A method, device and storage medium for intermittent high-resistance ground fault protection of an electrical system

Abstract

The application discloses an intermittent high-resistance grounding fault protection method and system of an electric system in the field of electric systems, and aims to solve the problem of protection action accuracy in the prior art, and collects zero sequence current and zero sequence voltage in real time; in response to the zero sequence current being greater than a preset current or the zero sequence voltage being greater than a preset voltage, a protection program is started; then, in response to the decision condition of the high-resistance grounding fault being met; in response to the duration of the fault current pulse being greater than a preset threshold value, in response to the decision condition of the effective fault current pulse being met, and in response to the number of effective fault current pulses being accumulated to be greater than a preset value, a protection action is output. The application calculates the proportion of the second harmonic component in the fault current pulse; the proportion of the second harmonic is used as a judgment basis to quickly distinguish the transformer excitation inrush phenomenon and the intermittent grounding fault, and the transformer excitation inrush phenomenon is excluded, and the accuracy of the protection action is increased.

Description

Technical Field

[0001] The present application relates to the field of relay protection technology, and in particular to a method for protecting an electric power system from intermittent high-resistance grounding faults. Background Art

[0002] Power plants are key nodes in the power system, and their stable operation is directly linked to national energy security and economic stability. Domestic power plant power systems often utilize medium-resistance grounding on the low-voltage side of the high-voltage transformer. Single-phase ground faults are the most common fault type in these systems. When a feeder ground fault occurs, the time-determined ground fault protection operates to trip the faulty feeder. However, when a feeder ground fault occurs due to high-resistance grounding, non-conductive media such as branches and dry soil can limit the ground fault current, making it difficult for the protection device to detect and clear it. Consequently, such ground faults can remain undetected for extended periods of time. If the fault persists, it can pose serious risks such as electric shock and fire.

[0003] Patent CN110601157B proposes a method and device for intermittent single-phase ground fault protection. By calculating the time accumulation criterion and the number statistical criterion of the zero-sequence current pulse, and judging the protection start and return, this method is simple and practical, and solves the defect that the current traditional zero-sequence overcurrent protection cannot timely eliminate intermittent ground faults, causing accidents to expand. The above method ignores the transformer excitation inrush current phenomenon, which affects the judgment of the protection maintenance program. Summary of the Invention

[0004] The purpose of this application is to provide a method, device and storage medium for intermittent high-resistance grounding fault protection in an electric power system, by calculating the proportion of the second harmonic component in the fault current pulse; and then judging whether the judgment condition of the effective fault current pulse is met based on the proportion of the second harmonic component in the fault current pulse, thereby excluding the fault current pulses that do not meet the judgment condition of the effective fault current pulse from being accumulated in the number of effective fault current pulses, thereby increasing the accuracy of the protection program.

[0005] In order to solve the above technical problems, the following technical solutions are adopted:

[0006] In a first aspect, the present invention provides a method for protecting an electric power system from intermittent high-resistance grounding faults, comprising the following steps:

[0007] Real-time collection of zero-sequence current and zero-sequence voltage in the power system;

[0008] In response to the zero-sequence current being greater than a preset current or the zero-sequence voltage being greater than a preset voltage, starting an intermittent high-resistance protection program;

[0009] After starting the intermittent high resistance protection program, it is judged whether the high resistance ground fault decision condition is met according to the zero sequence current and the zero sequence voltage; in response to the decision condition of the high resistance ground fault being met, the pulse of the corresponding zero sequence current is taken as a fault current pulse, and the duration of the fault current pulse is obtained;

[0010] In response to the duration of the fault current pulse being greater than a preset duration threshold, a second harmonic component proportion in the fault current pulse is calculated;

[0011] It is judged whether the decision condition of an effective fault current pulse is met according to the second harmonic component proportion in the fault current pulse; in response to the decision condition of the effective fault current pulse being met, the number of effective fault current pulses is accumulated;

[0012] In response to the number of effective fault current pulses being accumulated to be greater than a preset value, a protection action is output;

[0013] The judgment whether the high resistance ground fault decision condition is met according to the zero sequence current and the zero sequence voltage comprises:

[0014] After the collected zero sequence current and zero sequence voltage are normalized respectively, the zero sequence voltage is moved forward by one quarter of a cycle, and the zero sequence current and the zero sequence voltage moved forward by one quarter of a cycle are cross-correlated within one cycle, and the function of the cross-correlation calculation is:

[0015]

[0016] In the formula, R(k) is the cumulative value of the zero sequence current and the zero sequence voltage moved forward by one quarter of a cycle within one cycle, i0 is the zero sequence current, u0 is the zero sequence voltage, t is the time of one cycle, the value range of t is 0 to 0.02s, and k is the lag amount of the zero sequence voltage u0 after moving forward by one quarter of a cycle relative to the zero sequence current i0;

[0017] The lag amount k1 corresponding to the maximum value of R(k) is found, and k is calculated by substituting the following formula: max :

[0018]

[0019] k max is the cross-correlation coefficient of the zero sequence current and the zero sequence voltage moved forward by one quarter of a cycle;

[0020] If k max >k set , k set is a preset value; then the high resistance ground fault decision condition is met; otherwise, the high resistance ground fault decision condition is not met;

[0021] The fault current corresponding to the fault current pulse is a three-phase current, and the calculating the proportion of the second harmonic component in the fault current pulse includes:

[0022] Perform Fourier transform on each phase current of the three-phase current to obtain the spectrum I of each phase current. a (f) I b (f) I c (f):

[0023] I a (f) = F{i a (t)}

[0024] I b (f) = F{i b (t)}

[0025] I c (f) = F{i c (t)}

[0026] Where: f is the frequency of each current; i a (t), i b (t), i c (t) is the current of each phase of the three-phase current;

[0027] Let the spectrum of each phase current I a (f) I b (f) I c Where f in (f) is 2ω0, the harmonic component of each phase current at a frequency of 2ω0 is I a2 , I b2 , I c2 :

[0028] I a2 =I a (2ω0)

[0029] I b2 =I b (2ω0)

[0030] I c2 =I c (2ω0)

[0031] Where: ω0 is the fundamental frequency; 2ω0 is the frequency of the second harmonic component;

[0032] The proportion of the second harmonic component in the fault current pulse η2 is obtained by the following calculation:

[0033]

[0034] Among them: I total is the fault current; Ia , I b , I c is the current of each phase of the fault current, I a2 , I b2 , I c2 is the harmonic component of each phase current at a frequency of 2ω0.

[0035] The judgment condition of the effective fault current pulse is:

[0036] η2≤η set

[0037] Among them, η set The value range is 15% to 20%.

[0038] Optionally, obtaining the duration of the fault current pulse includes:

[0039] When the zero-sequence current corresponding to the fault current pulse is greater than the preset current, the logic value F is set to 1, otherwise, the logic value F is equal to 0, and the monitoring logic value F is equal to 1 or 0 and is reversed to 0 or 1. x ;

[0040] When the reversal time t x Less than the preset value t xmax , determine that the fault current pulse is in a continuous state, and continue to monitor the reversal of the logic value F and the reversal time t x ;

[0041] When the reversal time t x Greater than or equal to the preset value t xmax , determining that the fault current pulse is in an end state;

[0042] The time from the acquisition of the zero-sequence current corresponding to the fault current pulse to the determination that the fault current pulse is in the end state is the duration of the fault current pulse t c .

[0043] Optionally, the method further includes, after obtaining the duration of the fault current pulse:

[0044] In response to the duration of the fault current pulse being less than or equal to the preset duration threshold, it is determined that the fault current pulse is caused by noise or error signal. At this time, when the number of effective fault current pulses N≤1, the intermittent high resistance protection program is exited. When 1<N≤preset value N set , returning to the step of obtaining the duration of the fault current pulse.

[0045] Optionally, the second harmonic component in the fault current pulse accounts for η2>η setWhen the fault current pulse is determined to be caused by the excitation inrush current caused by the transformer no-load closing, when the number of effective fault current pulses N≤1, the intermittent high resistance protection program is exited. When 1<N≤preset value N set , returning to the step of obtaining the duration of the fault current pulse.

[0046] Optionally, the method further comprises, after accumulating the number of effective fault current pulses:

[0047] Get the time interval t between two adjacent effective fault current pulses d , when the time interval is less than the preset time interval threshold t dmax , return to the step of obtaining the duration of the fault current pulse, when the time interval t d To the preset time interval threshold t dmax When the next effective fault current pulse has not yet appeared, it is considered that the intermittent high-resistance grounding fault has disappeared, the number of effective fault current pulses is reset to 0, and the intermittent high-resistance protection program is exited.

[0048] In a second aspect, the present application provides a device for protecting an intermittent high-resistance ground fault in an electric power system. The device is configured to implement the steps of the method for protecting an intermittent high-resistance ground fault in an electric power system described in the first aspect, including:

[0049] Acquisition module, used for real-time acquisition of zero-sequence current and zero-sequence voltage in the power system;

[0050] A program starting module, configured to start an intermittent high-resistance protection program in response to a zero-sequence current being greater than a preset current or a zero-sequence voltage being greater than a preset voltage;

[0051] a judgment module, configured to, after starting the intermittent high-resistance protection program, judge whether a high-resistance grounding fault judgment condition is met based on the zero-sequence current and the zero-sequence voltage; in response to the high-resistance grounding fault judgment condition being met, use a corresponding zero-sequence current pulse as a fault current pulse, and obtain a duration of the fault current pulse;

[0052] a calculation module, in response to the duration of the fault current pulse being greater than a preset duration threshold, calculating a proportion of a second harmonic component in the fault current pulse;

[0053] a counting module, which determines whether a determination condition of a valid fault current pulse is satisfied according to a proportion of a second harmonic component in the fault current pulse, and accumulates the number of valid fault current pulses in response to satisfying the determination condition of the valid fault current pulse;

[0054] The action output module outputs a protection action in response to the effective fault current pulse number accumulating to be greater than a preset value.

[0055] According to a third aspect, a computer-readable storage medium stores a computer program, which, when executed by a processor, implements the steps of the method according to the first aspect.

[0056] Compared with the prior art, the present invention has the following beneficial effects:

[0057] 1. The present invention calculates the proportion of the second harmonic component in the fault current pulse; then determines whether the judgment condition of the effective fault current pulse is met based on the proportion of the second harmonic component in the fault current pulse, thereby excluding fault current pulses that do not meet the judgment condition of the effective fault current pulse from being accumulated in the number of effective fault current pulses. The second harmonic proportion is an important basis for distinguishing between the excitation inrush current phenomenon of the transformer and intermittent grounding faults. By using the second harmonic proportion as a judgment basis, the excitation inrush current phenomenon of the transformer and intermittent grounding faults can be quickly distinguished, and the excitation inrush current phenomenon of the transformer can be eliminated, thereby increasing the accuracy of the protection action.

[0058] 2. The present invention records the duration of the effective fault current pulse. When the duration is less than the set value, it is considered that the fault current pulse is caused by noise or error and is not accumulated in the pulse counter. When it is detected that the fault current pulse is caused by noise or error, the number N of effective fault current pulses on the pulse counter is judged. When N≤1, the protection program is directly exited. When the number N is greater than 1, the protection program continues, ensuring the accuracy of the pulse counting, ensuring that the protection program will not skip the level, ensuring the correctness of the protection program, and improving the reliability of the protection program. BRIEF DESCRIPTION OF THE DRAWINGS

[0059] Figure 1 1 is a flow chart of a method for protecting an intermittent high-resistance ground fault in an electric power system according to an embodiment of the present invention;

[0060] Figure 2 Schematic diagram of the phase relationship between zero-sequence current and zero-sequence voltage when a ground fault occurs in one embodiment of the present invention;

[0061] Figure 3 The waveform diagram of the zero-sequence current and the zero-sequence voltage after being shifted forward by a quarter of a cycle in one embodiment of the present invention;

[0062] Figure 4 A schematic diagram of the waveform of each phase of the three-phase current when the transformer is switched on at no load, in accordance with one embodiment of the present invention;

[0063] Figure 5 This is a simplified schematic diagram of a thermal power plant (6kV) system in one embodiment of the present invention;

[0064] Figure 6A parameter operation diagram of a simulation system based on an intermittent high-resistance grounding fault protection method for a power system according to an embodiment of the present invention;

[0065] Figure 7 This is a parameter operation diagram under another simulation system based on the intermittent high-resistance grounding fault protection method of the power system in one embodiment of the present invention. DETAILED DESCRIPTION

[0066] The following will be combined with the accompanying drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are only some embodiments of the present application, rather than all embodiments. The following description of at least one exemplary embodiment is actually only illustrative and is in no way intended to limit the present application, its application, or use.

[0067] Example 1

[0068] like Figure 1 As shown, this embodiment provides a method for protecting an intermittent high-resistance ground fault in an electric power system, comprising the following steps:

[0069] Real-time collection of zero-sequence current and zero-sequence voltage in the power system;

[0070] In response to the zero-sequence current being greater than a preset current or the zero-sequence voltage being greater than a preset voltage, starting an intermittent high-resistance protection program;

[0071] After the intermittent high-resistance protection program is started, whether a high-resistance grounding fault judgment condition is met is determined based on the zero-sequence current and the zero-sequence voltage: in response to the high-resistance grounding fault judgment condition being met, a corresponding zero-sequence current pulse is used as a fault current pulse, and a duration of the fault current pulse is obtained;

[0072] In response to the duration of the fault current pulse being greater than a preset duration threshold, calculating a proportion of a second harmonic component in the fault current pulse;

[0073] determining whether a determination condition of a valid fault current pulse is satisfied according to a proportion of a second harmonic component in the fault current pulse, and accumulating the number of valid fault current pulses in response to satisfying the determination condition of a valid fault current pulse;

[0074] In response to the effective fault current pulse number being accumulated to be greater than a preset value, a protection action is output.

[0075] The number of effective fault current pulses is accumulated by a pulse recorder.

[0076] like Figure 1As shown, by the above description, the specific steps of accumulating a valid fault current pulse on the pulse counter are described in detail as follows: the collected zero sequence current is three-phase current.

[0077] S1: Collecting the zero sequence current and the zero sequence voltage of the zero sequence transformer in the power system with point connection and small resistance grounding, and comparing the collected zero sequence current and the zero sequence voltage with the preset current and the preset voltage in the system.

[0078] S2: When the condition that the zero sequence current is greater than the preset current or the zero sequence voltage is greater than the preset voltage is met, starting the intermittent high resistance protection program; when the condition is not met, returning to S1.

[0079] S3: After starting the intermittent high resistance protection program, normalizing the collected zero sequence current and the zero sequence voltage, after the normalization, moving the zero sequence voltage forward by one quarter of a cycle, and performing cross-correlation calculation on the zero sequence current and the zero sequence voltage moved forward by one quarter of a cycle within one cycle, the function of the cross-correlation calculation being:

[0080]

[0081] In the formula, R(k) is the cumulative value of the zero sequence current and the zero sequence voltage moved forward by one quarter of a cycle within one cycle, i0 is the zero sequence current, u0 is the zero sequence voltage, t is the time of one cycle, the value range of t being 0 to 0.02s, and k is the lag amount of the zero sequence voltage u0 relative to the zero sequence current i0 after moving forward by one quarter of a cycle; the value range of k being 0 to 0.2.

[0082] In the above formula, the lag amount k1 corresponding to the maximum value of R(k) is found, and k is calculated by substituting the following formula: max

[0083]

[0084] k max is the cross-correlation coefficient of the zero sequence current and the zero sequence voltage moved forward by one quarter of a cycle;

[0085] S4: Comparing the calculated k max with the preset value k set , when k max > k set , determining that a high resistance grounding fault occurs; otherwise, returning to S3.

[0086] Determining that a high resistance grounding fault occurs, at this time, the collected zero sequence current is taken as a fault current, and the pulse of the fault current is a fault current pulse.

[0087] S5: Judging whether the fault current pulse is ended, including:​

[0088] When the zero-sequence current corresponding to the fault current pulse is greater than the preset current, the logic value F is set to 1, otherwise, the logic value F is equal to 0, and the monitoring logic value F is equal to 1 or 0 and is reversed to 0 or 1. x ;

[0089] When the reversal time t x Less than the preset value t xmax , determine that the fault current pulse has not ended, and continue to monitor the reversal of the logic value F and the reversal time t x ;

[0090] When the reversal time t x Greater than or equal to the preset value t xmax , it is determined that the fault current pulse ends.

[0091] S6: After determining that the fault current pulse ends, obtain the duration t of the ended fault current pulse c The time from the acquisition of the zero-sequence current corresponding to the fault current pulse to the determination that the fault current pulse is in the end state is the duration of the fault current pulse t c .

[0092] Obtain the duration t of the fault current pulse at the end c Afterwards, the duration t obtained c With the preset duration threshold t cmin For comparison, when t c ≤t cmin When t c >t cmin When the fault current pulse ends, the second harmonic proportion component in the fault current pulse is calculated.

[0093] S7: Calculating the proportion of the second harmonic in the finished fault current pulse, including:

[0094] Perform Fourier transform on each phase current of the three-phase current to obtain the spectrum I of each phase current. a (f) I b (f) I c (f):

[0095] I a (f) = F{i a (t)}

[0096] I b (f) = F{i b (t)}

[0097] Ic (f) = F{i c (t)}

[0098] Where: f is the frequency of each current; i a (t), i b (t), i c (t) is the current of each phase of the three-phase current;

[0099] Let the spectrum of each phase current I a (f) I b (f) I c Where f in (f) is 2ω0, the harmonic component of each phase current at a frequency of 2ω0 is I a2 , I b2 , I c2 :

[0100] I a2 =I a (2ω0)

[0101] I b2 =I b (2ω0)

[0102] I c2 =I c (2ω0)

[0103] Where: ω0 is the fundamental frequency; 2ω0 is the frequency of the second harmonic component;

[0104] The proportion of the second harmonic component in the fault current pulse η2 is obtained by the following calculation:

[0105]

[0106]

[0107] Among them: I total is the fault current; I a , I b , I c is the current of each phase of the fault current, I a2 , I b2 , I c2 is the harmonic component of each phase current at a frequency of 2ω0.

[0108] S8: The second harmonic component of the fault current pulse accounts for η2 and the set value η set Compare. When η2>η set When η2≤η setWhen the fault current pulse is determined to be a valid fault current pulse, the pulse counter value is increased by one.

[0109] The step of accumulating one valid fault current pulse on the pulse counter is completed.

[0110] The preset voltage range is 1V to 2V; the preset current range is 0.01A to 0.02A; k set The value ranges from 0.4 to 0.5; t xmax The value is generally 0.01s; the preset duration t cmin The value range of η is 0.01s to 0.02s, set The value range is 15% to 20%.

[0111] A valid fault current pulse is obtained through the above steps S1-S8. If it is determined in S6 that the fault current pulse is caused by noise or an error signal, the fault current pulse is not considered a valid fault current pulse, and the process proceeds to the phase of comparing the number of valid fault current pulses. If it is determined in S8 that the fault current pulse is caused by the transformer no-load closing magnetizing inrush current, the fault current pulse is not considered a valid fault current pulse, and the process proceeds to the phase of comparing the number of valid fault current pulses.

[0112] The comparison stage of the effective fault current pulse number includes:

[0113] When the number of effective fault current pulses N≤1, it is determined that no intermittent high-resistance grounding fault is detected, and the intermittent high-resistance protection program is exited. When the number of effective fault current pulses N>1, the number of effective fault current pulses N is compared with the preset value N. set Comparisons include:

[0114] When the number of effective fault current pulses N>N set When N≤N set When the fault current pulse is detected, the effective fault current pulse is continuously acquired and accumulated.

[0115] The preset value N set The value range is 5 to 10.

[0116] In the process of obtaining and accumulating effective fault current pulses, the time interval t between adjacent effective fault current pulses is obtained. d , when the pulse counter value increases by one, let the time interval t d = 0, continue to obtain effective fault current pulses and accumulate time interval t d , when the time interval accumulates to t d1 ≥Preset interval time t dmaxWhen the next zero-sequence current collected is not determined to be the fault current, that is, the zero-sequence current collected in real time has not entered S5 of the specific step of the effective fault current pulse, it is determined that the intermittent high-resistance grounding fault disappears and the intermittent high-resistance protection program is exited. d1 <t dmax When the time interval is t d1 Based on the continued accumulation, the duration t of the above effective fault current pulse is obtained in the specific steps d and reversal time t x Reset to zero. The time interval is t d1 Continue to accumulate on the basis of t, until the zero sequence current collected enters S5 in the specific step of the above effective fault current pulse, or exits the intermittent high resistance protection program, and the stop time interval is t d1 Continue to accumulate on the basis of dmax The value range is 1s to 1.5s.

[0117] like Figure 2 As shown in FIG. 1 , a phase relationship diagram of zero-sequence current and zero-sequence voltage when a fault occurs is shown. Under normal circumstances, the phase difference between the zero-sequence current and the zero-sequence voltage is ninety degrees, while when a fault occurs, the phase difference between the zero-sequence current and the normal zero-sequence voltage is greater than ninety degrees. Based on this feature, the collected zero-sequence current and zero-sequence voltage are subjected to the calculation process of S3 to obtain k max , and then according to the obtained k max With the preset value k set Comparison is performed to determine whether a fault has occurred in the power system.

[0118] like Figure 3 As shown in FIG, the waveforms of the zero-sequence voltage and zero-sequence current after the above S3 is shifted forward by a quarter of a cycle. When there is no fault in the power system, the waveform of the zero-sequence voltage shifted forward by a quarter of a cycle will coincide with the zero-sequence current. Through this characteristic, it is preliminarily judged whether a fault has occurred in the power system, and then the above S3 is calculated to determine whether a fault has occurred.

[0119] like Figure 4 As shown in Figure 1, the three-phase current waveform of the magnetizing inrush current when the transformer is switched on without load is shown. In the above S8, the magnetizing current generates a significant second harmonic, which is used to distinguish the magnetizing inrush current phenomenon from the ground fault phenomenon. In S7, the second harmonic component corresponds to the component with a frequency twice the fundamental frequency. If the fundamental frequency is ω0, then the frequency of the second harmonic component is 2ω0, thus obtaining the second harmonic component I of each phase current in the three-phase current. a2 , I b2 , I c2 .

[0120] During the process of obtaining a valid fault current pulse in steps S1-S8, if the fault current pulse is determined in step S6 to be caused by noise or an error signal, the fault current pulse is considered not to be a valid fault current pulse. This eliminates transient signals that do not conform to the characteristics of an intermittent high-resistance ground fault, thereby reducing the possibility of misjudgment and improving the accuracy of the intermittent high-resistance ground fault protection program.

[0121] In step S8, it is determined that the fault current pulse is caused by the transformer no-load closing excitation inrush current, and the fault current pulse is considered not to be a valid fault current pulse. This reduces the range of valid fault current pulses and improves the accuracy and sensitivity of the protection action.

[0122] Next, according to the above method, a simulation system is established for simulation.

[0123] like Figure 5 The figure shows a simplified diagram of the actual 6kV power system of a thermal power plant. Based on the actual 6kV power system of a thermal power plant, the following two simulation systems are established: The grounding resistance in both simulation systems is 1000Ω, and the protection action preset value N set Both are 3.

[0124] like Figure 6 As shown, it is a parameter operation chart under a simulation system. The first chart is a waveform chart of the second harmonic value in the zero-sequence current pulse on the fault line, the second chart is the number of effective fault current pulses recorded on the pulse counter, and the third chart represents the output state of the protection action. When the second harmonic value in the zero-sequence current continuously changes and the value is large, it is recorded as an effective fault current pulse. The duration of an effective fault current pulse can be obtained through the first chart, and the interval time between adjacent effective fault current pulses can be obtained through the first chart or the second chart. The duration and interval time are consistent with the judgment in the above method. The number of waveform fluctuations in the first chart corresponds to the effective fault current pulse count in the second chart. When the number of fault pulse counts reaches 3, the protection action is output, and the protection action lasts for 0.3s.

[0125] like Figure 7 As shown, the parameter chart under another simulation system is Figure 6 The simulation system diagrams shown are similar, except that the waveform of the second harmonic value in the zero-sequence current pulse on the fault line on the first diagram is different. The change of the second harmonic value on the first diagram is also recorded on the second diagram. The number of fault current pulse counts recorded on the second diagram is counted. When the number reaches 3, the output protection action is shown in the third diagram.

[0126] In summary, the present invention collects the zero-sequence current and zero-sequence voltage of the line, and determines whether a high-resistance grounding fault has occurred based on cross-correlation calculations. Based on the characteristics of intermittent high-resistance grounding faults, which are that the duration of a single fault current pulse is long and the time interval between adjacent fault current pulses is short, the minimum duration of a single fault current pulse and the maximum interval time of the fault pulse are set. The above parameters are set based on the zero-sequence current characteristics of intermittent high-resistance grounding faults to ensure that the protection action does not malfunction or refuse to operate. The characteristic of a high proportion of second harmonics in the zero-sequence current corresponding to the transformer excitation inrush current is analyzed, and the calculation is efficient and fast, ensuring the sensitivity of the protection. The proportion of the second harmonic component of the excitation inrush current is used as a criterion, so that the protection action avoids the excitation inrush current when the transformer is closed at no load.

[0127] Example 2

[0128] This embodiment provides a device for protecting intermittent high-resistance ground faults in a power system. By running the method provided in Example 1, the device can handle intermittent high-resistance ground faults in the power system and ensure the normal operation of the circuit system. It includes:

[0129] Acquisition module, used for real-time acquisition of zero-sequence current and zero-sequence voltage in the power system;

[0130] A program starting module, configured to start an intermittent high-resistance protection program in response to a zero-sequence current being greater than a preset current or a zero-sequence voltage being greater than a preset voltage;

[0131] a judgment module, configured to, after starting the intermittent high-resistance protection program, judge whether a high-resistance grounding fault judgment condition is met based on the zero-sequence current and the zero-sequence voltage: in response to the high-resistance grounding fault judgment condition being met, a corresponding zero-sequence current pulse is a fault current pulse, and obtain a duration of the fault current pulse;

[0132] a calculation module, in response to the duration of the fault current pulse being greater than a preset duration threshold, calculating a proportion of a second harmonic component in the fault current pulse;

[0133] a counting module, which determines whether a determination condition of a valid fault current pulse is satisfied according to a proportion of a second harmonic component in the fault current pulse, and accumulates the number of valid fault current pulses in response to satisfying the determination condition of the valid fault current pulse;

[0134] The action output module outputs a protection action in response to the effective fault current pulse number accumulating to be greater than a preset value.

[0135] Example 3

[0136] This embodiment provides a computer-readable storage medium based on embodiment 1, on which a computer program is stored. When the program is executed by a processor, the steps of the method described in embodiment 1 are implemented.

[0137] Those skilled in the art will appreciate that the embodiments of the present application can be provided as methods, systems, or computer program products. Therefore, the present application can adopt the form of a complete hardware embodiment, a complete software embodiment, or an embodiment in combination with software and hardware. Moreover, the present application can adopt the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to magnetic disk storage, CD-ROM, optical storage, etc.) that contain computer-usable program code.

[0138] The present application is described with reference to the flowcharts and / or block diagrams of the methods, devices (systems), and computer program products according to the embodiments of the present application. It should be understood that each process and / or box in the flowchart and / or block diagram, as well as the combination of the processes and / or boxes in the flowchart and / or block diagram, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing device to produce a machine, so that the instructions executed by the processor of the computer or other programmable data processing device generate instructions for implementing the steps in the process. Figure 1 a process or multiple processes and / or boxes Figure 1 A device that provides the functions specified in a block or multiple blocks.

[0139] These computer program instructions may also be stored in a computer readable memory that can direct a computer or other programmable data processing device to work in a specific manner, so that the instructions stored in the computer readable memory produce an article of manufacture comprising an instruction device, which implements the process Figure 1 a process or multiple processes and / or boxes Figure 1 The function specified in one or more boxes.

[0140] These computer program instructions can also be loaded onto a computer or other programmable data processing device so that a series of operational steps are executed on the computer or other programmable device to produce a computer-implemented process, thereby providing the instructions executed on the computer or other programmable device for implementing the process. Figure 1 a process or multiple processes and / or boxes Figure 1 A step that specifies a function in one or more boxes.

[0141] The above is only a preferred embodiment of the present application. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the technical principles of the present application. These improvements and modifications should also be regarded as the scope of protection of the present application.

Claims

1. A method for protecting an intermittent high-resistance ground fault in an electric power system, characterized in that: The following steps are involved: Real-time collection of zero-sequence current and zero-sequence voltage in the power system; In response to the zero-sequence current being greater than a preset current or the zero-sequence voltage being greater than a preset voltage, starting an intermittent high-resistance protection program; After the intermittent high-resistance protection program is started, whether a high-resistance grounding fault judgment condition is met is determined based on the zero-sequence current and the zero-sequence voltage: in response to the high-resistance grounding fault judgment condition being met, a corresponding zero-sequence current pulse is used as a fault current pulse, and a duration of the fault current pulse is obtained; In response to the duration of the fault current pulse being greater than a preset duration threshold, calculating a proportion of a second harmonic component in the fault current pulse; determining whether a determination condition for a valid fault current pulse is satisfied based on a proportion of a second harmonic component in the fault current pulse; accumulating the number of valid fault current pulses in response to the determination condition for a valid fault current pulse being satisfied; In response to the effective fault current pulse number being accumulated to be greater than a preset value, outputting a protection action; The determining whether a high-resistance grounding fault determination condition is met according to the zero-sequence current and the zero-sequence voltage includes: After normalizing the collected zero-sequence current and zero-sequence voltage, the zero-sequence voltage is shifted forward by a quarter of a cycle. The zero-sequence current and the zero-sequence voltage shifted forward by a quarter of a cycle are cross-correlated within one cycle. The function for the cross-correlation calculation is: Where R(k) is the cumulative value of the zero-sequence current and the zero-sequence voltage after moving forward a quarter of a cycle within one cycle, i0 is the zero-sequence current, u0 is the zero-sequence voltage, t is the time of one cycle, and k is the lag of the zero-sequence voltage u0 after moving forward a quarter of a cycle relative to the zero-sequence current i0; find the lag k1 corresponding to the maximum value of R(k), and substitute it into the following formula to calculate k max : k max is the cross-correlation coefficient between the zero-sequence current and the zero-sequence voltage shifted forward by a quarter of a cycle; If k max >k set , k set is a preset value; then the high-resistance ground fault judgment condition is met; otherwise, The high-resistance ground fault judgment condition is not met; The fault current corresponding to the fault current pulse is a three-phase current, and the calculating the proportion of the second harmonic component in the fault current pulse includes: Perform Fourier transform on each phase current of the three-phase current to obtain the spectrum I of each phase current. a (f) I b (f) I c (f): I a (f)=F{i a (t)} I b (f)=F{i b (t)} I c (f)=F{i c (t)} Where: f is the frequency of each current; i a (t), i b (t), i c (t) is the current of each phase of the three-phase current; Let the spectrum of each phase current I a (f) I b (f) I c Where f in (f) is 2ω0, the harmonic component of each phase current at a frequency of 2ω0 is I a2 , I b2 , I c2 : I a2 =I a (2ω0) I b2 =I b (2ω0) I c2 =I c (2ω0) Where: ω0 is the fundamental frequency; 2ω0 is the frequency of the second harmonic component; The proportion of the second harmonic component in the fault current pulse η2 is obtained by the following calculation: Among them: I total is the fault current; I a , I b , I c is the current of each phase of the fault current, I a2 , I b2 , I c2 is the harmonic component of each phase current at a frequency of 2ω0; The judgment condition of the effective fault current pulse is: η2≤η set Among them, η set is the preset second harmonic component ratio.

2. The intermittent high-resistance grounding fault protection method for a power system according to claim 1, characterized in that: The obtaining the duration of the fault current pulse includes: When the zero-sequence current corresponding to the fault current pulse is greater than the preset current, the logic value F is set to 1, otherwise, the logic value F is equal to 0, and the monitoring logic value F is equal to 1 or 0 and is reversed to 0 or 1. x ; When the reversal time t x Less than the preset value t xmax , determine that the fault current pulse is in a continuous state, and continue to monitor the reversal of the logic value F and the reversal time t x ; When the reversal time t x Greater than or equal to the preset value t xmax , determining that the fault current pulse is in an end state; The time from the acquisition of the zero-sequence current corresponding to the fault current pulse to the determination that the fault current pulse is in the end state is the duration of the fault current pulse t c .

3. The intermittent high-resistance grounding fault protection method for a power system according to claim 2, characterized in that: The method further includes, after obtaining the duration of the fault current pulse: In response to the duration of the fault current pulse being less than or equal to the preset duration threshold, it is determined that the fault current pulse is caused by noise or error signal. At this time, when the number of effective fault current pulses N≤1, the intermittent high resistance protection program is exited. When 1<N≤preset value N set , returning to the step of obtaining the duration of the fault current pulse.

4. The intermittent high-resistance ground fault protection method for a power system according to claim 1, characterized in that: The proportion of the second harmonic component in the fault current pulse is η2>η set When the fault current pulse is determined to be caused by the excitation inrush current caused by the transformer no-load closing, when the number of effective fault current pulses N≤1, the intermittent high resistance protection program is exited. When 1<N≤preset value N set , returning to the step of obtaining the duration of the fault current pulse.

5. The intermittent high-resistance grounding fault protection method for a power system according to claim 1, characterized in that: The method further includes, after accumulating the number of valid fault current pulses: Get the time interval t between two adjacent effective fault current pulses d , when the time interval is less than the preset time interval threshold t dmax , return to the step of obtaining the duration of the fault current pulse, when the time interval t d To the preset time interval threshold t dmax When the next effective fault current pulse has not yet appeared, it is considered that the intermittent high-resistance grounding fault has disappeared, the number of effective fault current pulses is reset to 0, and the intermittent high-resistance protection program is exited.

6. A device for protecting intermittent high-resistance ground faults in a power system, characterized in that: The protection device is used to implement the steps of the intermittent high-resistance grounding fault protection method for the power system according to any one of claims 1 to 5, including: Acquisition module, used for real-time acquisition of zero-sequence current and zero-sequence voltage in the power system; A program starting module, configured to start an intermittent high-resistance protection program in response to a zero-sequence current being greater than a preset current or a zero-sequence voltage being greater than a preset voltage; a judgment module, configured to, after starting the intermittent high-resistance protection program, judge whether a high-resistance grounding fault judgment condition is met based on the zero-sequence current and the zero-sequence voltage; in response to the high-resistance grounding fault judgment condition being met, use a corresponding zero-sequence current pulse as a fault current pulse, and obtain a duration of the fault current pulse; a calculation module, in response to the duration of the fault current pulse being greater than a preset duration threshold, calculating a proportion of a second harmonic component in the fault current pulse; a counting module, which determines whether a determination condition of a valid fault current pulse is satisfied according to a proportion of a second harmonic component in the fault current pulse, and accumulates the number of valid fault current pulses in response to satisfying the determination condition of the valid fault current pulse; The action output module outputs a protection action in response to the effective fault current pulse number accumulating to be greater than a preset value.

7. A computer-readable storage medium having a computer program stored thereon, characterized in that: When the program is executed by a processor, the steps of the method according to any one of claims 1 to 5 are implemented.

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