Electrified access protection device and method for neutral point current-limiting reactor of 330kV transformer

Abstract

The invention belongs to the technical field of electric power facility protection, and particularly relates to a 330kV transformer neutral point current-limiting reactor live access protection device and method, and the method comprises the steps: enabling a grounding end of a bypass grounding loop to be grounded, enabling the other end of the bypass grounding loop to be connected with a grounding copper bar to be connected to a transformer neutral point through a cable, and enabling the grounding end of the bypass grounding loop to be grounded; an insulation operating rod is used for inputting a bypass grounding loop, inputting a discharge gap protector to monitor that the voltage is within a safe range during construction of a worker in real time, inputting a discharge protector to provide a short-circuit current channel, and then grounding a grounding end to be connected to a current limiting reactor through a cable. After the other end of the current-limiting reactor to be connected is connected to the neutral point grounding copper bar of the transformer to be connected through a cable, the isolation switch of the neutral point current-limiting reactor is switched on, the current-limiting reactor can be connected in an electrified mode through the device and the method, and the power transmission amount of each transformer can be increased by 680 million kilowatt-hours.

Description

Technical Field

[0001] The present invention belongs to the technical field of power facility protection, and in particular relates to a live connection protection device and method for a neutral point current limiting reactor of a 330kV transformer. Background Art

[0002] Transformers play a crucial role in the power system, acting as the "heart" of substations, responsible for voltage conversion and energy transmission, ensuring stable operation. In recent years, with the vigorous economic growth of the Ningxia Hui Autonomous Region, the power system load has continued to climb, and the construction of self-powered power supplies by enterprises has accelerated. Consequently, the short-circuit capacity within the power grid has increased annually, leading to a continuous increase in the maximum short-circuit current faced by transformers, posing a serious threat to the stable operation of substations and the entire power grid.

[0003] A special inspection conducted in 2020 in a northwestern province revealed that 23 330 kV transformers under its jurisdiction had insufficient short-circuit resistance. These substations, mostly located in energy bases or local industrial parks, have high industrial electricity demand, placing higher demands on the substations for consistent power supply and quality of service. However, the transformers' insufficient short-circuit resistance has remained unresolved, posing a significant risk to the safe and stable operation of the power grid.

[0004] Currently, the industry generally believes that installing a current-limiting reactor at the transformer's neutral point is the most effective measure to address insufficient short-circuit protection. However, the traditional method of installing current-limiting reactors during power outages has significant drawbacks: power outages cannot meet the urgent needs of businesses for continuous power supply. Summary of the Invention

[0005] In view of this, the present invention provides a 330kV transformer neutral point current limiting reactor live connection protection device and method to solve the technical problem in the prior art that the installation of current limiting reactors during power outages cannot meet the urgent needs of corporate users for "continuous power supply".

[0006] To achieve the above objectives, this application adopts the following scheme:

[0007] A 330kV transformer neutral point current limiting reactor live access protection device, comprising a DC power supply, a protective grounding safety device and a bypass protection grounding circuit, wherein the DC power supply, the protective grounding safety device and the bypass protection grounding circuit are sequentially connected in parallel, the grounding end of the bypass protection grounding circuit is grounded, and the input end is connected to the neutral point of the transformer to be connected through a cable, the bypass protection grounding circuit is used to provide grounding protection before the protective grounding safety device is put into the neutral point of the transformer to be connected, the protective grounding safety device is used to discharge the voltage and current to the ground when an overvoltage occurs at the neutral point of the transformer, and the protective grounding safety device comprises a discharge protector, a discharge An electric gap protector, a resistor disk and a first isolating switch, the leakage protector, the discharge gap protector and the resistor disk are all arranged in parallel, the incoming terminal of the first isolating switch is connected to the input terminal of the bypass protection grounding loop, and the outgoing terminal of the first isolating switch is connected to the input terminal of the protective grounding safety device. The discharge gap protector is used to pass a voltage of 60V to 250V and release the passing voltage to no more than 36V by adjusting the gap width. The leakage protector is used to release the current when the voltage exceeds 250V. The resistor disk increases the grounding resistance, limits the size of the grounding current, and ensures the safety and stability of the grounding process.

[0008] Preferably, the protective grounding safety device further comprises at least one clamp ammeter, wherein one of the clamp ammeters is connected in series with the resistor disk.

[0009] Preferably, the discharge gap protector is a disc-type discharge gap protector, which includes two identical metal discs, the centers of the two metal discs are aligned, one of which is fixed to the neutral point of the transformer to be connected, and the other is grounded for adjusting the required voltage.

[0010] Preferably, the gap width between the two metal discs is 0.32 mm to 0.36 mm.

[0011] Preferably, the bypass protection grounding loop includes a second isolating switch and an insulating substrate, and the conductive part of the isolating switch is mounted on the insulating substrate.

[0012] A method for live connection of a neutral point current limiting reactor of a 330kV transformer comprises the following steps:

[0013] S10. Measure the initial current at the neutral point of the transformer to be connected, and select the appropriate resistance of the neutral point current limiting reactor of the 330kV transformer according to the initial current to connect the protection device;

[0014] S20. Activate the bypass protective grounding loop: After grounding the ground terminal of the bypass protective grounding loop, connect the input terminal of the bypass protective grounding loop to the grounding busbar of the transformer neutral point to be connected via a cable, and activate the bypass protective grounding loop.

[0015] S30. Put the discharge gap protector into operation: Put the discharge gap protector into operation and adjust the gap width to 0.32mm to 0.36mm to ensure that the voltage is within a safe range during real-time monitoring of personnel during construction.

[0016] S40. Activate the leakage protection device to provide a short-circuit current path.

[0017] S50. Connect the current-limiting reactor: Ground the grounding terminal of the current-limiting reactor through a cable, connect the other end of the current-limiting reactor to the neutral point grounding copper busbar of the transformer to be connected through a cable, and close the neutral point current-limiting reactor isolation switch to put it into operation.

[0018] Preferably, the method further includes an access acceptance step, wherein the access acceptance step includes the following steps:

[0019] S61. Apply a DC current of A to the upper end of the neutral point grounding copper busbar of the transformer using a DC source generator;

[0020] S62. Measure the current value A1 of the current-limiting reactor branch at the neutral point of the transformer.

[0021] S63. Measure the current value A2 of the protective earth safety device branch;

[0022] S64. If A=A1+A2 and A1 / A2=R2 / R1, it is determined that the neutral point current limiting reactor is well grounded, where R1 is the DC resistance value of the current limiting reactor branch that has been put into operation, and R2 is the DC resistance value of the protective grounding safety device branch.

[0023] Preferably, if it is determined that the put-in-powered current limiting reactor is well grounded, the step of restoring the operating state is executed, which specifically includes the following steps:

[0024] S71. Disconnect the protective grounding safety device: Use an insulating rod to pull out the first disconnector of the discharge gap protector and the leakage protector branch, and then dismantle the above branches.

[0025] S72. Disconnect the transformer neutral grounding busbar: Use a handheld electric reciprocating saw to cut the transformer neutral grounding busbar. Fill the gap with insulating material and securely wrap it securely.

[0026] S73. Exit the bypass protection grounding circuit: open the second isolating switch and exit the reliable bypass grounding.

[0027] Preferably, the cable is a single-core copper cable, and the minimum cross-section of the single-core copper cable must satisfy the following calculation formula:

[0028]

[0029] Where, Smin: minimum cross-section of the cable, unit: mm 2 Id: stable value of short-circuit current flowing through the cable, the maximum zero-sequence current flowing through the neutral point is 4.22kA; ti: circuit breaker tripping time, generally 0.25s; c: thermal stability coefficient, the thermal stability coefficient of cross-linked polyethylene insulated power cable is 80; the nominal cable cross-section is selected as 35mm for thermal stability verification 2 .

[0030] Preferably, a crimping connection method is adopted when connecting the cable to the transformer neutral point grounding copper busbar.

[0031] In the above-mentioned 330kV transformer neutral point current limiting reactor live connection protection device and method, by measuring the initial current of the neutral point of the transformer to be connected, a live connection protection device with appropriate resistance can be selected to ensure that the device matches the actual situation. Then, a bypass protection grounding loop is put into operation to provide a safe grounding channel for the operator, effectively discharge possible fault current or leakage current during the connection process, and reduce the risk of electric shock. Then, a discharge gap protector is put into operation. The discharge gap protector can pass a voltage of 60V to 250V and release the passing voltage to a human safety voltage by adjusting the gap width. It is used to monitor in real time whether the voltage during construction is within a safe range (not higher than 36V) to protect construction personnel from electric shock. The discharge protector is put into operation to provide a safe channel for short-circuit current. During the process of connecting the current limiting reactor, if a short-circuit fault occurs, the discharge protector can respond quickly. When the voltage exceeds 250V, the current flow is limited to protect the equipment from damage, so as to ensure that the current limiting reactor is correctly connected. The device and method provided by the present invention can be used to connect a current-limiting reactor under power, and the average working period for a single 330kV transformer to be connected under power to a neutral point current-limiting reactor is 4.6 hours. When a reactor is connected during a traditional power outage, the average power outage duration of a single transformer is 110.4 hours. In comparison, the device and method provided by the present invention can increase the power transmission by 6.8 million kWh when each transformer is connected to a current-limiting reactor. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 This is a schematic diagram of the principle of the live connection protection device of the current limiting inductor in the present invention.

[0033] Figure 2 It is a schematic diagram of the principle of the bypass protection grounding loop in the present invention.

[0034] Figure 3It is a schematic diagram of the principle of the protective grounding safety device in the present invention.

[0035] Figure 4 It is a structural schematic diagram of the live connection protection device of the current limiting reactor in the present invention.

[0036] Figure 5 This is a structural diagram of the connection point of the current-limiting inductor connected to the protection device in the present invention.

[0037] Figure 6 It is a structural diagram of the bypass protection grounding loop in the present invention.

[0038] Figure 7 This is a schematic diagram of the structure in which the protective grounding safety device is put into use in the present invention.

[0039] Figure 8 This is a structural diagram of the current-limiting reactor connected in the present invention.

[0040] Figure 9 The figure is a schematic diagram showing the principle of cutting off the neutral point grounding copper bar of the transformer in the present invention.

[0041] Figure 10 Graph showing resistance change for the compression-type connection method in the embodiment.

[0042] Figure 11 Graph showing resistance change in the clamp-type connection method in the embodiment.

[0043] Figure 12 Graph showing the operating voltage variation of the disc-type discharge gap protector in the embodiment.

[0044] Figure 13 This is a graph showing the change in operating voltage of the tip discharge gap protector in the embodiment.

[0045] Figure 14 Graph showing the operating voltage changes of the surge protector and lightning arrester in the embodiment.

[0046] In the figure, a DC power supply 100, a protective grounding safety device 200, a bypass protective grounding loop 300, a transformer neutral point 400, a leakage protector 210, a discharge gap protector 220, a resistor disk 230, a first isolating switch 240, a clamp ammeter 250, an insulating substrate 260, and a current limiting reactor 500 are shown. DETAILED DESCRIPTION

[0047] To facilitate understanding of the present application, a more comprehensive description of the present application will be provided below with reference to the accompanying drawings. Preferred embodiments of the present application will also be described. However, the present application can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a more thorough and comprehensive understanding of the disclosure of the present application.

[0048] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which this application pertains. The terms used herein in the specification of this application are intended only to describe specific embodiments and are not intended to limit this application. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0049] Please see Figures 1 to 4 The present invention provides a 330kV transformer neutral point current limiting reactor live connection protection device, comprising a DC power supply 100, a protective grounding safety device 200 and a bypass protection grounding loop 300, wherein the DC power supply 100, the protective grounding safety device 200 and the bypass protection grounding loop 300 are sequentially connected in parallel, the grounding end of the bypass protection grounding loop 300 is grounded, and the input end is connected to the neutral point of the transformer to be connected through a cable, the bypass protection grounding loop 300 is used to provide grounding protection before the protective grounding safety device 200 is put into the neutral point 400 of the transformer to be connected, the protective grounding safety device 200 is used to discharge the voltage and current to the ground when an overvoltage occurs at the neutral point 400 of the transformer, and the protective grounding safety device 200 includes a discharge protector 2 10. A discharge gap protector 220, a resistor disk 230, and a first isolating switch 240. The leakage protector 210, the discharge gap protector 220, and the resistor disk 230 are all arranged in parallel. The input end of the first isolating switch 240 is connected to the input end of the bypass protection grounding loop 300, and the output end of the first isolating switch 240 is connected to the input end of the protective grounding safety device 200. The discharge gap protector 220 is used to pass a voltage of 60V to 250V and release the passing voltage to no more than 36V by adjusting the gap width. The leakage protector 210 is used to release the current when the voltage exceeds 250V. The resistor disk 230 increases the grounding resistance, limits the magnitude of the grounding current, and ensures the safety and stability of the grounding process.

[0050] When integrating a 330kV transformer neutral point current limiting reactor live connection protection device, the current at the neutral point 400 of the transformer to be connected can be detected in advance to integrate a live connection protection device with appropriate resistance. When integrating the device, it is necessary to prepare the DC power supply 100, leakage protector 210, discharge gap protector 220, resistor disk 230 and cables in advance. Then, those skilled in the art will follow the instructions. Figure 1 and Figure 4Connect them one by one and confirm that the connections are intact. During use, first ensure that the 330kV transformer is in normal operation. Then, place the integrated device in a safe area near the neutral point 400 of the transformer to be connected. Check and confirm that the DC power supply 100 is connected to ensure that it can provide a stable power supply for the entire protection device. Put the protective grounding safety device 200 (including the discharge gap protector 220, the leakage protector 210 and the resistor disk 230) in a standby state and connect it in parallel with the bypass protective grounding loop 300. The grounding end of the bypass protection grounding loop 300 is reliably grounded to ensure that the grounding resistance meets the safety standards, and the input end of the bypass protection grounding loop 300 is connected to the neutral point 400 of the transformer to be connected (the grounding copper bar of the neutral point 400 of the transformer). In this embodiment, a press-type connection method is adopted when the input end of the bypass protection grounding loop 300 is connected to the neutral point 400 of the transformer to be connected, that is, a press-type connector is required to make it more secure. Subsequently, the protective grounding safety device 200 is put into operation. At this time, the discharge gap protector 220 provides additional protection in the event of overvoltage, releases overvoltage energy through the discharge gap, and ensures the safety of the equipment. The leakage protector 210 monitors the current changes passing through the neutral point 400 of the transformer. Once the current increases abnormally, it acts quickly to cut off or limit the current to prevent the equipment from being damaged due to overheating or short circuit. The resistor disk 230 increases the grounding resistance, limits the size of the grounding current, and ensures the safety and stability of the grounding process.

[0051] After confirming that the protective grounding safety device 200 is working properly and the neutral point 400 of the transformer is in a safe state, the current-limiting inductor 500 is formally connected. The grounding end of the current-limiting inductor 500 to be connected is grounded through a cable, and the connection end of the current-limiting inductor 500 to be connected is connected to the grounding copper bus of the neutral point 400 of the transformer to be connected through a cable. Then, the isolating switch of the neutral point current-limiting inductor 500 is closed to put it into operation. During the connection process, the voltage and current changes of the neutral point 400 of the transformer are continuously monitored to ensure the safety and stability of the connection process.

[0052] Furthermore, after successfully connecting to the transformer neutral point 400, the bypass protection grounding loop 300 can be gradually withdrawn to ensure that the connection between the bypass protection grounding loop 300 and the transformer neutral point 400 is reliably disconnected to avoid affecting the normal operation of the transformer.

[0053] By setting the protective grounding safety device 200 in parallel, damage to the neutral point 400 of the 330kV transformer and the current-limiting reactor 500 caused by factors such as operational overvoltage and abnormal increase in current is effectively prevented. The setting of the bypass protective grounding loop 300 ensures that the neutral point 400 of the transformer is in a safe grounding state before the current-limiting reactor 500 is officially connected, avoiding safety accidents caused by misoperation or equipment failure. The protection device can temporarily replace the original transformer neutral point 400 grounding loop, so that when the current-limiting reactor 500 is energized, there is no need to interrupt the normal operation of the transformer, thereby ensuring the stable operation of the power grid and the reliability of power supply.

[0054] The protective grounding safety device 200 further includes at least one clamp ammeter 250 , wherein one clamp ammeter 250 is connected in series with the resistor disk 230 to measure the branch current value of the protective grounding safety device 200 .

[0055] Furthermore, the discharge gap protector 220 is a disc-type discharge gap protector 220, which includes two identical metal discs, the centers of the two metal discs are aligned, and one of them is fixed to one side of the neutral point 400 of the transformer to be connected, and the other is grounded for adjusting the required voltage.

[0056] In the live connection protection device for the neutral point current limiting reactor of a 330kV transformer, the discharge gap protector 220 adopts the design of a disc-type discharge gap protector 220. Two identical metal discs of the disc-type discharge gap protector 220 are installed to ensure that the centers of the two metal discs are aligned. One of the metal discs is fixed to one side of the neutral point 400 of the transformer to be connected and maintains electrical connection with the neutral point 400 of the transformer. The other metal disc is grounded. By adjusting the distance (gap width) between the two metal discs, the voltage is adjusted to no more than 36V.

[0057] When the transformer is operating normally, the disc-type discharge gap protector 220 is in standby mode, and a certain gap is maintained between the two metal discs, and no discharge channel is formed. At this time, other parts of the protection device (such as the leakage protector 210 and the resistor disc 230) are also operating normally, jointly providing protection for the neutral point 400 of the transformer. However, when an overvoltage occurs at the neutral point 400 of the transformer, the voltage amplitude exceeds the set threshold of the disc-type discharge gap protector 220. Under the action of the overvoltage, the air gap between the two metal discs is broken down, forming a discharge channel. The overvoltage energy is released to the ground through the discharge channel, thereby protecting personnel, the transformer and the reactor from overvoltage damage; when the overvoltage disappears, the air gap between the two metal discs of the disc-type discharge gap protector 220 returns to an insulating state and continues to provide protection for the neutral point 400 of the transformer.

[0058] The disc-type discharge gap protector 220 can effectively prevent damage to the transformer neutral point 400 and the current-limiting inductor 500 caused by operational overvoltage. Through the breakdown and discharge of the discharge gap, the overvoltage (60V to 250V) energy can be quickly released to the ground, ensuring the safe operation of personnel and equipment. In addition, the present invention can flexibly adjust the required discharge voltage by adjusting the distance between the two metal discs, which enables the protection device to adapt to transformers of different voltage levels and different protection requirements.

[0059] Specifically, the gap width between the two metal discs is 0.32mm to 0.36mm. In this embodiment, the operating voltage of the discharge gap should be 36V, a human safety voltage. The operating voltage value is set by adjusting the gap. When the width of the disc-shaped discharge gap is 0.32mm to 0.36mm, the operating voltage can be stabilized at 36±0.4V, preferably 0.34mm.

[0060] The bypass protection grounding loop 300 includes a second isolating switch and an insulating substrate 260 , and the conductive part of the isolating switch is mounted on the insulating substrate 260 .

[0061] In the live access protection device for the neutral point current limiting reactor of a 330kV transformer, the bypass protection grounding loop 300 is a key component. Its design includes a second isolating switch and an insulating substrate 260. During installation, the insulating substrate 260 is fixed in an appropriate position to ensure that it is stable and has good insulation performance. The conductive part of the second isolating switch is installed on the insulating substrate 260 to ensure good electrical isolation between the conductive part and the insulating substrate 260. At the same time, the conductive part has good contact and reliable conductivity. The grounding end of the bypass protection grounding loop 300 is reliably connected to the earth to ensure that the grounding resistance meets safety standards. When the current reactor 500 is connected, the bypass protection grounding loop 300 is first connected to the neutral point 400 of the transformer to be connected by operating the second isolating switch. When the second isolating switch is in the closed state, it ensures that the electrical connection between the bypass protection grounding loop 300 and the neutral point 400 of the transformer is unobstructed. When overvoltage, overcurrent or other abnormal conditions occur at the neutral point 400 of the transformer, the bypass protection grounding loop 300 serves as a temporary grounding loop to introduce the abnormal current or voltage into the ground, thereby protecting the transformer and the reactor from damage. The insulating substrate 260 plays the role of electrical isolation, preventing abnormal current or voltage from causing harm to equipment or personnel through other paths.

[0062] Please see Figures 1 to 9 The present invention also provides a method for live connection of a neutral point current limiting reactor of a 330kV transformer, comprising the following steps:

[0063] S10. Use a current measuring device to measure the initial current of the neutral point 400 of the transformer to be connected. Based on the measurement result, select the above-mentioned 330kV transformer neutral point current limiting reactor with appropriate resistance to connect the protection device with power.

[0064] S20. Put the bypass protection grounding loop into operation: first, ground the ground terminal of the bypass protection grounding loop, connect the input terminal of the bypass protection grounding loop to the grounding busbar 400 to be connected to the neutral point of the transformer via a cable, and put the bypass protection grounding loop into operation;

[0065] First, reliably connect the ground terminal of the bypass protection grounding loop to the earth. Then, use a cable to connect the input terminal of the bypass protection grounding loop to the grounding busbar of the transformer neutral point 400 to be connected. Use an insulated operating rod to activate the bypass protection grounding loop to ensure that the transformer neutral point 400 has reliable grounding protection during the connection of the current-limiting reactor 500.

[0066] S30 input discharge gap protector 220: The discharge gap protector 220 input, and the gap width is adjusted to 0.32mm to 0.36mm, for real-time monitoring of the voltage during construction personnel within a safe range;

[0067] The discharge gap protector 220 can pass a voltage of 60V to 250V and adjust the discharge gap to keep the voltage within a safe range (not higher than 36V) to prevent overvoltage from causing harm to equipment and personnel.

[0068] S40 input leakage protector 210: the leakage protector 210 input to provide a short-circuit current channel;

[0069] The leakage protector 210 provides a short-circuit current channel. When the voltage exceeds 250V, it can quickly lead the current into the ground to protect the safety of equipment and personnel.

[0070] S50. Connect the current-limiting reactor 500: Ground the ground terminal of the current-limiting reactor 500 through a cable, connect the access terminal of the current-limiting reactor 500 to the grounding copper bus of the neutral point 400 of the transformer to be connected through a cable, and close the isolating switch of the neutral point current-limiting reactor 500 to put it into operation.

[0071] Ensure that during the process of live connection of the current-limiting inductor 500, the neutral point 400 of the transformer has reliable grounding protection and overvoltage and overcurrent protection, thereby improving the safety of the connection process and preventing damage to equipment and personnel. Ensure that the current-limiting inductor 500 can be correctly connected to the neutral point 400 of the transformer and play a current limiting role. By providing a reliable grounding channel and overvoltage and overcurrent protection, the safety of equipment and personnel is ensured.

[0072] Furthermore, the access acceptance step is included, and the access acceptance step includes the following steps:

[0073] S61. Apply a DC current of A to the upper end of the transformer neutral point 400 grounding copper busbar using a DC source generator;

[0074] S62. Measure the current value A1 of the current-limiting reactor 500 branch of the transformer neutral point 400 that has been put into operation;

[0075] S63. Measure the current value A2 of the protective grounding safety device 200 branch;

[0076] S64. If A=A1+A2 and A1 / A2=R2 / R1, it is determined that the neutral point current limiting reactor 500 is well grounded, where R1 is the DC resistance value of the neutral point current limiting reactor 500 branch that has been put into operation, and R2 is the DC resistance value of the protective grounding safety device 200 branch.

[0077] The primary purpose of the acceptance step in this embodiment is to verify that neutral-point current-limiting reactor 500 is correctly and effectively connected to the system and to ensure its proper grounding. By measuring and comparing the current values of each branch, it is possible to verify that the current distribution meets expectations, thereby indirectly assessing the reactor's connection status. If the measurement results meet the conditions A = A1 + A2 and A1 / A2 = R2 / R1, it can be determined that the neutral-point current-limiting reactor 500 is properly grounded, with no abnormalities such as short circuits or open circuits. This helps ensure the safe and stable operation of the power system and prevents faults caused by poor neutral-point grounding.

[0078] Furthermore, if it is determined that the neutral point current limiting reactor 500 is well grounded, the operation state recovery step is executed, which specifically includes the following steps:

[0079] S71. Exit the protective grounding safety device 200: Use the insulating rod to pull out the first disconnector 240 of the discharge gap protector 220 and the leakage protector 210 branch, and then remove the above branch;

[0080] S72. Disconnect the transformer neutral point 400 grounding copper busbar: Use a handheld electric reciprocating saw to cut the transformer neutral point 400 grounding copper busbar. Fill the broken end of the transformer neutral point 400 grounding copper busbar with insulating material and wrap it tightly.

[0081] S73. Exit the bypass protection grounding loop: open the second isolating switch of the bypass grounding branch and exit the reliable bypass grounding.

[0082] After the current-limiting reactor 500 to be connected is successfully connected to the neutral point 400 of the transformer to be connected, the bypass protection grounding loop 300 and the protective grounding safety device 200 are prevented from affecting the normal operation of the transformer. The bypass protection grounding loop 300 can be gradually withdrawn to ensure that the connection between the bypass protection grounding loop 300 and the neutral point 400 of the transformer is reliably disconnected. In this embodiment, the first disconnecting gap protector 220 and the first isolating switch 240 of the leakage protector 210 branch are first opened, and then the grounding copper busbar of the neutral point 400 of the transformer is cut off, and the fracture is filled with insulating material and wrapped intact.

[0083] Specifically, the cable is a single-core copper cable, and the minimum cross-section of the single-core copper cable must meet the following calculation formula:

[0084]

[0085] Where, Smin: minimum cross-section of the cable, unit: mm 2 Id: stable value of short-circuit current flowing through the cable, the maximum zero-sequence current flowing through the neutral point is 4.22kA; ti: circuit breaker tripping time, generally 0.25s; c: thermal stability coefficient, the thermal stability coefficient of cross-linked polyethylene insulated power cable is 80; the nominal cable cross-section is selected as 35mm for thermal stability verification 2 .

[0086] The precise calculation of the minimum cable cross-section ensures that, in the event of a short circuit, the cable can withstand the heat generated by the short-circuit current without being damaged. This is crucial for the safe operation of the power system. The appropriate cable cross-section selection can reduce the risk of failure due to cable overheating, thereby improving the reliability and stability of the entire power system. The precise calculation of the minimum cross-section ensures that safety is guaranteed while optimizing cost-effectiveness.

[0087] Specifically, a crimping connection method is used when connecting the cable to the transformer neutral point 400 grounding copper busbar to make it more secure.

[0088] In the above-mentioned 330kV transformer neutral point current-limiting reactor live connection protection device and method, by measuring the initial current of the transformer neutral point 400 to be connected, a live connection protection device with appropriate resistance can be selected to ensure that the device matches the actual situation. Then, a bypass protection grounding loop is activated, providing a safe grounding channel for operators, effectively discharging possible fault current or leakage current during the connection process, reducing the risk of electric shock. Then, the discharge gap protector 220 is activated. The discharge gap protector 220 can pass a voltage of 60V to 250V and release the voltage passing through it to a human safety voltage by adjusting the discharge gap. It is used to monitor in real time whether the voltage during construction is within a safe range (no higher than 36V) to protect construction workers from electric shock. The discharge protector 210 is activated to provide a safe channel for short-circuit current. During the connection process of the current-limiting reactor 500, if a short-circuit fault occurs, the discharge protector 210 can respond quickly. When the voltage exceeds 250V, the discharge protector 210 limits the current flow to protect the equipment from damage, thereby ensuring the correct connection of the current-limiting reactor 500. Using the device and method provided by the present invention, the average working period for a single 330kV transformer to be energized and connected to the neutral point current-limiting reactor 500 is 4.6 hours. When the reactor is connected during a traditional power outage, the average power outage duration of a single transformer is 110.4 hours. In comparison, the device and method provided by the present invention can increase the power transmission by 6.8 million kWh when each transformer is connected to the current-limiting reactor 500.

[0089] In order to further understand the present invention, the 330kV transformer neutral point current limiting reactor live connection protection device and method provided by the present invention are described in detail below with reference to the embodiments.

[0090] Example

[0091] 1. Selection of experimental plan

[0092] 1.1 Selection of diverter

[0093] It is known that the maximum zero-sequence current flowing through the neutral point is 4.22kA and the voltage is 22kV. The conductor selection is based on the thermal stability test. This test case proposes two solutions: cable and insulated copper busbar. According to the thermal stability test, the minimum cross-sectional area of the cable is 26.375mm 2 Therefore, the cable is selected with a nominal cross-section of 35mm for 20kV. 2 Single-core copper cable; the minimum cross-sectional area of the copper busbar is 162.3mm 2 Therefore, the cross-sectional area of the copper busbar is 40*5mm. 2 The grounding copper bus is wrapped with two layers of insulating heat shrink sleeves.

[0094] In the laboratory, the same group of personnel were arranged to carry out simulated installation using two different materials, copper cables and grounding copper busbars, in a real construction environment that highly simulated the site, and the construction time of each stage was accurately recorded.

[0095] Through market research, we calculated the required material costs, compared the material costs, and built a test environment that matched the actual site conditions in the laboratory. We simulated the installation using two different materials, accurately recorded the construction time of each stage, and compared them. The comparison results are shown in Table 1:

[0096] Table 1 Comparison of experimental data on diversion body selection

[0097]

[0098]

[0099] The data in Table 1 above show that when single-core copper cables and grounding copper busbars are used as the body conductors, the total material cost and installation time both meet the scheme selection index requirements. However, the cable has lower material cost and shorter total installation time, which is superior to the insulated copper busbar. This shows that copper cables are more convenient to use and more cost-effective. Therefore, this embodiment uses copper cables as the body conductors.

[0100] 1.2 Selection of flow guide connection method

[0101] Based on actual on-site use, two connection methods, crimping and caliper, were used respectively, and an experiment was designed to compare the clamping force, contact resistance and operation difficulty of the two connection schemes.

[0102] In the laboratory, the same group of personnel were arranged to use a loop resistance meter and a pressure tester to test the contact resistance and compression force of crimped joints and caliper-type joints after compression in a real construction environment that highly simulated the on-site construction environment.

[0103] The initial value of the clamping force is set to 50N, and the test is repeated 50 times. Two different connection methods are used to measure the clamping force after each connection, and the change rate of the clamping force under the two connection methods in the 50 tests is compared to see if it meets the requirements; and the operation time of each time is accurately recorded. After each connection is completed, the contact resistance of the joint is accurately measured and recorded. Among them, the test data changes of the clamping force, operation time, and contact resistance of the crimped joint in 50 tests are as follows: Figure 10 As shown in the figure, the test data of clamping force, operation time and contact resistance of caliper joint after 50 tests are as follows: Figure 11 shown.

[0104] contrast Figure 10 and Figure 11It can be seen that the operation time and contact resistance of the crimped joint and the caliper joint both meet the requirements of the scheme selection basis. However, the clamping force of the caliper joint continues to decrease with the number of tests, and the stability is poor. The contact resistance also continues to increase with the increase in the number of experiments. The clamping force and contact resistance of the crimped joint are superior to those of the caliper joint. Therefore, the fluid guide connection method in this embodiment adopts a crimped joint connection.

[0105] 1.3 Selection of discharge gap protector 220

[0106] Based on the reference content, two types of over-discharge gap protectors 220 are adopted, namely a disc-type discharge gap protector 220 and a pointed discharge gap protector 220, and an experiment is designed to compare the stability of the operating voltage of the two discharge gap protectors 220 after multiple conduction.

[0107] Adjust the operating voltage of the disc-type discharge gap protector 220 and the tip discharge gap to 36V, a human safety voltage, connect a load in series and start applying voltage. After conduction, add a 10A current and continue for 20 minutes. Then test its operating voltage again. The test is performed 30 times.

[0108] In the laboratory, the same group of personnel were arranged to adjust the operating voltage of the disc-type discharge gap protector 220 and the tip discharge gap protector 220 to 36V, a human safety voltage, in a highly simulated real construction environment. A load was connected in series to increase the voltage. After the voltage was turned on, a 10A current was added for 20 minutes. The operating voltage was tested again. The test was performed 20 times to compare the voltage stability and calculate whether the requirement of the operating voltage being stable at 36±3V was met. Among them, the stability of the operating voltage of the disc-type discharge gap protector 220 was as follows: Figure 12 As shown, the stability of the operating voltage of the tip spark gap protector 220 is as follows Figure 13 shown.

[0109] contrast Figure 12 and Figure 13 It can be seen that as the number of tests increases, the operating voltage of the material tip discharge gap continues to increase, exceeding the safety range of 36±3V. The disc-shaped discharge gap is more stable and meets the requirement that the operating voltage is stable at 36±3V. Therefore, the discharge gap protector 220 in this embodiment is a disc-shaped discharge gap protector 220.

[0110] 1.4 Selection of leakage protector 210

[0111] According to the demand analysis, two types of leakage protectors 210 are used, namely a surge protector with an operating voltage of 620V and a lightning arrester of 2kV. The maximum current of both is 10kA, both meeting the maximum current capacity of 4.22kA. The team designed a simulation test to compare the stability of the operating voltage.

[0112] The surge protector and lightning arrester were pressurized and their operating voltages were recorded. The experiment was conducted 20 times. In the laboratory, the same group of personnel were arranged to use a DC generator to test the operating voltages of the lightning arrester and surge protector in a highly simulated real construction environment. The test was conducted 20 times and the data were compared and analyzed to calculate whether the operating voltage deviation value was ≤±5%. The results are as follows: Figure 14 shown.

[0113] Depend on Figure 14 It can be seen that the action voltage deviation of the surge protector meets the requirements and is relatively stable, while the action voltage of the lightning arrester exceeds the requirements and does not meet the action voltage deviation value requirement of ≤±5%. Therefore, the leakage protector 210 in this embodiment is a surge protector.

[0114] 2. Conduct experiments based on the selected optimal solution

[0115] 2.1 Determine the voltage

[0116] The maximum zero-sequence current flowing through the transformer's neutral point 400 is 4.22 kA, and the voltage is 22 kV. Therefore, the selected cable must be able to withstand a voltage of 22 kV. Based on the selected solution, the YJV-12 / 20 kV-35 single-core XLPE insulated, armored, PE / PE sheathed power cable can withstand a maximum voltage of 35 kV.

[0117] 2.2 Determine the cross-sectional area of the cable

[0118] According to the thermal stability conditions, the minimum cross-section of the cable should meet the following conditions:

[0119]

[0120] Where, Smin: minimum cross-section of the cable, unit: mm 2 Id: stable value of short-circuit current flowing through the cable, the maximum zero-sequence current flowing through the neutral point is 4.22kA; ti: circuit breaker tripping time, generally 0.25s; c: thermal stability coefficient, the thermal stability coefficient of cross-linked polyethylene insulated power cable is 80; the nominal cable cross-section is selected as 35mm for thermal stability verification 2 .

[0121] 2.3 Determine the length of the cable

[0122] The actual cable length required to connect the neutral point 400 of 12 transformers to the current-limiting reactor 500 was measured and statistically analyzed. The statistical results are shown in Table 2:

[0123] Table 2 Cable distances from the neutral point of 12 transformers (400m) to the current-limiting reactor (500m)

[0124] Serial number Equipment Number Cable distance from transformer neutral point 400m to current limiting reactor 500m 1 Yingshuiqiao No. 3 main transformer 4.33 meters 2 Yingshuiqiao No. 4 main transformer 4.56 meters 3 Xujiazhuang No. 1 main transformer 3.52 meters 4 Xujiazhuang No. 2 main transformer 3.75 meters 5 Huayan No. 1 main transformer 3.98 meters 6 Huayan No. 3 main transformer 4.23 meters 7 Zhongwei No. 1 main transformer 4.45 meters 8 Ganlu No. 1 main transformer 4.57 meters 9 Ganlu No. 2 main transformer 4.41 meters 10 Ning'an No. 1 main transformer 3.98 meters 11 Ning'an No. 2 main transformer 4.21 meters 12 Zaoyuan No. 3 main transformer 4.17 meters

[0125] It can be seen from Table 2 that the cable length is between 3.52 meters and 4.57 meters. According to the requirements of the cable manufacturer, a 1-meter margin should be left on site when the cable head is produced. Therefore, the YJY-12 / 20kV-35 single-core cross-linked polyethylene insulated armored polyethylene / polyethylene sheathed power cable with a length of 5.5 meters is selected.

[0126] In accordance with 17.0.1 of GB 50150-2016 Electrical Equipment Acceptance Test Standard for Electrical Installation Engineering, the team members conducted insulation resistance and AC withstand voltage tests on the power cable lines. The test results showed that the insulation resistance of the outer sheath and inner lining of the rubber-plastic cable was ≥0.5MΩ and the cable could withstand voltage for 1 minute without breakdown or flashover.

[0127] 2.4 Making a crimped joint

[0128] 2.41 Measuring the size of the neutral point grounding flat iron

[0129] The width dimensions of the neutral point grounding flat irons of 12 main transformers were statistically analyzed. The statistical results are shown in Table 3:

[0130] Table 3 Statistics of the width of neutral point grounding flat irons of 12 main transformers

[0131]

[0132]

[0133] From the data in Table 3, it can be seen that the width of the neutral point grounding flat iron is between 60 mm and 100 mm. In order to meet the principle of universality, the size of the crimping joint should not be greater than 60 mm wide, and the crimping joint should be prepared according to this size.

[0134] 2.42 Establish inspection methods for copper busbar connections

[0135] Use a 0.03mm feeler gauge to insert into the gap between the copper busbar lap joints from four directions. The sum of the maximum depths of the feeler gauge inserted in the four directions shall not exceed 12.5% of the lap joint circumference, and the length of the feeler gauge inserted in a single direction shall not exceed 25% of the lap joint length.

[0136] 2.43 Determine the crimping method for crimped connectors

[0137] Four bolt connection methods for crimped joints were designed, namely: 1 bolt fixed in the center; 2 bolts fixed up and down; 4 bolts fixed at the four corners; 5 bolts fixed at the four corners and the center. Each of the four connection methods was tested 10 times. The maximum insertion depth of the feeler gauge in the four insertion directions of L1, L2, L3, and L4 of the crimped joint was measured by using a 0.03mm feeler gauge.

[0138] The results show that the maximum insertion depth of the feeler gauge is smaller for the connection methods of fixing the four corners with four bolts and fixing the four corners and the center with five bolts, and both meet the requirements of the regulations, indicating that there is not much difference between 4 bolts and 5 bolts. Considering the speed of installation, the four-bolt four-corner fixing method is more convenient in this embodiment.

[0139] 2.44 Conduct contact resistance test

[0140] Installation tests were carried out on site, with the screws tightened to a clamping force of 100 N*m. The contact resistance was tested and the contact resistance value for each installation was recorded. The test results showed that the contact resistance of the manufactured crimped connector met the target of less than 20 μΩ, which was in compliance with the standard.

[0141] 2.5 Making a disc-type discharge gap protector

[0142] 2.51 Design and manufacture of disc-shaped discharge gap

[0143] Use two identical metal discs to align their centers, fix one of them on the neutral point side, and set the other as a threaded adjustable device connected to the ground side to adjust the required voltage.

[0144] In terms of material selection, according to the flow capacity calculation formula:

[0145] Ix is the flow capacity; N is the metal melting constant, which is 4200 for stainless steel and 4680 for pure iron; Sx is the area of the metal disc;

[0146] According to the above formula, the flow capacity of the two materials is compared. The comparison results are shown in Table 4:

[0147] Table 4 Flow capacity test statistics

[0148] Material Diameter (cm) Flow capacity IX(A) Stainless steel 10 23.32 pure iron 10 25.98

[0149] According to the data in Table 4, this embodiment selects a pure iron metal disk with a larger metal melting constant N, which can ensure the maximum current flow capacity of the discharge gap and effectively improve safety.

[0150] 2.52 Determine the gap width between two metal disks

[0151] The width of the gap is gradually increased from 0 and the operating voltage is tested after adjustment. If the target is not reached, continue to adjust until the operating voltage reaches 36±3V. During the whole process, the gap is measured with a micrometer and the gap width is recorded. The adjustment process is repeated 10 times and the average value of the adjustment width is calculated. The results are shown in Table 5:

[0152] Table 5 Gap width adjustment values

[0153]

[0154] Through testing, it can be seen from the data in Table 5 above that the gap width adjustment value range should be 0.32 to 0.36 mm, preferably 0.34 mm.

[0155] 2.6 Select the model of leakage protector 210

[0156] After comparing the parameters of five surge protectors on the market, we selected the Chint NU6-II surge protector, which has an operating voltage (varistor voltage) of 385V, an allowable tolerance of ±10%, and a maximum current of 40kA.

[0157] 3. Based on the selected optimal solution and selected components, assemble the 330kV transformer neutral point current limiting reactor live connection protection device. The assembly results are as follows: Figure 4 shown.

[0158] 4. On-site access test

[0159] From June to August 2023, the neutral point current limiting reactor 500 will be connected live to the No. 1 and No. 2 main transformers of Xujiazhuang Substation, No. 1 and No. 2 main transformers of Yingshuiqiao Substation, and No. 1 and No. 2 330kV transformers of Ganlu Substation. The specific steps are as follows:

[0160] Step 1: Test the DC resistance value of the current-limiting reactor 500 to be connected (apply a DC current of 2A) and record the data (in order to select a suitable resistance value to protect the grounding safety device 200). Select a current-limiting reactor 500 with a suitable resistance value and connect it to the protection device under power. Perform a through-current test on it and record the data. Use a mobile platform to place the current-limiting reactor 500 under power and the protection device and safety tools in the designated maintenance area. Safety tools include: 110kV insulating operating rod, 35kV insulating gloves, 35kV insulating table, hand-held reciprocating saw, hydraulic punching machine, etc. Prepare them and conduct pre-construction inspection and commissioning to verify that they are functioning properly.

[0161] Step 2: If Figure 5 As shown, connect the current limiting reactor 500 to the grounding end cable of the protection device and connect it securely. After connecting the transformer neutral point 400 grounding copper busbar cable, check that all contact surfaces are securely connected (to ensure that the above devices are securely grounded, use a loop resistance tester to test that the resistance of each contact surface is ≤ 20μΩ). Use the insulating operating rod to put the bypass protection grounding loop 300 into operation. Figure 6 As shown;

[0162] Step 3: Use the insulating operating rod to put the protective grounding safety device 200 into operation. Figure 7 As shown;

[0163] Step 4: Ground the ground terminal of the current limiting reactor 500 to be connected through a cable, connect the access terminal of the current limiting reactor 500 to the grounding copper bus of the neutral point 400 of the transformer to be connected through a cable, and then close the neutral point current limiting reactor 500 isolation switch 240 to put it into operation. Figure 8 As shown;

[0164] Step 5: A DC source generator can be used to apply a 2A DC current (A) to the upper end of the transformer neutral point 400 grounding copper bar, and the current value A1 of the transformer neutral point 400 current limiting reactor 500 branch that has been put into operation is measured. The clamp ammeter 250 is used to measure the current value A2 of the protective grounding safety device 200 branch. The results satisfy A=A1+A2 and A1 / A2=R2 / R1, indicating that the neutral point current limiting reactor 500 that has been put into operation is well grounded.

[0165] Step 6: Use a 110kV insulating rod to pull open the first disconnector 240 of the leakage protector 210 and the discharge gap protector 220 branch. Then, remove the above branches and use a handheld electric reciprocating saw to cut off the transformer neutral point 400 grounding copper bar. Figure 9 As shown, the fracture of the transformer neutral point 400 grounding bar is filled with insulating material and wrapped tightly, the second isolating switch of the reliable bypass grounding branch is opened, and the reliable bypass grounding is exited.

[0166] 5. Access effect statistics

[0167] All processes were completed safely, and the safety rate reached 100%. The engineering effect statistics are shown in Table 6:

[0168] Table 6 Project effect statistics

[0169]

[0170] Table 6 shows that the live connection method for the neutral point current-limiting reactor of a 330 kV transformer is safe and effective. Six 330 kV transformer neutral point current-limiting reactors with a value of 400 and a value of 500 were successfully connected live. The main transformer did not need to be powered off during the construction process. The average construction period for live connection of a neutral point current-limiting reactor with a value of 500 on a single 330 kV transformer was 4.6 hours.

[0171] The duration of using the traditional power outage current-limiting reactor 500 from 2019 to 2021 was statistically analyzed, and the statistical results are shown in Table 7:

[0172] Table 7 Project effect statistics

[0173]

[0174] It can be seen from the data in Table 7 that, according to the traditional operation method, the average power outage duration of a single transformer is 110.4 hours. However, the live access method provided in the above embodiment does not require power outage, and the total duration of live access to the current-limiting reactor 500 is only 4.6 hours, which is equivalent to an additional 110.4 hours of power supply per transformer.

[0175] Furthermore, the power of the 10 main transformers connected to the current-limiting reactor 500 through the live connection method was counted during operation, and their average operating power was calculated to be 61.68 MW. According to the calculation method of power = time × power, each time the live connection method of the neutral point current-limiting reactor of the 330 kV transformer is used, the power transmission amount can be increased by 110.4 hours × 61.68 MW = 6.8 million kWh.

[0176] The above description is only a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any technician familiar with this technical field can easily think of various equivalent modifications or replacements within the technical scope disclosed by the present invention, and these modifications or replacements should all be included in the scope of protection of the present invention.

Claims

1. A 330kV transformer neutral point current limiting reactor live connection protection device, characterized in that: It includes a DC power supply, a protective grounding safety device and a bypass protective grounding circuit. The DC power supply, the protective grounding safety device and the bypass protective grounding circuit are connected in parallel in sequence. The grounding end of the bypass protective grounding circuit is grounded, and the input end is connected to the neutral point of the transformer to be connected through a cable. The bypass protective grounding circuit is used to provide grounding protection before the protective grounding safety device is put into the neutral point of the transformer to be connected. The protective grounding safety device is used to discharge the voltage and current to the ground when an overvoltage occurs at the neutral point of the transformer. The protective grounding safety device includes a leakage protector, a discharge gap protector, a resistor disk and a first The isolating switch, the leakage protector, the discharge gap protector and the resistor disk are all arranged in parallel, the incoming terminal of the first isolating switch is connected to the input terminal of the bypass protection grounding loop, and the outgoing terminal of the first isolating switch is connected to the input terminal of the protective grounding safety device. The discharge gap protector is used to pass a voltage of 60V to 250V and release the passing voltage to no more than 36V by adjusting the gap width. The leakage protector is used to release the current when the voltage exceeds 250V. The resistor disk increases the grounding resistance, limits the size of the grounding current, and ensures the safety and stability of the grounding process.

2. The 330kV transformer neutral point current limiting reactor live connection protection device according to claim 1, characterized in that: The protective grounding safety device further comprises at least one clamp ammeter, wherein one of the clamp ammeters is connected in series with the resistor disk.

3. The 330kV transformer neutral point current limiting reactor live connection protection device according to claim 1, characterized in that: The discharge gap protector is a disc-type discharge gap protector, which includes two identical metal discs. The centers of the two metal discs are aligned, one of which is fixed to the neutral point of the transformer to be connected, and the other is grounded for adjusting the required voltage.

4. The 330kV transformer neutral point current limiting reactor live connection protection device according to claim 1, characterized in that: The width of the gap between the two metal discs is 0.32 mm to 0.36 mm.

5. The 330kV transformer neutral point current limiting reactor live connection protection device according to claim 1, characterized in that: The bypass protection grounding loop includes a second isolating switch and an insulating substrate, and the conductive part of the isolating switch is mounted on the insulating substrate.

6. A method for live connection of a neutral point current limiting reactor of a 330kV transformer, characterized in that: The following steps are involved: S10. Measuring the initial current of the neutral point of the transformer to be connected, selecting the appropriate resistance according to the initial current according to any one of claims 1 to 5 of the 330kV transformer neutral point current limiting reactor live access protection device; S20. Activate the bypass protective grounding loop: After grounding the bypass protective grounding loop, connect the bypass protective grounding loop input to the grounding busbar at the transformer neutral point to be connected via a cable. Activate the bypass protective grounding loop. S30. Install the discharge gap protector: Install the discharge gap protector and adjust the gap width to 0.32mm to 0.36mm to ensure that the voltage is within a safe range during real-time monitoring. S40. Activate the current relief device: Activate the current relief device to provide a short-circuit current path. S50. Connect the current-limiting reactor: Connect the ground terminal of the current-limiting reactor to the ground via a cable. Connect the input terminal of the current-limiting reactor to the neutral grounding busbar of the transformer to be connected via a cable. Close the isolating switch of the neutral current-limiting reactor to activate it.

7. The method for live connection of a neutral point current limiting reactor of a 330kV transformer according to claim 6, characterized in that: The access acceptance step further includes the following steps: S61 using a DC source generator to the transformer neutral point grounding copper busbar upper end of the current value of A DC current is applied; S62 measured the transformer neutral point current limiting reactor branch current value A1; S63 measuring the current value of the protective earth safety device branch A2; S64. If A = A1 + A2 and A1 / A2 = R2 / R1, the neutral current-limiting reactor in operation is properly grounded. R1 is the DC resistance of the current-limiting reactor branch in operation, and R2 is the DC resistance of the protective grounding safety device branch.

8. The method for live connection of a neutral point current limiting reactor of a 330kV transformer according to claim 7, characterized in that: If the current-limiting reactor is properly grounded, execute the steps to restore the operating state, which include the following steps: S71. Disconnect the protective grounding safety device: Use an insulating rod to pull out the first disconnector of the discharge gap protector and the leakage protector branch, and then dismantle the above branches. S72. Disconnect the transformer neutral grounding busbar: Use a handheld electric reciprocating saw to cut the transformer neutral grounding busbar. Fill the gap with insulating material and securely wrap it securely. S73. Exit the bypass protection grounding circuit: open the second isolating switch and exit the reliable bypass grounding.

9. The method for live connection of a neutral point current limiting reactor of a 330kV transformer according to claim 6, characterized in that: The cable is a single-core copper cable, and the minimum cross-section of the single-core copper cable must meet the following calculation formula: ； Where, Smin: minimum cross-section of the cable, unit: mm 2 ; Id: The stable value of the short-circuit current flowing through the cable, taking the maximum zero-sequence current flowing through the neutral point as 4.22kA; ti: circuit breaker tripping time, generally 0.25s; c: thermal stability coefficient, the thermal stability coefficient of cross-linked polyethylene insulated power cable is 80; the nominal cable cross-section selected for thermal stability verification is 35mm 2 .

10. The method for live connection of a neutral point current limiting reactor of a 330kV transformer according to claim 6, characterized in that: A crimping connection method is used when connecting the cable to the transformer neutral point grounding copper busbar.

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