A method and system for analyzing and judging single-phase ground fault of power distribution network

Abstract

The application discloses a method and system for judging single-phase grounding fault of a power distribution network, and relates to the field of power distribution network fault judgment. The judgment system provided by the application adopts a starting algorithm for monitoring changes in fault component mutation variables in real time. After starting, the judgment system calculates relevant parameters of first-stage transient variables at the moment of fault and relevant parameters of second-stage steady-state variables after the fault is stabilized. After multi-criterion judgment and comprehensive fusion, reliable on-site judgment of single-phase grounding is realized. The method is simple and reliable, and has high calculation speed, thereby realizing on-site rapid judgment.

Description

Technical Field

[0001] This invention relates to the field of distribution network fault assessment, specifically to a method and system for assessing single-phase grounding faults in distribution networks. Background Technology

[0002] In power distribution networks, single-phase grounding faults are the most common type of fault. Current methods for locating single-phase grounding faults generally employ centralized approaches (such as low-current grounding fault location devices installed in substations) or distributed approaches (such as transient waveform recording fault indicators installed on lines). Both rely on global information (zero-sequence current information of the entire substation outgoing lines or waveform recording information of all fault indicators on the entire line) to perform single-phase grounding fault location judgment through big data analysis. Unlike conventional microcomputer protection devices, which can use simple and convenient equipment installed in the protection bay and reliable local judgment algorithms to perform local judgment of single-phase grounding faults by identifying and calculating their own parameters after a single-phase grounding fault occurs, these methods cannot achieve the same results. Summary of the Invention

[0003] To address the problems of existing technologies, this invention provides a method for diagnosing single-phase grounding faults in distribution networks, comprising the following steps:

[0004] S1. Collect the fault components of the power distribution equipment and obtain the fundamental effective value of the fault components;

[0005] S2. Set the fault setting value and determine whether the fundamental effective value is greater than or equal to the fault setting value. If the fundamental effective value is greater than or equal to the fault setting value, proceed to the next step. If the fundamental effective value is less than the fault setting value, proceed to S1.

[0006] S3. Collect the data of the four cycles before the fault and the data of the eight cycles after the fault starts to temporarily store the fault waveform. Based on the effective value of the three-phase voltage and the fundamental wave of the zero-sequence voltage of the eight cycles after the fault starts, determine whether it is a transient fault or a false grounding fault. If it is, proceed to S1 and store the fault waveform data. If not, proceed to the next step.

[0007] S4. Subtract the data corresponding to the first cycle from the data corresponding to the data corresponding to the 2nd to 12th cycles to construct a fault waveform diagram and find the fault initiation point by calculating the difference of sudden change.

[0008] S5. Based on the fault initiation point, obtain the three-phase current fault component, zero-sequence voltage fault component, and zero-sequence current fault component of the fault initiation point in different transient stages, perform multi-criteria analysis and calculation, and determine whether there is a grounding fault below the power distribution equipment after comprehensive integration.

[0009] Preferably, during the process of collecting fault components of the power distribution equipment, the zero-sequence voltage fault component and the three-phase current fault component of the power distribution equipment are calculated in real time to obtain the fault components. The fault components are obtained by subtracting the corresponding sampling point 5 cycles ago from the sampling point of the current cycle.

[0010] Preferably, S2 includes setting voltage fault settings and current fault settings;

[0011] If the zero-sequence voltage fault component is greater than or equal to the real-time voltage fault setting and / or the three-phase current fault component is greater than or equal to the current fault setting, then proceed to S3.

[0012] Preferably, S5 includes the following steps:

[0013] S5.1. Obtain the first judgment variable within the first half-cycle of the first stage transient state after the fault, wherein the first judgment variable includes the starting angle of the zero-sequence voltage fault component in the first stage transient state, the correlation coefficient between the derivative of the zero-sequence voltage fault component and the zero-sequence current fault component in the first stage transient state, the correlation coefficient between the zero-sequence voltage fault component and the zero-sequence current fault component in the first stage transient state, the effective value of the zero-sequence current fault component in the first stage transient state, and the attenuated DC component of the zero-sequence current fault component in the first stage transient state.

[0014] S5.2. Obtain the second judgment variable of the 5th cycle of the second stage steady state after the fault, wherein the second judgment variable includes the effective value of the zero-sequence current fault component of the second stage steady state, the effective value of the negative-sequence current fault component of the second stage steady state, and the angle between the zero-sequence voltage fault component and the zero-sequence current fault component of the second stage steady state.

[0015] S5.3. Determine the grounding fault based on the numerical relationship between the first and second judgment variables.

[0016] Preferably, in the process of judging grounding faults, the fault judgment for ungrounded systems includes: numerical relationships including at least 4 numerical relationships, and if a grounding fault is determined based on at least 2 numerical relationships, then the final judgment is a grounding fault.

[0017] Preferably, in the process of judging grounding faults, the fault judgment for the neutral point grounded through the arc suppression coil includes: the numerical relationship includes at least 4 numerical relationships, and if the grounding fault is determined based on at least 2 numerical relationships, then the grounding fault is finally determined.

[0018] Preferably, in the process of determining the ground fault, when the numerical relationship includes a transient attenuation DC relationship, the determination is made based on five numerical relationships. If the ground fault is determined based on at least three of the numerical relationships, then the ground fault is finally determined.

[0019] Preferably, the analysis method further includes the following steps:

[0020] S6. Based on the judgment result of S5, store the waveform data, and perform fault detection return based on the drop value of the voltage component of the fault component. When the voltage component is lower than 50% of the starting value, return to S1.

[0021] A system for diagnosing single-phase grounding faults in a power distribution network, comprising:

[0022] The data processing module is used to collect fault components from power distribution equipment and obtain the fundamental effective value of the fault components.

[0023] The data analysis module is used to determine whether the fundamental frequency RMS value is greater than or equal to the fault setpoint by setting a fault setpoint. If the fundamental frequency RMS value is greater than or equal to the fault setpoint, the process proceeds to the next module; if the fundamental frequency RMS value is less than the fault setpoint, the analysis continues.

[0024] The first fault analysis module interacts with the data analysis module to temporarily store fault waveforms by collecting data from the four cycles before the fault starts and the eight cycles after the fault starts. Based on the effective values ​​of the three-phase voltage and zero-sequence voltage fundamental wave in the eighth cycle after the fault starts, it determines whether it is a transient fault or a false grounding fault. If it is, it returns to the data analysis module and stores the fault waveform data. If it is not, it proceeds to the next module.

[0025] The fault point construction module interacts with the first fault analysis module to subtract the data corresponding to the first cycle from the data corresponding to the 2nd to 12th cycles, constructs a fault waveform diagram, and finds the fault initiation point by calculating the difference of sudden change.

[0026] The second fault analysis module interacts with the fault point construction module to obtain the three-phase current fault component, zero-sequence voltage fault component, and zero-sequence current fault component of the fault initiation point at different transient stages based on the fault initiation point. It performs multi-criteria analysis and calculation, and after comprehensive integration, determines whether there is a grounding fault below the power distribution equipment.

[0027] Preferably, the analysis system further includes a high-precision phase current measurement system for data acquisition, wherein the high-precision phase current measurement system is electrically connected to the data analysis module via a high-precision open-type phase current transformer;

[0028] The analysis system also includes an analysis return module, which interacts with the second fault analysis module to store waveform data based on the judgment result of the second fault analysis module and to return fault detection data based on the decrease value of the voltage component of the fault component. Specifically, when the voltage component is lower than 50% of the starting value, the data is returned to the data analysis module.

[0029] A high-precision open-type phase current transformer includes at least three 0.05SS-class high-precision open-type phase current transformers.

[0030] The present invention discloses the following technical effects:

[0031] The advantage of this invention is that the local assessment and protection device adopts a startup algorithm that monitors the sudden changes in the fault component of the power grid in real time. After startup, it calculates the relevant parameters of the transient quantity in the first stage at the moment of the fault and the relevant parameters of the steady-state quantity in the second stage after the fault stabilizes, and performs multi-criteria assessment and calculation. After comprehensive integration, it realizes reliable local assessment of single-phase grounding. This method has a simple and reliable algorithm, fast calculation speed, and can realize rapid local assessment. Attached Figure Description

[0032] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0033] Figure 1 This is a block diagram of the equipment system according to an embodiment of the present invention;

[0034] Figure 2 This is a schematic diagram of a typical structure of the current measurement channel according to an embodiment of the present invention;

[0035] Figure 3 This is a flowchart illustrating the method described in this invention. Detailed Implementation

[0036] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0037] like Figure 1-3 As shown, this invention provides a method for diagnosing single-phase grounding faults in a power distribution network, comprising the following steps:

[0038] S1. By using a high-precision phase current measurement system and voltage acquisition system, the fault components of the power distribution equipment are collected, and the fundamental effective value of the fault components is obtained;

[0039] S2. Fault initiation analysis: Determine whether the fundamental effective value of the fault component is greater than or equal to the fault set value. If the fundamental effective value of the fault component is greater than or equal to the fault set value, perform high-precision fault recording and proceed to the next step. If the fundamental effective value is less than the fault set value, proceed to S1.

[0040] S3. Collect the data of the four cycles before the fault and the data of the eight cycles after the fault starts to temporarily store the fault waveform. Based on the effective value of the three-phase voltage and the fundamental wave of the zero-sequence voltage of the eight cycles after the fault starts, determine whether it is a transient fault or a false grounding fault. If it is, proceed to S1 and store the fault waveform data. If not, proceed to the next step.

[0041] S4. Subtract the data corresponding to the first cycle from the data corresponding to the data corresponding to the 2nd to 12th cycles to construct a fault waveform diagram and find the fault initiation point by calculating the difference of sudden change.

[0042] S5. Based on the fault initiation point, obtain the three-phase current fault component, zero-sequence voltage fault component, and zero-sequence current fault component of the fault initiation point in different transient stages, perform multi-criteria analysis and calculation, and determine whether there is a grounding fault below the power distribution equipment after comprehensive integration.

[0043] Furthermore, during the process of collecting fault components of the power distribution equipment, the zero-sequence voltage fault component and the three-phase current fault component of the power distribution equipment are calculated in real time to obtain the fault components. The fault components are obtained by subtracting the corresponding sampling point 5 cycles ago from the sampling point of the current cycle.

[0044] Furthermore, S2 includes setting voltage fault settings and current fault settings;

[0045] If the zero-sequence voltage fault component is greater than or equal to the real-time voltage fault setting and / or the three-phase current fault component is greater than or equal to the current fault setting, then proceed to S3.

[0046] Furthermore, S5 includes the following steps:

[0047] S5.1. Obtain the first judgment variable within the first half-cycle of the first stage transient state after the fault, wherein the first judgment variable includes the starting angle of the zero-sequence voltage fault component in the first stage transient state, the correlation coefficient between the derivative of the zero-sequence voltage fault component and the zero-sequence current fault component in the first stage transient state, the correlation coefficient between the zero-sequence voltage fault component and the zero-sequence current fault component in the first stage transient state, the effective value of the zero-sequence current fault component in the first stage transient state, and the attenuated DC component of the zero-sequence current fault component in the first stage transient state.

[0048] S5.2. Obtain the second judgment variable of the 5th cycle of the second stage steady state after the fault, wherein the second judgment variable includes the effective value of the zero-sequence current fault component of the second stage steady state, the effective value of the negative-sequence current fault component of the second stage steady state, and the angle between the zero-sequence voltage fault component and the zero-sequence current fault component of the second stage steady state.

[0049] S5.3. Determine the grounding fault based on the numerical relationship between the first and second judgment variables.

[0050] Furthermore, in the process of judging grounding faults, the fault assessment for ungrounded systems includes: numerical relationships including at least 4 numerical relationships. If a grounding fault is determined based on at least 2 numerical relationships, then it is ultimately determined to be a grounding fault.

[0051] Furthermore, in the process of judging grounding faults, the fault judgment for a neutral point grounded through an arc suppression coil includes: when at least four numerical relationships are valid, if a grounding fault is determined based on at least two numerical relationships, then the final judgment is a grounding fault.

[0052] Furthermore, in the process of determining a ground fault, if the numerical relationship includes a transient attenuation DC relationship, the determination is made based on the above five numerical relationships. If the ground fault is determined based on at least three of the numerical relationships, then the ground fault is finally determined.

[0053] Furthermore, the analysis method also includes the following steps:

[0054] S6. Based on the judgment result of S5, store the waveform data, and perform fault detection return based on the drop value of the voltage component of the fault component. When the voltage component is lower than 50% of the starting value, return to S1.

[0055] A system for diagnosing single-phase grounding faults in a power distribution network, comprising:

[0056] The data processing module is used to collect fault components from power distribution equipment and obtain the fundamental effective value of the fault components.

[0057] The data analysis module is used to determine whether the fundamental frequency RMS value is greater than or equal to the fault setpoint by setting a fault setpoint. If the fundamental frequency RMS value is greater than or equal to the fault setpoint, the process proceeds to the next module; if the fundamental frequency RMS value is less than the fault setpoint, the analysis continues.

[0058] The first fault analysis module interacts with the data analysis module to temporarily store fault waveforms by collecting data from the four cycles before the fault starts and the eight cycles after the fault starts. Based on the effective values ​​of the three-phase voltage and zero-sequence voltage fundamental wave in the eighth cycle after the fault starts, it determines whether it is a transient fault or a false grounding fault. If it is, it returns to the data analysis module and stores the fault waveform data. If it is not, it proceeds to the next module.

[0059] The fault point construction module interacts with the first fault analysis module to subtract the data corresponding to the first cycle from the data corresponding to the 2nd to 12th cycles, constructs a fault waveform diagram, and finds the fault initiation point by calculating the difference of sudden change.

[0060] The second fault analysis module interacts with the fault point construction module to obtain the three-phase current fault component, zero-sequence voltage fault component, and zero-sequence current fault component of the fault initiation point at different transient stages based on the fault initiation point. It performs multi-criteria analysis and calculation, and after comprehensive integration, determines whether there is a grounding fault below the power distribution equipment.

[0061] Furthermore,

[0062] The analysis system also includes a high-precision phase current measurement system for data acquisition, wherein the high-precision phase current measurement system is electrically connected to the data analysis module by a high-precision open-type phase current transformer;

[0063] The analysis system also includes an analysis return module, which interacts with the second fault analysis module to store waveform data based on the judgment result of the second fault analysis module and to return fault detection data based on the decrease value of the voltage component of the fault component. Specifically, when the voltage component is lower than 50% of the starting value, the data is returned to the data analysis module.

[0064] A high-precision open-type phase current transformer includes at least three 0.05SS-class high-precision open-type phase current transformers.

[0065] Example 1: Composition of on-site assessment equipment:

[0066] It consists of three "0.05SS-grade high-precision open-type phase current transformers" and one "local analysis and protection device";

[0067] Typical parameters of a high-precision open-type phase current transformer are:

[0068] Transformer ratio: 600A / 1A, accuracy class: 0.05SS (accuracy class of 0.05SS is already at the international leading level in the current technology), load: 0.1Ω;

[0069] That is, the ratio difference of 5%In, 20%In, 100%In, and 120%In is ≤0.05%, and the phase difference is ≤2';

[0070] 1% In ratio difference ≤ ±0.1%, phase difference ≤ ±4'.

[0071] The high-precision open-type phase current transformer adopts a special passive compensation principle and a secondary light load design.

[0072] The three high-precision open-type phase current transformers A, B, and C have extremely small phase difference errors, ensuring that the phase consistency of the current sampling of the three phase current transformers is controlled within ≤±4', which meets the technical requirements for synthesized zero-sequence current.

[0073] The high-precision current converter design method employs a small current transformer and an IV current converter. Specifically, the small current transformer has a transformation ratio of 1A / 0.01A and an accuracy class of 0.01SS (achieving an accuracy class of 0.01SS is already at an internationally leading level in current technology). That is, at 5%In, 20%In, 100%In, and 120%In, the ratio difference is ≤0.01% and the phase difference is ≤0.3'; at 1%In, the ratio difference is ≤0.02% and the phase difference is ≤0.6'.

[0074] The IV current converter uses a zero-load impedance transformation method, requiring only a resistor (typically 353 ohms) for the secondary winding of the converter to achieve a rated 3.53V voltage output.

[0075] The high-precision AD converter typically uses an independent 16-bit true dual-stage low-power 8-channel high-precision AD converter (model: AD7606), with a typical sampling frequency of 12.8kHz (256 points / cycle).

[0076] A typical DSP system uses a 32-bit floating-point DSP for fast digital signal processing and grounding algorithm analysis.

[0077] Using three high-precision open-type phase current transformers, zero-sequence current and negative-sequence current can be accurately synthesized, providing basic current data for grounding analysis algorithms.

[0078] On-site assessment of protection devices, design of 3 current simulation channels (I a I b I c ) and 4 voltage analog channels (U a U b U c The device collects the three-phase voltage and zero-sequence voltage of the system, as well as the phase current information of the three high-precision open-type phase current transformers. After the DSP system starts the algorithm and the grounding algorithm is used for judgment, the device executes the alarm or trip to complete the local fault identification.

[0079] The three current simulation channels are designed with filter capacitors of good capacitance consistency selected in the circuit, or the filter capacitors are removed directly to ensure the phase consistency of the three-phase current simulation channels.

[0080] An independent 16-bit true dual-stage low-power 8-channel high-precision AD converter is selected to ensure phase consistency during three-phase current analog-to-digital conversion.

[0081] Configured with a 232 / 485 communication interface for long-distance communication, and a reserved small wireless interface module for short-range communication networking, enabling the aggregation of all data within the substation and facilitating centralized data transmission over long distances.

[0082] 1. Real-time fault component monitoring under normal conditions:

[0083] The system monitors fault components in real time: zero-sequence voltage fault component and negative-sequence current fault component. If the fault exceeds a set value, the ground fault assessment and initiation algorithm is activated. The equipment adopts a fault initiation algorithm that combines zero-sequence voltage and negative-sequence current. The specific implementation method is as follows:

[0084] a) The equipment calculates the zero-sequence voltage fault component and the three-phase current fault component in real time. The calculation formula is as follows:

[0085] ΔU 0k =U k -U k-5*N

[0086] ΔI ak =I ak -I ak-5*N

[0087] ΔI bk =I bk -I bk-5*N

[0088] ΔI ck =I ck -I ck-5*N

[0089] The fault component is calculated by subtracting the corresponding sampling point from 5 cycles ago from the sampling point of the current cycle.

[0090] A typical sampling period is 256 points, i.e., N=256.

[0091] b) Calculate the fundamental effective values ​​of the zero-sequence voltage fault component and the negative-sequence current fault component every 10ms, i.e., the real-time data of ΔU0fault and ΔI2fault, and determine whether they exceed the set values.

[0092] ΔU 0故 ≥ΔU 0SET

[0093] or ΔI2故 ≥ΔI 2SET

[0094] If the value exceeds the set limit, the single-phase grounding analysis process will begin. If the value does not exceed the set limit, the periodic monitoring of system fault components will continue.

[0095] ΔU 0SET =min{15V, 5 times the maximum historical unbalanced voltage value}, and select accordingly.

[0096] ΔI 2SET =min{1A, 10 times the maximum historical unbalanced negative sequence current}, and select accordingly.

[0097] ΔU 0SET The zero-sequence voltage setting is either a fixed value or selected to avoid the maximum value of the maximum unbalanced voltage.

[0098] ΔI 2SET The negative sequence current setting is either a fixed value or selected to avoid the maximum unbalanced negative sequence current.

[0099] 2. After the ground fault assessment is initiated, wait 160ms to record the waveform after the fault. Then, temporarily store the waveform data of the first 4 cycles before the fault and the waveform data of the first 8 cycles after the fault is initiated. Specifically, (I a I b I c U a U b U c (3U0 has a total of 7 analog channels)

[0100] The grounding assessment process is as follows:

[0101] 1) Calculate the three-phase voltage and the effective value of the fundamental zero-sequence voltage of the 8th cycle after the fault to determine whether it is a transient fault or a false grounding fault. If it is a transient fault or a false grounding fault, return to the grounding assessment process and simultaneously store the fault waveform data.

[0102] 2) Calculate the Δ3U0 waveform curve by subtracting the data corresponding to the first wave from the data corresponding to the data corresponding to the 2nd to 12th waves.

[0103] 3) Locate the fault initiation point

[0104] Based on the waveform of Δ3U0, the starting point is found using the method of calculating the difference in mutation amount.

[0105] 4) Based on the determined fault initiation point, calculate the three-phase current fault component, zero-sequence voltage fault component, and zero-sequence current fault component in the first stage transient (transient first half-cycle) after the fault.

[0106] ΔU 暂0k =U0k -U 0k-N

[0107] ΔI 暂ak =I ak -I ak-N

[0108] ΔI 暂bk =I bk -I bk-N

[0109] ΔI 暂ck =I ck -I ck-N

[0110] ΔI 暂0k =ΔI 暂ak +ΔI 暂bk +ΔI 暂ck

[0111] The value of k ranges from the point of failure to a full cycle after the failure.

[0112] 4) Calculate the following judgment variables within the first half-cycle of the first stage transient (i.e., 1 / 8 cycle after the fault):

[0113] The initiation angle of the first-stage transient zero-sequence voltage fault component: α 起始角 ;

[0114] The correlation coefficient between the derivative of the transient zero-sequence voltage fault component and the zero-sequence current fault component in the first stage is: ρ1;

[0115] The correlation coefficient between the transient zero-sequence voltage fault component and the zero-sequence current fault component in the first stage is: ρ2;

[0116] The effective value of the transient zero-sequence current fault component in the first stage: ΔI 0第一阶段有效值 ;

[0117] The attenuated DC component of the transient zero-sequence current fault component in the first stage: ΔI 0DC ;

[0118] The calculation methods for the above-mentioned parameters are as follows:

[0119] a)α 起始角 The calculation method involves extracting the zero-sequence voltage waveform of the fifth integer cycle after the determined fault initiation point, and then calculating the initial phase angle α using Fourier transform. 起始角N＝5 The initial phase angle is approximately α. 起始角 .

[0120] b) The derivative of the transient zero-sequence voltage fault component is calculated using the difference method for zero-sequence voltage faults, i.e.

[0121] dU(k)=U(k)-U(k-1)

[0122] c) The correlation coefficient is calculated using the following formula:

[0123]

[0124] When calculating the correlation coefficient only within the first half-wave, N = 32 is used.

[0125] d)ΔI 0第一阶段有效值 The calculation uses the root mean square method.

[0126]

[0127] Since only the correlation coefficient within the first half-wave is calculated, N = 32 is taken.

[0128] e)ΔI 0DC Calculation method

[0129]

[0130] The attenuated DC component is calculated based on the one-cycle data value after avoiding the first half-wave impact component.

[0131] 5) Based on the determined fault initiation point, calculate the fault components of the three-phase current, the fault components of the zero-sequence voltage, and the fault components of the zero-sequence current in the 5th cycle after the second stage steady-state fault.

[0132] ΔU 稳0k =U 0k+5N -U 0k-N

[0133] ΔI 稳ak =I ak+5N -I ak-N

[0134] ΔI 稳bk =I bk+5N -I bk-N

[0135] ΔI 稳ck =I ck+5N -I ck-N

[0136] ΔI 稳0k =ΔI 稳ak +ΔI 稳bk +ΔI 稳ck

[0137] The effective value of the steady-state zero-sequence current fault component ΔI in the second stage 0第二阶段有效值 ;

[0138] The effective value of the second-stage steady-state negative sequence current fault component ΔI 2第二阶段有效值 ;

[0139] The angle α between the steady-state zero-sequence voltage fault component and the zero-sequence current fault component in the second stage U0-I0 .

[0140] The calculation methods for the above-mentioned parameters are as follows:

[0141] a)ΔI 0第二阶段有效值 The calculation uses the root mean square method.

[0142]

[0143] x(n) is selected as the discrete sampling point of the zero-sequence current fault component of the 5th cycle;

[0144] The second stage is the stable stage, and N = 256 is generally selected.

[0145] b)ΔI 2第二阶段有效值 Calculation method

[0146] Extract the waveform data of the three-phase current fault component within the 5th cycle after the fault.

[0147] The real and imaginary parts of the three-phase currents are obtained separately using the fundamental Fourier transform algorithm.

[0148] R a X a R b X b R c X c

[0149] Calculate the real and imaginary parts of the negative sequence current using the following formula.

[0150]

[0151] The magnitude of the negative sequence current was finally calculated.

[0152] ;

[0153] c)α U0-I0 Calculation method

[0154] Extract the fault component waveform data of zero-sequence voltage and zero-sequence current within the 5th cycle after the fault.

[0155] The fundamental initial phase angles α of the voltage and current are obtained using the fundamental Fourier transform algorithm. U0 α I0 ;

[0156] α U0-I0 =α U0 -α I0 ;

[0157] 6) On-site assessment process: The following convenient, simple and reliable on-site assessment methods are adopted to achieve rapid on-site fault identification and assessment.

[0158] Calculate the transient intensity variable.

[0159] For ungrounded systems, the following algorithms are used to calculate the fault results:

[0160] a) If BB > 2, it indicates a significant transient process. The transient zero-sequence voltage derivative current polarity determination method should be applied.

[0161] If ρ1 < ρ 1SET If the condition is met, it is considered grounded; otherwise, no judgment is made.

[0162] b) If BB≤2, it indicates that the transient process is not obvious, and the transient zero-sequence voltage and current polarity determination method is applied:

[0163] If ρ2 < ρ 2SET If the condition is met, it is considered grounded; otherwise, no judgment is made.

[0164] c) Steady-state fault negative sequence current discrimination method

[0165] If ΔI2>ΔI 2SET If the condition is met, it is considered grounded; otherwise, no judgment is made.

[0166] d) Steady-state zero-sequence voltage-current angle discrimination method:

[0167] If α U0-I0 If the angle is ∈(65°~115°), then it is considered grounded; otherwise, no judgment is made.

[0168] e) Result fusion: If at least two results in the above algorithm result are grounded, then the final judgment is grounded; otherwise, it is considered not a fault.

[0169] For neutral-point grounded systems via arc-suppression coils, the following algorithms are used to calculate fault results:

[0170] a) If α 起始角 For values ​​∈(-15°~15°), perform the transient attenuation DC discrimination method:

[0171] ΔI DC ≥ΔI DCSET ;

[0172] b) If BB > 2, it indicates a significant transient process. The transient zero-sequence voltage derivative current polarity determination method is used.

[0173] If ρ1 < ρ 1SET If it is true, then it is grounded; otherwise, it is not judged.

[0174] c) If BB≤2, it indicates that the transient process is not obvious. Transient zero-sequence voltage and current polarity determination method:

[0175] If ρ2 < ρ 2SET If it is true, then it is grounded; otherwise, it is not judged.

[0176] d) Steady-state fault negative sequence current discrimination method

[0177] If ΔI2>ΔI 2SET If the condition is met, it is considered grounded; otherwise, no judgment is made.

[0178] e) Steady-state zero-sequence voltage-current angle discrimination method:

[0179] If α U0-I0 If the angle is ∈(250°~265°), then it is grounded; if it does not meet the condition, then no judgment is made.

[0180] f) Result fusion: In the above algorithm results, as long as at least 2 results (or at least 3 results if the transient attenuation DC discrimination method can be used) are judged as grounding, the final judgment is grounding; otherwise, it is considered non-fault.

[0181] 7) On-site assessment of fault recovery process

[0182] After fault diagnosis, the changes in 3U0 are monitored in real time. When 3U0 drops below 50% of the starting value, the fault monitoring is returned after a 1-second delay, and real-time variable monitoring under normal conditions is performed again.

[0183] It should be noted that similar labels and letters in the following figures indicate similar items. Therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures. In addition, the terms "first", "second", "third", etc. are used only to distinguish descriptions and should not be construed as indicating or implying relative importance.

[0184] Finally, it should be noted that the above-described embodiments are merely specific implementations of the present invention, used to illustrate the technical solutions of the present invention, and not to limit it. The scope of protection of the present invention is not limited thereto. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that any person skilled in the art can still modify or easily conceive of changes to the technical solutions described in the foregoing embodiments within the technical scope disclosed in the present invention, or make equivalent substitutions for some of the technical features; and these modifications, changes, or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention. All should be covered within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A method for diagnosing single-phase grounding faults in a power distribution network, characterized in that, Includes the following steps, S1. Collect the fault components of the power distribution equipment and obtain the fundamental effective value of the fault components; S2. Set a fault setting value, and determine whether the fundamental effective value is greater than or equal to the fault setting value. If the fundamental effective value is greater than or equal to the fault setting value, proceed to the next step; if the fundamental effective value is less than the fault setting value, proceed to S1. S3. Collect the 4-cycle data before the fault and the 8-cycle data after the fault starts to temporarily store the fault waveform. Based on the effective values ​​of the three-phase voltage and zero-sequence voltage fundamental wave of the 8th cycle after the fault starts, determine whether it is a transient fault or a false grounding fault. If it is, proceed to S1 and store the fault waveform data. If not, proceed to the next step. S4. Subtract the data corresponding to the first cycle from the data corresponding to the data corresponding to the 2nd to 12th cycles to construct a fault waveform diagram and find the fault initiation point by calculating the difference of sudden change. S5. Based on the fault initiation point, obtain the three-phase current fault component, zero-sequence voltage fault component, and zero-sequence current fault component of the fault initiation point in different transient stages, perform multi-criteria analysis and calculation, and determine whether there is a grounding fault below the power distribution equipment after comprehensive integration. During the process of collecting the fault components of the power distribution equipment, the zero-sequence voltage fault component and the three-phase current fault component of the power distribution equipment are calculated in real time to obtain the fault components. The fault components are obtained by subtracting the corresponding sampling point 5 cycles ago from the sampling point of the current cycle. S2 includes setting voltage fault settings and current fault settings; If the zero-sequence voltage fault component is greater than or equal to the real-time voltage fault setting and / or the three-phase current fault component is greater than or equal to the current fault setting, then proceed to step S3; S5 includes the following steps: S5.

1. Obtain the first judgment variable within the first half-cycle of the first stage transient state after the fault, wherein the first judgment variable includes the starting angle of the first stage transient zero-sequence voltage fault component, the correlation coefficient between the derivative of the first stage transient zero-sequence voltage fault component and the zero-sequence current fault component, the correlation coefficient between the first stage transient zero-sequence voltage fault component and the zero-sequence current fault component, the effective value of the first stage transient zero-sequence current fault component, and the attenuated DC component of the first stage transient zero-sequence current fault component. S5.

2. Obtain the second judgment variable of the 5th cycle of the second stage steady state after the fault, wherein the second judgment variable includes the effective value of the zero-sequence current fault component of the second stage steady state, the effective value of the negative-sequence current fault component of the second stage steady state, and the angle between the zero-sequence voltage fault component and the zero-sequence current fault component of the second stage steady state. S5.

3. Determine the grounding fault based on the numerical relationship between the first judgment variable and the second judgment variable.

2. The method for judging single-phase grounding faults in a distribution network according to claim 1, characterized in that, In the process of determining the grounding fault, the fault assessment for the ungrounded system includes: the numerical relationship includes at least 4 numerical relationships, and if the grounding fault is determined based on at least 2 of the numerical relationships, then the grounding fault is finally determined.

3. The method for judging single-phase grounding faults in a distribution network according to claim 1, characterized in that, In the process of determining the grounding fault, the fault assessment of the neutral point grounded through the arc suppression coil includes: the numerical relationship includes at least 4 numerical relationships, and if the grounding fault is determined based on at least 2 of the numerical relationships, then the grounding fault is finally determined.

4. The method for judging single-phase grounding faults in a distribution network according to claim 3, characterized in that, In the process of determining the ground fault, when the numerical relationship includes a transient attenuation DC relationship, the determination is made based on the five numerical relationships. If the ground fault is determined based on at least three of the numerical relationships, then the ground fault is finally determined.

5. The method for judging single-phase grounding faults in a distribution network according to claim 1, characterized in that, The assessment method also includes the following steps: S6. Based on the determination result of S5, store the waveform data, and perform fault detection return based on the decrease value of the voltage component of the fault component, wherein when the voltage component is lower than 50% of the start value, return to S1.

6. A system for assessing single-phase grounding faults in a power distribution network, used to implement the method described in any one of claims 1-5, characterized in that, include, The data processing module is used to collect fault components of power distribution equipment and obtain the fundamental effective value of the fault components; The data analysis module is used to determine whether the fundamental frequency effective value is greater than or equal to the fault set value by setting a fault set value. If the fundamental frequency effective value is greater than or equal to the fault set value, the process proceeds to the next module; if the fundamental frequency effective value is less than the fault set value, the analysis continues. The first fault analysis module interacts with the data analysis module to temporarily store fault waveforms by collecting data from the four cycles before the fault and the eight cycles after the fault starts. Based on the effective values ​​of the three-phase voltage and the fundamental wave of the zero-sequence voltage in the eighth cycle after the fault starts, it determines whether it is a transient fault or a false grounding fault. If it is, it returns to the data analysis module and stores the fault waveform data; otherwise, it proceeds to the next module. The fault point construction module interacts with the first fault judgment module to subtract the data corresponding to the first cycle from the data corresponding to the 2nd to 12th cycles, constructs a fault waveform diagram, and finds the fault initiation point by calculating the difference of sudden change. The second fault analysis module interacts with the fault point construction module to obtain the three-phase current fault component, zero-sequence voltage fault component, and zero-sequence current fault component of the fault initiation point at different transient stages based on the fault initiation point. It performs multi-criteria analysis and calculation, and after comprehensive integration, determines whether there is a grounding fault below the power distribution equipment.

7. The system for assessing single-phase grounding faults in a power distribution network according to claim 6, characterized in that, The analysis system also includes a high-precision phase current measurement system for data acquisition, wherein the high-precision phase current measurement system is electrically connected to the data analysis module via a high-precision open-type phase current transformer. The analysis system also includes an analysis return module, which interacts with the second fault analysis module to store the waveform data based on the judgment result of the second fault analysis module, and performs fault detection return based on the decrease value of the voltage component of the fault component. When the voltage component is lower than 50% of the start value, the data is returned to the data analysis module. The high-precision open-type phase current transformer includes at least three 0.05SS-class high-precision open-type phase current transformers.

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