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

Abstract

The utility model 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, which comprises a direct-current power supply, a protection grounding safety device and a bypass protection grounding loop, and is characterized in that the direct-current power supply and the protection grounding safety device are both connected with the bypass protection grounding loop in parallel; a cable is used as a diversion body of a bypass protection loop, one end of the bypass protection loop is grounded, the other end of the bypass protection loop is connected with a neutral point of a transformer to be accessed, and the bypass protection grounding loop is used for protecting the grounding safety device to provide protection grounding before the grounding safety device is put into the neutral point grounding loop of the transformer to be accessed. The protection grounding safety device comprises an over-discharge protector, a discharge gap protector, a resistance disc and a first isolation switch, the over-discharge protector, the discharge gap protector and the resistance disc are arranged in parallel, the device provided by the utility model can be accessed to the current limiting reactor in an electrified manner, and the power transmission amount of each device can be increased by 680 million kilowatt-hours.

Description

TECHNICAL FIELD

[0001] The utility model belongs to the technical field of power facilities protection, specifically relates to a 330kV transformer neutral point current -limiting reactor live access protection device. BACKGROUND

[0002] In the power system, the transformer as the core equipment of the transformer substation, bears the key task of voltage conversion and energy transmission, and has irreplaceable role for ensuring the stable operation of the power system. In recent years, with the rapid development of China's economy, especially the economic boom in Ningxia Hui Autonomous Region and other regions, the load of the power system continues to rise, and the enterprise self-use power supply construction accelerates. This trend leads to the increase of internal short-circuit capacity of the power grid year by year, and the maximum short-circuit current borne by the transformer also rises continuously, which constitutes a severe challenge to the stable operation of the transformer substation and even the whole power grid.

[0003] In a certain province in the northwest, the special investigation results in 2020 show that the 23 330kV transformers within its jurisdiction have the problem of insufficient short-circuit resistance. Most of these transformer substations are located in their energy bases or local industrial parks, and these areas have large industrial electricity demand, which puts forward very high requirements for the continuous power supply and power supply service quality of the transformer substation. However, the problem of insufficient short-circuit resistance of the transformer has existed for a long time and has not been effectively solved, which has become a major hidden danger affecting the safe and stable operation of the power grid. Once the transformer fails under the impact of short-circuit current, not only will it cause large-area power outage, but also may cause a chain reaction, causing immeasurable losses to the whole power grid.

[0004] In view of the problem of insufficient short-circuit resistance of the transformer, the industry has carried out extensive research and exploration. At present, it is generally believed that installing a current-limiting reactor at the neutral point of the transformer is an effective solution. The current-limiting reactor can limit the size of the short-circuit current, thereby reducing the mechanical stress and thermal stress of the transformer under short-circuit fault, and improving its short-circuit resistance. However, the traditional method of installing a current-limiting reactor during power outage has obvious drawbacks: since power outage is required for construction, it cannot meet the urgent demand of enterprise users for "continuous power supply".

[0005] Therefore, there is an urgent need for a protection device for live access of a reactor to solve the problem caused by the traditional method of installing a reactor during power outage. SUMMARY

[0006] In view of this, the present application provides a 330kV transformer neutral point current-limiting reactor live access protection device to solve the technical problem that the load is lost due to the installation of a current-limiting reactor during power outage in the prior art, and the urgent demand of enterprise users for "continuous power supply" cannot be met.

[0007] To achieve the above-mentioned purpose, the following solutions are adopted in the present application:

[0008] The application discloses a 330kV transformer neutral point current limiting reactor live access protection device, which comprises a DC power supply, a protection grounding safety device and a bypass protection grounding circuit, wherein the DC power supply, the protection grounding safety device and the bypass protection grounding circuit are connected in parallel, the grounding end of the bypass protection grounding circuit is grounded, the input end is connected with a transformer neutral point to be accessed through a cable, the bypass protection grounding circuit is used for providing grounding protection before the protection grounding safety device is put into the transformer neutral point to be accessed, the protection grounding safety device is used for discharging voltage and current to the ground when overvoltage occurs in the transformer neutral point, the protection grounding safety device comprises a current leakage protector, a discharge gap protector, a resistance disc and a first isolation switch, the current leakage protector, the discharge gap protector and the resistance disc are arranged in parallel, the input end of the bypass protection grounding circuit is connected with the incoming line end of the first isolation switch, and the outgoing line end of the first isolation switch is connected with the input end of the protection grounding safety device, the discharge gap protector is used for passing through a voltage of 60V to 250V and discharging the passed voltage to not higher than 36V by adjusting the gap width, and the current leakage protector is used for discharging current when the voltage is higher than 250V, the resistance disc increases the grounding resistance and limits the size of the grounding current, thereby ensuring the safety and stability of the grounding process.

[0009] Preferably, the discharge gap protector is a disc type discharge gap protector, the disc type discharge gap protector comprises two identical metal discs, the two metal discs are arranged in the center and one of the two metal discs is fixed on one side of the transformer neutral point to be accessed and the other is grounded, and the discharge gap protector is used for adjusting the required voltage.

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

[0011] Preferably, the gap width of the two metal discs is 0.34mm.

[0012] Preferably, the metal disc is a pure iron metal disc.

[0013] Preferably, the current leakage protector is a surge protector.

[0014] Preferably, the resistance disc provides a resistance of 50mΩ to 100mΩ.

[0015] Preferably, the bypass protection grounding circuit comprises an insulation switch and an insulation substrate, and the conductive part of the insulation switch is mounted on the insulation substrate.

[0016] Preferably, the bypass protection grounding circuit further comprises a press type joint, and the other end of the bypass protection grounding circuit is connected with the transformer neutral point to be accessed through the press type joint.

[0017] Preferably, the cable is a single-core copper cable.

[0018] In the charged access protection device for the 330kV transformer neutral point current limiting reactor, a bypass protection grounding circuit is set up to provide a safe grounding channel for the operator, effectively discharge possible fault current or leakage current during the access process, reduce the risk of electric shock, and effectively ensure the safety of the operator during the charged access process; the discharge protection device and the discharge gap protection device are connected in parallel in the protection grounding safety device, the discharge gap protection device is used for real-time monitoring of whether the voltage during personnel construction is within a safe range, the discharge gap protection device can pass through a voltage of 60V to 250V, the voltage passing through the discharge gap protection device is released to a human body safe voltage by adjusting the gap width, and the discharge gap protection device is used for real-time monitoring of whether the voltage during personnel construction is within a safe range (not higher than 36V), so as to protect the construction personnel from electric shock, and the discharge protection device can provide a safe channel for short-circuit current, and if a short-circuit fault occurs during the access of the current limiting reactor, the discharge protection device can quickly respond and limit the current flow when the voltage exceeds 250V, so as to protect the equipment from damage and ensure correct access of the current limiting reactor. The device provided in the application can be used for charged access of the current limiting reactor, and the average construction period of a single 330kV transformer for charged access of the neutral point current limiting reactor is 4.6 hours, while in the traditional power-off access of the reactor, the average power-off time of a single transformer is 110.4h. Compared with the prior art, the device provided in the application can increase the power supply capacity by 6.8 million kilowatt hours when a transformer accesses the current limiting reactor. BRIEF DESCRIPTION OF DRAWINGS

[0019] Figure 1 It is a principle schematic view of the charged access protection device for the current limiting reactor in the utility model.

[0020] Figure 2 It is a principle schematic view of the bypass protection grounding circuit in the utility model.

[0021] Figure 3 It is a principle schematic view of the protection grounding safety device in the utility model.

[0022] Figure 4 It is a principle schematic view of the copper bar cutting of the transformer neutral point grounding in the utility model.

[0023] Figure 5 It is a resistance change graph of the crimping type connection mode in the embodiment.

[0024] Figure 6 It is a resistance change graph of the caliper type connection mode in the embodiment.

[0025] Figure 7 It is a voltage change graph of the disc type discharge gap protection device in the embodiment.

[0026] Figure 8 Figure showing the variation of the surge protector and arrester operating voltage for the example.

[0027] Figure 9 Figure showing the variation of the surge protector and arrester operating voltage for the example.

[0028] In the figure, DC power source 100, protective grounding safety device 200, bypass protection grounding circuit 300, transformer neutral point 400, current leakage protector 210, discharge gap protector 220, resistor panel 230, first isolation switch 240, current limiting reactor 500. DETAILED DESCRIPTION

[0029] For the purpose of understanding the present application, a more complete description of the application will be provided in connection with the accompanying drawings. The preferred embodiments of the present application are described below in connection with the accompanying drawings. However, the present application can be realized in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided as a basis for understanding the present application.

[0030] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used in the description of the application herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. As used herein, the term "and / or" includes any and all combinations of one or more of the associated listed items.

[0031] Reference will now be made to Figures 1 to 3In one specific embodiment, a 330kV transformer neutral point current limiting reactor live access protection device includes a DC power supply 100, a protection grounding safety device 200, and a bypass protection grounding circuit 300, the DC power supply 100, the protection grounding safety device 200, and the bypass protection grounding circuit 300 are connected in parallel, the grounding end of the bypass protection grounding circuit 300 is grounded, the input end is connected with the transformer neutral point to be accessed through a cable, the bypass protection grounding circuit 300 is used to provide grounding protection before the protection grounding safety device 200 is put into the transformer neutral point 400 to be accessed, the protection grounding safety device 200 is used to discharge voltage and current to the ground when overvoltage occurs in the transformer neutral point 400, the protection grounding safety device 200 includes a current leakage protector 210, a discharge gap protector 220, a resistor disc 230, and a first disconnecting switch 240, the current leakage protector 210, the discharge gap protector 220, and the resistor disc 230 are all connected in parallel, the incoming end of the first disconnecting switch 240 is connected with the input end of the bypass protection grounding circuit 300, the outgoing end of the first disconnecting switch 240 is connected with the input end of the protection grounding safety device 200, the discharge gap protector 220 is used to pass through a voltage of 60V to 250V, and release the passed voltage to not higher than 36V by adjusting the gap width, the current leakage protector 210 is used to release current when the voltage exceeds 250V or above, and the resistor disc 230 increases the grounding resistance, limits the size of the grounding current, and ensures the safety and stability of the grounding process.

[0032] When the integrated 330kV transformer neutral point current limiting reactor live access protection device is accessed, the current of the transformer neutral point 400 to be accessed can be detected in advance to integrate a suitable resistance live access protection device. When the device is integrated, the DC power supply 100, the current leakage protector 210, the discharge gap protector 220, the resistor disc 230, and the cable are prepared in advance, then the person skilled in the art connects them in order and confirms that the connection is good. Figure 1

[0033] ​In use, first, ensure that the 330kV transformer is in normal operation, then place the integrated device near the safety area of the neutral point 400 to be connected to the transformer, check and confirm that the DC power supply 100 is turned on to ensure that it can provide stable power supply for the entire protection device, and make the protection grounding safety device 200 (including the discharge gap protector 220, the discharge protector 210 and the resistance disc 230) in standby state, and connect the bypass protection grounding circuit 300 in parallel. The grounding end of the bypass protection grounding circuit 300 is reliably grounded to ensure that the grounding resistance meets the safety standards, the input end of the bypass protection grounding circuit 300 is connected to the neutral point 400 to be connected to the transformer (the transformer neutral point 400 grounding copper bar), in this embodiment, the input end of the bypass protection grounding circuit 300 is connected to the neutral point 400 to be connected to the transformer by pressing type connection, that is, a pressing type joint is used to make it more secure, then the protection grounding safety device 200 is put into operation, at this time, the discharge gap protector 220 provides additional protection under overvoltage conditions, releases overvoltage energy through the discharge gap to ensure the safety of the equipment, the discharge protector 210 monitors the current change through the transformer neutral point 400, and once the current abnormally increases, it quickly acts to cut off or limit the current to prevent the equipment from being damaged due to overheating or short circuit, and the resistance disc 230 increases the grounding resistance to limit the size of the grounding current, ensuring the safety and stability of the grounding process.

[0034] After confirming that the protection grounding safety device 200 is working normally and the transformer neutral point 400 is in a safe state, the current limiting reactor 500 is formally connected, the grounding end of the current limiting reactor 500 to be connected is grounded through a cable, the connection end of the current limiting reactor 500 to be connected is connected to the grounding copper bar of the transformer neutral point 400 to be connected through a cable, and then the disconnecting switch of the neutral point current limiting reactor 500 is closed to put it into operation. During the connection process, the voltage and current changes of the transformer neutral point 400 are continuously monitored to ensure the safety and stability of the connection process.

[0035] Further, after successfully connecting the transformer neutral point 400, the bypass protection grounding circuit 300 can be gradually withdrawn to avoid affecting the normal operation of the transformer. The first disconnecting switch 240 of the discharge gap protector 220 and the discharge protector 210 branch is pulled open using an insulating rod, and then the above branch is removed, as shown in Figure 4 The transformer neutral point 400 grounding copper bar is disconnected: the transformer neutral point 400 grounding copper bar is cut off using a handheld electric reciprocating saw, the fracture of the transformer neutral point 400 grounding copper bar is filled with insulating material and wrapped well to avoid affecting the normal operation of the transformer, the insulating switch of the bypass protection circuit is disconnected, and the branch is removed.

[0036] By setting up the bypass protection grounding circuit 300, a safe grounding channel is provided for the operator, the possible fault current or leakage current is effectively discharged during the access process, the risk of electric shock is reduced, and the safety of the operator during the live access process is effectively ensured; the discharge gap protector 220 and the discharge gap protector 220 are arranged in parallel in the protection grounding safety device 200, the discharge gap protector 220 is used to monitor whether the voltage during the personnel construction is within the safe range in real time, the discharge gap protector 220 can pass through the voltage of 60V to 250V, and the voltage passing through the gap width is discharged to the human body safe voltage, which is used to monitor whether the voltage during the personnel construction is within the safe range (not higher than 36V) in real time, and protect the construction personnel from electric shock, and the discharge current protector 210 can provide a safe channel for the short-circuit current, and if a short-circuit fault occurs during the access of the current limiting reactor 500, the discharge current protector 210 can quickly respond, and when the voltage exceeds 250V, the current is limited to flow, the equipment is protected from damage, and the correct access of the current limiting reactor 500 is ensured. The device provided by the application can be used to access the current limiting reactor 500 under voltage, and the average construction period of a single 330kV transformer under voltage for accessing the neutral point current limiting reactor is 4.6 hours, while the average power-off time of a single transformer for accessing the reactor in the traditional power-off mode is 110.4h. Compared with the prior art, the device provided by the application can increase the power supply capacity of 6.8 million kilowatt hours per transformer for accessing the current limiting reactor.

[0037] Specifically, the discharge gap protector 220 is a disc type discharge gap protector 220, the disc type discharge gap protector 220 includes two identical metal discs, the centers of the two metal discs are aligned, and one of the two metal discs is fixed on one side of the neutral point 400 of the transformer to be accessed, and the other metal disc is grounded, and is used to adjust the required voltage.

[0038] In the 330kV transformer neutral point current limiting reactor live access protection device, the disc type discharge gap protector 220 is adopted, two identical metal discs of the disc type discharge gap protector 220 are installed, the centers of the two metal discs are aligned, one of the two metal discs is fixed on one side of the neutral point 400 of the transformer to be accessed and is electrically connected with the neutral point 400 of the transformer, and the other metal disc is grounded, and the distance between the two metal discs can be adjusted to adjust the required discharge voltage.

[0039] In the 330kV transformer neutral point current limiting reactor live access protection device, the discharge gap protector 220 adopts the design of the disc type discharge gap protector 220, installs two identical metal discs of the disc type discharge gap protector 220, ensures the center alignment of the two metal discs, one of the metal discs is fixed on one side of the transformer neutral point 400 to be accessed and is electrically connected with the transformer neutral point 400, the other metal disc is grounded, and the distance (gap width) between the two metal discs is adjusted to adjust the voltage to not higher than 36V.

[0040] In the normal operation of the transformer, the disc type discharge gap protector 220 is in standby state, a certain gap is kept between the two metal discs, and no discharge channel is formed, at this time, other parts (such as the current leakage protector 210 and the resistance disc 230) of the protection device are also in normal work, and the transformer neutral point 400 is jointly protected, but when the overvoltage occurs in the transformer neutral point 400, 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 to form a discharge channel, and the overvoltage energy is released to the ground through the discharge channel, so as to protect the personnel, the transformer and the reactor from the damage of the overvoltage; when the overvoltage disappears, the air gap between the two metal discs of the disc type discharge gap protector 220 restores the insulation state, and continues to protect the transformer neutral point 400.

[0041] The disc type discharge gap protector 220 can effectively prevent the damage of the transformer neutral point 400 and the current limiting reactor 500 caused by the operating overvoltage, and through the breakdown and discharge of the discharge gap, the overvoltage (60V to 250V) energy can be rapidly released to the ground, so as to ensure the safe operation of the personnel and the equipment, and the discharge voltage required can be flexibly adjusted by adjusting the distance between the two metal discs, so that the protection device can adapt to the transformers of different voltage grades and different protection requirements.

[0042] Further, the gap width between the two metal discs is 0.32mm to 0.36mm, and in the embodiment, it is preferably 0.34mm, at this time, the operating voltage of the discharge gap should be the human body safety voltage 35.9V.

[0043] As preferred, the metal disc is a pure iron metal disc.

[0044] Further, the current leakage protector 210 is a surge protector.

[0045] Specifically, the resistance disc 230 provides a resistance of 50mΩ to 100mΩ.

[0046] In a specific embodiment, the bypass protection grounding circuit 300 comprises an insulation switch and an insulation substrate, and the conductive part of the insulation switch is mounted on the insulation substrate.

[0047] The bypass protection grounding circuit 300 is a key component, and its design comprises an insulation switch and an insulation substrate 260. When mounted, the insulation substrate 260 is fixed in place to ensure that it is stable and has good insulation performance. The conductive part of the insulation switch is mounted on the insulation substrate 260 to ensure good electrical isolation between the conductive part and the insulation substrate 260, while ensuring good contact and reliable electrical conductivity of the conductive part. The grounding end of the bypass protection grounding circuit 300 is reliably connected to the ground to ensure that the grounding resistance meets safety standards. When it is necessary to access the current limiting reactor 500 with power on, the bypass protection grounding circuit 300 is first connected to the neutral point 400 of the transformer to be accessed by operating the insulation switch. In the closed state of the insulation switch, the electrical connection between the bypass protection grounding circuit 300 and the neutral point 400 of the transformer is unobstructed. When the neutral point 400 of the transformer has an overvoltage, overcurrent or other abnormal conditions, the bypass protection grounding circuit 300 acts as a temporary grounding circuit to introduce abnormal current or voltage into the ground, thereby protecting the transformer and the reactor from damage. The insulation substrate 260 serves as an electrical isolation to prevent abnormal current or voltage from causing harm to equipment or personnel through other paths.

[0048] In a preferred embodiment, a press-type joint is further included, and the other end of the bypass protection grounding circuit is connected to the neutral point 400 of the transformer to be accessed through the press-type joint, making it more secure.

[0049] Preferably, the cable is a single-core copper cable. In this embodiment, the minimum cross-section of the single-core copper cable needs to satisfy the following calculation formula:

[0050]

[0051] In the formula, Smin represents the minimum cross-section of the cable, in mm 2 Id represents the steady value of short-circuit current flowing through the cable, which is the maximum zero sequence current 4.22 kA flowing through the neutral point; ti represents the breaking time of the circuit breaker, which is generally 0.25 s; c represents the thermal stability coefficient, which is 80 for a cross-linked polyethylene insulated power cable; and the thermal stability verification selects the nominal cross-section of the cable as 35 mm 2 .

[0052] In order to further understand the present utility model, the 330kV transformer neutral point current limiting reactor live access protection device provided by the present utility model will be described in detail in combination with the embodiments.

[0053] Embodiment

[0054] 1. Test scheme selection

[0055] 1.1 Selection of the flow conductor

[0056] The maximum zero sequence current flowing through the neutral point is known to be 4.22 kA, and the voltage is 22 kV. According to the thermal stability check, two schemes of cable and insulated copper bar are proposed for conductor selection. According to the thermal stability check, the minimum cross-sectional area of the cable is 26.375 mm 2 Therefore, the cable is selected to be a single-core copper cable with a nominal cross-section of 35 mm 2 The minimum cross-sectional area of the copper bar is 162.3 mm 2 Therefore, the copper bar is selected to be a grounding copper bar with a cross-sectional area of 40*5 mm 2 and is wrapped with two layers of insulating heat-shrink sleeves.

[0057] In the laboratory, the same group of people is arranged to simulate installation using copper cable and grounding copper bar in a highly simulated on-site actual construction environment, and the construction time of each stage is accurately recorded.

[0058] Through market research to calculate the cost of materials needed, the material cost is compared, and a test environment conforming to the actual site is built in the laboratory. The construction time of each stage is accurately recorded by using two different materials to simulate installation, and the comparison results are shown in Table 1:

[0059] Table 1 Comparison of experimental data of flow conductor selection

[0060]

[0061] From the data in Table 1 above, it is reflected that when single-core copper cable and grounding copper bar are used as flow conductors, the total cost of materials and installation time meet the requirements of the scheme selection indicators, but the material cost of the cable is less and the total installation time is short, which is better than the insulated copper bar. It is more convenient and cost-effective to use copper cable, so this embodiment uses copper cable as the flow conductor.

[0062] 1.2 Selection of the flow conductor connection method

[0063] Based on the actual use on site, two connection methods of crimping and clamp are used, and tests are designed to compare the compression force, contact resistance and operation difficulty when the two schemes are connected.

[0064] In the laboratory, the same group of people is arranged to simulate installation using copper cable and grounding copper bar in a highly simulated on-site actual construction environment, and the construction time of each stage is accurately recorded.

[0065] The initial clamping force was set to 50N, and the test was conducted 50 times. Two different connection methods were used, and the clamping force after each connection was measured. The rate of change of clamping force under the two connection methods over 50 tests was compared to determine if the requirements were met. The operation time for each test was accurately recorded, and the contact resistance at the joint was accurately measured and recorded after each connection. The changes in clamping force, operation time, and contact resistance for the crimped joint over 50 tests are as follows: Figure 5 As shown, the changes in clamping force, operating time, and contact resistance test data for the caliper connector after 50 tests are as follows: Figure 6 As shown.

[0066] contrast Figure 5 and Figure 6 It can be seen that both the crimp connector and the caliper connector meet the requirements for scheme selection in terms of operation time and contact resistance. However, the clamping force of the caliper connector decreases continuously with the number of tests, resulting in poor stability. The contact resistance also increases continuously with the number of tests. The crimp connector is superior to the caliper connector in terms of clamping force and contact resistance. Therefore, the crimp connector is used for fluid guiding connection in this embodiment.

[0067] 1.3 Selection of Discharge Gap Protector 220

[0068] Based on the referenced content, two types of over-discharge gap protectors 220 were adopted, namely disc-type discharge gap protector 220 and tip discharge gap protector 220, and an experiment was designed to compare the stability of the operating voltage of the two types of discharge gap protectors 220 after multiple conductions.

[0069] Adjust the operating voltage of the disc-type discharge gap protector 220 and the tip discharge gap to the 36V human safety voltage, connect the load in series to start applying voltage, and after conduction, apply a 10A current for 20 minutes. Then test its operating voltage again. Repeat the test 30 times.

[0070] In the laboratory, the same team of personnel, in a highly simulated on-site construction environment, adjusted the operating voltages of the disc-type discharge gap protector 220 and the tip discharge gap protector 220 to a safe human body voltage of 36V. A load was connected in series and voltage was applied. After conduction, a 10A current was applied and maintained for 20 minutes. The operating voltage was then tested again. This test was repeated 20 times to compare voltage stability and calculate whether the requirement of a stable operating voltage of 36±3V was met. The stability of the operating voltage of the disc-type discharge gap protector 220 was as follows: Figure 7 As shown, the stability of the operating voltage of the tip discharge gap protector 220 is as follows: Figure 8 As shown.

[0071] contrast Figure 7 and Figure 8It can be seen that the material tip discharge gap increases with the increase of the test number, and the operating voltage is continuously increased, which exceeds the safety range of 36±3V. The disc type 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 the embodiment is a disc type discharge gap protector 220.

[0072] 1.4 Selection of discharge protector 210

[0073] According to the requirement decomposition, two kinds of discharge protectors 210 are adopted, which are a surge protector with an operating voltage of 620V and a lightning arrester with an operating voltage of 2kV. The maximum current of both is 10kA, which meets the maximum current of 4.22kA. The team designs a simulation test to compare the stability of the operating voltage.

[0074] The surge protector and the lightning arrester are respectively pressurized, and the operating voltage is recorded. The experiment is carried out for 20 times. In the laboratory, the same group of people arranges the same group of people in the highly simulated field of the true working environment, and uses the direct current generator to test the operating voltage of the lightning arrester and the surge protector. The test is carried out for 20 times, and the data is compared and analyzed to calculate whether the operating voltage deviation value meets ≤±5%. The result is shown in Figure 9

[0075] It can be seen from Figure 7 that the operating voltage deviation of the surge protector meets the requirement and is relatively stable. The operating voltage of the lightning arrester exceeds the requirement and does not meet the requirement of operating voltage deviation value ≤±5%. Therefore, the discharge protector 210 in the embodiment is a surge protector.

[0076] 2. Test based on the optimal scheme selected

[0077] 2.1 Determine the voltage

[0078] It is known that the maximum zero sequence current flowing through the transformer neutral point 400 is 4.22kA, and the voltage is 22kV. That is, the selected cable should be able to withstand a voltage of 22kV. According to the scheme selection, the YJV-12 / 20kV-35 type single-core cross-linked polyethylene insulated and armored polyethylene / polyethylene sheathed power cable can withstand a maximum voltage of 35kV.

[0079] 2.2 Determine the cross-sectional area of the cable

[0080] According to the thermal stability condition, the minimum cross section of the cable should meet the following condition:

[0081]

[0082] In the formula, Smin: minimum cross section of the cable, unit: mm 2 ​; Id: the short-circuit current stability value flowing through the cable, taking the maximum zero sequence current 4.22kA flowing through the neutral point; ti: the breaking time of the circuit breaker, generally taking 0.25s; c: the thermal stability coefficient, taking 80 for the thermal stability coefficient of the cross-linked polyethylene insulated power cable; the thermal stability verification selects the nominal cross section of the cable as 35mm 2 .

[0083] 2.3 Determine the length of the cable

[0084] The actual cable length required for connecting the neutral point 400 of 12 transformers to the current limiting reactor 500 was measured, and the statistical results are shown in Table 2:

[0085] Table 2 Cable distance from the neutral point 400 of 12 transformers to the current limiting reactor 500

[0086]

[0087] As can be seen from Table 2, the cable length is between 3.52 meters and 4.57 meters. According to the requirements of the cable manufacturer, a margin of 1 meter should be left on site when the cable head is made. Therefore, YJY-12 / 20kV-35 type single-core cross-linked polyethylene insulated and armored polyethylene / polyethylene sheathed power cable with a length of 5.5 meters is selected.

[0088] According to GB 50150-2016 Electrical Equipment Installation Engineering Electrical Equipment Commissioning Test Standard 17.0.1, the team members carried out insulation resistance and AC voltage withstand test on the power cable line, and the test results were: the insulation resistance of the outer sheath and inner lining of the rubber-plastic cable was ≥0.5MΩ and the voltage withstand was 1min without breakdown and flashover phenomenon.

[0089] 2.4 Making compression joint

[0090] 2.41 Measure the size of the neutral point grounding flat iron

[0091] The width size of the neutral point grounding flat iron of 12 main transformers was counted, and the statistical results are shown in Table 3:

[0092] Table 3 Width statistical table of neutral point grounding flat iron of 12 main transformers

[0093]

[0094] As can be seen from the data in Table 3, the width size of the neutral point grounding flat iron is between 60mm and 100mm. In order to meet the principle of universality, the size of the compression joint should be not more than 60mm wide, and the compression joint is prepared according to the size.

[0095] 2.42 Formulate the test method for the copper bar connection

[0096] The 0.03 mm plug gauge is inserted into the gap of the copper bar lap joint surface from four directions, and the sum of the maximum depths of the plug gauge inserted in four directions is not greater than 12.5% of the lap joint circumference. The length of the plug gauge inserted in a single direction is not greater than 25% of the lap joint length.

[0097] 2.43 Determine the crimping method of the crimp joint

[0098] Four crimp joint bolt connection methods are designed, which are: 1 bolt center fixed, 2 bolts up and down fixed, 4 bolts four corners fixed, and 5 bolts four corners and center fixed. Ten tests are conducted for each of the four connection methods, and the maximum plug insertion depth of the 0.03 mm plug gauge is used to test the L1, L2, L3, and L4 insertion directions of the crimp joint.

[0099] The results show that the maximum plug insertion depth of the 4-bolt four-corner fixed and 5-bolt four-corner and center fixed connection methods is smaller and meets the requirements of the regulations, indicating that the difference between the 4-bolt and 5-bolt is not large. Considering the rapidity of installation, the 4-bolt four-corner fixed method is more convenient in this embodiment.

[0100] 2.44 Perform contact resistance test

[0101] On-site installation test is conducted, and the screw is tightened to a compression force of 100 N*m. The contact resistance is tested, and the contact resistance value of each installation is recorded. The test results are: the contact resistance of the crimp joint meets the target of less than 20 μΩ, and meets the standard.

[0102] 2.5 Make a disc type discharge gap protector

[0103] 2.51 Design and make a disc type discharge gap

[0104] Two identical metal discs are aligned at the center, one is fixed on the neutral point side, and the other is connected to the ground side as a threaded adjustable device for adjusting the required voltage.

[0105] In terms of material selection, according to the formula for calculating the flow capacity:

[0106] 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;

[0107] According to the above formula, the flow capacities of the two materials are compared, and the comparison results are shown in Table 4:

[0108] Table 4 Flow capacity test statistics table

[0109]

[0110] The data in Table 4, the embodiment selects a pure iron metal disc with a larger metal melting constant N, which can ensure the maximum through-flow capacity of the discharge gap and effectively improve safety.

[0111] 2.52 Determine the gap width of two metal discs

[0112] The gap width is gradually increased from 0. After adjustment, the operating voltage test is performed. If the target is not reached, continue to adjust until the operating voltage reaches 36±3V. The micrometer is used to measure the gap and record the gap width. The adjustment process is repeated 10 times, and the average value of the adjustment width is calculated. The results are shown in Table 5:

[0113] Table 5 Gap width adjustment value

[0114]

[0115] 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, and the preferred value is 0.34 mm.

[0116] 2.6 Select the model of the discharge protector 210

[0117] Compare the parameters of five surge protectors on the market, select the CHINT NU6-II type surge protector, the operating voltage (voltage) is 385V, the allowable tolerance is ±10%, and the maximum current is 40kA.

[0118] 3. According to the selected optimal scheme and the selected components, assemble the 330kV transformer neutral point current limiting reactor with live access protection device.

[0119] 4. On-site access test

[0120] From June 2023 to August 2023, the 330kV transformer neutral point current limiting reactor 500 was live accessed in Xujiayuan No.1 and No.2 main transformers, Yingshuiqiao No.1 and No.2 main transformers, and Ganlu No.1 and No.2 main transformers. The specific steps are as follows:

[0121] Step one: test the DC resistance value of the current limiting reactor 500 to be accessed (apply DC 2A current), and record the data (in order to select the appropriate resistance value of the bypass grounding safety device), select the appropriate resistance value of the current limiting reactor 500 with live access protection device, and perform through-flow test and record the data. Use the mobile platform to place the current limiting reactor 500 with live access protection device and safety tools in the designated maintenance area. The safety tools include: 110kV insulated operating rod, 35kV insulated gloves, 35kV insulated platform, handheld reciprocating saw, hydraulic puncher, etc. Prepare and perform pre-construction inspection and debugging to verify the normal function;

[0122] Step two: after the current limiting reactor 500 is connected to the ground cable of the protection device and the neutral point 400 of the transformer is connected to the ground copper cable, check the reliable connection of all contact surfaces (in order to ensure the reliable grounding of the above device, use a loop resistance tester to detect the resistance of each contact surface ≤20 μΩ), and use an insulated operating rod to put the bypass protection grounding loop 300 into operation;

[0123] Step three: use an insulated operating rod to put the protection grounding safety device 200 into operation;

[0124] Step four: connect the grounding end of the current limiting reactor 500 to be connected to the ground cable, connect the access end of the current limiting reactor 500 to be connected to the ground copper bar of the neutral point 400 of the transformer to be connected, and then close the disconnector of the neutral point current limiting reactor 500 to put it into operation;

[0125] Step five: use a DC source generator to apply a DC current of 2A to the end of the ground copper bar of the transformer neutral point 400, measure the current value A1 of the transformer neutral point 400 current limiting reactor 500 branch that has been put into operation, use a clamp ammeter to measure the current value A2 of the bypass grounding safety device branch, and the results meet A=A1+A2, A1 / A2=R2 / R1, which indicates that the neutral point current limiting reactor 500 grounding is good;

[0126] Step six: use a 110kV insulated rod to pull the first disconnector 240 of the discharge protector 210 and the discharge gap protector 220 branch, as shown in Figure 7 , then remove the above branch, use a handheld electric reciprocating saw to cut off the transformer neutral point 400 grounding copper bar, as shown in Figure 2 , and fill the fracture of the transformer neutral point 400 grounding bar with insulating material and wrap it well, pull the reliable bypass grounding branch of the insulating switch, and exit the reliable bypass grounding.

[0127] 5. Access effect statistics

[0128] Each process is completed safely, and the safety reaches 100%, and the engineering effect statistics are shown in Table 6:

[0129] Table 6 Engineering effect statistics table

[0130]

[0131] From the above table 6, it is known that the 330kV transformer neutral point 400 current limiting reactor 500 brings the access method safely and effectively, successfully brings the access of 6 330kV transformer neutral point 400 current limiting reactor 500, and the main transformer does not need to be powered off during the construction process. The average construction period of single 330kV transformer with current limiting reactor 500 is 4.6 hours.

[0132] The duration of traditional power-off access of current limiting reactor 500 from 2019 to 2021 is counted, and the statistical results are shown in table 7:

[0133] Table 7 Engineering effect statistical table

[0134]

[0135] From the data in table 7, according to the traditional operation method, the average power-off time of single transformer is 110.4h, and the above-mentioned live access method does not need to be powered off, and the total time of live access of current limiting reactor 500 is only 4.6h, and each transformer is equivalent to 110.4h of power supply.

[0136] Further, the power of 10 main transformers in operation by the live access method of current limiting reactor 500 is counted, and the average power in operation is calculated as 61.68MW. According to the calculation of electric quantity = time × power, the power supply quantity can be increased by 110.4 hours × 61.68MW = 6.8 million kilowatt hours each time the 330kV transformer neutral point 400 current limiting reactor 500 live access method is used.

[0137] The above is only a specific embodiment of the present application, but the protection scope of the present application is not limited thereto. Any person skilled in the art can easily think of various equivalent modifications or replacements within the technical range disclosed in the present application, and these modifications or replacements should be covered within the protection scope of the present application.

Claims

1. A 330 kV transformer neutral point current limiting reactor live access protection device, characterized in that, The device comprises a direct current power supply, a protection grounding safety device and a bypass protection grounding circuit, which are connected in parallel, the grounding end of the bypass protection grounding circuit is grounded, the input end is connected with 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 protection grounding safety device is connected with the neutral point of the transformer, the protection grounding safety device is used to discharge voltage and current to the ground when overvoltage occurs in the neutral point of the transformer, the protection grounding safety device comprises a current leakage protector, a discharge gap protector, a resistance disc and a first isolation switch, the current leakage protector, the discharge gap protector and the resistance disc are arranged in parallel, the input end of the bypass protection grounding circuit is connected with the incoming line end of the first isolation switch, the outgoing line end of the first isolation switch is connected with the input end of the protection grounding safety device, the discharge gap protector is used to pass through a voltage of 60V to 250V and release the passed voltage to not higher than 36V by adjusting the gap width, the current leakage protector is used to release current when the voltage is higher than 250V, and the resistance disc increases the grounding resistance and limits the size of the grounding current to ensure the safety and stability of the grounding process.

2. The 330 kV transformer neutral current limiting reactor live access protection device according to claim 1, characterized in that, The discharge gap protector is a disc type discharge gap protector, which comprises two identical metal discs, the centers of the two metal discs are aligned, and one of the two metal discs is fixed on one side of the neutral point of the transformer to be connected and the other is grounded, and is used to adjust the required voltage.

3. The 330 kV transformer neutral current limiting reactor live access protection device according to claim 2, characterized in that, The gap width of the two metal discs is 0.32mm to 0.36mm.

4. The 330 kV transformer neutral current limiting reactor live access protection device according to claim 2, characterized in that, The gap width of the two metal discs is 0.34mm.

5. The 330 kV transformer neutral current limiting reactor live access protection device according to claim 2, characterized in that, The metal disc is a pure iron metal disc.

6. The 330 kV transformer neutral current limiting reactor live access protection device according to claim 1, characterized in that, The current leakage protector is a surge protector.

7. The 330 kV transformer neutral current limiting reactor live access protection device according to claim 1, characterized in that, The resistance disc provides a resistance of 50mΩ to 100mΩ.

8. The 330 kV transformer neutral current limiting reactor live access protection device according to claim 1, characterized in that, The bypass protection grounding circuit comprises an insulation switch and an insulation substrate, and the conductive part of the insulation switch is mounted on the insulation substrate.

9. The 330 kV transformer neutral current limiting reactor live access protection device according to claim 1, characterized in that, A press joint is further provided, and the other end of the bypass protection grounding circuit is connected with the neutral point of the transformer to be connected through the press joint.

10. The 330 kV transformer neutral current limiting reactor live access protection device according to claim 1, characterized in that, The cable is a single-core copper cable.

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