A method for finding cable grounding fault

Abstract

The present invention relates to a cable grounding fault finding method, comprising the following steps: step 1, extracting fault recording data in a booster station; step 2, judging whether there is a grounding fault; step 3, setting the line troubleshooting priority according to the fault recording data and the current phase comparison; step 4, locking the fault branch, and setting the troubleshooting sequence according to the magnitude of the zero-sequence current; step 5, applying for dispatching consent and executing the grounding troubleshooting procedure; step 6, judging whether the grounding is restored. The cable grounding fault finding method provided by the technical solution of the present invention improves the existing single-phase grounding fault processing technology, which is beneficial for the operators of new energy power stations to quickly handle the single-phase grounding fault of the grounding transformer system under the complex working conditions of multiple collector lines, and provides a new technical solution for the single-phase grounding fault processing of the grounding transformer system.

Description

Technical Field

[0001] The invention relates to the field of electric power detection, and in particular to a method for finding a cable grounding fault. Background Art

[0002] The development of new energy is accelerating, and the layout of electrical primary circuits such as 35kV collector lines is dense, especially in photovoltaic power stations. There are many 35KV buried cables between each box transformer. How to accurately judge the grounding fault of each branch is a practical problem before us. The 35kV grounding variable small current grounding system of new energy power stations is widely used in new energy power stations due to its superior power supply reliability. After a single-phase grounding fault occurs in the grounding variable small current grounding system, it may cause a short circuit fault between two phases of the same line or a short circuit at multiple points and different phases on different lines, causing a power outage. The occurrence of a grounding fault may lead to the breaking of the original capacitance and inductance balance of the new energy power station, which may cause arc grounding. In severe cases, it may even cause a resonant overvoltage, destroy the insulation of power equipment, and expand the scope of the accident.

[0003] At present, the treatment of single-phase grounding in the small current grounding system of new energy power stations relies on the local line selection device to determine the fault line, or through manual judgment by dispatchers. At present, there is a situation where the feeder is selected incorrectly in the local line selection, and the centralized line selection system does not work when grounding occurs; there are unsafe factors such as unreasonable line pulling sequence in the manual grounding search link; the traditional single-phase grounding treatment method of the small current grounding system will increase the probability of uncertain power outages. Summary of the invention

[0004] The purpose of the present invention is to provide a cable grounding fault locating method to solve the problem that the existing cable grounding fault judgment is complex and difficult to handle.

[0005] To achieve the above object, the present invention adopts the following technical solutions:

[0006] A method for finding a cable grounding fault comprises the following steps:

[0007] Step 1: Extract fault recording data in the booster station, extract branches with large voltage and current mutations and large zero-sequence currents in the station, and extract grounding transformer voltage and current;

[0008] Step 2: Determine whether there is a ground fault, based on the alarm signal and the duration of the alarm signal, or the voltage and current amplitudes; if there is a ground fault, proceed to step 3; if there is no single-phase ground fault, proceed to step 6 to determine whether the grounding is restored;

[0009] Step 3: According to the fault recording data, the sudden change branch and the grounding transformer branch are immediately expanded for recording, the current phases of the sudden change branch and the grounding transformer branch are compared, and the line troubleshooting priority is set according to the current phase comparison;

[0010] Step 4: Lock the fault branch and set the troubleshooting sequence according to the magnitude of the zero-sequence current;

[0011] Step 5: Apply for dispatch approval and execute the grounding investigation procedure; perform grounding investigation on the faulty line in sequence, which includes opening and closing the outgoing line switch on the faulty line;

[0012] Step 6: Determine whether the grounding is restored. When the 35kV bus grounding alarm signal is restored, it is determined that the single-phase grounding fault has been restored. After the single-phase grounding fault is restored, exit the single-phase grounding fault search;

[0013] If all outgoing lines of the substation bus are grounded, but single-phase grounding still exists, it is determined to be a bus fault; the single-phase grounding intelligent detection program detects a single-phase grounding reset signal and automatically exits the program.

[0014] Preferably, in step 1, the system is patrolled with a sampling step length of 2 seconds to continuously detect the grounding fault signal of the small current grounding system. The detection method of the single-phase grounding fault signal is as follows:

[0015] If at time t1, the voltage of any phase or more of the busbar is lower than 70% of the rated operation, and the 35kV busbar voltage UO is greater than 3V (secondary value), the signal is recorded as M1;

[0016] If a 35kv grounding transformer current appears at time t2, and the current value is greater than 0.05A (secondary value), the signal is recorded as M2;

[0017] If the zero-sequence current of a branch suddenly increases at time t3, and the zero-sequence current is greater than 0.05 (secondary value), the signal is recorded as M3.

[0018] Preferably, in step 2,

[0019] If the M1 and M2 signals persist for more than 2 minutes and there is no line and transformer branch alarm signal, it is determined that a single-phase grounding fault has occurred on the bus, which is recorded as the TZ1 signal, and the time t4 when the bus grounding characteristic quantity first appears is recorded. ;

[0020] If the M1 and M2 signals persist for more than 2 minutes and the M3 signal appears at the same time, it is determined that a ground fault has occurred in the line. When the above situation occurs in the control system, the control system records the bus or distribution line where the ground fault occurs, completes the detection of the ground characteristic quantity TZ2, and records the time t5 when the cable ground characteristic quantity first appears;

[0021] When one or more of the above situations occur in the central control system, the central control system records the bus or distribution line where the grounding fault occurs, and a grounding fault exists, and proceed to step three.

[0022] Preferably, in step 3, if only metallic grounding faults are considered, the fault phase current of the fault line is approximately equal to the zero-sequence current of the grounding transformer; if non-metallic grounding conditions such as offset grounding resistance are considered, the fault phase current angle of the fault line is approximately equal to the zero-sequence current angle of the grounding transformer, and the grounding transformer IA=IB=IC=I0. According to the magnitude of the zero-sequence current, the closer the zero-sequence current amplitude and angle are to the grounding transformer, the more likely the fault line is to be determined.

[0023] Preferably, in step five, a ground search is performed on the faulty branch in sequence, and the ground search includes opening and closing the outgoing line switch on the faulty branch.

[0024] If the single-phase grounding characteristic disappears after the outgoing line switch of line L1 is opened, the intelligent grounding detection program is terminated;

[0025] If the single-phase grounding characteristic disappears after the L2 outgoing line switch is opened, the outgoing line switch that has been opened before is closed in reverse order. If the grounding characteristic appears again after the L3 outgoing line switch is closed, the L3 outgoing line switch is opened and the execution of the grounding intelligent detection program is terminated at the same time; it is determined that both L2 and L3 have grounding faults;

[0026] If a ground fault still occurs after all outgoing line switches of the faulty bus are opened, it is considered that a ground fault has occurred in the bus, and all switches related to the bus are opened.

[0027] Preferably, in step six, the remote signal in the main grid control system is patrolled with a sampling step of 2 seconds. When the 35kV bus grounding alarm signal is restored, it is determined that the grounding fault has been restored; after the grounding fault is restored, the grounding fault search is exited.

[0028] Compared with the prior art, the present invention has the following beneficial effects:

[0029] The cable grounding fault finding method provided in the above technical solution can quickly find the cable grounding fault through the steps of grounding feature detection, judging whether there is a grounding fault, obtaining fault recorder data, judging by comparing the current phase method, locking the fault branch, applying for dispatching consent to perform the grounding intelligent detection program, and judging whether the grounding is restored. It has the following advantages:

[0030] (1) It can adapt to single-phase grounding faults in multiple scenarios, quickly find the grounding faults of new energy power stations, determine the lines where single-phase grounding occurs, improve the rapid handling capability of single-phase grounding faults in new energy power stations, and improve the level of accurate handling of single-phase grounding faults in new energy power stations;

[0031] (2) It can comprehensively utilize the existing fault recorder data to promptly handle single-phase grounding faults, effectively avoid the possibility of incorrect line selection results between the automatic line selection switch and the original small current line selection device, and restore the voltage of the new energy power station to a normal level as soon as possible to ensure the safe and economical operation of the power station;

[0032] (3) This method does not require the additional arrangement of new equipment and has good economic efficiency. It has strong adaptability and can adapt to small grounding systems such as neutral point ungrounded systems and neutral point arc suppression coils. It also improves the existing single-phase grounding fault handling technology, which is beneficial for the operation and analysis personnel of new energy power stations to master the analysis, command and handling of single-phase grounding faults in grounding transformer grounding systems, and provides a new technical solution for handling single-phase grounding faults in grounding transformer systems. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] In order to more clearly illustrate the specific implementation methods of the present invention or the technical solutions in the prior art, the drawings required for use in the specific implementation methods or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some implementation methods of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0034] Figure 1 The present invention provides a flow chart of a cable grounding fault detection method.

[0035] Figure 2 A multiphase voltage diagram of a cable grounding fault locating method provided by an embodiment of the present invention.

[0036] Figure 3 A multiphase current diagram of the cable grounding fault locating method provided by an embodiment of the present invention.

[0037] Figure 4 Another multi-phase current diagram of the cable grounding fault locating method provided by an embodiment of the present invention.

[0038] Figure 5 A logic diagram of a cable grounding fault locating method provided by an embodiment of the present invention.

[0039] Figure 6 A schematic diagram of a portion of a circuit provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0040] The technical solution of the present invention will be described clearly and completely below in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0041] An embodiment of the present invention provides a method for finding a cable grounding fault, the method comprising the following steps:

[0042] Step 1: Extract fault recording data in the booster station, extract branches with large voltage and current mutations and large zero-sequence currents in the station, and extract grounding transformer voltage and current;

[0043] Specifically, the system is patrolled with a sampling step length of 2 seconds to continuously detect the ground fault signal of the small current grounding system. The detection method of the single-phase ground fault signal is as follows:

[0044] If at time t1 the voltage of any phase or more of the busbar is lower than 70% of the rated operating voltage, and the 35kV busbar voltage UO is greater than 3V (secondary value), the signal is recorded as M1. Figure 2 The C phase voltage drops as shown;

[0045] If a 35kv grounding transformer current appears at time t2, and the current value is greater than 0.05A (secondary value), the signal is recorded as M2. Figure 3 The grounding changes A, B, C and I0 shown are obviously increased suddenly;

[0046] If the zero-sequence current of a branch suddenly increases at time t3, and the zero-sequence current is greater than 0.05 (secondary value), the signal is recorded as M3. Figure 4 The grounding variables A, B, C and I0 shown clearly increase suddenly.

[0047] Step 2: Determine whether there is a ground fault, based on the alarm signal and the duration of the alarm signal, or the voltage and current amplitudes; if there is a ground fault, proceed to step 3; if there is no single-phase ground fault, proceed to step 6 to determine whether the grounding is restored;

[0048] If the M1 and M2 signals persist for more than 2 minutes and there are no line and transformer branch alarm signals, it is determined that a single-phase grounding fault has occurred on the bus, which is recorded as the TZ1 signal, and the time t4 when the bus grounding characteristic quantity first appears is recorded.

[0049] As attached Figure 5As shown, if the M1 and M2 signals persist for more than 2 minutes and the M3 signal appears at the same time, it is determined that a ground fault has occurred in the line. When the above situation occurs in the control system, the control system records the bus or distribution line where the ground fault occurs, completes the detection of the grounding characteristic quantity TZ2, and records the time t5 when the cable grounding characteristic quantity first appears;

[0050] When one or more of the above situations occur in the central control system, the central control system records the bus or distribution line where the grounding fault occurs, and a grounding fault exists, and proceed to step three.

[0051] Step 3: According to the fault recording data, the sudden change branch and the grounding transformer branch are immediately expanded for recording, and the current phases of the sudden change branch and the grounding transformer branch are compared. According to the comparison of the current phases, the line troubleshooting priority is set; the details are as follows:

[0052] As attached Figure 6 As shown, when the short circuit occurs at point k1, the three-phase currents flowing through the current transformer TA1 on the grounding transformer winding side are: IA = IB = IC = I0;

[0053] The current flowing through the grounding transformer neutral point current transformer TA4 is: IN = 3I0

[0054] If only metallic grounding faults are considered, the fault phase current I of the fault line is approximately equal to IN; if non-metallic grounding conditions such as offset grounding resistance are considered, the fault phase current I of the fault line is approximately equal to IN.

[0055] Step 4: Lock the fault branch and set the troubleshooting sequence according to the magnitude of the zero-sequence current;

[0056] Step 5: Apply for dispatch approval and execute the grounding investigation procedure; perform grounding investigation on the faulty line in sequence, which includes opening and closing the outgoing line switch on the faulty line;

[0057] The faulty branch is grounded in sequence, and the grounding search includes opening and closing the outgoing switch on the faulty branch.

[0058] If the single-phase grounding characteristic disappears after the outgoing line switch of line L1 is opened, the intelligent grounding detection program is terminated;

[0059] If the single-phase grounding characteristic disappears after the L2 outgoing line switch is opened, the outgoing line switch that has been opened before is closed in reverse order. If the grounding characteristic appears again after the L3 outgoing line switch is closed, the L3 outgoing line switch is opened and the execution of the grounding intelligent detection program is terminated at the same time; it is determined that both L2 and L3 have grounding faults;

[0060] If a ground fault still occurs after all outgoing line switches of the faulty bus are opened, it is considered that a ground fault has occurred in the bus, and all switches related to the bus are opened.

[0061] Step 6: Determine whether the grounding is restored. When the 35kV bus grounding alarm signal is restored, it is determined that the single-phase grounding fault has been restored. After the single-phase grounding fault is restored, exit the single-phase grounding fault search;

[0062] Patrol the remote signal in the main grid control system with a sampling step of 2 seconds. When the 35kV bus grounding alarm signal is restored, it is determined that the grounding fault has been restored; exit the grounding fault search after the grounding fault is restored.

[0063] The cable grounding fault detection method provided by the above technical solution improves the existing single-phase grounding fault handling technology, which is beneficial for the operation and analysis personnel of new energy power stations to master the analysis, command and handling of single-phase grounding faults in grounding transformer systems, and provides a new technical solution for handling single-phase grounding faults in grounding transformer systems.

[0064] The above-mentioned embodiments are only preferred embodiments of the present invention and cannot be used to limit the scope of protection of the present invention. Any non-substantial changes and substitutions made by technicians in this field on the basis of the present invention shall fall within the scope of protection required by the present invention.

Claims

1. A cable grounding fault locating method, characterized in that: The following steps are involved: Step 1: Extract fault recording data in the booster station, extract branches with large voltage and current mutations and large zero-sequence currents in the station, and extract grounding transformer voltage and current; Step 2: Determine whether there is a ground fault, based on the alarm signal and the duration of the alarm signal, or the voltage and current amplitudes; if there is a ground fault, proceed to step 3; if there is no single-phase ground fault, proceed to step 6 to determine whether the grounding is restored; Step 3: According to the fault recording data, the sudden change branch and the grounding transformer branch are immediately expanded for recording, the current phases of the sudden change branch and the grounding transformer branch are compared, and the line troubleshooting priority is set according to the current phase comparison; Step 4: Lock the fault branch and set the troubleshooting sequence according to the magnitude of the zero-sequence current; Step 5: Apply for dispatch approval and execute the grounding investigation procedure; perform grounding investigation on the faulty line in sequence, which includes opening and closing the outgoing line switch on the faulty line; Step 6: Determine whether the grounding is restored. When the 35kV bus grounding alarm signal is restored, it is determined that the single-phase grounding fault has been restored. After the single-phase grounding fault is restored, exit the single-phase grounding fault search; If all outgoing lines of the substation bus are grounded, but single-phase grounding still exists, it is determined to be a bus fault; the single-phase grounding intelligent detection program automatically exits the program operation when it detects a single-phase grounding reset signal; In step 1, the system is patrolled with a sampling step length of 2 seconds to continuously detect the ground fault signal of the small current grounding system. The detection method of the single-phase ground fault signal is as follows: If at time t1, the voltage of any phase or more of the busbar is lower than 70% of the rated operation, and the 35kV busbar voltage UO is greater than 3V, the signal is recorded as M1; If a 35kv grounding transformer current appears at time t2 and the current value is greater than 0.05A, the signal is recorded as M2; If the zero-sequence current of a branch suddenly increases at time t3, and the zero-sequence current is greater than 0.05A, the signal is recorded as M3; In step 2, If the M1 and M2 signals persist for more than 2 minutes and there are no line and transformer branch alarm signals, it is determined that a single-phase grounding fault has occurred on the bus, which is recorded as the TZ1 signal, and the time t4 when the bus grounding characteristic quantity first appears is recorded; If the M1 and M2 signals persist for more than 2 minutes and the M3 signal appears at the same time, it is determined that a ground fault has occurred in the line; when the above situation occurs in the control system, the control system records the bus or distribution line where the ground fault occurs, completes the detection of the grounding characteristic quantity TZ2, and records the time t5 when the cable grounding characteristic quantity first appears; When one or more of the above situations occur in the central control system, the central control system records the bus or distribution line where the grounding fault occurs, and a grounding fault exists, and proceed to step three.

2. The cable grounding fault detection method according to claim 1, characterized in that: In step 3, if only metallic grounding fault is considered, the fault phase current of the fault line is approximately equal to the grounding transformer zero-sequence current; if the offset grounding resistance non-metallic grounding is considered, the fault phase current angle of the fault line is approximately equal to the grounding transformer zero-sequence current angle, and the grounding transformer IA=IB=IC=I0; According to the magnitude of zero-sequence current, the closer the zero-sequence current amplitude and angle are to the grounding transformer, the fault line is determined.

3. The cable grounding fault detection method according to claim 1, characterized in that: In step 5, the fault branch is grounded in sequence, and the grounding search includes opening and closing the outgoing line switch on the fault branch; If the single-phase grounding characteristic disappears after the outgoing line switch of line L1 is opened, the intelligent grounding detection program is terminated; If the single-phase grounding characteristic disappears after the L2 outgoing line switch is opened, the outgoing line switch that has been opened before is closed in reverse order. If the grounding characteristic appears again after the L3 outgoing line switch is closed, the L3 outgoing line switch is opened and the execution of the grounding intelligent detection program is terminated at the same time; it is determined that both L2 and L3 have grounding faults; If a ground fault still occurs after all outgoing line switches of the faulty bus are opened, it is considered that a ground fault has occurred in the bus, and all switches related to the bus are opened.

4. The cable grounding fault detection method according to claim 1, characterized in that: In step six, the remote signal in the main grid control system is patrolled with a sampling step of 2 seconds. When the 35kV bus grounding alarm signal is restored, it is determined that the grounding fault has been restored; the grounding fault search is exited after the grounding fault is restored.

Images