin{array}{cc}{d}_{p.u.}={\left[\frac{\underset{n=1}{\overset{M}{.Math.}}{\left[i_{01}\left(n\right)-i_{02}\left(n\right)\right]}^2}{\min \left\{\underset{n=1}{\overset{M}{.Math.}}{i_{01}\left(n\right)}^2,\underset{n=1}{\overset{M}{.Math.}}{i_{02}\left(n\right)}^2\right\}}\right]}^{\frac{1}{2}}& \left(7\right)\end{array}$ wherein i.sub.01(n) and i.sub.02(n) are sequences of the characteristic current as collected at the two adjacent measurement points along the faulty line; n is a sampling sequence, and M is a data length, determining that a section between the two adjacent points is not a faulty section when the standard deviation is near zero and determining that a section between the two adjacent points is a faulty section when the standard deviation exceed a threshold value.

5. The method as claimed in claim 4, wherein the threshold value is from 1 to 3.

6. The method as claimed in claim 4, wherein data of the current is collected in two cycles.

7. The method as claimed in claim 6, wherein each of the two cycles is taken on the same length of time, and calculation of d.sub.p.u. is repeated for 3 to 5 times.

8. The method as claimed in claim 1, further comprising detecting no over-current on the three-phase current on the busbar and detecting no increase in the zero-sequence voltage, and determining that all lines work and the busbar is faulty.

9. The method as claimed in claim 1, further comprising detecting an increase in the zero-sequence voltage on the busbar and determining the type of the fault to be a grounding fault; and determining the time of the grounding fault to be a time period the increase in the zero-sequence voltage detected to the action of the arc suppression coil.

10. The method as claimed in claim 9, further comprising collecting a sampling sequence of the zero-sequence voltage U.sub.0(m) and the zero-sequence current I.sub.0(m) at the initial ends of each line during the time period of the grounding fault, calculating a maximum value R.sub.ui(τ) of a cross correlation function of formula (6): $\begin{array}{cc}{R}_{\mathrm{ui}}\left(m\right)=\underset{i=0}{\overset{N-m-1}{.Math.}}{I}_0\left(i\right)U_0\left(i+m\right)& \left(6\right)\end{array}$ wherein R(m) is a similarity of the zero-sequence voltage and the zero-sequence current at different relative positions, m is an integer from 0 to N−1, N is a frequency of the sampling, τ is to time delay of I.sub.0(m) in correspondence with U.sub.0(m), determining that a line having a τ between N/2and N is the faulty line.

11. The method as claimed in claim 10, further comprising collecting the zero-sequence current of each of the measurementpoints along the faulty line as characteristic current, calculating a standard deviation d.sub.p.u. of formula (7) based on the characteristic current, $\begin{array}{cc}{d}_{p.u.}={\left[\frac{\underset{n=1}{\overset{M}{.Math.}}{\left[i_{01}\left(n\right)-i_{02}\left(n\right)\right]}^2}{\min \left\{\underset{n=1}{\overset{M}{.Math.}}{i_{01}\left(n\right)}^2,\underset{n=1}{\overset{M}{.Math.}}{i_{02}\left(n\right)}^2\right\}}\right]}^{\frac{1}{2}}& \left(7\right)\end{array}$ wherein i.sub.01(n) and i.sub.02(n) are sequences of the characteristic current as collected at the two adjacent measurement points along the faulty line; n is a sampling sequence, and M is a data length, determining that a section between the two adjacent measurement points is not a faulty section when the standard deviation is near zero and determining that the section between the two adjacent measurement points is a faulty section when the standard deviation exceed a threshold value.

12. The method as claimed in claim 11, wherein the threshold value is from 1 to 3.

13. The method as claimed in claim 11, wherein data of the current is collected in two cycles.

14. The method as claimed in claim 13, wherein each of the two cycles is taken on the same length of time, and calculation of d.sub.p.u. is repeated for 3 to 5 times.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 shows the structure of the system for locating the faulty section on the distribution network.

(2) FIG. 2 is a simulation diagram for a 10 kV system.

(3) FIG. 3 shows a fault-phase current waveform at the initial end of the inter-phase short-circuit line.

(4) FIG. 4 shows a fault-phase current waveform along inter-phase short-circuit line 1.

(5) FIG. 5 shows the zero-sequence voltage and zero-sequence current waveform at the initial end of the faulty line in case of a grounding fault.

(6) FIG. 6 shows the zero-sequence voltage and zero-sequence current waveform at the initial end of a non-faulty line in case of a grounding fault.

(7) FIG. 7 shows the zero-sequence current waveform along a grounding faulty line 1.

DETAILED DESCRIPTION OF THE INVENTION AND PREFERRED EMBODIMENTS

(8) The faulty waveform used in the present invention is provided by the distribution fault location system. The structure of the system is shown in FIG. 1. The system for locating the faulty section on the distribution network comprises a main monitoring station, a measuring device of the transformer station (busbar), and location devices for faulty nodes installed at various sections along the distribution line. The line is topologically divided by the fault location nodes into numerous sections, and each node is installed with three measuring devices for real-time synchronized collection of the three-phase current and voltage on the line.

(9) According to the fault location method provided by the present invention, different types of faults are set in the simulated 10 kV distribution network system. The structure of the system as shown in FIG. 2 shows that the busbar has three back lines numbered as line 1, 2 and 3; {circle around (1)}, {circle around (2)} and {circle around (3)} are section numbers; detection points are numbered with Roman numerals; fault is set at section {circle around (2)}. Sampling frequency is set at 20 kHz (400 points in 1 cycle); fault occurrence time is 0.3s; action time of the arc suppression device in case of grounding fault is set as 0.04s; and the threshold value for the standard deviation is set as 3.

EXAMPLE 1

Detection and Location of the Inter-Phase Fault

(10) In the example having an inter-phase fault, the method of the present invention provides that

(11) Step 1 (S1): the three-phase current and zero-sequence voltage of the busbar are monitored, an over-current to the busbar appears while the zero-sequence voltage is zero, where the over-current to phases A and B occurs and a current variation at 0.3s occurs; therefore, an AB inter-phase fault occurring at 0.3s is determined.

(12) Step 2 (S2): fault-phase current to the detection points I, II and III are measured at the initial end of the three lines. As shown in FIG. 3, an over-current obviously occurs on the fault-phase current at the initial end of line 1, exceeding the preset value, while the fault-phase current to the initial ends of lines 2 and 3 remains unchanged. Therefore, line 1 is determined to be faulty.

(13) Step 3 (S3): fault-phase current at detection points IV, V, VI and VII are measured along line 1 as shown in FIG. 4; the standard deviation at section {circle around (1)}, {circle around (2)} and {circle around (3)} are calculated according to the formula. The results are shown in Table 1: the standard deviation to section {circle around (2)} is over 3, and thus section {circle around (2)} is determined to be faulty.

(14) TABLE-US-00001 TABLE 1 Simulation Results of Inter-Phase Fault. Line Loca- selection Standard deviation tion Fault type result {circle around (1)} {circle around (2)} {circle around (3)} result AB Over-current 9.9840E−5 6.7268 3.1274E−4 {circle around (2)} inter-phase to line 1 ABC 6.3319E−5 8.3460 1.3835E−4 {circle around (2)} three-phase

EXAMPLE 2

Detection and Location of the Grounding Fault

(15) In the example of having a grounding fault, the method of the present invention provides that:

(16) Step 1 (S1): three-phase current and zero-sequence voltage to the busbar are monitored, the zero-sequence voltage exceeds the phase voltage by 10% while there is no over current on the three-phase current to the busbar; zero-sequence voltage at 0.3s has a sudden change, thus, a grounding fault is determined at the moment of 0.3s.

(17) Step 2 (S2): zero-sequence current and zero-sequence voltage at detection points I, II and III at the initial ends of the three lines are measured. As shown in FIGS. 5 and 6, the maximum values of the cross correlation function of the zero-sequence current and zero-sequence voltage at the three detection points are calculated, which are the time delays of the zero-sequence current corresponding to the zero-sequence voltage. As shown in Table 2., the maximum value of the cross correlation function of the initial end of line 1 exceeds the half cycle, i.e., the zero-sequence current lags behind the zero-sequence voltage, while the maximum values of the cross correlation function of the initial ends of lines 2 and 3 are below the half cycle. Thus, line 1 is determined to be faulty.

(18) Step 3 (S3): fault-phase current at detection points IV, V, VI and VII along line 1 are measured as shown in FIG. 7; standard deviations at section {circle around (1)}, {circle around (2)}, and {circle around (3)} are calculated according to the formula and results are shown in Table 2. The standard deviation at section {circle around (2)} is over 3, thus, section {circle around (2)} is determined to be faulty.

(19) TABLE-US-00002 TABLE 2 Simulation Results of Single-Phase Grounding Fault. T.sub.1 time interval Time Arc Fault delay (point) of U.sub.0 Line suppression transition corresponding to I.sub.0 selection Standard deviation Location coil type resistance 1 2 3 result {circle around (1)} {circle around (2)} {circle around (3)} result Preset 100Ω 309 85 84 1 0.0056 11.1430 0.0601 {circle around (2)} 500Ω 309 89 89 1 0.0069 9.2385 0.0604 {circle around (2)}  1 kΩ 309 89 89 1 0.0071 8.9771 0.0608 {circle around (2)}  2 kΩ 309 87 112 1 0.0071 9.0845 0.0615 {circle around (2)} Random 100Ω 310 86 85 1 0.0063 9.9320 0.0601 {circle around (2)} 500Ω 311 96 96 1 0.0079 8.1268 0.0603 {circle around (2)}  1 kΩ 311 101 101 1 0.0082 7.8480 0.0606 {circle around (2)}  2 kΩ 310 103 103 1 0.0085 7.6261 0.0611 {circle around (2)}