Small current grounding fault discrimination and location method

Abstract

The present invention provides a method for discriminating and locating small-current grounding faults, belonging to the technical field of power grid electric power. The method includes: according to the power grid line topology diagram, using a mobile small-current grounding detection device to sequentially detect each primary switch cabinet of the substation, and judging whether the fault location of the small-current grounding fault is on the bus side or the line side of the substation. If no small-current grounding fault is detected in the lines where each primary switch cabinet is located, it is determined that it is on the bus side of the substation, belonging to a bus grounding fault; if a small-current grounding fault is detected in the line where one of the primary switch cabinets is located, it is determined that it is on the line side; in accordance with the hierarchical order, sequentially detect each ring main unit and user transformer carried by the primary switch cabinet where the small-current grounding fault exists until the fault location of the small-current grounding fault is found.

Description

Technical Field

[0001] The present invention relates to the technical field of power grid electricity, and particularly relates to a method for discriminating and locating small current grounding faults. Background Art

[0002] Among the faults in a small current grounding system, the most common one is a single-phase grounding fault. When a single-phase grounding fault occurs, the small current grounding system does not damage the symmetry of the system voltage, and the fault current value is small, which does not affect the continuous power supply to users. The system can operate for 1 - 2 hours. However, during long-term operation, the phase-to-ground voltage of the non-fault phase becomes 1.732 times the original value, which may cause the breakdown of weak insulation links and develop into an inter-phase short circuit, resulting in further faults, such as inter-phase insulation breakdown, ferromagnetic resonance overvoltage, intermittent arc grounding overvoltage, etc. Therefore, it is necessary to find the fault point in time and eliminate the fault.

[0003] To determine the location of the fault point, usually the power-off method is adopted to disconnect each line one by one to judge which line has a fault. This is time-consuming and laborious, and it will also cause an impact on the power grid due to the opening and closing of switches. The existing improvement method is to modify power equipment, install small current grounding fault detection devices for collecting and reporting device currents on each necessary node device in the power grid, and when a small current grounding system fault occurs, collect current data centrally for fault location analysis. The solution of the existing technology requires the transformation of the secondary circuit of the current transformer of the device, which will correspondingly lead to the risk of misoperation of the protection device and the risk of open circuit of the secondary circuit of the current transformer during the installation process. The failure rate of the detection device during long-term operation is high; secondly, there is not enough modification space in the secondary room of the switch cabinet equipment, and some switch cabinet equipment cannot install small current grounding fault detection devices, and the traditional power-off method still needs to be used for investigation, so it is difficult to systematically analyze the fault location at one time, with poor safety and low efficiency. Summary of the Invention

[0004] In view of this, the present invention provides a method for discriminating and locating small current grounding faults, which does not require the modification of power grid equipment and can efficiently discriminate and locate small current grounding faults in a line.

[0005] The technical solution adopted by the embodiment of the present invention to solve its technical problems is as follows:

[0006] A method for discriminating and locating small current grounding faults, characterized by comprising:

[0007] According to the power grid line topology diagram, use a mobile small current grounding detection device to sequentially detect each primary switch cabinet of the substation, and judge whether the fault location of the small current grounding fault is on the bus side or the line side of the substation. The mobile small current grounding detection device is composed of a small current grounding detection device and a secondary circuit current transformer;

[0008] If no small current grounding fault is detected in all the lines where the primary switchgear is located, it is determined that the fault is located on the substation bus side, indicating a grounding fault on the bus.

[0009] If a small current grounding fault is detected in the line where one of the primary switchgears is located, it is determined that the fault location is on the line side.

[0010] In hierarchical order, the secondary switchgears carried by the primary switchgear with the detected small current grounding fault are sequentially detected until the fault location of the small current grounding fault is found.

[0011] Preferably, the step of sequentially detecting the secondary switchgears carried by the primary switchgear with the detected small current grounding fault in hierarchical order until the fault location of the small current grounding fault is found includes:

[0012] First, use the mobile small current grounding detection device to detect each first-level secondary switchgear carried by the primary switchgear. The detection object is the next-level secondary switchgear connection interval in each first-level secondary switchgear.

[0013] If no small current grounding fault is detected in all the first-level secondary switchgears 1i it is determined that a small current grounding fault has occurred in the connection cable from the rear section of the primary switchgear to each first-level secondary switchgear.

[0014] If a small current grounding fault is detected in one of the first-level secondary switchgears 1i detect each second-level secondary switchgear carried by the first-level secondary switchgear. The detection objects are the next-level secondary switchgear connection interval and the second-level secondary switchgear outgoing line interval in each second-level secondary switchgear. 1i If no small current grounding fault is detected in all the second-level secondary switchgears

[0015] it is determined that a small current grounding fault has occurred in the connection cable from the rear section of the first-level secondary switchgear to each second-level secondary switchgear. 1i If a small current grounding fault is detected in one of the second-level secondary switchgears

[0016] and the detected location is the second-level secondary switchgear outgoing line interval, it is determined that a small current grounding fault has occurred in the cable between the second-level secondary switchgear outgoing line interval and the user-side equipment it carries. 2i If a small current grounding fault is detected in one of the second-level secondary switchgears 2i and the detected location is the second-level secondary switchgear outgoing line interval, it is determined that a small current grounding fault has occurred in the cable between the second-level secondary switchgear outgoing line interval and the user-side equipment it carries.

[0017] If a small current grounding fault is detected in one of the second-level secondary switchgears 2i and the detected location is the second-level secondary switchgear 2iFor the next-level ring main unit connection interval, further detect the secondary ring main unit u 2i for each of the tertiary ring main units it powers;

[0018] If it is detected that one of the tertiary ring main units u 3i has the small current grounding fault and the detected location is the connection interval of the next-level ring main unit of the tertiary ring main unit u 3i then further detect each of the next-level ring main units powered by the tertiary ring main unit u 3i until it is determined that the connection cable from the rear section of the n-level ring main unit u ni to each (n + 1)-level ring main unit has the small current grounding fault, or the cable between the outgoing line interval of the n-level ring main unit of the n-level ring main unit u ni and the user-side equipment it powers has the small current grounding fault.

[0019] Preferably, the method for the mobile small current grounding detection device to detect whether the equipment has the small current grounding fault is: connect the secondary circuit current transformer to the secondary side of the primary CT of the equipment, collect the three-phase secondary voltage and current of the equipment in real time and perform grounding fault judgment, and the types of the equipment include ring main units, switch cabinets, and user transformers.

[0020] Preferably, the acquisition connector of the secondary circuit current transformer matches the wire diameter of the secondary side outgoing line of the primary CT of the equipment.

[0021] Preferably, a 24V DC power supply module is built into the mobile small current grounding detection device, the DC power supply module is connected to the small current grounding detection device, and the small current grounding detection device is connected to the secondary circuit current transformer.

[0022] As can be seen from the above technical solutions, the small current grounding fault discrimination and location method provided by the embodiments of the present invention, according to the power grid line topology diagram, uses a mobile small current grounding detection device to sequentially detect each primary switch cabinet of the substation, and determines whether the fault location of the small current grounding fault is on the bus side or the line side of the substation. The mobile small current grounding detection device consists of a small current grounding detection device and a secondary circuit current transformer; if no small current grounding fault is detected in the lines where each primary switch cabinet is located, it is determined that it is on the bus side of the substation, belonging to a bus grounding fault; if a small current grounding fault is detected in the line where one of the primary switch cabinets is located, it is determined that it is on the line side; in accordance with the hierarchical order, sequentially detect each level of ring main unit powered by the primary switch cabinet with the small current grounding fault until the fault location of the small current grounding fault is found. Through the method of the present invention, it is possible to eliminate the risk of open circuit in the secondary circuit of the current transformer without modifying the power grid equipment, and can efficiently perform discrimination and location of small current grounding faults in the line. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is the flowchart of the small current grounding fault discrimination and location method of the present invention.

[0024] Figure 2 This is the schematic diagram of the composition of the mobile small current grounding detection device in the present invention.

[0025] Figure 3 This is the waveform diagram of the small current grounding fault detected in Example 1.

[0026] Figure 4 This is the waveform diagram of the small current grounding fault detected in Example 2. Detailed implementation manner

[0027] The following further elaborates in detail on the technical solutions and technical effects of the present invention in combination with the accompanying drawings of the present invention.

[0028] As Figure 1 shown, the present invention provides a small current grounding fault discrimination and location method, including the following steps:

[0029] Step S1: According to the power grid line topology diagram, use the mobile small current grounding detection device to sequentially detect each primary switch cabinet of the substation, and judge whether the fault location of the small current grounding fault is on the bus side or the line side of the substation;

[0030] Among them, the used mobile small current grounding detection device is as Figure 2 shown, and is composed of a small current grounding detection device based on the amplitude comparison method of the phase-to-phase power frequency current change amount and a secondary circuit current transformer. The acquisition joint of the secondary circuit current transformer matches the wire diameter of the secondary side outlet of the primary CT of the equipment, and can be quickly connected without modifying the secondary side CT interface of the power grid equipment. A 24V DC power supply module is built into the mobile small current grounding detection device, and there is no need to connect power from the power grid equipment. The DC power supply module is connected to the small current grounding detection device, and the small current grounding detection device is connected to the secondary circuit current transformer. The method for the mobile small current grounding detection device to detect whether there is a small current grounding fault in the equipment is: connect the secondary circuit current transformer to the secondary side of the primary CT of the power grid equipment, collect the three-phase secondary voltage and current of the equipment in real time and perform grounding fault judgment. The types of power grid equipment include ring main units, switch cabinets, and user transformers.

[0031] Step S2: If no small current grounding fault is detected in the lines where each primary switch cabinet is located, it is determined that the fault is on the bus side of the substation, belonging to a bus grounding fault;

[0032] Step S3: If a small current grounding fault is detected in the line where one of the primary switch cabinets is located, it is determined that the fault is on the line side;

[0033] Step S4: Detect each level of ring main unit (RMU) connected to the primary switchgear with a small current grounding fault in hierarchical order until the fault location of the small current grounding fault is found.

[0034] The specific implementation process of the above step S4 is as follows:

[0035] Step S41: First, use a mobile small current grounding detection device to detect each first-level RMU connected to the primary switchgear. The detection object is the next-level RMU connection interval in each first-level RMU.

[0036] Step S42: If no small current grounding fault is detected in all first-level RMUs u 1i it is determined that a small current grounding fault has occurred in the connection cable from the rear section of the primary switchgear to each first-level RMU, where u 1i ∈[u 11 , u 12 , … u 1I , and I is the total number of first-level RMUs.

[0037] Step S43: If a small current grounding fault is detected in one of the first-level RMUs u 1i , detect each second-level RMU connected to the first-level RMU u 1i . The detection objects are the next-level RMU connection interval and the outgoing line interval of each second-level RMU.

[0038] Step S44: If no small current grounding fault is detected in all second-level RMUs, it is determined that a small current grounding fault has occurred in the connection cable from the rear section of the first-level RMU u 1i to each second-level RMU.

[0039] Step S45: If a small current grounding fault is detected in one of the second-level RMUs u 2i and the detected location is the outgoing line interval of the second-level RMU, it is determined that a small current grounding fault has occurred in the cable between the outgoing line interval j of the second-level RMU u 2i and the user-side equipment it serves. Among them, the total number of second-level RMUs u 2i is I2, and j is the interval serial number of the RMU.

[0040] Step S46: If a small current grounding fault is detected in one of the second-level RMUs u 2i and the detected location is the next-level RMU connection interval of the second-level RMU u 2i , further detect each third-level RMU connected to the second-level RMU u 2i .

[0041] Step S47: If a small current grounding fault is detected in one of the third-level RMUs u 3iThere is a small current grounding fault, and the detected location is the connection interval of the next-level ring main unit u of the three-level ring main unit 3i Then further detect each next-level ring main unit carried by the three-level ring main unit u 3i until the determined result is the n-level ring main unit u ni A small current grounding fault occurs in the connection cable from the latter section to each n+1-level ring main unit, or a small current grounding fault occurs in the cable between the outgoing line interval j of the n-level ring main unit u of the n-level ring main unit and the user-side equipment it carries ni

[0042] Two specific implementation examples are provided below

[0043] Figure 3 Example 1, a small current grounding fault occurs in a 10kV distribution network line of a certain substation. The maintenance personnel put into operation a movable small current grounding fault detection device based on the phase-interphase power frequency current change ratio amplitude method on the side of the ring main unit. The device power supply is taken from the internal DC 24V power supply of the equipment. A small high-precision open-type current transformer is used to sample the three-phase secondary current of the line in real time for grounding judgment. After detecting each secondary ring main unit carried by this line one by one, no abnormality is found. According to the line topology diagram, it is judged that a grounding fault occurs in the overhead line branch carried by the latter section of the first-level ring main unit. After verification, on-site, the insulation of the cable intermediate joint deteriorated, resulting in a small current grounding fault Figure of the small current grounding fault waveform detected

[0044] Figure 4 Example 2, a small current grounding fault occurs in a 10kV distribution network line of a certain substation. The maintenance personnel put into operation a movable small current grounding fault detection device based on the phase-interphase power frequency current change ratio amplitude method in the switch cabinet on the 10kV line side. The device power supply is taken from the internal DC 24V power supply of the equipment. A small high-precision open-type current transformer is used to sample the three-phase secondary current of the line in real time for grounding judgment. After detecting each ring main unit carried by this line one by one, it is found that no grounding fault occurs in the latter section of the line. After verification, on-site, the cable terminal head in the 10kV switch cabinet in the substation failed, resulting in a small current grounding fault Figure of the small current grounding fault waveform detected

[0045] The present invention uses a movable small current grounding detection device for real-time sampling and analysis. When a grounding fault occurs, a small high-precision open-type current transformer can sample the three-phase secondary current of the switch cabinet in real time and input it into the small current grounding fault detection device. Based on the phase-interphase power frequency current change ratio amplitude method, it is judged whether a small current grounding fault occurs in the latter section of the line; the device itself carries a 24V DC power supply, avoiding the problem of no power supply in the switch cabinet. The operation process of the device is simple and safe, there are no risks to personnel safety and equipment safety, it can detect small current grounding faults in harsh environments, avoiding the restrictions of the equipment operation environment and the problem of no power supply, with a wide range of applications, stable and controllable, practical and reliable

[0046] For the power grid, there is no need for the long-term operation of the detection device based on the amplitude comparison method of the phase-interval power frequency current variation, breaking through the constraints of the operating environment and avoiding the problem of high failure rate during the long-term operation of the device; the mobile operation is simple, there is no need to transform the secondary circuit of the current transformer, and the risk of misoperation of the protection device and open circuit of the secondary circuit of the current transformer can be effectively avoided.

[0047] The above-disclosed are only the preferred embodiments of the present invention. Of course, the scope of the rights of the present invention cannot be limited thereby. Those of ordinary skill in the art can understand all or part of the processes of implementing the above embodiments, and the equivalent changes made according to the claims of the present invention still fall within the scope covered by the invention.

Claims

1. A method for discriminating and locating small current grounding faults, characterized in that, Including: According to the power grid line topology diagram, use the mobile small current grounding detection device to sequentially detect each primary switch cabinet of the substation, and judge whether the fault location of the small current grounding fault is on the bus side or the line side of the substation. The mobile small current grounding detection device is composed of a small current grounding detection device and a secondary circuit current transformer; If no small current grounding fault is detected in the lines where each of the primary switch cabinets is located, it is determined that it is on the bus side of the substation, belonging to a bus grounding fault; If a small current grounding fault is detected in the line where one of the primary switch cabinets is located, it is determined that it is on the line side; In accordance with the hierarchical order, sequentially detect each ring main unit carried by the primary switch cabinet where the small current grounding fault exists until the fault location of the small current grounding fault is found; The step of sequentially detecting each ring main unit carried by the primary switch cabinet where the small current grounding fault exists in accordance with the hierarchical order until the fault location of the small current grounding fault is found includes: First, use the mobile small current grounding detection device to detect each first-level ring main unit carried by the primary switch cabinet, and the detection object is the next-level ring main unit connection interval in each of the first-level ring main units; If no small current grounding fault is detected in all the first-level ring main units u 1i it is determined that a small current grounding fault has occurred in the connection cables from the rear section of the first-level switchgear to each of the first-level ring main units; If one of the first-level ring main units u is detected 1i with the small current grounding fault, the first-level ring main unit u is detected 1i for each of the second-level ring main units it serves. The objects to be detected are the next-level ring main unit connection intervals and the second-level ring main unit outgoing line intervals of each of the second-level ring main units; If no small current grounding fault is detected in all the secondary ring main units, it is determined that the fault occurs in the primary ring main unit u 1i The small current grounding fault occurs in the connection cables from the latter section to each of the secondary ring main units; If one of the secondary ring main units u is detected 2i and the small current grounding fault exists, and the detected location is the outgoing line interval of the secondary ring main unit, it is determined that 2i a small current grounding fault occurs in the cable between the outgoing line interval of the secondary ring main unit u and the user-side equipment it serves; If one of the secondary ring main units u is detected 2i has the small current grounding fault and the detected location is the connection interval of the secondary ring main unit u 2i at the next-level ring main unit, then further detect each tertiary ring main unit carried by the secondary ring main unit u 2i ; If one of the tertiary ring main units u is detected 3i and there is the small current grounding fault, and the detected location is the tie interval of the next-level ring main unit of the tertiary ring main unit u 3i then further detect each of the next-level ring main units carried by the tertiary ring main unit u 3i until the determined result is that the small current grounding fault occurs in the tie cable from the nth-level ring main unit u ni to each (n + 1)th-level ring main unit in the back section, or the small current grounding fault occurs in the cable between the outgoing line interval of the nth-level ring main unit of the nth-level ring main unit u ni and the equipment on the user side it carries.

2. The small current grounding fault discrimination and location method according to claim 1, characterized in that, The method for the mobile small current grounding detection device to detect whether there is a small current grounding fault in the equipment is: connect the secondary circuit current transformer to the secondary side of the primary CT of the equipment, and collect the three-phase secondary current of the equipment in real time and perform grounding fault judgment. The types of the equipment include ring main units and switch cabinets.

3. The small current grounding fault discrimination and location method according to claim 2, characterized in that, The collection connector of the secondary circuit current transformer matches the wire diameter of the secondary side outgoing line of the primary CT of the equipment.

4. The small current grounding fault discrimination and location method according to claim 3, characterized in that, A 24V DC power supply module is built in the mobile small current grounding detection device. The DC power supply module is connected to the small current grounding detection device, and the small current grounding detection device is connected to the secondary circuit current transformer.

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