Single-phase earth fault location detection method
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- SUZHOU YINJU ELECTRIC POWER TECH CO LTD
- Filing Date
- 2022-09-28
- Publication Date
- 2026-07-21
Smart Images
Figure CN115877117B_ABST
Abstract
Description
Technical Field
[0001] This invention relates to a fault location and detection method, and more particularly to a single-phase grounding fault location and detection method. Background Technology
[0002] In existing power distribution systems, 6-35kV systems often employ low-current grounding operation. Because the line voltage remains symmetrical after a single-phase ground fault, the load power supply is unaffected, allowing power to continue without immediate tripping, thus significantly improving system reliability. However, prolonged operation with a fault, with current continuously flowing through the grounding point, can easily burn out line insulation, causing short-circuit faults and expanding the scope of the accident. Especially for unstable ground faults, the phase voltage surge can reach several times the phase voltage, severely damaging the system's insulation and affecting equipment lifespan. Furthermore, single-phase ground faults caused by broken lines can also lead to wildfires or personal injury.
[0003] Therefore, accurate location and rapid isolation of single-phase grounding faults are urgently needed. However, in low-current systems, single-phase grounding faults are difficult to pinpoint due to the small fault current and inconspicuous electrical quantities. Furthermore, the system's diverse operating modes and complex structure, influenced by transition resistance, make fault location difficult. Currently, traditional methods rely on manual line inspection to determine the fault point, which is not only time-consuming and labor-intensive but also fails to locate the fault quickly and accurately.
[0004] In recent years, many algorithms for fault location based on the steady-state or transient characteristics of zero-sequence current have emerged. Except for the zero-sequence overcurrent method, which is not applicable to low-current grounding systems, they all require comparison of zero-sequence currents collected or synthesized synchronously by multiple sets of equipment.
[0005] Meanwhile, algorithms that rely solely on locally acquired data, primarily based on the zero-sequence active or reactive power method according to the phase relationship between zero-sequence current and zero-sequence voltage, have a certain dead zone. When high-resistance faults or grounding faults are unstable, the phase relationship between zero-sequence current and zero-sequence voltage becomes blurred, making it impossible to clearly identify whether there are grounding fault characteristics.
[0006] Therefore, existing fault location algorithms still have certain shortcomings and are costly to implement.
[0007] In view of the above-mentioned shortcomings, the designer has actively researched and innovated in order to create a single-phase grounding fault location and detection method, making it more valuable for industrial applications. Summary of the Invention
[0008] To address the aforementioned technical problems, the purpose of this invention is to provide a method for locating and detecting single-phase grounding faults.
[0009] The single-phase ground fault location and detection method of the present invention includes the following steps:
[0010] Step 1: Obtain the zero-sequence current waveform data at the moment the ground fault occurs;
[0011] Step two: Preprocess the zero-sequence current data to obtain a new data sequence I. d (n);
[0012] Step 3, for data sequence I d (n) Perform integration to obtain the new sequence I. s (n);
[0013] Step four: Determine the start time of steady-state recording and perform a test on the new sequence I. s (n) Starting from time Ts, the amplitude value of its power frequency component is estimated cycle by cycle to obtain A(m), where m represents the m-th cycle. For I after time Ts... s (n) Perform weighted summation to obtain a new sequence I. c (n);
[0014] Step 5, the zero-sequence voltage sequence U corresponding to time Ts. o (n), of length N, is the sampling data of one power frequency cycle, used to obtain U. o (n) and I c (n) The normalized correlation coefficient C of the two sequences. If C is greater than the threshold, the point is located upstream of the fault point on the faulty line. If C is lower than the threshold, the point is located downstream of the fault point or on a non-faulty line.
[0015] Furthermore, in the above-mentioned single-phase ground fault location and detection method, in step one, a zero-sequence voltage start-up threshold is set. When the zero-sequence voltage exceeds the threshold, the moment is determined to be the ground fault occurrence moment T0. The moment is recorded, and the zero-sequence current waveform data I0(n) at that moment is obtained. Let P be the number of cycles before and Q after the ground fault occurrence moment, where P and Q are both integers, P≥3, Q≥8.
[0016] Furthermore, in the above-mentioned single-phase ground fault location and detection method, in step two, the preprocessing process involves subtracting the data of the first cycle from the zero-sequence current recording data cycle by cycle; let I... d (n)=I o (n)-[I o [(n-floor(n / N)*N)], where N is the number of sampling points per cycle, and floor represents rounding down.
[0017] Furthermore, in the above-mentioned single-phase ground fault location and detection method, in step three, by... The process is performed using N, where N is the number of sampling points per cycle.
[0018] Furthermore, in the above-mentioned single-phase ground fault location and detection method, in step four, the steady-state recording start time Ts = To + Tz is determined, where Tz represents the length of the transient window, with a default range of 5ms to 20ms. For the new sequence I... s Starting from time Ts, the amplitude value of the power frequency component of (n) is estimated cycle by cycle to obtain A(m), where m represents the m-th cycle. Then, the amplitude value of I after time Ts is calculated. s (n) Perform weighted summation to obtain a new sequence I. c (n),
[0019]
[0020] Where M represents the total number of full power frequency cycles from time Ts to the end of the recorded data, m represents the m-th power frequency cycle, and N is the number of sampling points for each cycle.
[0021] Furthermore, in the above-mentioned single-phase ground fault location and detection method, the zero-sequence voltage sequence U corresponding to time Ts is confirmed. o (n), calculate U o (n) and I c The normalized correlation coefficient C of (n), where,
[0022]
[0023] Where mean(U) o ) and mean(I c ), where represent the averages of the Uo and Ic sequences, respectively.
[0024] If C is greater than the threshold, the point is located upstream of the fault point on the faulty line; if C is lower than the threshold, the point is located downstream of the fault point or on a non-faulty line. The threshold is between 0.8 and 1.
[0025] By means of the above-described solution, the present invention has at least the following advantages:
[0026] It is suitable for locating single-phase grounding faults when the zero-sequence current at the installation location and the zero-sequence voltage of the same bus section at the same time are collected. The zero-sequence current can be directly collected by the zero-sequence CT or synthesized synchronously from three-phase currents. The zero-sequence voltage can be synthesized at the installation location by the zero-sequence PT or by the three-phase voltage, or it can be measured on the bus section. The specific method of obtaining the zero-sequence current and zero-sequence voltage is not limited.
[0027] This invention utilizes weighted integration to improve the identification accuracy and anti-interference capability of zero-sequence current under high-resistance grounding faults. Simultaneously, it allows for direct calculation of the correlation between the integration results and zero-sequence voltage, thus constructing a simple and effective method to improve the accuracy of grounding fault location.
[0028] The above description is merely an overview of the technical solution of the present invention. In order to better understand the technical means of the present invention and to implement it in accordance with the contents of the specification, the preferred embodiments of the present invention are described in detail below with reference to the accompanying drawings. Attached Figure Description
[0029] Figure 1 It is the original zero-sequence current waveform upstream of the fault point.
[0030] Figure 2 It is the data waveform after integration.
[0031] Figure 3 This is a partial waveform diagram of the zero-sequence current amplitude.
[0032] Figure 4 This is the original zero-sequence current waveform of the non-faulty line.
[0033] Figure 5 It is the waveform diagram of the processed result data sequence Is.
[0034] Figure 6 It shows the weighted and accumulated data waveform and the zero-sequence voltage waveform at the corresponding time. Detailed Implementation
[0035] The specific embodiments of the present invention will be described in further detail below with reference to the accompanying drawings and examples. The following examples are for illustrative purposes only and are not intended to limit the scope of the invention.
[0036] like Figures 1 to 6 A method for locating and detecting single-phase ground faults, comprising the following steps:
[0037] Step 1: At the moment of the ground fault occurrence, obtain the zero-sequence current waveform data at that moment. Specifically, set a zero-sequence voltage threshold, typically ranging from 10 to 30V. When the zero-sequence voltage exceeds the threshold, determine that moment as the ground fault occurrence moment T0 and record it. Simultaneously, obtain the zero-sequence current waveform data I0(n) at that moment, assuming P cycles before and Q cycles after the ground fault occurrence moment. Here, P and Q are integers, with P ≥ 3 and Q ≥ 8. During implementation, the preferred values for P and Q are integers ≤ 16.
[0038] Step two: Preprocess the zero-sequence current data to obtain a new data sequence I. d (n). Specifically, the preprocessing process involves subtracting the data of the first cycle from the zero-sequence current recording data cycle by cycle. Let I be... d (n)=I o (n)-[I o[(n-floor(n / N)*N)], where N is the number of sampling points per cycle, for example, 128 or 256. During implementation, N can preferably be greater than or equal to 128, and floor represents rounding down.
[0039] Step 3, for data sequence I d (n) Perform integration to obtain the new sequence I. s (n).
[0040] pass This is used for processing. Here, N is the number of sampling points per cycle.
[0041] Step four: Determine the start time of steady-state recording and perform a test on the new sequence I. s (n) Starting from time Ts, the amplitude value of its power frequency component is estimated cycle by cycle to obtain A(m), where m represents the m-th cycle. For I after time Ts... s (n) Perform weighted summation to obtain a new sequence I. c (n).
[0042] Specifically, the steady-state recording start time is set as Ts, where Ts = To + Tz. Here, Tz represents the length of the transient window, with a default range of 5ms to 20ms, and a typical value of 10ms, which is half the length of a power frequency cycle. To represents the fault initiation time, equivalent to time zero (no value range), which is the moment when the zero-sequence voltage threshold exceeds the limit. Then, the new sequence I... s Starting from time Ts, the amplitude value of the power frequency component of (n) is estimated cycle by cycle to obtain A(m), where m represents the m-th cycle. Then, the amplitude value of I after time Ts is... s (n) Perform weighted summation to obtain a new sequence I. c (n).
[0043] After that, through Perform the calculation.
[0044] Where M represents the total number of full power frequency cycles from time Ts to the end of the recorded data, m represents the m-th power frequency cycle, and N is the number of sampling points for each cycle. During implementation, the amplitude estimation of the power frequency components can be obtained by FFT calculation. Alternatively, for cycles dominated by the power frequency component, the maximum amplitude can be directly approximated.
[0045] Step 5, the zero-sequence voltage sequence U corresponding to time Ts. o (n), of length N, is the sampling data of one power frequency cycle, used to obtain U. o (n) and I c (n) The normalized correlation coefficient C of the two sequences. Thus, if C is greater than the threshold, the point is located upstream of the fault point on the faulty line; if C is lower than the threshold, the point is located downstream of the fault point or on a non-faulty line.
[0046] Specifically, this can be achieved by confirming the zero-sequence voltage sequence U at time Ts. o (n), calculate U o (n) and I c The normalized correlation coefficient C of (n).
[0047] in,
[0048]
[0049] Where mean(U) o ) and mean(I c ), where represent the average values of the Uo and Ic sequences, respectively. During the judgment period, the threshold value used is between 0.8 and 1, preferably 0.9.
[0050] The working principle of this invention is as follows:
[0051] Suppose the original zero-sequence current waveform upstream of the fault point is as follows: Figure 1 As shown. The waveform of the data after integration is... Figure 2 As shown. The weighted and accumulated data waveform and the corresponding zero-sequence voltage waveform at the given time are as follows. Figure 3 As shown, to better illustrate the phase correlation between the two, Figure 3 The amplitude of the zero-sequence current is compressed to 1 / 4 of the original waveform. The correlation coefficient between the two is 0.951.
[0052] Assume the original zero-sequence current waveform of the non-faulty line is as follows Figure 4 As shown. The data sequence Is after integration is as follows. Figure 5 As shown. Figure 6 The image shows the weighted and accumulated data waveform and the corresponding zero-sequence voltage waveform at that moment. To better illustrate the phase correlation between the two, Figure 6 The zero-sequence current amplitude is compressed to 1 / 4 of the original waveform. Furthermore, the correlation coefficient between the two is -0.992, which makes the correlation coefficient between the upstream of the faulty line and the non-faulty line very significantly different, facilitating rapid identification.
[0053] As can be seen from the above description and the accompanying drawings, the present invention has the following advantages: it is suitable for locating single-phase ground faults when the zero-sequence current at the installation location and the zero-sequence voltage of the same busbar segment at the same time are collected. The zero-sequence current can be directly collected by a zero-sequence current transformer (CT) or it can be synthesized from synchronous three-phase currents. The zero-sequence voltage can be synthesized at the installation location using a zero-sequence current transformer (PT) or by synthesizing three-phase voltages, or it can be measured on the busbar segment. The specific method of obtaining the zero-sequence current and zero-sequence voltage is not limited.
[0054] This invention utilizes weighted integration to improve the identification accuracy and anti-interference capability of zero-sequence current under high-resistance grounding faults. Simultaneously, it allows for direct calculation of the correlation between the integration results and zero-sequence voltage, thus constructing a simple and effective method to improve the accuracy of grounding fault location.
[0055] Furthermore, the orientations or positional relationships described in this invention are based on the orientations or positional relationships shown in the accompanying drawings. They are only for the purpose of facilitating the description of this invention and simplifying the description, and are not intended to indicate or imply that the device or structure referred to must have a specific orientation, or to operate in a specific orientation. Therefore, they should not be construed as limitations on this invention.
[0056] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the technical principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.
Claims
1. A method for locating and detecting single-phase grounding faults, characterized in that... Includes the following steps: Step 1: Obtain the zero-sequence current waveform data at the moment the ground fault occurs; Step two: Preprocess the zero-sequence current data to obtain a new data sequence I. d (n); The preprocessing process involves subtracting the data of the first cycle from the zero-sequence current recording data cycle by cycle; let I d (n)=I o (n)-[I o (n-floor(n / N) [N)], where N is the number of sampling points per cycle, and floor indicates rounding down; Step 3, process data sequence I d (n) Perform integration to obtain the new sequence I. s (n); Step 4: Determine the starting time of steady-state recording. Estimate the amplitude of the power frequency component of the new sequence Is(n) starting from time Ts to obtain A(m), where m represents the m-th cycle. Perform a weighted summation on Is(n) after time Ts to obtain the new sequence Ic(n). The steady-state recording start time is determined as Ts = To + Tz, where Tz represents the length of the transient window (default range 5ms to 20ms), and To represents the fault initiation time, equivalent to time zero, which is the moment when the zero-sequence voltage threshold exceeds the threshold. For the new sequence I... s Starting from time Ts, the amplitude value of the power frequency component of (n) is estimated cycle by cycle to obtain A(m), where m represents the m-th cycle. Then, the amplitude value of I after time Ts is calculated. s (n) Perform weighted summation to obtain a new sequence I. c (n), ， Where M represents the total number of full power frequency cycles from time Ts to the end of the recorded data, m represents the m-th power frequency cycle, and N is the number of sampling points for each cycle; Step 5, the zero-sequence voltage sequence U corresponding to time Ts. o (n), of length N, is the sampling data of one power frequency cycle, used to obtain U. o (n) and I c (n) The normalized correlation coefficient C of the two sequences. If C is greater than the threshold, the point is located upstream of the fault point on the faulty line. If C is lower than the threshold, the point is located downstream of the fault point or on a non-faulty line.
2. The single-phase ground fault location and detection method according to claim 1, characterized in that: In step one, a threshold for the zero-sequence voltage is set. When the zero-sequence voltage exceeds the threshold, the moment is determined to be the moment T0 when the ground fault occurs. The moment is recorded, and the zero-sequence current waveform data I0(n) at that moment is obtained. Let there be P cycles before and Q cycles after the moment when the ground fault occurs, where P and Q are integers, P≥3, Q≥8.
3. The single-phase ground fault location and detection method according to claim 1, characterized in that: In step three, through The process is performed using N, where N is the number of sampling points per cycle.
4. The single-phase ground fault location and detection method according to claim 1, characterized in that: In step five, the zero-sequence voltage sequence U corresponding to time Ts is confirmed. o (n), calculate U o (n) and I c The normalized correlation coefficient C of (n), where, ， Where mean(U) o ) and mean(I c ), where represent the averages of the Uo and Ic sequences, respectively. If C is greater than the threshold, the point is located upstream of the fault point on the faulty line; if C is lower than the threshold, the point is located downstream of the fault point or on a non-faulty line. The threshold is between 0.8 and 1.