Transformer live detection signal acquisition device and method

Abstract

The embodiment of the invention discloses a transformer live-line detection signal acquisition device and method, and relates to the technical field of transformer operation maintenance, and the device comprises an end screen leading-out wiring unit which is used for being detachably and electrically connected with an end screen; the anti-ground-loss grounding unit is provided with a main grounding loop and an auxiliary grounding loop which are connected in parallel, the main grounding loop enables an end screen to be directly grounded, the auxiliary grounding loop is connected with a current limiting element in series and then grounded, and the resistance value of the current limiting element is configured as follows: during normal operation, grounding current mainly flows through the main grounding loop; when the main grounding loop is broken, the end screen is still grounded through the auxiliary grounding loop; the end screen ground loss early warning unit comprises an electrostatic induction pole plate and an alarm, the electrostatic induction pole plate and the end screen form a coupling capacitor, and an alarm signal is sent out when the end screen is ground loss; and the signal acquisition unit is used for acquiring a current signal of the main grounding loop so as to calculate the dielectric loss and the capacitance of the bushing.

Description

Technical Field

[0001] This invention relates to the field of transformer operation and maintenance technology, and in particular to a transformer live-line detection signal acquisition device and method. Background Technology

[0002] Transformers are core equipment in the power grid. In recent years, there have been many cases of sudden transformer failures in the power system, which have even led to transformer fires and caused huge economic losses to the power grid.

[0003] Currently, the monitoring and testing of transformer bushings mainly relies on preventative outage tests. These tests use low voltages and involve long outage periods, failing to provide timely and accurate information about the transformer's operating status. In recent years, to better monitor transformer operation, live-line detection and online monitoring technologies have been further developed. However, existing online and live-line detection methods require obtaining signals from the bushing's end screen and transmitting these signals to the ground or a control center for on-site testing or monitoring. This can lead to the bushing's end screen losing ground, potentially causing transformer failures. Therefore, it is necessary to protect against end screen ground loss in online monitoring and live-line detection technologies while ensuring reliable signal transmission to the testing equipment.

[0004] In summary, existing technologies suffer from problems such as the safety risks associated with the loss of grounding of the end screen, inadequate protective measures, and insufficient measurement accuracy, which hinder the full realization of the effectiveness of live-line detection technology. Therefore, there is an urgent need in this field for a comprehensive solution that can achieve high-precision signal acquisition while ensuring the absolute grounding safety of the end screen, in order to provide reliable technical support for transformer condition-based maintenance and fault early warning. Summary of the Invention

[0005] The main objective of this invention is to provide a transformer live-line detection signal acquisition device and method. Based on a parallel double-circuit grounding structure, it eliminates the major safety hazard of "end-screen grounding failure" while ensuring high-precision acquisition of live-line detection signals.

[0006] To achieve the above objectives, the first aspect of this application provides a transformer live-line detection signal acquisition device, the device comprising a terminal screen lead-out wiring unit, a grounding prevention wiring unit, a terminal screen grounding early warning unit, and a signal acquisition unit, wherein: The terminal screen lead-out wiring unit is used for detachable electrical connection with the terminal screen; The grounding protection unit has a main grounding circuit and an auxiliary grounding circuit connected in parallel. The main grounding circuit directly grounds the end screen, and the auxiliary grounding circuit is grounded after connecting a current-limiting element in series. The resistance value of the current-limiting element is configured such that, during normal operation, the grounding current mainly flows through the main grounding circuit; and when the main grounding circuit is disconnected, the end screen remains grounded through the auxiliary grounding circuit. The end screen loss early warning unit includes an electrostatic induction plate and an alarm. The electrostatic induction plate forms a coupling capacitor with the end screen, which is used to drive the alarm to emit an alarm signal when the end screen loses ground. The signal acquisition unit, located on the ground side, is used to acquire the current signal of the main grounding circuit in order to calculate the bushing dielectric loss and capacitance.

[0007] A second aspect of this application provides a method for acquiring transformer live-line detection signals, comprising an application to a transformer live-line detection signal acquisition device as described in the first aspect, the method comprising: Based on the lead-out method of the end screen, determine the docking lead-out method of the lead-out wiring unit of the end screen; The parameters of the anti-grounding wiring unit are determined based on the cable length and resistance value during installation. Based on the space of the end screen and the end screen lead-out wiring unit, determine the area of ​​the electrostatic induction plate and its installation position, and calculate the parameters of the end screen ground loss early warning unit. The structure and wiring method of the signal acquisition device are determined based on the on-site spatial location of the main transformer being tested. The transformer live-line detection signal acquisition device is connected to the end screen to perform live-line detection.

[0008] The transformer live-line detection signal acquisition device and method provided in this application adopts a main / auxiliary dual circuit in parallel and a current-limiting element in series in the auxiliary circuit, so that the current is almost entirely carried by the main circuit during normal operation, ensuring that the ground sampling accuracy is consistent with the power outage test; once the main grounding line is broken, the end screen still maintains reliable grounding through the current-limiting element, instantly eliminating the floating voltage, and achieving the integrated effect of "zero ground loss, zero control, high precision, and live-line maintenance". Attached Figure Description

[0009] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0010] in: Figure 1 This is a schematic diagram of the structure of a transformer live-line detection signal acquisition device provided in an embodiment of this application; Figure 2 This is a schematic diagram of the structure of a terminal screen loss early warning unit provided in an embodiment of this application; Figure 3 This is a schematic diagram illustrating the wiring principle of a transformer live-line detection signal acquisition device provided in an embodiment of this application. Figure 4 This is a schematic diagram of a terminal screen take-off method provided in an embodiment of this application; Figure 5 This is a flowchart illustrating a transformer live-line detection signal acquisition device provided in an embodiment of this application; Figure 6 This is a schematic diagram of a typical integrated interface board layout provided in an embodiment of this application. Detailed Implementation

[0011] To enable those skilled in the art to better understand the present application, the technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present application, and not all embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present application.

[0012] The terms "first," "second," etc., in the specification, claims, and accompanying drawings of this application are used to distinguish different objects, not to describe a specific order. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover non-exclusive inclusion. For example, a process, method, system, product, or apparatus that includes a series of steps or units is not limited to the listed steps or units, but may optionally include steps or units not listed, or may optionally include other steps or units inherent to these processes, methods, products, or apparatuses.

[0013] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0014] The embodiments of this application are described below with reference to the accompanying drawings.

[0015] Figure 1 This is a schematic diagram of a transformer live-line detection signal acquisition device provided in an embodiment of this application. Figure 1 As shown, the transformer live-line detection signal acquisition device 100 includes a terminal screen lead-out wiring unit 110, a grounding prevention wiring unit 120, a terminal screen grounding early warning unit 130, and a signal acquisition unit 140, wherein: The aforementioned terminal screen lead-out wiring unit 110 is used for detachable electrical connection with the terminal screen; The aforementioned grounding protection unit 120 has a main grounding circuit and an auxiliary grounding circuit connected in parallel. The main grounding circuit directly grounds the end screen, and the auxiliary grounding circuit is grounded after being connected in series with a current-limiting element. The resistance value of the current-limiting element is configured such that, during normal operation, the grounding current mainly flows through the main grounding circuit, and when the main grounding circuit is disconnected, the end screen remains grounded through the auxiliary grounding circuit. The aforementioned end-screen ground loss early warning unit 130 includes an electrostatic induction plate and an alarm. The electrostatic induction plate forms a coupling capacitor with the end screen, which is used to drive the alarm to emit an alarm signal when the end screen loses ground. The aforementioned signal acquisition unit 140 is located on the ground side and is used to acquire the current signal of the aforementioned main grounding circuit in order to calculate the bushing dielectric loss and capacitance.

[0016] Specifically, in the transformer live-line detection signal acquisition device in this application embodiment, the end-screen lead-out wiring unit 110 is mainly used to provide a matching lead-out scheme by measuring the end-screen structure; the grounding protection unit 120 can prevent grounding loss during operation through backup protection means such as matching resistors and protection gaps; the end-screen grounding loss early warning unit 130 can use the principle of electrostatic induction to send an alarm (early warning light) through induced current when the end-screen loses ground, and will issue an early warning signal when the end-screen loses ground; the signal acquisition unit 140 can be installed on the ground near the transformer, and can acquire signals by using a through-core current transformer and series connection.

[0017] In an alternative embodiment, the auxiliary grounding circuit is further provided with a bypass switch, which can be closed to short-circuit the current limiting element to form a low-impedance redundant grounding channel.

[0018] In one alternative implementation, the auxiliary grounding circuit is further connected in parallel with a protective gap for grounding breakdown when the voltage of the end screen exceeds a set value.

[0019] In one optional embodiment, the current limiting element is a linear resistor, and its resistance is continuously adjustable in the range of 100 × main grounding circuit resistance to 2000V / I, where I is the bushing operating capacitor current.

[0020] In order to prevent the above-mentioned prevention and control measures from failing, an electrostatic induction board can be installed at the end screen position, and an alarm (alarm light) can be installed inside the induction board. When the induced voltage exceeds a certain value, the alarm light will light up, indicating that the end screen has lost ground and can be dealt with in time.

[0021] Figure 2 This is a schematic diagram of a terminal screen ground loss early warning unit provided in an embodiment of this application. Specifically, the voltage of the electrostatic induction plate can be calculated using the following formula: , Where C2 is the capacitance of the end screen to the sensing plate, C1 is the capacitance of the sensing plate to ground, U0 is the induced voltage of the end screen when it loses ground, U s The voltage of the sensing panel is given. According to the equipment test procedures, the end screen itself can withstand a withstand voltage of 2kV, and the voltage is 0 when grounded. A certain margin can be considered in setting the sensing voltage alarm value to prevent false alarms or untimely alarms. Optionally, the sensing voltage of the alarm can be set to 1kV. Therefore, the alarm value of the U0 sensing voltage can be calculated based on the values ​​of C1 and C2, and the indicator light will illuminate as a warning.

[0022] Please see Figure 3 , Figure 3 This is a schematic diagram illustrating the wiring principle of a transformer live-line detection signal acquisition device provided in an embodiment of this application.

[0023] like Figure 3 As shown, where I L The operating capacitance current of the bushing can be understood as the current flowing through the bushing under operating conditions. G is the disconnecting switch, D is the protective gap, and R is the resistance.

[0024] Specifically, this application proposes a grounding lead-out method for the end screen based on an electrical connection structure, and also proposes grounding prevention and early warning measures for preventing the end screen from losing ground. Regarding grounding prevention, this method ensures the grounding of the end screen by connecting the grounding lead and the series resistor grounding line in parallel. Simultaneously, because the other circuit is connected in series with a certain proportion of resistor, the grounding current flowing through the bushing mainly flows from the main grounding circuit. When the main circuit is accidentally lost due to external force or other circumstances, the end screen grounding is protected by the series resistor circuit. When the line is broken, if the voltage exceeds the allowable voltage of the end screen due to the presence of the series resistor, a protective gap D is added. Furthermore, after confirming that the main grounding line is broken, the resistor can be short-circuited through the bypass switch G to ensure reliable grounding of the end screen.

[0025] Among them, I L =ωCU, ω=314, C is the bushing capacitance, and U is the operating voltage.

[0026] In one alternative embodiment, the end-screen lead-out wiring unit 110 may have a mating lead-out interface that matches the end-screen structure of the sleeve, and the interface may be one of the following forms: Spring-cap type contact finger interface; Spiral cap type tightening nut interface; Slot-type pin-type contact finger interface; Spring-loaded pin-type contact finger interface; External tightening nut interface; Normally grounded top contact finger interface.

[0027] Figure 4This application provides a schematic diagram of a tail screen lead-out method, which illustrates specific lead-out recommendations for different tail screen lead-out methods, for example: (a) The last screen is brought out using a spring cap, which can be brought out by touch; (b) The lead-out method of the end screen is a screw cap type, which can be led out by tightening the nut; (c) The last screen is brought out by a slot pin type, and can be brought out by a touch finger; (d) The last screen is led out by a spring-loaded pin, and can be led out by a finger. (e) The end screen is externally mounted and can be led out using a tightening nut method; (f) The lead-out method of the end screen is normally grounded, and it can be led out by top connection or touch finger method.

[0028] The docking and lead-out method of the terminal screen lead-out wiring unit 110 can be determined or adjusted according to the lead-out method of the terminal screen on site. This application embodiment does not limit this.

[0029] Based on the description of the foregoing device embodiments, this application also provides a method for acquiring transformer live detection signals.

[0030] Figure 5 This is a schematic flowchart of a transformer live-line detection signal acquisition device provided in an embodiment of this application.

[0031] like Figure 5 As shown, the specific steps of the method in this embodiment are described below: 501. Based on the lead-out method of the end screen, determine the docking lead-out method of the lead-out wiring unit of the end screen.

[0032] The device structure involved in the method in the embodiments of this application can be referred to Figure 1 The specific descriptions of the embodiments shown will not be repeated here; it can be understood that the aforementioned transformer live-line detection signal acquisition device can be constructed using the methods in the embodiments of this application to achieve detection.

[0033] The connection method for the terminal block's wiring unit can be determined based on the terminal block's connection method on site. Specific recommendations for different terminal block connection methods for different bushings can be found here. Figure 4 The details and their corresponding descriptions will not be repeated here.

[0034] 502. Determine the parameters of the anti-grounding wiring unit based on the cable length and resistance value during installation.

[0035] In an optional implementation, step 502 includes: Determine the resistance value of the current-limiting element in the auxiliary grounding circuit; Based on the bushing capacitance and operating voltage level, calculate the current flowing through the bushing under operating conditions to obtain the bushing operating capacitance current; The upper limit of the current limiting element is further determined based on the above-mentioned bushing operating capacitance current and the above-mentioned end screen withstand value. The withstand value of the above-mentioned end screen is determined according to the withstand voltage test value during transformer end screen maintenance. The breakdown voltage of the protective gap is determined based on the above withstand voltage test values; the current carrying capacity of the bypass switch is selected based on the above bushing operating capacitance current.

[0036] Specifically, the series resistance value R of the auxiliary circuit can be calculated. Generally, the series resistance value R is greater than or equal to 100 times the main grounding resistance to ensure that the grounding current of the bushing end screen flows into the ground from the main circuit during normal operation and to ensure the accuracy of live testing.

[0037] The following formula can be used to calculate the current flowing through the bushing under operating conditions, based on the bushing capacitance and operating voltage level: I= , Where I: bushing operating capacitance current; ω represents angular velocity (2πf); C: bushing capacitance; U: bushing operating voltage, which can be calculated based on the system's highest operating voltage.

[0038] Then, the upper limit of the series resistance can be further determined based on the operating capacitor current I of the bushing and the withstand value of the bushing end screen. The withstand value of the bushing end screen can be determined according to the withstand voltage test value during the maintenance of the transformer end screen. The AC test voltage is taken as 2kV, so the series resistance value of the auxiliary circuit R≤2000V / I.

[0039] Finally, the breakdown voltage of the protection gap D can be determined based on the withstand voltage test value of the end screen, and a certain margin can be considered when selecting it at 1kV; the current carrying capacity of the bypass switch G can be determined based on the current of the end screen, for example, it should be selected at least 5 times the current flowing through the bushing, and the resistance value should be as small as possible.

[0040] 503. Based on the space of the aforementioned end screen and the aforementioned end screen lead-out wiring unit, determine the area of ​​the electrostatic induction plate and its installation position, and calculate the parameters of the end screen ground loss early warning unit.

[0041] Specifically, the area of ​​the sensing plate and its installation position can be determined based on the space of the end screen and the matching end screen lead-out wiring unit, and the parameters of the end screen ground loss early warning device can be calculated. The calculation of the voltage value of the end screen alarm can be referred to the description in the previous embodiment, which will not be repeated here. 504. Determine the structure and wiring method of the signal acquisition device based on the on-site spatial location of the main transformer being tested.

[0042] Specifically, the structure and wiring method of the signal acquisition device can be determined according to the spatial location of the main transformer being tested. A through-hole current transformer and a series connection method can be used to acquire signals.

[0043] Figure 6 This is a schematic diagram of a typical integrated interface board layout provided for an embodiment of this application. For example... Figure 6 As shown, the specific implementation of the terminal screen lead-out wiring unit and the anti-grounding wiring unit is as follows: End screen: The end screen lead of the bushing is first connected to the "input terminal" on this interface board; Open-circuit protection device: connected in parallel with the protection gap D and the current limiting resistor R, to achieve overvoltage clamping at the moment of ground failure of the last screen, and to prevent open-circuit overvoltage from endangering the bushing; Protection pressure plate: Provides a removable hardware shorting piece, corresponding to the mechanical or pluggable implementation of the bypass switch G, which facilitates direct grounding of the end screen during maintenance; Disconnect switch: also known as bypass switch G, forms a double redundancy with the pressure plate. It can be manually or electrically short-circuited to the current limiting element in the energized state to complete the bypass grounding function; Measurement end: This refers to the current sampling point of the signal acquisition unit. The current of the main grounding circuit is led to the background dielectric loss tester through a through-core CT or a series sampling resistor to realize live detection of dielectric loss and capacitance. Input end: Serves as a detachable electrical connection port between the end screen and this device, compatible with various docking methods such as spring caps and screw caps, ensuring the universality and hot-swappable capability of the end screen lead-out wiring unit.

[0044] 505. Connect the above-mentioned transformer live-line detection signal acquisition device to the above-mentioned terminal screen to carry out live-line detection.

[0045] Once the parameters are determined, the transformer live-line detection signal acquisition device can be connected to the bushing end screen for live-line testing. The circuit logic is as follows: during normal operation, the bushing is grounded through the main circuit and an auxiliary circuit with a parallel series resistor. Due to the series resistor, the bushing grounding current flows to the ground through the main circuit, and the test current of the main circuit meets the requirements for live-line testing. When a fault occurs in the main circuit, the bushing end screen is grounded through the series resistor circuit. When a grounding fault occurs in the system or other problems, and the end screen experiences an unacceptable voltage, the protection gap will activate to ensure proper grounding of the end screen. If a broken wire or other problem is found in the main grounding circuit during on-site live-line testing, a bypass switch G can be used to bypass the series resistor to ensure reliable grounding of the end screen. The current in this circuit can be tested to ensure that dielectric loss and capacitance tests can be performed normally.

[0046] Current online monitoring and live-line detection of transformers require obtaining signals from the bushing end screen and transmitting the end screen signals to the ground or a control center for on-site detection or monitoring. This may cause the bushing end screen to lose ground, potentially leading to transformer failure. Furthermore, some measurements are not considered, which can result in inaccurate live-line detection or online monitoring measurements. Therefore, there is an urgent need for a reliable protection method and device to prevent the end screen of transformer bushing live-line detection devices from losing ground, ensuring long-term reliable and effective grounding of the end screen, and guaranteeing the accuracy of live-line detection and online monitoring.

[0047] The method for acquiring transformer live-line detection signals in this embodiment of the application can ensure effective grounding of the bushing end screen, and at the same time ensure the accuracy of live-line detection capacitance and dielectric loss values, providing support for timely understanding of bushing problems and prevention of bushing faults.

[0048] Those skilled in the art will understand that all or part of the processes in the above embodiments can be implemented by a computer program instructing related hardware. The program can be stored in a non-volatile computer-readable storage medium, and when executed, it can include the processes of the embodiments described above. Any references to memory, storage, databases, or other media used in the embodiments provided in this application can include non-volatile and / or volatile memory. Non-volatile memory can include read-only memory (ROM), programmable ROM (PROM), electrically programmable ROM (EPROM), electrically erasable programmable ROM (EEPROM), or flash memory. Volatile memory can include random access memory (RAM) or external cache memory. By way of illustration and not limitation, RAM is available in various forms, such as static RAM (SRAM), dynamic RAM (DRAM), synchronous DRAM (SDRAM), dual data rate SDRAM (DDRSDRAM), enhanced SDRAM (ESDRAM), synchronous link DRAM (SLDRAM), RAMbus direct RAM (RDRAM), direct memory bus dynamic RAM (DRDRAM), and RAMbus dynamic RAM (RDRAM), etc.

[0049] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0050] The embodiments described above are merely illustrative of several implementation methods of this application, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of this patent application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this patent application should be determined by the appended claims.

Claims

1. A transformer live-line detection signal acquisition device, characterized in that, The device includes a terminal screen lead-out wiring unit, a grounding prevention wiring unit, a terminal screen grounding early warning unit, and a signal acquisition unit, wherein: The terminal screen lead-out wiring unit is used for detachable electrical connection with the terminal screen; The grounding protection unit has a main grounding circuit and an auxiliary grounding circuit connected in parallel. The main grounding circuit directly grounds the end screen, and the auxiliary grounding circuit is grounded after connecting a current-limiting element in series. The resistance value of the current-limiting element is configured such that, during normal operation, the grounding current mainly flows through the main grounding circuit; and when the main grounding circuit is disconnected, the end screen remains grounded through the auxiliary grounding circuit. The end screen loss early warning unit includes an electrostatic induction plate and an alarm. The electrostatic induction plate forms a coupling capacitor with the end screen, which is used to drive the alarm to emit an alarm signal when the end screen loses ground. The signal acquisition unit, located on the ground side, is used to acquire the current signal of the main grounding circuit in order to calculate the bushing dielectric loss and capacitance.

2. The transformer live-line detection signal acquisition device according to claim 1, characterized in that, The auxiliary grounding circuit is also equipped with a bypass switch, which can be closed to short-circuit the current limiting element to form a low-impedance redundant grounding channel.

3. The transformer live-line detection signal acquisition device according to claim 2, characterized in that, The auxiliary grounding circuit is also connected in parallel with a protective gap, which is used to break down the ground when the voltage of the end screen exceeds a set value.

4. The transformer live-line detection signal acquisition device according to claim 1, characterized in that, The current limiting element is a linear resistor, and its resistance is continuously adjustable within the range of 100 × main grounding circuit resistance to 2000V / I, where I is the bushing operating capacitor current.

5. The transformer live-line detection signal acquisition device according to claim 1, characterized in that, The end-screen lead-out wiring unit has a docking lead-out interface that matches the end-screen structure of the sleeve, and the interface is one of the following forms: Spring-cap type contact finger interface; Spiral cap type tightening nut interface; Slot-type pin-type contact finger interface; Spring-loaded pin-type contact finger interface; External tightening nut interface; Normally grounded top contact finger interface.

6. The transformer live-line detection signal acquisition device according to claim 1, characterized in that, The signal acquisition unit uses a through-hole current transformer connected in series to acquire signals.

7. A method for acquiring live-line detection signals of a transformer, characterized in that, Applied to the apparatus of any one of claims 1-6, the method comprises: Based on the lead-out method of the end screen, determine the docking lead-out method of the lead-out wiring unit of the end screen; The parameters of the anti-grounding wiring unit are determined based on the cable length and resistance value during installation. Based on the space of the end screen and the end screen lead-out wiring unit, determine the area of ​​the electrostatic induction plate and its installation position, and calculate the parameters of the end screen ground loss early warning unit. The structure and wiring method of the signal acquisition device are determined based on the on-site spatial location of the main transformer being tested. The transformer live-line detection signal acquisition device is connected to the end screen to perform live-line detection.

8. The transformer live-line detection signal acquisition method according to claim 7, characterized in that, The process of determining the parameters of the anti-grounding wiring unit based on the cable parameters during installation includes: Determine the resistance value of the current-limiting element in the auxiliary grounding circuit; Based on the bushing capacitance and operating voltage level, calculate the current flowing through the bushing under operating conditions to obtain the bushing operating capacitance current; The upper limit of the current limiting element is further determined based on the operating capacitor current of the bushing and the withstand value of the end screen. The withstand value of the end screen is determined according to the withstand voltage test value during transformer end screen maintenance. The breakdown voltage of the protective gap is determined based on the withstand voltage test value; the current carrying capacity of the bypass switch is selected based on the bushing operating capacitor current.

9. The transformer live-line detection signal acquisition method according to claim 7, characterized in that, The step of determining the docking lead-out method of the end-screen lead-out wiring unit according to the lead-out method of the end screen includes: The end screen is led out using a spring cap type, and the end screen lead-out wiring unit is led out using a finger-type method; The end screen is led out using a screw cap type, and the end screen lead-out wiring unit is led out using a tightened nut method; The end screen is led out using a slot pin type, and the end screen lead-out wiring unit is led out using a finger type; The end screen is led out using a spring-loaded pin method, and the end screen lead-out wiring unit is led out using a finger-type method; The end screen is externally mounted, and the end screen lead-out wiring unit is led out using a tightening nut method; The terminal screen is grounded, and the terminal screen lead-out wiring unit is led out using a top-connection and contact finger method.

10. The transformer live-line detection signal acquisition method according to claim 7, characterized in that, The current limiting element is a linear resistor, and its resistance is continuously adjustable within the range of 100 × main grounding circuit resistance to 2000V / I, where I is the bushing operating capacitor current.

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