Fault phase identification method and system during intermittent grounding of small resistance grounding system

Abstract

The invention discloses a phase fault identification method and system during intermittent grounding of a small resistance grounding system, and the method comprises the following steps: collecting voltage and current waveform signals in real time through distributed waveform collection equipment; carrying out filtering processing on the collected signals; extracting fault features in the processed signals; judging whether the intermittent characteristics are intermittent grounding faults or not by utilizing a self-adaptive threshold value, and if the frequency spectrum energy of the signal exceeds the threshold value, judging that the signal is a fault signal; the fault signals are divided according to three phases of the power system, fault features of each phase are extracted and compared with normal signals, and the phase where the fault occurs is further determined. Through adaptive threshold determination and short-time analysis, a normal operation state and an intermittent grounding fault can be effectively distinguished, misjudgment is avoided, the fault identification accuracy is improved, and it is ensured that the grounding fault can be found in time.

Description

Technical Field

[0001] The present invention relates to the technical field of power system fault diagnosis, and in particular to a method and system for identifying intermittent grounding phase faults in a low-resistance grounding system. Background Art

[0002] As the scale of power systems continues to expand, the operating environment of power equipment has become increasingly complex, especially in high-voltage transmission lines and substations, where low-resistance grounding systems have gradually been widely used. Low-resistance grounding systems have lower grounding resistance values ​​(usually between a few ohms and tens of ohms), allowing the system to maintain a lower short-circuit current in the event of a ground fault, thereby helping to reduce the risk of damage to electrical equipment. However, ground fault detection in such systems faces greater challenges, especially intermittent ground faults, which are easily overlooked or misjudged by traditional fault detection methods because their fault currents are small and change periodically.

[0003] Traditional ground fault identification methods mainly rely on the judgment of current and voltage amplitude and the action of protection relays, but these methods are not applicable to low-resistance grounding systems because the fault current is relatively small and the characteristics of intermittent grounding phases are often masked by background noise. In addition, the fault detection method based on frequency response still faces the problems of signal analysis accuracy and real-time performance when processing complex power system waveforms, especially when multiple fault types occur simultaneously, the accuracy and real-time performance of identification cannot meet the requirements. Summary of the invention

[0004] In order to solve the deficiencies in the prior art, the present invention provides a method for identifying intermittent grounding phase faults in a low-resistance grounding system, the method specifically comprising the following steps:

[0005] Select sampling points of the low-resistance grounding system and use distributed waveform acquisition equipment to collect voltage and current waveform signals in real time;

[0006] Filter the collected voltage and current waveform signals to remove noise interference and retain fault characteristic signals;

[0007] Extract the spectrum characteristics of the signal after filtering at the time of fault;

[0008] Based on the extracted frequency spectrum characteristics of the fault, an adaptive threshold is used to detect whether there is an intermittent grounding fault in the signal after filtering. If there is an intermittent grounding fault, the signal is determined to be a fault signal;

[0009] The fault signal is divided into three phases of the power system, and the frequency spectrum characteristics of each phase fault are extracted and compared with the normal signal to further confirm the phase where the fault is located.

[0010] Preferably, the spectrum energy is expressed by the following formula:

[0011] E(ω,t)=|X(ω,t)| 2 (2)

[0012] Among them, E(ω,t) represents the energy density of the fault characteristic signal at time t and frequency ω.

[0013] Preferably, the adaptive threshold is expressed by the following formula:

[0014] Adaptive threshold = α1E1 + α2E2 (3)

[0015] Among them, α1 and α2 are weighting coefficients used to adjust the signal impact of different time periods, ΔT is the short-time analysis window, E1 is the accumulated signal spectrum energy in the entire sampling period T, and E2 is the accumulated signal spectrum energy in the analysis window [t-ΔT].

[0016] Preferably, the signal spectrum energy E1 accumulated in the entire sampling period T is expressed by the following formula:

[0017]

[0018] Where T is the sampling period of the signal, E(ω,t) is the energy density of the signal at time t and frequency ω, and p is a parameter that controls the spectral energy sensitivity.

[0019] Preferably, the signal spectrum energy E2 accumulated within the analysis window [t-ΔT] is expressed by the following formula:

[0020]

[0021] Where T is the sampling period of the signal, t-ΔT is the short-time analysis window, E(ω,t) is the energy density of the signal at time t and frequency ω, and q is the parameter that controls the spectral energy sensitivity.

[0022] Preferably, the set fault judgment function is expressed by the following formula:

[0023]

[0024] Wherein, F(t)=1 indicates that an intermittent ground fault occurs, and F(t)=0 indicates that the signal is normal.

[0025] Preferably including:

[0026] Perform Fourier transform on the three-phase voltage and current respectively to obtain the spectrum V of the three-phase voltage k (w) and the spectrum of the three-phase current I k(w), extract the frequency spectrum characteristics of each phase voltage and current fault, and determine the phase where the fault is located by comparing the difference between the current and voltage spectrum of each phase k and the size of the set threshold;

[0027] Wherein, k=a, b, c represents any phase among the three phases.

[0028] Preferably, the fault characteristic signals of the voltage and current of each phase in the three-phase system are compared with the normal signals to assist in determining the phase where the fault is located and increase the confidence of fault identification.

[0029] Preferably, the difference between the current and voltage spectra of each phase is expressed as follows:

[0030]

[0031] Among them, α κ is the amplification factor, which is used to adjust the proportional relationship between voltage and current, σ κ is the standard deviation, which quantifies the variation between voltage and current.

[0032] The second aspect of the present invention discloses a system for identifying intermittent grounding phase faults in a low-resistance grounding system, and the system runs the method for identifying intermittent grounding phase faults in a low-resistance grounding system as described above, and the system comprises:

[0033] Signal acquisition and processing module, used to collect signals from low-resistance grounding systems in real time and perform filtering processing;

[0034] Time domain and frequency domain analysis module, used to extract the spectrum energy of the fault characteristic signal after filtering;

[0035] An adaptive threshold determination module is used to determine whether an intermittent grounding phase fault occurs based on spectrum energy and adaptive threshold;

[0036] The fault phase division module is used to determine the phase where the fault is located.

[0037] Beneficial effects of the present invention:

[0038] 1. The present invention can effectively distinguish between normal operating status and intermittent grounding faults through adaptive threshold judgment and short-time analysis, avoid misjudgment, and improve the accuracy of fault identification, ensuring that grounding faults can be discovered in time;

[0039] 2. The present invention adopts a bandpass filter and a multiple signal analysis method combining high-frequency signals and power frequency signals, which effectively suppresses the noise interference that may exist in the power system and improves the system's sensitivity to real fault signals;

[0040] 3. Through spectrum analysis and phase division methods, the present invention can accurately analyze the three-phase signals in the power system, identify the specific fault phase, improve the accuracy of fault location, ensure that the fault is isolated in time, and reduce the risk of equipment damage. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 This is a schematic diagram of the overall flow of the intermittent grounding phase fault identification method for a low-resistance grounding system proposed by the present invention. DETAILED DESCRIPTION

[0042] In order to make the purpose, technical scheme and advantages of the present invention clearer, the technical scheme of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. The described embodiments are only embodiments of a part of the present invention, not all embodiments. Based on the spirit of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work belong to the protection scope of the present invention.

[0043] A first embodiment of the present invention provides a method for identifying intermittent grounding phase faults in a low-resistance grounding system, the method comprising the following steps:

[0044] Step 1: Select appropriate sampling points in the power system and use distributed waveform acquisition equipment to collect voltage and current waveform signals in real time, especially focusing on changes in high-frequency and power-frequency signals, because these signals can reflect signs of faults. In order to ensure that subtle changes in ground faults can be captured, it is necessary to set a sufficiently high sampling frequency. By using sensors (such as current transformers and digital voltage transformers) to collect transient voltage and current signals in the power system, ensure that the sampling frequency is high enough to capture subtle changes in ground faults.

[0045] Step 2: Filter the collected signal to remove noise interference, retain the fault characteristic signal, use a bandpass filter to extract the power frequency signal and high-frequency transient signal, and filter out the low-frequency noise that is not related to the fault;

[0046] Step 3: Extract the fault features in the signal processed in step 2. The specific operation is: perform fast Fourier transform on the signal, extract the spectrum energy in each time window of the fast Fourier transformed signal as the spectrum feature of the fault, so as to compare with the normal state.

[0047] Specifically, the process of Fourier transform is:

[0048] Perform short-time Fourier transform on the fault characteristic signal x(τ) to obtain the spectrum X(ω,t), which can be expressed by the following formula:

[0049]

[0050] Among them, x(τ) represents the original signal, w(t-τ) is the window function used to limit the time window of the short-time Fourier transform, ω represents the frequency variable, and j represents the imaginary unit.

[0051] The spectrum energy E(ω,t) of the fault characteristic signal is calculated as the square amplitude of the spectrum at frequency ω and time t, which can be expressed by the following formula:

[0052] E(ω,t)=|X(ω,t)| 2 (2)

[0053] Among them, E(ω,t) represents the energy density of the signal at time t and frequency ω.

[0054] Based on the spectrum characteristics of the fault obtained in the previous step, it is necessary to further determine whether there are characteristics of intermittent grounding faults in the signal. Intermittent grounding faults usually manifest as periodic changes in the signal, and the spectrum characteristics of the fault will repeat multiple times within a short set time.

[0055] Step 4: Use the adaptive threshold to determine whether these intermittent features are intermittent ground faults. If the spectrum energy of the signal exceeds the threshold, it is determined to be a fault signal.

[0056] Specifically, the adaptive threshold is set by weighted average based on the signal spectrum energy, which can be expressed by the following formula:

[0057] Adaptive threshold = α1E1 + α2E2 (3)

[0058] Among them, α1 and α2 are weighting coefficients, which are used to adjust the signal influence in different time periods. The weighting coefficients are set according to the degree of signal influence in different time periods. E1 is the accumulated signal spectrum energy in the entire sampling period T, reflecting the global signal spectrum energy distribution. E2 is the accumulated signal spectrum energy in the short-term analysis window [t-ΔT], reflecting the local spectrum energy change of the signal, that is, the dynamic characteristics of the signal near a certain moment.

[0059] The signal spectrum energy E1 accumulated during the entire sampling period T can be expressed by the following formula:

[0060]

[0061] Where T is the sampling period of the signal, E(ω,t) is the energy density of the signal at time t and frequency ω, and p is the parameter that controls the spectral energy sensitivity within the entire sampling period.

[0062] The signal spectrum energy E1 accumulated within the short-time analysis window [t-ΔT] can be expressed by the following formula:

[0063]

[0064] Where T is the sampling period of the signal, t-ΔT is the short-time analysis window, E(ω,t) is the energy density of the signal at time t and frequency ω, and q is the parameter that controls the spectral energy sensitivity within the short-time analysis window.

[0065] And set a fault judgment function F(t). If the energy of the signal is greater than the adaptive threshold, it means that a fault has occurred, which can be expressed by the following formula:

[0066]

[0067] Wherein, F(t)=1 indicates that an intermittent ground fault occurs, and F(t)=0 indicates that the signal is normal.

[0068] Step 5: Divide the fault signal according to the three phases of the power system, extract the spectrum energy of the fault characteristic signal of each phase, and compare it with the normal signal. Through spectrum analysis, compare the voltage and current waveforms of different phases to further confirm in which phase the fault occurs.

[0069] Specifically, the three-phase voltage and current are Fourier transformed to obtain their spectrum representation V k (ω) and I k (ω); k = a, b, c, representing any phase among the three phases;

[0070] Define the spectral error metric E between current and voltage k (t) is the difference between the current and voltage spectra of each phase k, which can be expressed as follows:

[0071]

[0072] Among them, α κ is the amplification factor, which is used to adjust the proportional relationship between voltage and current, σ κ is the standard deviation, which is used to quantify the change between voltage and current, and Ω is the whole set. It is also necessary to set a fault judgment threshold ∈. If E a (t) or E b (t) or E c If (t) is greater than the fault judgment threshold ∈, it means that the fault occurs in the corresponding phase.

[0073] Furthermore, on the basis of determining the fault phase through the spectrum error, the fault characteristics of each phase are compared with the normal signal to provide a clearer background reference, thereby assisting in confirming which phase has a fault. Because sometimes the fault signal errors of different phases may be close, by introducing the comparison of normal signals, the confidence of fault judgment can be increased and the fuzzy area can be reduced.

[0074] A second embodiment of the present invention provides a system for identifying intermittent grounding phase faults in a low-resistance grounding system, and runs the method for identifying intermittent grounding phase faults in a low-resistance grounding system described in Embodiment 1. The system includes:

[0075] Signal acquisition module, used to collect voltage and current signals in the power system in real time, especially high-frequency and industrial frequency signals;

[0076] Signal filtering module, used to remove noise and retain the characteristics of fault signals;

[0077] Time domain and frequency domain analysis module, used to extract fault characteristics of filtered signals;

[0078] An adaptive threshold determination module is used to identify whether an intermittent ground fault occurs in the system and distinguish it from a normal operating state;

[0079] The time phase fault classification module is used to extract the fault characteristics of each phase of the fault signal and compare it with the normal signal to confirm the fault phase;

[0080] The data storage and historical analysis module stores various signal sampling data, analysis results, fault location data and alarm information.

[0081] In summary, the present invention can effectively distinguish between normal operating status and intermittent ground faults through adaptive threshold judgment and short-time analysis, avoid misjudgment, and improve the accuracy of fault identification, ensuring that ground faults can be discovered in time. The use of a multiple signal analysis method that combines a bandpass filter and a high-frequency signal with an industrial frequency signal effectively suppresses possible noise interference in the power system and improves the system's sensitivity to real fault signals. Through spectrum analysis and phase division methods, the three-phase signals in the power system can be accurately analyzed, the specific fault phase can be identified, the accuracy of fault location can be improved, and the fault can be isolated in time to reduce the risk of equipment damage.

[0082] Embodiment 3 of the present invention provides an electronic device, comprising a memory, a processor, and a computer program stored in the memory and executable on the processor. When the computer program is loaded into the processor, the method for identifying intermittent grounding phase faults in a low-resistance grounding system according to Embodiment 1 is implemented.

[0083] Embodiment 4 of the present invention provides a computer-readable storage medium, which stores a computer program. When the computer program is executed by a processor, the method for identifying intermittent grounding phase faults in a low-resistance grounding system according to Embodiment 1 is implemented.

[0084] The present disclosure may be a system, a method and / or a computer program product. The computer program product may include a computer-readable storage medium carrying computer-readable program instructions for causing a processor to implement various aspects of the present disclosure.

[0085] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, ordinary technicians in the relevant field should understand that the specific implementation methods of the present invention can still be modified or replaced by equivalents, and any modifications or equivalent replacements that do not depart from the spirit and scope of the present invention should be covered within the scope of protection of the claims of the present invention.

Claims

1. A method for identifying fault phases in intermittent grounding of a low-resistance grounding system, characterized in that: The method comprises the following steps: Collect the three-phase voltage and three-phase current waveform signals of the low-resistance grounding system in real time and perform filtering to retain the fault characteristic signals; Extracting the fault characteristic signal spectrum energy of the three-phase voltage and three-phase current after filtering; Perform weighted averaging on the spectrum energy of the extracted fault characteristic signal to obtain an adaptive threshold; According to the spectrum energy and adaptive threshold of the three-phase voltage and three-phase current signals, it is determined whether an intermittent grounding fault occurs through a set fault judgment function; When an intermittent ground fault occurs, if the spectrum energy difference between the voltage and current signals of a phase in the three-phase system exceeds a set threshold, the phase is determined to be a faulty phase.

2. The method for identifying a fault phase when a low-resistance grounding system is intermittently grounded according to claim 1, characterized in that: The spectrum energy is expressed as follows: E(ω,t)=|X(ω,t)| 2 (2) Among them, E(ω,t) represents the spectrum energy of the fault characteristic signal at time t and frequency ω, and X(ω,t) is the spectrum of the fault characteristic signal.

3. The method for identifying a fault phase when a low-resistance grounding system is intermittently grounded according to claim 1, characterized in that: The adaptive threshold is expressed as follows: Adaptive threshold = α1E1 + α2E2 (3) where α1 and α2 are weighting coefficients used to adjust the signal impact of different time periods, ΔT is the short-time analysis window, E1 is the accumulated signal spectrum energy within the entire sampling period T, and E2 is the accumulated signal spectrum energy within the analysis window [t-ΔT].

4. The method for identifying intermittent grounding phase faults in a low-resistance grounding system according to claim 3 is characterized in that: The signal spectrum energy E1 accumulated during the entire sampling period T is expressed as follows: Where T is the sampling period of the signal, E(ω,t) is the energy density of the signal at time t and frequency ω, and p is the parameter that controls the spectral energy sensitivity within the entire sampling period.

5. The method for identifying intermittent grounding phase faults in a low-resistance grounding system according to claim 3 is characterized in that: The signal spectrum energy E2 accumulated within the analysis window [t-ΔT] is expressed as follows: Where T is the sampling period of the signal, t-ΔT is the analysis window, E(ω,t) is the energy density of the signal at time t and frequency ω, and q is a parameter that controls the spectral energy sensitivity within the analysis window.

6. The method for identifying intermittent grounding phase faults in a low-resistance grounding system according to claim 1 is characterized in that: The set fault judgment function is expressed by the following formula: Wherein, F(t)=1 indicates that an intermittent ground fault occurs, and F(t)=0 indicates that the signal is normal.

7. The method for identifying intermittent grounding phase faults in a low-resistance grounding system according to claim 1 is characterized by: Determining the phase where the fault is located includes: Perform Fourier transform on the three-phase voltage and current respectively to obtain the spectrum of the three-phase voltage and the spectrum of the three-phase current, extract the spectrum energy of each phase voltage and current fault, compare the difference between the current and voltage spectrum of the k-th phase with the size of the set threshold, if the spectrum energy difference between the voltage and current signals of the k-th phase is greater than the set threshold, then determine that the phase is a fault phase; Wherein, k=a, b, c represents any phase among the three phases.

8. The method for identifying intermittent grounding phase faults in a low-resistance grounding system according to claim 7 is characterized in that: The fault characteristic signals of the voltage and current of each phase in the three-phase system are compared with the normal voltage and current signals to assist in determining the phase where the fault is located and increase the confidence of fault identification.

9. The method for identifying intermittent grounding phase faults in a low-resistance grounding system according to claim 7, characterized in that: The difference between the current and voltage spectra of the kth phase is expressed as follows: Among them, α κ is the amplification factor, which is used to adjust the proportional relationship between voltage and current, σ κ is the standard deviation, used to quantify the change between voltage and current, Ω is the full set, E k (t) is the difference between the current and voltage spectra of the kth phase.

10. A system for identifying intermittent grounding phase faults in a low-resistance grounding system, running a method for identifying intermittent grounding phase faults in a low-resistance grounding system according to any one of claims 1 to 9, characterized in that: include: Signal acquisition and processing module, used to collect signals from low-resistance grounding systems in real time and filter them to retain fault characteristic signals; Time domain and frequency domain analysis module, used to extract the spectrum energy of the fault characteristic signal after filtering; An adaptive threshold determination module is used to determine whether an intermittent grounding phase fault occurs based on spectrum energy and adaptive threshold; The fault phase division module is used to determine the phase where the fault is located.

Images