Single-phase grounding fault determination method and device for distribution network based on phase current analysis

Abstract

The application provides a distribution network single-phase grounding fault determination method and device based on phase current comprehensive analysis. The phase current collected at the outgoing end of each line of the distribution network is used as a judgment signal to monitor the zero sequence current amplitude of the three-phase current synthesis to determine whether a single-phase grounding fault occurs. If a single-phase grounding fault occurs, the phase current signals before and after the fault occur are obtained for signal processing and fault characteristic analysis. The transient sudden change characteristics and steady-state phase characteristics of the phase current are comprehensively analyzed, and finally, the line determination result is obtained according to the comprehensive analysis algorithm. The application can determine multiple types of single-phase grounding faults such as metal, high resistance and intermittent arc grounding, expands the feasible region of the line determination technology, solves the problem that the positioning technology is only applicable to a single fault type, and simultaneously, only uses the phase current as a judgment signal, can obtain the signal through the phase current transformer already installed in the transformer substation, does not need to additionally install a zero sequence voltage or current transformer, and has strong technical adaptability and robustness.

Description

Technical Field

[0001] This invention belongs to the field of power automation technology, and relates to the field of single-phase grounding faults in distribution networks. More specifically, it relates to a method and device for determining single-phase grounding faults in distribution networks based on phase current analysis. Background Technology

[0002] With economic development, the coverage area of ​​my country's power distribution network is continuously expanding, and the proportion of connected power electronic equipment is constantly increasing. This has led to various types of single-phase grounding faults in the distribution network, with complex characteristics. However, the feasible domain of traditional line identification and location technologies is relatively small, making them unsuitable for various fault types and challenging the reliability of location. To ensure the quality of life and production for a large number of power users, it is urgent to propose a fault line identification technology with a feasible domain encompassing multiple fault types.

[0003] Common fault location techniques include: the test circuit method, the zero-sequence amplitude and phase comparison method, and the first half-wave method. The test circuit method, a traditional fault location method, involves on-site personnel sequentially operating the circuit breakers of each substation line to check if the fault is located on that outgoing line when a single-phase ground fault occurs. If the single-phase ground fault is on that outgoing line, the fault disappears after the switch is opened; if the fault is on another line, the fault does not disappear after the switch is operated. This method determines the fault location through multiple circuit breaker and sectionalizing switch openings and closings, greatly increasing the wear and tear on the circuit breakers and switches, affecting their service life. Furthermore, each switch opening and closing impacts the electrical equipment in the system, causing irreversible damage. Therefore, current and voltage signals are increasingly being used for fault location assessment on-site. The zero-sequence amplitude and phase comparison method is a widely used technique for determining single-phase ground faults in distribution network systems with ungrounded neutral points. When a single-phase ground fault occurs in a distribution network system with multiple outgoing lines, the zero-sequence current to ground of each outgoing line returns to the line through the grounding point. This causes a difference in the direction and amplitude of the zero-sequence current between the faulty and non-faulty lines. The zero-sequence current of the faulty line flows from the line to the busbar and has the largest amplitude, while the zero-sequence current of the normal line flows from the busbar to the line and has a smaller amplitude. This allows for relatively sensitive identification of the faulty line. However, with the increasing proportion of power electronic equipment in the system, intermittent arcing has occurred at the grounding fault point, making the steady-state characteristics of the current ambiguous and compromising the reliability of the line identification technology. Furthermore, due to the compensation effect of the arc suppression coil, this technology is not applicable to systems where the neutral point is grounded via an arc suppression coil. The first half-wave method is a technique for identifying the faulty line by utilizing the characteristics of the first half-wave of the zero-sequence current and voltage after a single-phase ground fault. This technique is based on the fact that after a single-phase ground fault occurs, the polarities of the first half-wave zero-sequence current and zero-sequence voltage on the faulty line are opposite, while the polarities of the zero-sequence current and voltage on the non-faulty line are the same. This allows for the identification of the faulty line. However, when a high-resistance grounding occurs in the system, the transient polarity characteristics of its zero-sequence current and voltage are weak and easily affected by harmonics and noise, thus failing to meet the requirements for line judgment. Summary of the Invention

[0004] To overcome the shortcomings of existing technologies, this invention proposes a method and device for determining single-phase grounding faults in distribution networks based on comprehensive phase current analysis. Using phase currents collected from the outgoing terminals of each line in the distribution network as judgment signals, the method first determines whether a single-phase grounding fault has occurred by monitoring the magnitude of the zero-sequence current synthesized from the three-phase currents. When the zero-sequence current amplitude exceeds a threshold, a single-phase grounding fault is determined to have occurred. Phase current signals before and after the fault occurrence are acquired for signal processing and fault feature analysis. The phase current signals are processed using transient and steady-state algorithms, comprehensively analyzing the transient change characteristics and steady-state phase characteristics of the phase current. Finally, the line determination result is obtained based on the comprehensive analysis algorithm. This method, by comprehensively analyzing the transient change characteristics and steady-state phase characteristics of the phase current, can determine multiple types of single-phase grounding faults, including metallic, high-resistance, and intermittent arc-grounded faults, expanding the feasible domain of line determination technology and solving the problem that location technology is only applicable to a single fault type. Furthermore, by using only phase current as the judgment signal, the line determination technology can obtain signals from the phase current transformers already installed in the substation, eliminating the need for additional zero-sequence voltage or current transformers, thus exhibiting strong technical adaptability and robustness.

[0005] Specifically, this invention proposes a method for determining single-phase grounding faults in distribution networks based on comprehensive phase current analysis, characterized by the following steps: S1: The three-phase current on the line is collected by the positioning device installed at the outgoing end of each line of the distribution network and the zero-sequence current is synthesized. The line fault is determined according to the set zero-sequence current amplitude threshold. S2: When the zero-sequence current amplitude is greater than the threshold, it is determined that a single-phase ground fault has occurred in the system. The device protection extracts the fault waveform and performs fault characteristic analysis. S3: Calculate the exact time of fault occurrence using wavelet modulus maxima; then make judgments based on transient mutation algorithm and steady-state phase algorithm respectively, and obtain the corresponding numerical results for both. S4: Based on the weighting coefficients calculated from the zero-sequence current amplitude of the line, the phase current is comprehensively analyzed and judged using a comprehensive analysis algorithm combined with the numerical results of transient and steady-state algorithms. When the judgment result is greater than the threshold value, the line is determined to be a faulty line; otherwise, it is a normal line.

[0006] Preferably, step S1 includes: According to the formula Zero-sequence current can be obtained, where , , These represent the three-phase currents on the line. This represents the synthesized zero-sequence current.

[0007] Preferably, step S2 includes: By setting the zero-sequence current amplitude threshold using on-site data, the line fault and normal conditions can be distinguished.

[0008] Preferably, step S3 includes: When a single-phase ground fault occurs, the zero-sequence current will undergo a sudden change at the moment of fault occurrence. The wavelet modulus maxima algorithm is used to process the zero-sequence current, identifying the point and timing of the current abrupt change, thus determining the precise time of fault occurrence. By analyzing the direction of the transient current abrupt change and the steady-state phase characteristics, and using both transient abrupt change and steady-state phase algorithms to determine whether the line is faulty, the judgment result RES based on the transient abrupt change algorithm is obtained. ti The steady-state phase algorithm judgment result RES si .

[0009] Preferably, the determination based on the transient mutation algorithm includes: S31: Based on the sampling point x0 corresponding to the accurate time of fault occurrence obtained from the wavelet modulus maxima, a calculation interval is defined near the sampling point. This interval can include the accurate time of fault occurrence x0. The calculation interval is set to [x0-4, x0+5]. S32: Calculate the difference between the corresponding function value and the adjacent value within the calculation interval, and take the absolute value of the result. Find the sampling point corresponding to the maximum change value as the point for determining the direction of the mutation. S33: Determine the direction of the phase current change by using the function value corresponding to the point where the change direction is determined and the reference value corresponding to the sampling point at the accurate time of the fault occurrence; S34: By comparing the sudden change direction Dir of the three-phase current obtained from the outgoing terminal of the same line, if two phases have the same Dir calculation result, but the other phase is different, it can be judged as a faulty line; if all three phases have the same Dir calculation result, it can be judged as a normal line.

[0010] Preferably, step S32 includes: Assuming the phase current is y = f(x) Where x is the sampling point; y is the current value; Find the corresponding maximum change value y using the following formula. max and its corresponding sampling point x max And obtain the mutation direction Dir: y max =max{|f(x0-4)-f(x0-3)|,|f(x0-3)-f(x0-2)|...|f(x0+5)-f(x0+6)|} x max =f -1 (y max )

[0011] Preferably, the determination based on the steady-state phase algorithm includes: When a single-phase ground fault occurs, the exact time of fault occurrence is determined as x0 by the wavelet modulus maxima. Then, a fault current signal with a length of one cycle is acquired two cycles after the exact time of fault occurrence. The zero-sequence current value of the current line is subtracted to obtain the positive-sequence and negative-sequence currents. The phase of each current is then determined based on its phase. And determine its range, and determine the result value as follows:

[0012] By comparing the phase results of each outgoing line, the faulty line can be identified if the results differ from those of the normal line.

[0013] Preferably, step S4 includes: According to the formula Calculate the weighting coefficient δ. Among the settings As a reference value for the adjustment coefficient, it is set by... Different values ​​are used to complete the adaptive process for different power distribution network systems. A value of 5A is typically used; I is the amplitude of the zero-sequence current of the line. Using the function RES i =δ·RES si +(1-δ)RES ti Among them RES i The value of the judgment result for line i; RES si The value of the steady-state phase process judgment result for line i; RES ti The numerical value represents the result of judging the transient change process of line i; By comprehensively considering the judgment results of the transient mutation algorithm and the steady-state phase algorithm, the judgment numerical result is obtained to determine whether this line is a faulty line.

[0014] Considering the existence of harmonic measurement errors in the system, which may result in false alarms or no alarms, a threshold value RES0 = 0.2 is set for the results. When the result is greater than the threshold value, line i can be identified as a faulty line.

[0015] This invention also proposes a single-phase grounding fault determination device for distribution networks based on phase current comprehensive analysis, comprising: Fault identification module: The positioning device installed at the outgoing end of each line in the distribution network collects the three-phase current on the line and synthesizes the zero-sequence current. The module determines whether the line is faulty based on the set zero-sequence current amplitude threshold. Feature analysis module: When the zero-sequence current amplitude is greater than the threshold, it is determined that a single-phase ground fault has occurred in the system. The device protection extracts the fault waveform and performs fault feature analysis. Algorithm analysis module: Calculates the exact time of fault occurrence using wavelet modulus maxima; then makes judgments based on transient mutation algorithm and steady-state phase algorithm respectively, and obtains the corresponding numerical results for both. Comprehensive Judgment Module: Based on the weighting coefficients calculated from the zero-sequence current amplitude of the line, the module uses a comprehensive analysis algorithm combined with the numerical results of transient and steady-state algorithms to complete the comprehensive analysis and judgment of the phase current. When the judgment result is greater than the threshold value, the line is determined to be a faulty line; otherwise, it is a normal line.

[0016] The present invention also proposes a computer-readable storage medium having a computer program stored thereon, which, when executed by a processor, implements the steps of the method described in the present invention.

[0017] The advantages of this invention are: (1) By comprehensively analyzing the transient change characteristics and steady-state phase characteristics of phase current, this invention can determine multiple types of single-phase grounding faults, such as metal, high resistance and grounding through intermittent arc, thus expanding the feasible domain of line determination technology and solving the problem that the location technology is only applicable to a single type of fault. (2) Only the phase current is used as the judgment signal. The line judgment technology can obtain the signal through the phase current transformers already installed in the substation. There is no need to install zero-sequence voltage or current transformers. It is technically and economically efficient. (3) This invention is applicable to distribution network systems with ungrounded neutral points and systems grounded through arc suppression coils, and the line determination technology is robust.

[0018] (4) The method has a simple logic for determining the line, strong programming feasibility, and high engineering application value. Attached Figure Description

[0019] Figure 1 This is a structural diagram of a neutral point grounded system via an arc suppression coil.

[0020] Figure 2 This is a transient equivalent circuit diagram.

[0021] Figure 3 It is an orthogonal network diagram.

[0022] Figure 4 This is a flowchart of the circuit determination method described in this invention.

[0023] Figure 5 This is a structural diagram of the simulation experiment system.

[0024] Figure 6 This is a normal circuit current waveform.

[0025] Figure 7 This is the current waveform of the faulty line. Detailed Implementation

[0026] The present application will be further described below with reference to the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solutions of the present invention, and should not be construed as limiting the scope of protection of the present application.

[0027] This embodiment uses a neutral point grounded via an arc suppression coil system for illustration. The system structure diagram is attached. Figure 1 As shown. The system includes four outgoing lines, each with a signal acquisition device installed at its outgoing end to collect the phase current signal required for line determination technology. The single-phase ground fault occurred in line 2.

[0028] After a single-phase ground fault occurs, the system phase current is in a transient process within 0.5 to 1 cycle, with violent current fluctuations, before entering a steady-state process. The transient and steady-state processes of the phase current contain rich fault information. This invention analyzes the transient and steady-state characteristics of the phase current in the system, respectively.

[0029] A single-phase ground fault causes a deviation in the neutral point voltage of the system, resulting in changes in the phase voltages of each phase and thus inducing the charging and discharging process of the system's capacitance to ground. According to the superposition theorem, the phase voltage can be divided into the neutral point voltage and the phase voltages before the fault, which act as a superposition on the line.

[0030]

[0031]

[0032]

[0033] In the formula, The three-phase voltages after a single-phase ground fault occurs; The three-phase voltages before a single-phase ground fault occurs; This is the neutral point voltage.

[0034] Taking an arc-suppression coil grounding system as an example, the capacitive current on each line flows into the ground, then through the fault point into phase A of the faulty line, and back to the original line via the busbar and transformer. To simplify the analysis process and calculate the transient current characteristics, multiple inductors and capacitors in the equivalent circuit can be combined into a single inductor and capacitor. This approximation leads to the loss of high-frequency components, but the transient process can still be qualitatively analyzed. The equivalent transient circuit diagram of the system is shown in the attached figure. Figure 2 As shown.

[0035] Where C0 is the capacitance to ground of the distribution network; L0 is the equivalent inductance of the three-phase lines, power sources, and transformers; R0 is the equivalent resistance of the line, which includes grounding resistance and arc resistance; RL And L represents the active power loss resistance and inductance of the arc suppression coil; u0 is the zero-sequence power supply voltage. From this, the transient current i of the fault phase on the faulty line can be obtained. f The transient inductance current i on the arc suppression coil L and transient capacitive current i in the line C Superposition:

[0036] Where ω is the power frequency angular frequency; The initial phase of the zero-sequence voltage; τ L ω is the time constant of the inductor circuit; f τ is the angular frequency of the free oscillating current. C I is the time constant of the inductor circuit. Cm I Lm , I' Cm , I' Lm These represent the steady-state amplitude and the decay amplitude of the capacitor and inductor currents, respectively.

[0037] The above formula shows that there is a DC attenuation component in the phase current, causing a sudden change in the phase current after a single-phase ground fault, followed by attenuation. However, this attenuation component is affected by the grounding resistance; the larger the resistance, the smaller the sudden change. In contrast, the fault current in a normal system line flows from the line-to-ground capacitance to the fault point, through the faulty phase line along the fault path to the busbar, and back to its respective line. This results in a difference in the flow direction of the fault current on the faulty line compared to the non-faulty lines: the direction of the sudden change in the faulty phase in the faulty line differs from that in other lines.

[0038] Meanwhile, due to the large time constant of the arc suppression coil circuit, the compensation current is extremely small during the transient process of phase current change in the early stage of the fault. Therefore, the transient characteristics of phase current are the same for the neutral point ungrounded system and the system with arc suppression coil.

[0039] In summary, after a low-resistance or intermittent arcing single-phase ground fault occurs in a distribution network system, the phase current of the faulty phase in the faulty line changes direction differently from that of the non-faulty phases, while the three-phase currents at the beginning of the non-faulty line change direction in the same direction. However, when a high-resistance ground fault occurs, the amplitude of the fault current attenuation component decreases due to the larger ground resistance, resulting in blurred transient change characteristics.

[0040] Analysis of the transient formula shows that the sudden change is caused by the DC component. Therefore, the sudden change should be the largest current change at the moment of the fault and decrease as the DC component decays.

[0041] Therefore, this invention designs a method for determining the direction of a sudden current change based on the local maximum change value, comprising the following steps: First, the sampling point x0 corresponding to the accurate occurrence time of the fault is obtained from the wavelet modulus maxima, and a calculation interval is defined near the sampling point, which can include the fault occurrence time x0.

[0042] In this invention, the calculation interval is set to [x0-4, x0+5].

[0043] A well-designed interval can avoid errors caused by inaccurate sampling points at the time of a fault.

[0044] Subsequently, the corresponding function value within the calculation interval is subtracted from the adjacent value, and the absolute value of the result is taken to find the sampling point corresponding to the maximum change value as the point for determining the direction of the mutation.

[0045] Assuming the phase current is y = f(x) Where x is the sampling point; y is the current value. Therefore, the corresponding maximum change y can be found using the following formula. max and its corresponding sampling point x max And obtain the mutation direction Dir.

[0046] .y max =max{|f(x0-4)-f(x0-3)|,|f(x0-3)-f(x0-2)|...|f(x0+5)-f(x0+6)|} x max =f -1 (y max )

[0047] Finally, the direction of the phase current change is determined by using the function value corresponding to the point where the change direction is determined and the reference value corresponding to the sampling point at the time of the fault.

[0048] By comparing the abrupt change directions of the three-phase currents obtained from the outgoing terminals of the same line, if two phases have the same Dir calculation result while the other phase is different, it can be determined that the line is faulty; if all three phases have the same Dir calculation result, it can be determined that the line is normal.

[0049] Based on the principle of symmetrical component analysis, fault current can be decomposed into positive-sequence, negative-sequence, and zero-sequence currents. In a neutral-point ungrounded system, the zero-sequence current in the faulty line is opposite in direction and has the largest amplitude to the zero-sequence current in the non-faulty line. However, in a system with an arc-suppression coil at the neutral point, the zero-sequence current is affected by the compensation current of the arc-suppression coil, and the zero-sequence current characteristics on the faulty and non-faulty lines are no longer obvious, making it impossible to reliably determine the fault location. To avoid interference from the zero-sequence current, this invention subtracts the zero-sequence current from the fault current and analyzes the remaining positive-sequence and negative-sequence currents.

[0050] Since the distribution network diagrams corresponding to positive-sequence current and negative-sequence current are the same, this embodiment uses positive-sequence current as an example for analysis. To simplify the analysis process, the positive-sequence network diagram of the system is simplified while ensuring the correctness of the results. The structure diagram is attached. Figure 3 As shown.

[0051] In the picture: Z1 is the positive sequence voltage at the fault point; Z2 is the positive sequence line impedance upstream of the fault point in the faulty line; Z'2 is the positive sequence impedance of the downstream line and load at the fault point; Z ∑ The equivalent impedances of lines 1, 3, and 4 in normal circuits; Z T This is the equivalent positive sequence impedance of the transformer and its high-voltage side.

[0052] Assume the positive sequence current at the fault point is The positive sequence current obtained at the beginning of the faulty line is:

[0053] The sum of the positive sequence currents in normal circuits 1, 3, and 4 is:

[0054] The positive-sequence current in the fault current is shunt at the fault point, flowing to the upstream and downstream lines respectively. The positive-sequence current in the upstream line continues to shunt at the busbar, flowing to the transformer side and the normal line respectively. Because the positive-sequence impedance of the lines and the equivalent positive-sequence impedance of the transformer and high-voltage side in the system are much smaller than the positive-sequence impedance at the load, Z'2 >> Z2 + Z K Z ∑ >>Z T This results in most of the positive sequence current being concentrated between the fault point and the transformer, with less content in the downstream lines and normal lines. Furthermore, the phase of the positive sequence current differs between the fault path and the non-fault path.

[0055] Meanwhile, since the arc suppression coil circuit does not exist in the positive sequence network diagram, the presence or absence of the arc suppression coil will not affect the distribution and phase characteristics of the positive sequence current.

[0056] In summary, when a metallic or high-resistance single-phase ground fault occurs, the positive-sequence and negative-sequence currents collected at the outgoing terminals of each line in the distribution network system will differ: the positive-sequence and negative-sequence currents collected in the faulty line are out of phase with those in the non-faulty lines. However, when an arc-ground fault occurs, due to the intermittent nature of the grounding at the fault point, the steady-state process of the phase current will no longer be stable, making it impossible to obtain accurate current phase characteristics for judgment.

[0057] Because the positive-sequence and negative-sequence currents are shunt at the fault point and then diverted to the normal line via the faulty line and busbar, the phase difference between the positive-sequence and negative-sequence currents in the faulty line and the normal line is 180°. However, in actual operating conditions, due to interference from harmonics, noise, and errors in measuring instruments, the current phase difference is difficult to meet the theoretical value. Therefore, this invention determines the phase result based on the range of the current phase to complete the judgment.

[0058] When a single-phase ground fault occurs, the fault occurrence time is determined as x0 by the wavelet modulus maxima. Then, a fault current signal with a length of one cycle is acquired two cycles after the fault occurrence time. The zero-sequence current value of the current line is subtracted to obtain the positive-sequence and negative-sequence currents. The phase of each current is then determined based on its phase. And determine its range, and determine the result value.

[0059] By comparing the phase results of each outgoing line, the faulty line can be identified if the results differ from those of the normal line.

[0060] As can be seen from the above analysis, when a low-resistance single-phase ground fault occurs in the system, it can be judged by transient or steady-state algorithms. However, when a high-resistance or intermittent arc ground fault occurs, both algorithms have their limitations.

[0061] Therefore, this invention considers combining the characteristics of two algorithms with a comprehensive analysis algorithm to expand the feasible domain of line determination technology and complete line determination and location under various grounding conditions. Considering the different grounding methods of the neutral point in the distribution network and the different proportions of power electronic equipment connected to the system, resulting in differences in the magnitude of the zero-sequence current after a grounding fault, the fundamental amplitude of the zero-sequence current in the line can be used as an adjustment coefficient to set... As a reference value for the adjustment coefficient, it is set by... Different values ​​are used to complete the adaptive process for different power distribution network systems. A value of 5A is typically used. The weighting coefficient δ and the resulting function are as follows:

[0062] RES i =δ·RES si +(1-δ)RES ti Among them, RES i The value of the judgment result for line i; RES si The value of the steady-state phase process judgment result for line i; RES ti This represents the numerical result of the transient change process judgment for line i. When the judgment result based on the transient or steady-state algorithm indicates a faulty line, the result value RES is... ti or RESsi It is 1 if it is true, otherwise it is 0.

[0063] The numerical result corresponding to line i can be calculated using the above formula. Considering the existence of harmonic measurement error in the system, the result may be false or fail to operate. In this embodiment, the result threshold value RES0 = 0.2 is set. When the result is greater than the threshold value, line i can be judged as a faulty line.

[0064] The simulation experiment structure diagram is as follows Figure 5 As shown. To verify the reliability of the proposed line determination technology, this embodiment uses ATP power system simulation software for simulation experiments. The simulation experiment includes four lines, from top to bottom: lines 1, 2, 3, and 4. Lines 1 and 4 are cable lines, and lines 2 and 3 are overhead lines. A single-phase ground fault occurs in phase A of line 2, with a grounding resistance of 5000Ω, and the fault occurs at 0.0042 seconds.

[0065] For single-phase grounding faults in neutral point grounded systems with arc suppression coils or neutral point ungrounded systems, the single-phase grounding fault determination technology for distribution networks based on phase current comprehensive analysis disclosed in this application can be used. After installing positioning devices at each outgoing terminal of the distribution network system, the fault characteristics are analyzed by acquiring the phase current on the line, and the faulted line can be determined in the end. The specific implementation steps are attached. Figure 4 As shown.

[0066] Step 1: Collect the three-phase current on each line by installing a positioning device at the outgoing end of each line in the distribution network and synthesize the zero-sequence current. Determine whether there is a line fault based on the set zero-sequence current amplitude threshold. Step 2: When the zero-sequence current amplitude is greater than the threshold, it is determined that a single-phase ground fault has occurred in the system. The device protection extracts the fault waveform and performs fault characteristic analysis. Step 3: Calculate the exact time of fault occurrence using wavelet modulus maxima; then, make judgments based on the transient mutation algorithm and the steady-state phase algorithm respectively, and obtain the corresponding numerical results for both. Step 4: Based on the weighting coefficients calculated from the zero-sequence current amplitude of this line, use the comprehensive analysis algorithm combined with the numerical results of transient and steady-state algorithms to complete the comprehensive analysis and judgment of the phase current. When the judgment result is greater than the threshold value, the line is determined to be a faulty line; otherwise, it is a normal line.

[0067] The current waveform of normal circuit 1 is shown in the attached figure. Figure 6 As shown in the attached figure, the current waveform of faulty line 2 is as follows. Figure 7 As shown in Table 1, after obtaining the phase current signals at the outgoing terminals of each line for fault characteristic analysis, the steady-state and transient judgment results of each line and the line judgment results are as follows: Table 1

[0068] The results from step 4 show that under high-resistance grounding conditions, the direction of current abrupt change is not obvious, but the steady-state phase characteristics of the positive and negative sequence currents are significant, and the faulty line is in phase with the normal line. Based on the comprehensive analysis algorithm, which analyzes the transient and steady-state characteristics of the current, line 2 can be correctly selected as the faulty line.

[0069] This invention also proposes a single-phase grounding fault determination device for distribution networks based on phase current comprehensive analysis, comprising: Fault identification module: The positioning device installed at the outgoing end of each line in the distribution network collects the three-phase current on the line and synthesizes the zero-sequence current. The module determines whether the line is faulty based on the set zero-sequence current amplitude threshold. Feature analysis module: When the zero-sequence current amplitude is greater than the threshold, it is determined that a single-phase ground fault has occurred in the system. The device protection extracts the fault waveform and performs fault feature analysis. Algorithm analysis module: Calculates the exact time of fault occurrence using wavelet modulus maxima; then makes judgments based on transient mutation algorithm and steady-state phase algorithm respectively, and obtains the corresponding numerical results for both. Comprehensive Judgment Module: Based on the weighting coefficients calculated from the zero-sequence current amplitude of the line, the module uses a comprehensive analysis algorithm combined with the numerical results of transient and steady-state algorithms to complete the comprehensive analysis and judgment of the phase current. When the judgment result is greater than the threshold value, the line is determined to be a faulty line; otherwise, it is a normal line.

[0070] Furthermore, the present invention also proposes a computing device comprising: one or more processors, a memory, and one or more programs, wherein the one or more programs are stored in the memory and configured to be executed by the one or more processors, the one or more programs comprising instructions for performing any of the methods described in the present invention.

[0071] The present invention also proposes a computer-readable storage medium for storing one or more programs, said one or more programs including instructions that, when executed by a computing device, cause the computing device to perform the method according to the present invention.

[0072] The applicant of this invention has provided a detailed description of the embodiments of the invention in conjunction with the accompanying drawings. However, those skilled in the art should understand that the above embodiments are merely preferred embodiments of the invention. The detailed description is only intended to help readers better understand the spirit of the invention and is not intended to limit the scope of protection of the invention. On the contrary, any improvements or modifications made based on the inventive spirit of the invention should fall within the scope of protection of the invention.

Claims

1. A method for determining single-phase grounding faults in distribution networks based on comprehensive phase current analysis, characterized in that, Includes the following steps: S1: The three-phase current on the line is collected by the positioning device installed at the outgoing end of each line of the distribution network and the zero-sequence current is synthesized. S2: When the zero-sequence current amplitude is greater than the threshold, it is determined that a single-phase ground fault has occurred in the system. The device protection extracts the fault waveform and performs fault characteristic analysis. S3: Calculate the exact time of fault occurrence using wavelet modulus maxima; then make judgments based on transient mutation algorithm and steady-state phase algorithm respectively, and obtain the corresponding numerical results for both. S4: Calculate the weighting coefficient based on the zero-sequence current amplitude of the line, and use the comprehensive analysis algorithm combined with the numerical results of transient and steady-state algorithms to complete the comprehensive analysis and judgment of the phase current. When the judgment result is greater than the threshold value, the line is determined to be a faulty line; otherwise, it is a normal line.

2. The method according to claim 1, characterized in that, Step S1 includes: According to the formula Zero-sequence current can be obtained, where , , They represent The three-phase current on the line, This represents the synthesized zero-sequence current.

3. The method according to claim 2, characterized in that, Step S2 includes: By setting the zero-sequence current amplitude threshold using on-site data, the line fault and normal conditions can be distinguished.

4. The method according to claim 3, characterized in that, Step S3 includes: When a single-phase ground fault occurs, the zero-sequence current will undergo a sudden change at the moment of fault occurrence. The wavelet modulus maxima algorithm is used to process the zero-sequence current to identify the point and time of the current abrupt change, thus determining the precise moment of fault occurrence. By analyzing the direction of the transient current abrupt change and the characteristics of the steady-state phase, and using both transient abrupt change and steady-state phase algorithms to determine whether the line is faulty, the judgment result based on the transient abrupt change algorithm is obtained. and steady-state phase algorithm judgment results .

5. The method according to claim 4, characterized in that, The judgment based on the transient mutation algorithm includes: S31: Based on the sampling points corresponding to the accurate time of fault occurrence obtained from the wavelet modulus maxima. The calculation interval is defined near the sampling point, and this interval can accurately determine the time when the fault occurred. Included in, where the calculation interval is set as ; S32: Calculate the difference between the corresponding function value and the adjacent value within the calculation interval, and take the absolute value of the result. Find the sampling point corresponding to the maximum change value as the point for determining the direction of the mutation. S33: Determine the direction of the phase current change by using the function value corresponding to the point where the change direction is determined and the reference value corresponding to the sampling point at the accurate time of the fault occurrence; S34: By comparing the directions of abrupt changes in the three-phase currents obtained from the outgoing terminals of the same line. When two-phase calculation results appear If one phase is the same, but the other is different, it can be determined that the line is faulty; when the three-phase calculation results of the line are the same, it can be determined that the line is faulty. If all are the same, then it can be determined that it is a normal circuit.

6. The method according to claim 5, characterized in that, Step S32 includes: Assuming the phase current is in For sampling points; This is the current value; Find the corresponding maximum change value y using the following formula. max and its corresponding sampling point x max And obtain the mutation direction Dir: 。 7. The method according to claim 4, characterized in that, The determination based on the steady-state phase algorithm includes: When a single-phase ground fault occurs, the exact time of fault occurrence is determined by the wavelet modulus maxima. Then, the fault current signal with a length of 1 cycle is obtained 2 cycles after the exact time of the fault occurrence, and the zero-sequence current value of this line is subtracted to obtain the positive-sequence and negative-sequence currents. The phase of the positive-sequence and negative-sequence currents is then obtained. And determine its range, and determine the result value as follows: By comparing the phase results of each outgoing line, the faulty line can be identified if the results differ from those of the normal line.

8. The method according to claim 7, characterized in that, Step S4 includes: According to the formula Calculate the weighting coefficients , Among the settings As a reference value for the adjustment coefficient, it is set by... Different values ​​complete the adaptive process for different power distribution network systems. This represents the zero-sequence current amplitude of the line. Using functions Taking into account the judgment results of both the transient mutation algorithm and the steady-state phase algorithm, the judgment numerical result is obtained to determine whether this line is a faulty line. For the line The numerical value of the judgment result; For the line The numerical result of the steady-state phase algorithm process is determined; For the line The transient mutation algorithm process determines the numerical result.

9. The method according to claim 8, characterized in that, Set a threshold for results , When the numerical result is greater than the threshold value, the line can be... The circuit was determined to be faulty.

10. A single-phase grounding fault determination device for distribution networks based on phase current comprehensive analysis, used to implement the method described in any one of claims 1-9, characterized in that, include: Fault identification module: The positioning device installed at the outgoing end of each line in the distribution network collects the three-phase current on the line and synthesizes the zero-sequence current. The module determines whether the line is faulty based on the set zero-sequence current amplitude threshold. Feature analysis module: When the zero-sequence current amplitude is greater than the threshold, it is determined that a single-phase ground fault has occurred in the system. The device protection extracts the fault waveform and performs fault feature analysis. Algorithm analysis module: Calculates the exact time of fault occurrence using wavelet modulus maxima; then makes judgments based on transient mutation algorithm and steady-state phase algorithm respectively, and obtains the corresponding numerical results for both. Comprehensive Judgment Module: Based on the weighting coefficients calculated from the zero-sequence current amplitude of the line, the module uses a comprehensive analysis algorithm combined with the numerical results of transient and steady-state algorithms to complete the comprehensive analysis and judgment of the phase current. When the judgment result is greater than the threshold value, the line is determined to be a faulty line; otherwise, it is a normal line.

11. A computer-readable storage medium having a computer program stored thereon, characterized in that, When executed by a processor, the program implements the steps of the method according to any one of claims 1-9.

Images