A single-phase grounding fault detection method based on phase shift deformation and first half wave

Abstract

This invention discloses a single-phase grounding fault detection method based on phase-shift deformation and the first half-wave. This method starts from the deformation of the zero-voltage and zero-current signals after a grounding fault occurs. It detects phase-shift deformation of the collected zero-voltage and zero-current signals, determines the fault occurrence time, and classifies different fault conditions. Furthermore, it combines the first half-wave method to achieve efficient diagnosis of fault sections in medium-voltage distribution networks. Specific embodiments verify the feasibility, effectiveness, and robustness of the invention's technical solution, overcoming the shortcomings of existing traditional single-phase grounding fault detection methods in diagnosing various single-phase grounding faults (such as gradual faults, intermittent faults, and successive faults). In addition, another major advantage of the proposed method is that it does not require frequency domain or power energy transformation, does not increase hardware or computational requirements, and can be directly embedded into existing detection devices.

Description

Technical Field

[0001] The present invention belongs to the technical field of power system distribution network operation and maintenance automation, machine learning and fault diagnosis, and relates to single-phase grounding fault feature extraction, fault diagnosis and intelligent operation and maintenance of medium-voltage distribution network based on phase misalignment deformation, and specifically to a single-phase grounding fault detection method based on phase misalignment deformation and the first half wave. Background Art

[0002] In my country's 10kV distribution network, a small current grounding method is generally used, that is, the neutral point is not grounded or grounded through an arc suppression coil. According to statistics, in the medium-voltage distribution network, the incidence of single-phase grounding faults accounts for more than 80% of all faults. At present, the existing single-phase grounding fault types include metallic grounding faults, intermittent grounding faults, gradual grounding faults, resonant grounding faults, sequential grounding faults, etc., especially when the excessive resistance is high resistance, the corresponding grounding fault characteristics are extremely unclear. If it cannot be detected in time, it will affect the safe operation of the distribution network, and in severe cases, it will cause personal injury or fire accidents. Therefore, it is of great significance to detect it accurately and quickly.

[0003] At present, the detection methods for single-phase grounding faults in medium-voltage distribution networks are mainly divided into two categories, namely transient method and steady-state method. The idea of ​​the transient method is to extract time domain and frequency domain features and compare thresholds based on the transient process data of the zero-sequence voltage signal. The main feature extraction methods include transient direction method, empirical mode decomposition and wavelet transform. The idea of ​​the steady-state method is to compare the characteristic changes of the zero-sequence current signal in the steady-state stage after the fault occurs. The main methods include steady-state zero-sequence power direction method, negative sequence current method, deep learning, etc. These methods have played different roles in the diagnosis of conventional single-phase grounding faults. However, for the detection of neutral point grounding through arc suppression coils and high-resistance faults, these methods are difficult to extract fault features when the zero-sequence voltage or zero-sequence current is relatively small, especially when there is a three-phase voltage imbalance. The effectiveness of its single-phase grounding fault detection needs to be further verified. There are problems such as insufficient detection accuracy and difficulty in accurately determining the time when the grounding fault occurs.

[0004] The patent document with application number CN202111533753.5 discloses a single-phase ground fault detection method on the converter valve side of a flexible DC transmission system, the method comprising: identifying the disconnected state of the circuit breaker in the flexible DC transmission system; selecting different single-phase ground fault detection strategies according to the disconnected state of the circuit breaker; wherein the single-phase ground fault detection strategy includes a neutral point overvoltage fault detection strategy and a neutral point overcurrent fault detection strategy. This patented technical solution effectively improves the sensitivity of the converter valve side ground fault discrimination through different single-phase ground fault detection strategies, but there is no report on the detection of single-phase ground faults in medium voltage distribution networks, and there is no relevant technical record on the single-phase ground fault detection method based on phase misalignment deformation and the first half wave.

[0005] The patent document with application number CN202020216941.X discloses a single-phase ground fault detection system for a distribution network, which includes: two synchronous signal sources, which are respectively arranged at the two ends of the fault line, and under the control of the GNSS time reference, a high-voltage signal with a completely consistent voltage waveform is injected into the fault line at both ends of the fault phase simultaneously and synchronously; since the current reference direction is from one signal source to another signal source, the current phases of the fault lines on both sides of the fault point are opposite; a synchronous detector, which determines the ground fault point by detecting the current phase reversal point on the fault line under the control of the GNSS time reference. The single-phase ground fault detection system for a distribution network provided by the technical solution of the patent document can effectively solve the problem that the amplitude detection threshold is difficult to determine and misjudgment often occurs in the existing detection process, but there is no relevant technical record about the single-phase ground fault detection method based on phase misalignment deformation and the first half wave.

[0006] For single-phase grounding faults of various fault types, whether based on transient quantities or steady-state quantities, the zero-voltage waveform shape and zero-current waveform shape must change relative to the normal state without fault. Therefore, based on this characteristic, the present invention realizes the effective extraction and identification of the slight change characteristics of the zero-sequence voltage waveform and the zero-sequence current waveform caused by the single-phase grounding fault from the perspective of morphological changes. The proposed deformation feature detection is basically applicable to most single-phase grounding fault types, especially the accurate detection of high-resistance faults; further, after finding the starting point of the fault based on the phase shift deformation, the phase comparison of the first half-wave of the zero-sequence voltage and the zero-sequence current can be used to determine whether the fault is inside or outside the boundary. However, there are currently no relevant technical reports on this method. Summary of the invention

[0007] The technical problem solved by the present invention is to provide a single-phase grounding fault detection method based on out-of-phase deformation and the first half-wave. The method is different from the existing single-phase grounding fault detection technology and method. The present invention starts from the deformation angle of the zero-voltage signal and the zero-current signal after the grounding fault occurs, and performs out-of-phase deformation detection, fault occurrence time determination and judgment under different faults on the collected zero-voltage signal and zero-current signal, and further combines the first half-wave method to realize efficient diagnosis of the fault section of the medium-voltage distribution network.

[0008] The present invention adopts the following technical solution to solve the above technical problems, a single-phase grounding fault detection method based on phase shift deformation and the first half wave, and its specific process is as follows:

[0009] (1) The zero-sequence voltage signal is measured by the zero-voltage transformer and the zero-current transformer and recorded as the zero-voltage signal , zero-sequence current signal is recorded as zero-current signal , is the sampling time, is the total number of samples;

[0010] (2) Design an all-pass filter The phase of the all-pass filter is delayed by 180°, which converts the zero-voltage signal Feed into the all-pass filter Get the corresponding phase-shifted zero-voltage signal ;

[0011] (3) The phase-shifted zero-pressure signal that passes through the all-pass filter and the corresponding original zero-pressure signal are combined into a phase-shifted two-dimensional zero-pressure signal, which is recorded as ;

[0012] (4) Based on the current detection point As the benchmark, 128 is the length of a whole cycle of the zero-pressure signal and the zero-current signal. The Euclidean distance is calculated between the phase-shifted two-dimensional zero-pressure signal of the current detection point and the zero-pressure two-bit graphs of the first three points to obtain the difference values ​​of the three two-dimensional zero-pressure signal diagrams. , , , , recorded as the phase deviation value of the zero-pressure signal ;

[0013] (5) Take the average value of the three zero-pressure signal phase shift deformation values ​​obtained and record it as the current moment Adaptive zero-pressure signal detection threshold: ; Since the zero-pressure signal detection threshold at the current moment is only related to the previous three moments and is updated in real time, the problem of insufficient detection sensitivity of the traditional fixed threshold is avoided;

[0014] (6) The adaptive judgment criterion for single-phase grounding fault is: calculate the Euclidean distance between the two-dimensional zero-voltage signal at the current moment and the corresponding two-dimensional signal at the previous moment, which is recorded as the zero-voltage signal phase deformation value. , and then the zero-pressure signal at the current moment is shifted into the phase deformation value The corresponding adaptive zero-pressure signal detection threshold For comparison, if , it is determined that a single-phase grounding fault occurs;

[0015] (7) The basis for determining the fault time point is: Based on the single-phase grounding fault adaptive judgment criterion, if at time , , then it is determined that the time point when the single-phase grounding fault occurs is Department;

[0016] (8) The intermittent single-phase grounding fault judgment mechanism is: within a full cycle, if If the number of occurrences is greater than 5 times in a row, it is considered that an intermittent single-phase grounding fault has occurred in the distribution network, and the time point of the intermittent fault is the time when the first judgment is accurately determined;

[0017] (9) The criterion for determining internal and external faults is as follows: after determining the time point at which a single-phase grounding fault occurs, compare the first zero-voltage half-wave signal after the fault point. and the first zero-current half-wave signal phase, to analyze whether an internal fault or an external fault has occurred. If the first zero-voltage half-wave signal and the first zero-current half-wave signal If the polarity is opposite, it is considered that an internal fault has occurred, otherwise it is considered that an external fault has occurred.

[0018] Compared with the prior art, the present invention has the following advantages and beneficial effects: the present invention aims at the problem that the single-phase grounding fault of the distribution network is not easy to detect, and with the help of the idea of ​​fluid mechanics deformation, the start-up control and accurate detection of the single-phase grounding fault of the distribution network are realized from the slight changes of the zero-sequence voltage signal waveform, i.e., the zero-voltage signal, and the zero-sequence current signal waveform, i.e., the zero-current signal after the single-phase grounding fault occurs in the distribution network. First, based on the change law of the waveform of the zero-voltage signal before and after the fault point, a new method of "phase-shifted deformation" is innovatively proposed, and the original zero-voltage signal is passed through an all-pass filter so that the filtered signal and the original signal have a phase difference, and a two-bit zero-voltage signal trajectory diagram is formed with the original signal. Secondly, the Euclidean distance of the zero-voltage signal trajectory at two adjacent moments before and after is calculated, which is the deformation amount of the current point, and an adaptive threshold is designed based on the change of the deformation amount before and after. Then, based on the basic principle of "phase-shifted deformation", according to the occurrence mechanism and evolution characteristics of different types of faults, a single-phase grounding fault detection criterion suitable for practical application is proposed. If the deformation amount (Euclidean distance value) at the current moment is greater than the adaptive threshold, it is determined that a single-phase grounding fault has occurred. Finally, based on accurate startup, the deformation point, that is, the fault point, is determined by whether the polarity of the first half-wave of the zero-voltage signal and the zero-current signal is opposite to determine whether the fault is outside the boundary or inside the boundary. The feasibility, effectiveness and robustness of the technical solution of the present invention are verified through specific embodiments, solving the shortcomings of the existing traditional single-phase grounding fault detection method in the diagnosis of various single-phase grounding faults (such as gradual faults, intermittent faults, sequential faults, etc.). In addition, another major advantage of the new method proposed in the present invention is that it does not require frequency domain or power energy conversion, does not increase hardware and example requirements, and can be directly embedded in existing detection devices. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 This is a schematic diagram of the single-phase grounding fault detection principle in the present invention.

[0020] Figure 2 It is a network topology diagram of a 10kV medium voltage distribution network in an embodiment.

[0021] Figure 3 It is a zero-voltage signal waveform diagram when a single-phase grounding fault occurs in the embodiment.

[0022] Figure 4 It is a zero-current signal waveform diagram of a single-phase grounding fault in the embodiment.

[0023] Figure 5 Schematic diagram of the deformation detection of the phase-out zero-pressure signal in the embodiment.

[0024] Figure 6 This is a diagram for determining the faults within and outside the first half-wave limit in the embodiment. DETAILED DESCRIPTION

[0025] The above contents of the present invention are further described in detail below through examples, but this should not be understood as the scope of the above subject matter of the present invention being limited to the following examples, and all technologies implemented based on the above contents of the present invention belong to the scope of the present invention. Example

[0026] The structure topology of the 10kV medium voltage distribution network single-phase ground fault simulation model used in this embodiment is as follows: Figure 2 As shown in Figure 1, there are three feeder lines, namely Line#1, Line#2 and Line#3. Figure 2 The network topology diagram shown in the figure uses PSCAD / EMTDC software to simulate a single-phase grounding fault, in which the arc suppression coil is set to overcompensation, the compensation degree is 5%, and a single-phase grounding fault is set on the third line Line#3. The arc suppression coil inductance is calculated to be L=0.7116H based on the line parameters and length. Considering the asymmetry of the three-phase parameters, a single-phase grounding fault occurs in the C phase of Line 3 at 0.1s, and the grounding fault transition resistance is set to R=50Ω, R=2000Ω and R=5000Ω respectively. Taking the transition resistance set to 50Ω as an example, the zero-sequence voltage signal waveform and the corresponding zero-current signal waveform generated by the simulation are shown as follows: Figure 3 and Figure 4 shown.

[0027] The single-phase grounding fault detection method based on phase shift deformation and the first half wave has the following specific process:

[0028] (1) The zero-sequence voltage signal is measured by the zero-voltage transformer and the zero-current transformer and recorded as the zero-voltage signal , zero-sequence current signal is recorded as zero-current signal , is the sampling time, is the total number of samples;

[0029] (2) Design an all-pass filter The phase of the all-pass filter is delayed by 180°, which converts the zero-voltage signal Feed into the all-pass filter Get the corresponding phase-shifted zero-voltage signal ;

[0030] (3) The phase-shifted zero-pressure signal that passes through the all-pass filter and the corresponding original zero-pressure signal are combined into a phase-shifted two-dimensional zero-pressure signal, which is recorded as ;

[0031] (4) Based on the current detection point As the benchmark, 128 is the length of a whole cycle of the zero-pressure signal and the zero-current signal. The Euclidean distance is calculated between the phase-shifted two-dimensional zero-pressure signal of the current detection point and the zero-pressure two-bit graphs of the first three points to obtain the difference values ​​of the three two-dimensional zero-pressure signal diagrams. , , , , recorded as the phase deviation value of the zero-pressure signal ;

[0032] (5) Take the average value of the three zero-pressure signal phase shift deformation values ​​obtained and record it as the current moment Adaptive zero-pressure signal detection threshold: ; Since the zero-pressure signal detection threshold at the current moment is only related to the previous three moments and is updated in real time, the problem of insufficient detection sensitivity of the traditional fixed threshold is avoided;

[0033] (6) The adaptive judgment criterion for single-phase grounding fault is: calculate the Euclidean distance between the two-dimensional zero-voltage signal at the current moment and the corresponding two-dimensional signal at the previous moment, which is recorded as the zero-voltage signal phase deformation value. , and then the zero-pressure signal at the current moment is shifted into the phase deformation value The corresponding adaptive zero-pressure signal detection threshold For comparison, if , it is determined that a single-phase grounding fault occurs;

[0034] (7) The basis for determining the fault time point is: Based on the single-phase grounding fault adaptive judgment criterion, if at time , , then it is determined that the time point when the single-phase grounding fault occurs is Department;

[0035] (8) The intermittent single-phase grounding fault judgment mechanism is: within a full cycle, if If the number of occurrences is greater than 5 times in a row, it is considered that an intermittent single-phase grounding fault has occurred in the distribution network, and the time point of the intermittent fault is the time when the first judgment is accurately determined;

[0036] (9) The criterion for determining internal and external faults is as follows: after determining the time point at which a single-phase grounding fault occurs, compare the first zero-voltage half-wave signal after the fault point. and the first zero-current half-wave signal phase, to analyze whether an internal fault or an external fault has occurred. If the first zero-voltage half-wave signal and the first zero-current half-wave signal If the polarity is opposite, it is considered that an internal fault has occurred, otherwise it is considered that an external fault has occurred.

[0037] According to the technical idea of ​​phase-shift fault detection proposed in the present invention, the phase-shift signal of the original zero-pressure signal is obtained based on step (2), the two-dimensional phase-shift zero-pressure signal is obtained based on step (3), and then the deformation value is obtained based on step (4), wherein the adaptive threshold detection of the phase-shift zero-pressure signal when R=50Ω is as follows: Figure 5 As shown. Figure 5 It can be obtained that the adaptive detection mechanism proposed according to steps (5) and (6) can realize the accurate detection of single-phase grounding fault. When the phase error deformation value at the time point 0.1004s is greater than the average value of the previous three deformation values, the fault point can be accurately located at 0.1004s, which is consistent with the actual occurrence time of the fault. Finally, the first half-wave method can be used to obtain the corresponding first half-wave phase contrast Figure 6 As shown, the phase polarity is opposite, which is an in-bounds fault.

[0038] The above embodiments describe the basic principles, main features and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The above embodiments and descriptions are only for illustrating the principles of the present invention. Without departing from the scope of the principles of the present invention, the present invention may have various changes and improvements, and these changes and improvements all fall within the scope of protection of the present invention.

Claims

1. A single-phase grounding fault detection method based on phase shift deformation and first half wave, the specific process is as follows: (1) The zero-sequence voltage signal is measured by the zero-voltage transformer and the zero-current transformer and recorded as the zero-voltage signal , the zero-sequence current signal is recorded as the zero-current signal , is the sampling time, is the total number of samples; (2) Design an all-pass filter The phase of the all-pass filter is delayed by 180°, which converts the zero-voltage signal Feed into the all-pass filter Get the corresponding phase-shifted zero-voltage signal ; (3) The phase-shifted zero-pressure signal that passes through the all-pass filter and the corresponding original zero-pressure signal are combined into a phase-shifted two-dimensional zero-pressure signal, which is recorded as ; (4) Based on the current detection point As the benchmark, 128 is the length of a whole cycle of the zero-pressure signal and the zero-current signal. The Euclidean distance is calculated between the phase-shifted two-dimensional zero-pressure signal of the current detection point and the zero-pressure two-bit graphs of the first three points to obtain the difference values ​​of the three two-dimensional zero-pressure signal diagrams. , , , , recorded as the phase deviation value of the zero-pressure signal ; (5) Take the average value of the three zero-pressure signal phase shift deformation values ​​and record it as the current moment Adaptive zero-pressure signal detection threshold: ; (6) The adaptive judgment criterion for single-phase grounding fault is: calculate the Euclidean distance between the two-dimensional zero-voltage signal at the current moment and the corresponding two-dimensional signal at the previous moment, which is recorded as the zero-voltage signal phase deformation value. , and then the zero-pressure signal at the current moment is shifted into the phase deformation value The corresponding adaptive zero-pressure signal detection threshold For comparison, if , it is determined that a single-phase grounding fault occurs; (7) The basis for determining the fault time point is: Based on the single-phase grounding fault adaptive judgment criterion, if at time , , then it is determined that the time point when the single-phase grounding fault occurs is Department; (8) The intermittent single-phase grounding fault identification mechanism is: within a full cycle, if If the number of occurrences is greater than 5 times in a row, it is considered that an intermittent single-phase grounding fault has occurred in the distribution network, and the time point of the intermittent fault is the time when the first judgment is accurately determined; (9) The criterion for determining internal and external faults is as follows: after determining the time point at which a single-phase grounding fault occurs, compare the first zero-voltage half-wave signal after the fault point. and the first zero-current half-wave signal phase, to analyze whether an internal fault or an external fault has occurred. If the first zero-voltage half-wave signal and the first zero-current half-wave signal If the polarity is opposite, it is considered that an internal fault has occurred, otherwise it is considered that an external fault has occurred.

Images