High resistance grounding protection method and system under looped power supply mode of small resistance grounding system

Abstract

The application discloses a high-resistance grounding protection method and system under a small-resistance grounding system ring string power supply mode, and belongs to the field of relay protection of power systems. The method comprises the following steps: collecting a zero sequence voltage of a bus of a transformer substation in the system and a zero sequence current of an interval in the substation in real time and calculating the amplitudes in real time; judging whether a grounding fault occurs in the system in real time through a zero sequence ratio overcurrent criterion; if it is judged that a grounding fault occurs, sending an interval grounding start signal to the outside through a communication network and receiving a grounding start signal of a neighboring interval at the same time; and performing logical comparison and selection on the grounding start signal received by the interval, so as to judge whether an intra-zone fault occurs. The method can accurately judge the fault area and quickly isolate the fault in the initial stage of the high-resistance grounding fault, and maximally improves the power supply reliability of the system.

Description

Technical Field

[0001] This application relates to the field of relay protection in power systems, specifically to a method and system for protecting against high-resistance grounding faults in a low-resistance grounding system with a ring-series power supply mode. Background Technology

[0002] Currently, some urban power distribution networks use low-resistance grounding, with grounding resistance values ​​ranging from approximately 5 to 15 Ω. Urban subway AC power supply systems often use a neutral point grounding method with low resistance. When a high-resistance grounding fault occurs in the system, the fault characteristics are not obvious, and it often cannot be cleared for a long time. This not only seriously affects the reliability of the system's power supply but also easily causes personal injury.

[0003] Currently, considering the strong damping effect of high-resistance grounding, traditional zero-sequence overcurrent protection is still the primary protection scheme for high-resistance grounding faults. Generally, when designed to avoid metallic grounding faults outside the fault zone, the sensitivity of the capacitor current setting is low, often failing to operate during high-resistance grounding. Furthermore, subway AC power supply systems often use a ring-sequence power supply method. Under this method, when a high-resistance grounding fault occurs in a certain interval of the ring-sequence, all incoming and outgoing lines of substations along the upstream line will detect zero-sequence currents of similar magnitude, making it impossible to locate the fault section. Traditional zero-sequence overcurrent protection primarily relies on setting time increments for selectivity. However, with the continuous rise in resource prices, subway builders increasingly need to adopt large-ring-sequence power supply methods to save resources and reduce construction costs. In this method, the time increments of traditional schemes are no longer sufficient to set the zero-sequence overcurrent protection to essentially lack selectivity, making the contradiction between selectivity and speed irreconcilable.

[0004] Therefore, there is an urgent need to provide a high-resistance grounding protection method for a low-resistance grounding system with a ring-series power supply mode, in order to overcome the shortcomings of the existing technology. Summary of the Invention

[0005] The purpose of this application is to provide a high-resistance grounding protection method and system for a low-resistance grounding system with a ring-series power supply mode, which can overcome the defects of the prior art.

[0006] To achieve the above objectives, the solution proposed in this application is as follows.

[0007] This application provides a high-resistance grounding protection method for a low-resistance grounding system with a ring-series power supply, comprising the following steps:

[0008] Real-time acquisition of zero-sequence voltage of substation busbars and zero-sequence current of bays within the system, and real-time calculation of amplitude;

[0009] The zero-sequence ratio overcurrent criterion is used to determine in real time whether a ground fault has occurred in the system.

[0010] If the grounding fault is determined to have occurred, the grounding start signal of the interval is sent out via multicast through the communication network, and grounding start signals from adjacent intervals are received simultaneously.

[0011] By performing logical comparison on the grounding start signal received by the interval from the adjacent interval, it is possible to determine whether the fault occurs within the interval, thus accurately identifying the fault area.

[0012] Optionally, in some embodiments of this application, the logical comparison method is as follows:

[0013] After the grounding start signal is sent at the specified interval:

[0014] If the interval receives grounding start signals from the adjacent two sides (ring network side and bus side), it is determined that the interval is outside the fault zone and no protection action is performed.

[0015] If the interval only receives a grounding start signal from an adjacent interval on one side or does not receive a grounding start signal from an adjacent interval, it is determined that there is a fault in the interval area, and a tripping and isolation fault protection action is performed.

[0016] If the interval is the first interval of a ring series, and a grounding start signal is received on the opposite side, it is determined to be an external fault in the interval area, and no protection action is performed.

[0017] Optionally, in some embodiments of this application, the zero-sequence ratio overcurrent criterion is as follows, wherein if the interval satisfies any one of the following three formulas (1) to (3), a ground fault is determined to have occurred in the system:

[0018] I0>I set.low (U0 th (1)

[0019]

[0020] I0>I set.high (U0 is any value) (3)

[0021] In the formula:

[0022] I0 is the zero-sequence current of the interval;

[0023] U0 is the zero-sequence voltage of the bus where the interval is located;

[0024] U g This is the zero-sequence voltage that occurs at the metallic grounding busbar;

[0025] U th This is the zero-sequence voltage at the inflection point;

[0026] I set.high The high setpoint is set for zero-sequence overcurrent operation;​

[0027] I set.low The low setpoint value is for zero-sequence overcurrent action.

[0028] Optionally, in some embodiments of this application, in the zero-sequence ratio overcurrent criterion, I set.high =K r ×I c Among them, K r For reliability, set it to 1.2 or higher; I c This is the capacitive current to ground of this interval when a metallic ground fault occurs outside the zone.

[0029] Optionally, in some embodiments of this application, in the zero-sequence ratio overcurrent criterion, I set.low Set the current to avoid unbalanced current and zero drift current, and set the primary current to 1-2A.

[0030] Optionally, in some embodiments of this application, the zero-sequence ratio overcurrent criterion,

[0031] Optionally, in some embodiments of this application, after a system ground fault is detected at any interval, a ground fault initiation signal for that interval is immediately multicast outward via the communication network, while also receiving ground fault initiation signals from adjacent intervals. Specifically, the first interval of the ring string will only receive ground fault initiation signals from adjacent intervals on the opposite side.

[0032] Optionally, in some embodiments of this application, after determining that the fault is within the interval, trip isolation protection is activated, which can achieve rapid tripping and accurate fault isolation.

[0033] Correspondingly, this application also provides a high-resistance grounding protection system under a ring-series power supply mode in a low-resistance grounding system, including a high-resistance grounding protection device; and the high-resistance grounding protection device includes:

[0034] The sampling and filtering module is used to acquire the sampling signals of the bus zero-sequence voltage and the zero-sequence current of each branch, and to calculate their amplitude in real time.

[0035] The zero-sequence ratio overcurrent module is used to determine in real time whether a ground fault has occurred in the system;

[0036] The grounding start signal transceiver module is used to send the grounding start signal of this interval to the outside multicast, and at the same time receive the grounding start signal of the adjacent interval.

[0037] The logic comparison module is used to perform logic comparison on the received grounding start signals of adjacent intervals to accurately determine the fault area.

[0038] Optionally, in some embodiments of this application, the high-resistance grounding protection device further includes:

[0039] The protection trip module is used to issue trip commands, trip the corresponding switch, and accurately isolate the fault.

[0040] Optionally, in some embodiments of this application, the high-resistance grounding protection device is installed in each substation on the ring power supply line; the high-resistance grounding protection device is connected to the same communication network and is connected to communication through the communication network.

[0041] The beneficial effects of this application are as follows:

[0042] The method of this application uses the zero-sequence ratio overcurrent criterion to determine high-resistance grounding, which can effectively identify high-resistance grounding faults; and it realizes the sharing of grounding start signals of each interval within the system based on the communication network. By performing logical comparison of the received grounding start signals of adjacent intervals, the fault area can be accurately located; the combination of the two can ultimately accurately and quickly isolate the fault in the early stage of high-resistance grounding faults, thereby maximizing the reliability of system power supply. Attached Figure Description

[0043] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0044] Figure 1 The zero-sequence ratio overcurrent criterion action curve provided in the embodiments of this application;

[0045] Figure 2 A schematic flowchart illustrating the high-resistance grounding protection method provided in this application embodiment;

[0046] Figure 3 A schematic diagram of a high-resistance grounding protection device provided in the embodiments of this application;

[0047] Figure 4 This is a schematic diagram of a single-phase grounding fault in a ring-type cable provided in an embodiment of this application;

[0048] Figure 5 This is a schematic diagram of a single-phase ground fault on a busbar provided in an embodiment of this application;

[0049] Figure 6 This is a schematic diagram of a single-phase grounding fault in a feeder provided in an embodiment of this application. Detailed Implementation

[0050] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application. In addition, in the description of this application, the term "comprising" means "including but not limited to". Furthermore, it should be understood that the specific embodiments described herein are only for illustration and explanation of this application and are not intended to limit this application.

[0051] This application provides a ground fault protection method and system for a low-resistance grounding system in a ring-series power supply configuration. The following provides a detailed description of each. It should be noted that the order of description of the following embodiments is not intended to limit the preferred order of the embodiments.

[0052] The method and system of this application can dynamically adjust the zero-sequence overcurrent action threshold according to the bus zero-sequence voltage. Compared with the fixed threshold of traditional zero-sequence overcurrent protection, it has higher sensitivity and can effectively identify single-phase high-resistance grounding faults. For ring-sequence power supply, the method and system can use the communication network to realize the real-time sharing of grounding start signals of each corresponding interval. By logically comparing the grounding start signals of the corresponding interval, the fault area can be accurately determined, thereby realizing rapid tripping and fault isolation.

[0053] This application provides a high-resistance grounding protection method for a low-resistance grounding system with a ring-series power supply, comprising the following steps:

[0054] The zero-sequence voltage of the busbar of each substation along the ring string and the zero-sequence current of each bay in the substation are collected and the amplitude is calculated in real time; each bay is judged in real time whether a ground fault has occurred by the zero-sequence ratio overcurrent criterion.

[0055] If a ground fault is detected, the ground fault initiation signal of this interval is sent out via multicast through the communication network, and the ground fault initiation signal of the adjacent interval is received at the same time.

[0056] By logically comparing the grounding start signals received from adjacent intervals, the fault area can be accurately determined.

[0057] Furthermore, in some embodiments of this application, once the fault is determined to be within the interval, trip isolation protection is activated, which can achieve rapid tripping and accurate fault isolation.

[0058] In this embodiment, the method uses the zero-sequence ratio overcurrent criterion to determine the high-resistance grounding start; it uses a communication network to realize the sharing of grounding start signals of each corresponding interval in the system; by logically comparing the grounding start signals of this interval and its adjacent intervals, it can finally realize the accurate location of high-resistance grounding faults under the ring-series power supply mode, and thus can quickly isolate the fault in the early stage of the fault, thereby improving the reliability of the system power supply.

[0059] In some embodiments of this application, the zero-sequence ratio overcurrent criterion is as follows: if any one of the following three formulas (1) to (3) is satisfied, it is determined that a single-phase ground fault has occurred in the system, and the ground fault of this interval is initiated:

[0060] I0>I set.low (U0 th (1)

[0061]

[0062] I0>I set.high (U0 is any value) (3)

[0063] In the formula:

[0064] I0 is the zero-sequence current of the interval;

[0065] U0 is the zero-sequence voltage of the bus where the interval is located;

[0066] U g This is the zero-sequence voltage that occurs at the metallic grounding busbar;

[0067] U th Zero-sequence voltage at the inflection point

[0068] I set.high The high setpoint is set for zero-sequence overcurrent operation;

[0069] I set.low The low setpoint value is for zero-sequence overcurrent action.

[0070] Furthermore, I set.high =K r ×I c K r The reliability factor is typically set to 1.2 or higher. c This refers to the capacitive current of this bay pair when an external metallic ground fault occurs. set.low The current is set to avoid unbalanced current and zero drift current, and is generally set to 1-2A for the primary current.

[0071] Please see Figure 1 As shown, Figure 1 This is the action curve diagram for the zero-sequence ratio overcurrent criterion. Figure 1 ​The zero-sequence ratio overcurrent criterion in this application shows I0, I... set.high I set.low 、U0、U g U th Equal parameter relationships.

[0072] In some embodiments of this application, in the logic comparison method, after periodically sending a ground start signal:

[0073] If a bay receives grounding start signals from adjacent bays on both sides (ring network side and busbar side), it is determined to be an external fault and no protection action is taken.

[0074] If the bay only receives a grounding start signal from an adjacent bay on one side (ring network side or bus side) or does not receive a grounding start signal from an adjacent bay, it is determined to be a fault within the bay area, and a tripping isolation fault protection action is performed.

[0075] If the interval is the first interval of the ring string and only needs to receive a grounding start signal on one side of the ring network, it is judged as an external fault and no protection action is performed.

[0076] In some embodiments of this application, when a system grounding fault is detected at any interval, a grounding start signal for that interval is immediately sent out via multicast through the communication network, and the grounding start signals corresponding to the adjacent intervals on both sides are also received.

[0077] Furthermore, for the first bay of a ring-string busbar, the other bays on the same busbar do not participate in the logic comparison. Therefore, it only has adjacent bays on the opposite side. Thus, it is only necessary to consider whether a grounding start signal from the opposite side bay is received before determining the fault area. For other bays that are not the first bay of a ring-string busbar, there are adjacent bays on both sides. Therefore, it is necessary to consider whether grounding start signals from the corresponding bays on both sides are received before determining the fault area.

[0078] Specifically, when any bay detects a ground fault in the system, it immediately sends a ground fault initiation signal to the outside via multicast through the communication network, and simultaneously receives the corresponding ground fault initiation signals from adjacent bays. Further, "adjacent bays" here refers to adjacent bays on both sides, meaning bays directly electrically connected to this bay, without any circuit breaker in between. Specifically, for the first bay in a ring series, the adjacent bays are the bays on the opposite side, therefore it only needs to receive the ground fault initiation signal from the opposite side. It can be imagined that, except for the first bay in a ring series, other bays simultaneously receive the ground fault initiation signals corresponding to their adjacent bays on both sides.

[0079] Specifically, in the high-resistance grounding protection method under the ring-series power supply mode of the low-resistance grounding system of this application, the logic comparison method may include: after a ground fault is detected in a certain bay, if no ground fault start signal is received or only received from an adjacent bay on one side within a certain period of time (within 1000ms, which can be 500~1000ms considering communication delay), then the ground fault is determined to be a fault within the bay area, and the tripping operation isolates the fault; if ground fault start signals are received simultaneously from adjacent bays on both sides within a certain period of time, then the ground fault is determined to be a fault outside the bay area, and the protection does not operate, that is, it does not trip. Further, the first bay in the ring series only needs to receive a ground fault start signal from the opposite side of the ring series to determine that the ground fault is a fault outside the bay area, and the protection does not operate.

[0080] Specifically, please see Figure 2 As shown in this embodiment, the high-resistance grounding protection method under the ring-series power supply mode of a low-resistance grounding system may include the following steps:

[0081] Step 1: Collect and calculate in real time the zero-sequence voltage U0 of the substation bus and the zero-sequence current I0 of each bay within the system;

[0082] Step 2: Use the zero-sequence ratio overcurrent criterion to determine in real time whether a ground fault has occurred. The zero-sequence ratio overcurrent criterion is as follows:

[0083] I0>I set.low (U0 th (1)

[0084]

[0085] I0>I set.high (U0 is any value) (3)

[0086] In the formula:

[0087] I0 is the zero-sequence current of this interval.

[0088] U0 is the zero-sequence voltage of the bus where this interval is located.

[0089] U g For the occurrence of zero-sequence voltage on the metallic grounding bus,

[0090] U th Zero-sequence voltage at the inflection point

[0091] I set.high For zero-sequence overcurrent operation, the high setpoint is I. set.high =K r ×I c K r The reliability factor is typically set to 1.2 or higher.​c This refers to the capacitive current of this bay to ground when an external metallic ground fault occurs.

[0092] I set.low The low setting value for zero-sequence overcurrent operation is set to avoid unbalanced current and zero-drift current, and is generally set to 1-2A for the primary current.

[0093] If any one of the above three formulas is satisfied, it is determined that a single-phase ground fault has occurred and the system has been grounded and started; if the zero-sequence ratio overcurrent criterion is satisfied, proceed to step three.

[0094] Step 3: If a certain interval detects a ground fault in the system, it initiates grounding and immediately sends a grounding start signal to the outside via multicast through the communication network. At the same time, it also receives grounding start signals from the corresponding intervals on both sides. The corresponding intervals on both sides refer to the upper and lower level intervals that are directly electrically connected to this interval (without crossing the circuit breaker).

[0095] Step 4: After startup, within a certain period of time (considering communication network latency, this can generally be set to 500-1000ms), determine the fault location (by checking whether grounding startup signals are received from both sides):

[0096] If no ground fault start signal is received or only a ground fault start signal is received from an adjacent bay on one side, the ground fault is determined to be a fault within this bay area, and the protection trips to isolate the fault.

[0097] If ground fault start signals are received simultaneously from adjacent bays on both sides (the first bay of the ring string only needs to receive the ground fault start signal from the opposite side of the ring string), then the ground fault is determined to be an external fault in this bay, and the protection will not operate.

[0098] This application also provides a high-resistance grounding protection system for a low-resistance grounding system in a ring-series power supply mode, including a high-resistance grounding protection device. The high-resistance grounding protection system of this application can use the above-described method to accurately determine the fault area and accurately isolate the fault, thereby improving the reliability of the system power supply and effectively preventing personal injury caused by line faults.

[0099] The high-resistance grounding protection system of this application includes multiple high-resistance grounding protection devices. For example... Figure 3 As shown, each high-resistance grounding protection device includes: a sampling and filtering module 1001, a zero-sequence ratio overcurrent discrimination module 1002, a grounding start signal transceiver module 1003, a logic comparison module 1004, and a protection tripping module 1005. Furthermore, the high-resistance grounding protection devices are installed in each substation on the ring-series power supply line, and each high-resistance grounding device is connected to the same communication network for easy communication connection.

[0100] Furthermore, the sampling and filtering module 1001 is used to acquire the bus zero-sequence voltage and the zero-sequence current sampling signals of each branch, and calculate the amplitude in real time.

[0101] Furthermore, the zero-sequence ratio overcurrent discrimination module 1002 is used to determine in real time whether a ground fault has occurred in the system.

[0102] Furthermore, the grounding start signal transceiver module 1003 is used to multicast the grounding start signal of this interval to the outside, and at the same time receive the grounding start signals of the corresponding intervals on both sides.

[0103] Furthermore, the logic comparison module 1004 is used to perform logic analysis and comparison on the received grounding start signal to accurately determine the fault area.

[0104] Furthermore, the protection trip module 1005 is used to issue a grounding trip command, trip the switch, and accurately isolate the fault.

[0105] It should be understood that the above-described device embodiments are merely illustrative, and the device disclosed in this application can also be implemented in other ways. For example, the division of units / modules in the above embodiments is only a logical functional division, and there may be other division methods in actual implementation. For example, multiple units, modules, or components may be combined, or integrated into another system, or some features may be ignored or not executed.

[0106] Furthermore, unless otherwise specified, the functional units / modules in the various embodiments of this application can be integrated into one unit / module, or each unit / module can exist physically separately, or two or more units / modules can be integrated together. The integrated units / modules described above can be implemented in hardware or as software program modules.

[0107] In this application, if the integrated unit / module is implemented in hardware, the hardware can be digital circuits, analog circuits, etc. The physical implementation of the hardware structure includes, but is not limited to, transistors, memristors, etc. Unless otherwise specified, the processor or chip can be any suitable hardware processor, such as a CPU, GPU, FPGA, DSP, and ASIC, etc. Unless otherwise specified, on-chip cache, off-chip memory, and storage can be any suitable magnetic or magneto-optical storage medium, such as resistive random access memory (RRAM), dynamic random access memory (DRAM), static random access memory (SRAM), enhanced dynamic random access memory (EDRAM), high-bandwidth memory (HBM), hybrid memory cube (HMC), etc.

[0108] In this application, if the integrated unit / module is implemented as a software program module and sold or used as an independent product, it can be stored in a computer-readable storage device (CMD). Based on this understanding, the technical solution of this application, in essence, or the part that contributes to the prior art, or all or part of the technical solution, can be embodied in the form of a software product. This computer software product is stored in a memory and includes several instructions to cause a computer device (which may be a personal computer, server, or network device, etc.) to execute all or part of the steps of the methods of the various embodiments disclosed herein. The aforementioned memory includes various media capable of storing program code, such as a USB flash drive, read-only memory (ROM), random access memory (RAM), portable hard drive, magnetic disk, or optical disk.

[0109] This application uses an example of grounding faults occurring in the ring-string cable, busbar, and feeder of a substation in the system to briefly introduce the basic process of implementing the method of this application. Furthermore, these three types of faults are basically common fault types in subway AC power supply systems. Details are shown below.

[0110] Please see Figure 4 , Figure 4This diagram illustrates a single-phase ground fault in a ring-type cable, where K1 is the fault point. When a ground fault occurs at point K1, all incoming and outgoing line bays upstream of K1 will detect zero-sequence currents of similar magnitude. The zero-sequence ratio overcurrent criterion will determine that a ground fault has been initiated, and each bay will immediately send a ground fault initiation signal via the communication network. Furthermore, within a certain period after initiation, bays 102 and 104 of substation S1 will simultaneously receive ground fault initiation signals from their respective sides, while bay 312 of the main substation will receive a ground fault initiation signal from the opposite side (bay 312 of the main substation is the first bay in the ring-type cable; receiving only a ground fault initiation signal from the opposite side is sufficient to determine it as an external fault). Therefore, all will determine that this fault is an external fault and will not activate the outgoing signals (e.g., bay 102 of substation S1 will simultaneously receive ground fault initiation signals from bay 104 on the busbar side of this substation and bay 312 on the ring-type cable side of the opposite substation). Furthermore, the 104 bay of the S2 substation will only receive the grounding start signal from the bus side (102 bay) within the station, and will not receive the grounding start signal from the ring string side (the 102 bay of the S3 station on the opposite side of the ring string will basically not detect the zero-sequence current not starting). Therefore, the 104 bay will determine that this fault is an intra-zone fault with rapid action to clear the fault.

[0111] Please see Figure 5 , Figure 5 This is a schematic diagram of a single-phase ground fault on the busbar, where K2 is the fault point. When a ground fault occurs at point K2, all incoming and outgoing line bays upstream of K2 will detect zero-sequence currents of similar magnitude. The zero-sequence ratio overcurrent criterion will determine that it is a ground fault and initiate the fault, and each will immediately send a ground fault initiation signal to the outside via the communication network. Furthermore, bays 102 and 104 of substation S1 will simultaneously receive ground fault initiation signals from their respective sides, and bay 312 of the main substation will also receive a ground fault initiation signal from the opposite side (bay 312 of the main substation is the first bay of the ring series, and only needs to receive a ground fault initiation signal from the opposite side to determine that it is an external fault). Therefore, all of them will determine that this fault is an external fault and will not activate the outgoing signals (e.g., bay 104 of substation S1 will simultaneously receive initiation signals from bay 102 on the busbar side of this substation and bay 102 on the ring series side of substation S2). Furthermore, the 102 protection device at S2 station will only receive the grounding start signal from the ring string side (S1 station 104 bay), and will not receive the grounding start signal from the bus side (because S2 station 104, 312, and 100 bays will basically not detect zero-sequence current). Therefore, the 102 bay will determine that this fault is an intra-zone fault fast-acting output cut-off fault.

[0112] Please see Figure 6 , Figure 6This is a schematic diagram of a single-phase ground fault in a feeder, where K3 is the fault point. When a ground fault occurs at point K3, all incoming and outgoing line bays upstream of K3 will detect zero-sequence currents of similar magnitude. The zero-sequence ratio overcurrent criterion will determine that it is a ground fault and initiate the fault response, with each bay immediately sending a ground fault initiation signal via the communication network. Furthermore, bay 102 of substation S2 and bays 102 and 104 of substation S1 will receive ground fault initiation signals from their respective sides. Bay 312 of the main substation will also receive a ground fault initiation signal from the opposite side (bay 312 of the main substation is the first bay in the ring series, and only needs to receive a ground fault initiation signal from the opposite side to determine that it is an external fault). Therefore, all of them will determine that this fault is an external fault and will not activate the outgoing signals (e.g., bay 102 of substation S2 will simultaneously receive ground fault initiation signals from bay 312 of the busbar side and bay 104 of the ring series side of substation S1). Furthermore, since 312 in the S2 substation is the power supply end (not the first bay of the ring series), it will only receive the grounding start signal from the bus side (S2 station 102 bay). Therefore, the 312 bay will determine that this fault is an intra-zone fault fast-acting exit clearance fault.

[0113] In summary, the method and system of this application can dynamically adjust the zero-sequence overcurrent action threshold according to the bus zero-sequence voltage, which is more sensitive than the fixed threshold of traditional zero-sequence overcurrent protection and can effectively identify single-phase high-resistance grounding faults. For ring-sequence power supply, the method and system of this application can use a communication network to realize real-time sharing of grounding start signals for each corresponding bay. By using the zero-sequence ratio overcurrent criterion and logic comparison to select the grounding start signal of the corresponding bay, the fault area can be accurately determined, thereby achieving rapid tripping and fault isolation.

[0114] The above embodiments are merely illustrative of the technical concept of this application and should not be construed as limiting the scope of protection of this application. Those skilled in the art should understand that any modifications or equivalent substitutions to the specific embodiments of this application that do not depart from the technical concept and scope proposed in this application should be covered within the scope of the claims of this application.

Claims

1. A high-resistance grounding protection method under a ring-series power supply mode in a low-resistance grounding system, characterized in that, Includes the following steps: Real-time acquisition of zero-sequence voltage of substation busbars and zero-sequence current of bays within the system, and real-time calculation of amplitude; The zero-sequence ratio overcurrent criterion is used to determine in real time whether a ground fault has occurred in the system. If the grounding fault is determined to have occurred, the grounding start signal of the interval is sent out via multicast through the communication network, and the grounding start signal of the adjacent interval is received at the same time. The adjacent interval refers to the interval directly electrically connected to this interval and not crossing the upper or lower level of the circuit breaker in between. Within a preset time period after sending the grounding start signal, the grounding start signals of the adjacent intervals are logically compared to determine whether a fault occurs within the interval. The preset time period is used to overcome communication delay.

2. The high-resistance grounding protection method under ring-series power supply mode in a low-resistance grounding system according to claim 1, characterized in that, The logical comparison method is as follows: After the grounding start signal is sent at the specified interval: If the interval receives a grounding start signal from the adjacent two intervals respectively, it is determined that the fault is outside the interval area and no protection action is performed; If the interval only receives a grounding start signal from an adjacent interval on one side or does not receive a grounding start signal from an adjacent interval, it is determined that there is a fault in the interval area, and a tripping and isolation fault protection action is performed. If the interval is the first interval of a ring series and only needs to receive a grounding start signal on the opposite side, it is determined to be an external fault in the interval area, and no protection action is performed.

3. The high-resistance grounding protection method under ring-series power supply mode in a low-resistance grounding system according to claim 1, characterized in that, The zero-sequence ratio overcurrent criterion is as follows, wherein if the interval satisfies any one of the following three formulas (1) to (3), then a ground fault is determined to have occurred in the system: I0>I set.low (U0<U th )(1) I0>I set.high (U0 is any value)(3) In the formula: I0 is the zero-sequence interval current; U0 is the zero-sequence voltage of the bus where the interval is located; U g This is the zero-sequence voltage that occurs at the metallic grounding busbar; U th This is the zero-sequence voltage at the inflection point; I set.high The high setpoint is set for zero-sequence overcurrent operation; I set.low The low setpoint value is for zero-sequence overcurrent action.

4. The high-resistance grounding protection method under ring-series power supply mode in a low-resistance grounding system according to claim 3, characterized in that, In the zero-sequence ratio overcurrent criterion, I set.high =K r ×I c Among them, K r For reliability, set it to 1.2 or higher; I c This refers to the capacitive current to ground of the interval when a metallic ground fault occurs outside the affected area.

5. The high-resistance grounding protection method under ring-series power supply mode in a low-resistance grounding system according to claim 3, characterized in that, In the zero-sequence ratio overcurrent criterion, I set.low Set the current to avoid unbalanced current and zero drift current, and set the primary current to 1-2A.

6. The high-resistance grounding protection method under ring-series power supply mode in a low-resistance grounding system according to claim 3, characterized in that, In the zero-sequence ratio overcurrent criterion .

7. The high-resistance grounding protection method under ring-series power supply mode in a low-resistance grounding system according to claim 1, characterized in that, Once the fault is determined to be within the specified interval, trip isolation protection is activated.

8. A high-resistance grounding protection system under a ring-series power supply mode in a low-resistance grounding system, characterized in that, Including high-resistance grounding protection devices; Furthermore, the high-resistance grounding protection device includes: The sampling and filtering module is used to acquire the sampling signals of the bus zero-sequence voltage and the zero-sequence current of each branch, and to calculate their amplitude in real time. The zero-sequence ratio overcurrent module is used to determine in real time whether a ground fault has occurred in the system; The grounding start signal transceiver module is used to send the interval grounding start signal to the outside multicast and receive the grounding start signal corresponding to the adjacent interval. The adjacent interval refers to the upper and lower level intervals that are directly electrically connected to this interval and do not cross the circuit breaker in the middle. The logic comparison module is used to perform logic comparison on the received grounding start signal within a preset time period after the grounding start signal is sent, so as to accurately determine the fault area. The preset time period is used to overcome communication delay.

9. The high-resistance grounding protection system under the ring-series power supply mode of the low-resistance grounding system according to claim 8, characterized in that, The high-resistance grounding protection device is installed in each substation on the ring power supply line; the high-resistance grounding protection device is connected to the same communication network for communication.

10. The high-resistance grounding protection system under the ring-series power supply mode of the low-resistance grounding system according to claim 8, characterized in that, The high-resistance grounding protection device also includes: The protection trip module is used to issue trip commands, trip the corresponding switch, and accurately isolate the fault.

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