Distribution network cable fault location method and system based on double-end grounding wire current amplitude ratio

Abstract

The present invention discloses a distribution network cable fault location method and system based on the double-end grounding wire current amplitude ratio, comprising calculating the impedance, inductive capacitance and other parameters of each line and storing them in a database; measuring the fault current of each cable grounding wire and the zero-sequence current waveform of the overhead line head end and filtering them to identify the faulty cable; extracting the waveforms of the current of the first and end grounding wires of the faulty cable after the fault, and calculating the measured amplitude ratio of the first and end grounding wire currents; constructing an equation for accurately locating the faulty cable; solving the power frequency components of the current of the first and end grounding wires of the faulty cable; calculating the theoretical amplitude ratio of the first and end grounding wire currents of the faulty cable, comparing it with the measured amplitude ratio of the first and end grounding wire currents, and determining a new fault interval until the length of the fault interval is less than or equal to a set threshold. The present invention is simple and easy to implement, has high positioning accuracy, and the positioning result is basically not affected by the fault transition resistance. Moreover, the required grounding wire current signal can be easily obtained without the need for high-speed sampling, and has high practicality.

Description

Technical Field

[0001] The present invention relates to the field of precise cable fault positioning, and in particular to a method and system for positioning cable faults in a distribution network based on the current amplitude ratio of a double-ended grounding wire. Background Art

[0002] With the continuous development of power distribution systems and rising urbanization levels, the proportion of cable lines continues to increase, and the current capacitance also increases accordingly. Coupled with factors such as the complexity of cable paths, cable aging, and external damage, the cable failure rate is gradually increasing.

[0003] Existing methods for locating single-phase grounding faults in distribution networks can be roughly divided into two categories: offline and online methods. Offline methods are based on externally injected signals for fault location, but they cannot locate the fault point in a timely manner. In contrast, online fault location technology is more practical and is mainly divided into traveling wave methods, impedance methods, and machine learning methods. Due to the complex topology and short lines of the distribution network, the superposition problem of traveling wave signals is serious, making it impossible to effectively extract and identify them. The traveling wave method is limited in practical application. Machine learning methods require a lot of calculations and require relearning after topology transformation. Most impedance methods do not take into account the multi-conductor structure of three-core cables, and a considerable part of them are based on the zero-sequence current distribution characteristics for fault location. However, due to the limitations of the acquisition method, there are errors in the zero-sequence current measurement, resulting in large errors in the ranging accuracy. Summary of the Invention

[0004] In order to solve the problems mentioned in the above background technology, the present invention proposes a distribution network cable fault location method and system based on the double-end grounding wire current amplitude ratio.

[0005] In order to achieve the above technical objectives and the above technical effects, the present invention first proposes a method for locating a distribution network cable fault based on the current amplitude ratio of a double-ended grounding wire, which includes the following steps:

[0006] (1) Based on the distribution network line structure and material characteristics, the impedance, inductive capacitance and other parameters of each line are calculated and stored in the database.

[0007] (2) Measure and filter the waveforms of the grounding fault current of each cable and the zero-sequence current at the head end of the overhead line, and identify the faulty cable based on the correlation coefficient between the grounding current at the head end and the zero-sequence current. The steps for identifying the faulty cable are as follows: take the direction of the grounding current at the head end of any cable as a reference, use the Pearson correlation coefficient to determine the direction of the grounding current at the head end of the remaining cables and the zero-sequence current at the head end of the overhead line, and identify the faulty cable.

[0008] (3) Extract the waveforms of the grounding currents at the first and last terminals of the faulty cable in the third to fourth power frequency cycles after the fault, use FFT to extract the power frequency components, and calculate the measured amplitude ratio of the grounding currents at the first and last terminals.

[0009] (4) Based on the distribution network line parameters in the database, construct the fault cable accurate location equation. The specific steps are as follows:

[0010] (a) Construct a fault equivalent circuit model based on the distribution network line parameters in the database;

[0011] (b) Establish the precise location equation of the faulty cable based on the constructed circuit model:

[0012] f(x·Z f ,x·jωC f ,(lx)·Z f ,(lx)·jωC f ,R,Z h ,jωC h )=I

[0013] Where l is the length of the fault cable, x is the fault distance; Z f 、C f is the impedance and inductive capacitance per unit length of the fault cable; R is the equivalent resistance of the grounding wire; Z h 、C h is the impedance and inductive capacitance of the sound line; I is the grounding current of the fault cable.

[0014] (5) According to the bisection method, set the virtual fault point and substitute it into the equation to solve the power frequency component of the grounding wire current at the beginning and end of the fault line. The grounding wire current at the beginning of the fault cable I is obtained. f_s , end grounding wire current I f_e .

[0015] (6) Calculate the theoretical amplitude ratio of the current at the beginning and end of the fault cable grounding wire, compare it with the measured amplitude ratio, and determine the new fault interval. cal The calculation formula is:

[0016]

[0017] Among them, the theoretical and measured amplitude ratio of the first and last grounding wire currents is k rel Compare and determine the new fault range. The specific steps are as follows:

[0018] (a) Set the midpoint α1 of the fault cable interval [a, b] (a=0, b=l) as the virtual fault point and calculate k at this time. cal , compare k cal With k rel The size relationship;

[0019] (b) If k cal =k rel , then the fault point is α1;

[0020] (c) If k cal >k rel , then the fault point is between [a, α1], keep this interval, let b = α1, then generate a new interval [a, b];

[0021] (d) If k cal <k rel , then the fault point is between [α1,b]. Keep this interval and let a=α1, then a new interval [a,b] is generated.

[0022] (7) If the length of the fault interval is greater than the set allowable error, jump to step 5) and continue to reduce the fault interval. If it is not greater than the set allowable error, take the midpoint of the fault interval as the fault location. The specific steps for determining the fault location are as follows:

[0023] (a) Compare the fault interval length ba with the set allowable error ε to see whether ba ≤ ε is true;

[0024] (b) If ba>ε, continue to set the virtual fault point in the new fault interval using the bisection method;

[0025] (c) If ba≤ε, the midpoint of the fault interval is taken as the fault location, that is, the fault distance x is:

[0026] x=(a+b) / 2

[0027] Secondly, the present invention provides a distribution network cable fault location system based on the double-end grounding wire current amplitude ratio, including: a measurement device, a fault location device, and a master station.

[0028] The measuring equipment is a high-precision current transformer used to measure the current of the cable grounding wire;

[0029] A fault location device, configured to determine the location of a fault point according to the fault location method;

[0030] The main station is used to perform alarm work and display the current waveform of the fault cable grounding wire and the fault point location.

[0031] Finally, the present invention provides a distribution network cable fault location system based on the double-end grounding wire current amplitude ratio, wherein the fault location device includes: a sampling module, a storage module, a communication module, a time module, a power supply module, and a main control module.

[0032] Sampling unit, used for sampling the current waveform of the cable grounding wire;

[0033] A storage unit for storing parameters of each line of the distribution network and ground wire current data;

[0034] Communication module, used for communication between the fault location device, measuring equipment and the master station;

[0035] Time module, used to obtain time values;

[0036] A power module is used to provide power to the fault locating device;

[0037] The main control module is used to execute any step in the above-mentioned fault location method.

[0038] Compared with the prior art, the present invention has the following beneficial effects:

[0039] The disclosed method and system for locating distribution network cable faults based on the dual-end grounding wire current amplitude ratio identifies the faulty cable based on the correlation coefficient between the grounding wire current at the cable's head end and the zero-sequence current at the head end of the overhead line. The specific fault location is determined based on the mapping relationship between the grounding wire current amplitude ratio at the head and tail ends of the faulty cable and the fault location. This method is simple and easy to implement, offers high positioning accuracy, and the positioning results are largely unaffected by the fault transition resistance. Furthermore, the required grounding wire current signal can be easily acquired, eliminating the need for high-speed sampling and demonstrating high practicality. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 Flowchart of the distribution network cable fault location method based on the current amplitude ratio of the double-terminal grounding wire;

[0041] Figure 2 This is the topology diagram of the simulation model of a 10kV neutral point ungrounded distribution network. DETAILED DESCRIPTION

[0042] The present invention will be further described below with reference to the accompanying drawings.

[0043] The present invention proposes a method for locating distribution network cable faults based on the current amplitude ratio of the double-ended grounding wires. The overall process is as follows: Figure 1 As shown, the following steps are included:

[0044] (1) Based on the distribution network line structure and material characteristics, the impedance, inductive capacitance and other parameters of each line are calculated and stored in the database;

[0045] (2) Measure the fault current of each cable grounding wire and the zero-sequence current waveform of the overhead line head end and filter them, and identify the faulty cable based on the correlation coefficient between the head end grounding wire current and the zero-sequence current;

[0046] (3) Extract the waveforms of the grounding currents at the first and last terminals of the faulty cable in the third to fourth power frequency cycles after the fault, extract the power frequency components using FFT, and calculate the measured amplitude ratio of the grounding currents at the first and last terminals;

[0047] (4) Based on the distribution network line parameters in the database, the fault cable precise location equation is constructed;

[0048] (5) According to the bisection method, a virtual fault point is set and substituted into the equation to solve the power frequency component of the grounding wire current at the beginning and end of the fault cable;

[0049] (6) Calculate the theoretical amplitude ratio of the grounding wire current at the beginning and end of the fault cable, compare it with the measured amplitude ratio, and determine the new fault interval;

[0050] (7) If the length of the fault interval is greater than the set allowable error, jump to step 5) and continue to reduce the fault interval. If it is not greater, take the midpoint of the fault interval as the fault location.

[0051] The present invention provides a distribution network cable fault location system based on the current amplitude ratio of a double-ended grounding wire, comprising: a measuring device, a fault location device, and a master station.

[0052] The measuring equipment is a high-precision current transformer used to measure the current of the cable grounding wire;

[0053] A fault location device, configured to determine the location of a fault point according to the fault location method;

[0054] The main station is used to perform alarm work and display the current waveform of the fault cable grounding wire and the fault point location.

[0055] The present invention provides a distribution network cable fault location system based on the current amplitude ratio of the double-end grounding wire, wherein the fault location device includes: a sampling module, a storage module, a communication module, a time module, a power supply module, and a main control module.

[0056] Sampling unit, used for sampling the current waveform of the cable grounding wire;

[0057] A storage unit for storing parameters of each line of the distribution network and ground wire current data;

[0058] Communication module, used for communication between the fault location device, measuring equipment and the master station;

[0059] Time module, used to obtain time values;

[0060] A power module is used to provide power to the fault locating device;

[0061] The main control module is used to execute any step in the above-mentioned fault location method.

[0062] Simulation Verification

[0063] In order to verify the reliability and effectiveness of the present invention, the present invention is based on PSCAD / EMTDC to construct Figure 2The topology diagram of the 10kV ungrounded neutral distribution network simulation model is shown in Figure 1. The simulation system includes five outgoing lines, of which L4 is an overhead line, and the remaining outgoing lines are cable lines. The cable shields are grounded at the beginning and end via 2Ω resistors. Lines L1-L4 are in operation, and line L5 is in standby mode. A short-circuit fault between phase A and the shield is set on line L1. The simulation simulates different fault transition resistances, different fault distances, and different fault initial phase angles. The simulation sampling frequency is set to 3.2kHz, and the model solution time step is set to 1μs. The precise location results are shown in Table 1 below, where the fault distance represents the distance between the fault point and the line head end.

[0064] Table 1 Accurate positioning results under different fault transition resistance, fault distance and fault initial phase angle

[0065]

[0066] The results show that the positioning error under different fault transition resistances, fault distances, and fault initial phase angles does not exceed 30m, meeting the accuracy requirements on site. Therefore, the proposed method for accurate fault location is essentially unaffected by the fault transition resistance, fault distance, and fault initial phase angle.

[0067] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for locating distribution network cable faults based on the current amplitude ratio of two-terminal grounding wires, characterized in that: The steps include: Step 1) Based on the distribution network line structure and material characteristics, the impedance and inductive capacitance parameters of each line are calculated and stored in the database; Step 2) measuring and filtering the waveforms of the grounding fault current of each cable and the zero-sequence current at the head end of the overhead line, and identifying the faulty cable based on the correlation coefficient between the head end grounding current and the zero-sequence current; Step 3) extracting the waveforms of the grounding currents at the first and last terminals of the faulty cable in the third to fourth power frequency cycles after the fault, extracting the power frequency components using FFT, and calculating the measured amplitude ratio of the grounding currents at the first and last terminals; Step 4) constructing a fault cable accurate location equation based on the distribution network line parameters in the database; Step 5) Setting a virtual fault point according to the bisection method and substituting it into the equation to solve the power frequency components of the grounding current at the beginning and end of the fault cable; Step 6) Calculate the theoretical amplitude ratio of the grounding wire current at the beginning and end of the fault cable, compare it with the measured amplitude ratio, and determine the new fault interval; Step 7) If the length of the fault interval is greater than the set allowable error, jump to step 5) and continue to reduce the fault interval. If it is not greater, take the midpoint of the fault interval as the fault location.

2. The method for locating distribution network cable faults based on the double-end grounding wire current amplitude ratio according to claim 1, characterized in that: In step 2), the step of identifying the faulty cable is: taking the direction of the grounding wire current at the head end of any cable as a reference, using the Pearson correlation coefficient to determine the direction of the grounding wire current at the head end of the remaining cables and the zero-sequence current at the head end of the overhead line, and identifying the faulty cable.

3. The method for locating a distribution network cable fault based on the double-terminal grounding wire current amplitude ratio according to claim 1, characterized in that: In step 4), based on the distribution network line parameters in the database, an equation for accurately locating the faulty cable is constructed, and the specific steps are as follows: (a) Construct a fault equivalent circuit model based on the distribution network line parameters in the database; (b) Establish the equation for accurately locating the faulty cable based on the constructed circuit model: f(x·Z f ,x·jωC f ,(l-x)·Z f ,(l-x)·jωC f ,R,Z h ,jωC h )=I Where l is the length of the fault cable, x is the fault distance; Z f 、C f is the impedance and inductive capacitance per unit length of the fault cable; R is the equivalent resistance of the grounding wire; Z h 、C h The impedance and inductive capacitance of the sound line; I is the fault cable grounding wire current.

4. The method for locating distribution network cable faults based on the double-end grounding wire current amplitude ratio according to claim 3, characterized in that: In step 5), after setting the virtual fault point according to the dichotomy method, the virtual fault distance x is substituted into the positioning equation to obtain the grounding current I at the head end of the fault cable. f_s , end grounding wire current I f_e .

5. The method for locating a distribution network cable fault based on the double-end grounding wire current amplitude ratio according to claim 4, characterized in that: In step 6), the theoretical amplitude ratio of the grounding current at the beginning and end of the fault cable is k cal The calculation formula is:

6. The method for locating a distribution network cable fault based on the double-terminal grounding wire current amplitude ratio according to claim 5, characterized in that: In step 6), the theoretical and measured amplitude ratio of the first and last grounding wire currents is k rel Compare and determine the new fault range. The specific steps are as follows: (a) Set the midpoint α1 of the fault cable interval [a, b] as the virtual fault point, where a=0, b=l, and calculate k at this time. cal , compare k cal With k rel The size relationship; (b) If k cal =k rel , then the fault point is α1; (c) If k cal >k rel , then the fault point is between [a, α1], keep this interval, let b = α1, then generate a new interval [a, b]; (d) If k cal <k rel , then the fault point is between [α1,b]. Keep this interval and let a=α1, then a new interval [a,b] is generated.

7. The method for locating a distribution network cable fault based on the double-end grounding wire current amplitude ratio according to claim 6, characterized in that: In step 7), the specific steps for determining the fault location are as follows: (a) Compare the fault interval length ba with the set allowable error ε to see whether ba ≤ ε is true; (b) If ba>ε, continue to set the virtual fault point in the new fault interval using the bisection method; (c) If ba≤ε, the midpoint of the fault interval is taken as the fault location, that is, the fault distance x is: x=(a+b) / 2.

8. A distribution network cable fault location system based on the current amplitude ratio of the double-terminal grounding wire, characterized in that: The system includes: measuring equipment, fault location device, and master station; wherein: The measuring equipment is a high-precision current transformer used to measure the current of the cable grounding wire; A fault location device, configured to determine the location of a fault point according to the fault location method according to any one of claims 1 to 7; The main station is used to perform alarm work and display the current waveform of the fault cable grounding wire and the fault point location.

9. The distribution network cable fault location system based on the double-end grounding wire current amplitude ratio according to claim 8, characterized in that: The fault location device includes: a sampling module, a storage module, a communication module, a time module, a power module, and a main control module; wherein: Sampling unit, used for sampling the current waveform of the cable grounding wire; A storage unit for storing parameters of each line of the distribution network and ground wire current data; Communication module, used for communication between the fault location device, measuring equipment and the master station; Time module, used to obtain time values; A power module is used to provide power to the fault locating device; A main control module, configured to execute the steps of the method according to any one of claims 1 to 7.

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