Intelligent closed neutral point protection device for transformer

Abstract

The application discloses a kind of transformer intelligent enclosed neutral point protection devices, including maintenance switch, lightning arrester, capacitive voltage divider, filter module, isolation transformer, charge-discharge module, voltage detection module, gap discharge unit, digital control unit;Filter module is used to filter the voltage signal of capacitive voltage divider after voltage division flows into isolation transformer, removes high-frequency signal, retains power frequency or its multiple frequency signal, realizes the distinction of transient overvoltage signal and steady overvoltage signal;Voltage detection module is used to detect the voltage amplitude of four capacitors in charge-discharge module, duration, and real-time transmission detection data to digital control unit, and digital control unit real-time uploads detection data to main control background, control pulse trigger controllable switch opens or closes, control discharge of enclosed discharge gap.The application realizes the accurate identification of transformer neutral point overvoltage type, solves the problem of high misoperation rate of existing device, damage transformer.

Description

Technical Field

[0001] This invention relates to a transformer neutral point protection technology, and more specifically, to a transformer intelligent enclosed neutral point protection device. Background Technology

[0002] Currently, transformer neutral point protection devices generally employ two types of discharge gap structures: air insulation and SF6 gas insulation. Air-insulated transformer neutral point protection devices have the following problems: ① They are easily affected by the external environment. The withstand voltage of the discharge gap is easily affected by factors such as altitude, atmospheric humidity, temperature, salt spray, high and low temperatures, and atmospheric pressure, leading to significant errors in the corrected discharge gap distance. During long-term operation, the discharge gap is affected by wind, sand, and corrosion, increasing the dispersion of its withstand voltage. ② The on-site calibration workload is large. Due to the susceptibility of the discharge gap to external influences, determining the discharge gap distance for each substation's transformer neutral point protection device requires on-site withstand voltage tests, resulting in a large amount of repetitive work and high costs. ③ They cannot correctly distinguish overvoltage types, easily causing malfunctions. Currently, SF6 gas-insulated transformer neutral point protection devices cannot correctly identify the type of transformer neutral point overvoltage and lack the function of distinguishing between steady-state and transient overvoltages. This easily causes malfunctions in the grounding switch of the protection device, leading to a substation-wide power outage. For low-amplitude steady-state overvoltages, the discharge gap cannot discharge.

[0003] Existing similar patents also have different problems, as follows:

[0004] (1) A controllable gap and a protection device and method for the neutral point of a 110kV transformer based on the controllable gap (application number 201310233419.7). This device has the following two drawbacks: ① The signal input to the isolation transformer T1 is not filtered. For transient overvoltages, which are generally high-frequency signals in MHz, the isolation transformer T1 will experience magnetic saturation, resulting in severe distortion of the transient overvoltage signal; ② The high-voltage trigger diode D2 is used. Due to the limitation of its conduction voltage, the overvoltage at the transformer neutral point must reach a certain limit before the gap discharge can be triggered. However, in power systems, the overvoltage situation at the transformer neutral point is complex, and the amplitude of some steady-state overvoltages is difficult to reach the trigger value of the high-voltage diode, thus failing to effectively trigger the high-voltage diode to control the gap discharge.

[0005] (2) A neutral point protection device and scheme for a 110kV transformer (application number 201710482423.5). The device has the following problems: ① The discharge gap adopts an open structure, and the discharge gap withstand voltage is highly dispersed, making the protection device prone to malfunction; ② The judgment is made by directly collecting signals from the low-voltage capacitor on the primary side. Due to the high voltage on the primary side, the secondary and control circuits are prone to breakdown and damage.

[0006] In the above context, steady-state overvoltage refers to overvoltage caused by power frequency voltage rise and resonance phenomena, characterized by its long duration or even prolonged existence. This voltage is characterized by low frequency (mostly 50Hz or harmonics). Transient overvoltage, on the other hand, refers to a voltage rise that significantly exceeds the normal operating value of a certain part of the power system when the insulation of electrical equipment is under the rated voltage of the power supply during normal operation, due to factors such as lightning strikes, operation, faults, or parameter configuration changes. This voltage is characterized by high frequency (mostly around tens of MHz). Summary of the Invention

[0007] The purpose of this invention is to overcome the shortcomings of the prior art and propose an intelligent enclosed neutral point protection device for transformers. This device achieves accurate identification of the type of overvoltage at the transformer neutral point. Specifically, under steady-state overvoltage, the controllable gap can release the overvoltage at the neutral point; under transient overvoltage, the surge arrester can release the overvoltage at the neutral point. By accurately identifying the type of overvoltage at the transformer neutral point, this invention solves the problems of high malfunction rate and transformer damage caused by existing devices for transformer neutral point protection.

[0008] The objective of this invention is achieved through the following technical solutions.

[0009] This invention relates to an intelligent enclosed neutral point protection device for transformers, comprising a surge arrester, a capacitive voltage divider, an isolation transformer, and a charging / discharging module. The surge arrester and the capacitive voltage divider are respectively connected to the transformer neutral point. The primary side of the isolation transformer is connected to the output of the capacitive voltage divider, and the secondary side is connected to the input of the charging / discharging module. The charging / discharging module consists of a second resistor, a third resistor, a fourth capacitor, and a rectifier bridge. The transformer neutral point is also connected to a maintenance switch and a gap discharge unit. The gap discharge unit includes a pulse transformer. The primary side of the pulse transformer is connected in series with a pulse-triggered controllable switch, a power supply, and a fourth resistor. One terminal of the secondary side of the pulse transformer is connected to a trigger electrode, which is embedded in the low-voltage terminal connector of the enclosed discharge gap. The other terminal of the secondary side of the pulse transformer and the low-voltage terminal connector of the enclosed discharge gap are both grounded via a current transformer. The high-voltage terminal connector of the enclosed discharge gap is connected to the transformer neutral point.

[0010] A filter module is connected between the output terminal of the capacitor voltage divider and the primary side of the isolation transformer. The filter module is used to filter the voltage signal flowing into the isolation transformer after voltage division by the capacitor voltage divider, remove high-frequency signals, retain the power frequency or its multiples, and realize the distinction between transient overvoltage signals and steady-state overvoltage signals.

[0011] The output terminal of the charging and discharging module is connected to a voltage detection module. The voltage detection module is used to detect the voltage amplitude and continuous charging time across the No. 4 capacitor and transmit the detection data to the digital control unit in real time. The digital control unit uploads the detection data to the main control backend in real time. At the same time, the digital control unit compares the detection data with a preset threshold and controls the pulse-triggered controllable switch to open or close based on the comparison result, thereby controlling the discharge of the closed discharge gap. In addition, the digital control unit is also used to control the opening and closing of the maintenance switch.

[0012] Furthermore, the neutral point of the transformer is grounded via a maintenance switch, which is used to provide a reliable grounding point during equipment maintenance.

[0013] Furthermore, one end of the surge arrester is connected to the neutral point of the transformer, and the other end is grounded.

[0014] Furthermore, the capacitor voltage divider consists of a first capacitor and a second capacitor connected in series. One end of the first capacitor is connected to the neutral point of the transformer, and the other end is grounded through the second capacitor.

[0015] Furthermore, the filter module consists of a resistor and a capacitor. One end of the resistor is connected to the high-voltage side of the capacitor, and the other end is grounded through the capacitor. The capacitor is connected to the primary side of the isolation transformer.

[0016] Furthermore, the isolation transformer has a turns ratio of 1:1, and is used to isolate the unit modules at its primary and secondary ends.

[0017] Furthermore, the charging and discharging module consists of resistor No. 2, resistor No. 3, capacitor No. 4, and a rectifier bridge. One end of the AC signal of the rectifier bridge is connected to one terminal of the secondary side of the isolation transformer via resistor No. 2, and the other end of the AC signal of the rectifier bridge is connected to the other terminal of the secondary side of the isolation transformer. The negative terminal of the DC signal of the rectifier bridge is grounded, and the positive terminal of the DC signal of the rectifier bridge is grounded via resistor No. 3 and capacitor No. 4 connected in parallel.

[0018] Furthermore, the voltage detection module uses a voltmeter with data transmission function, which is connected in parallel across capacitor number four.

[0019] Furthermore, the enclosed discharge gap includes an enclosed busbar filled with insulating gas, and a high-voltage terminal joint and a low-voltage terminal joint are arranged opposite to each other inside the enclosed busbar.

[0020] Compared with the prior art, the beneficial effects of the technical solution of the present invention are:

[0021] (1) The gap discharge unit in this invention adopts a closed gas insulation structure, which can achieve stable breakdown of the discharge gap while solving the problem of false breakdown caused by the reduction of the discharge gap withstand voltage due to changes in external temperature and humidity of the open discharge gap. It also overcomes the problem that the withstand voltage of the discharge gap is easily affected by multiple variables of the external environment.

[0022] (2) The present invention adds a filtering module to block transient high-frequency signals at the neutral point of the transformer, retains the power frequency or its multiples, avoids magnetic saturation of the isolation transformer output line, and distinguishes between transient and steady-state overvoltages from the frequency perspective.

[0023] (3) The isolation transformer in this invention can achieve the functions of primary and secondary isolation and voltage amplitude limitation, thereby protecting the secondary components.

[0024] (4) In this invention, the charging and discharging module can control the charging time of the voltage across capacitor four by setting the parameters of resistor two and capacitor four, thereby distinguishing between steady-state overvoltage and residual low-frequency transient signals. It can accurately identify steady-state overvoltage and transient overvoltage based on the signal duration.

[0025] (5) In this invention, the voltage detection module realizes the detection of the voltage amplitude and duration across capacitor No. 4.

[0026] (6) In this invention, the digital control unit reads the voltage detection module. When the voltage amplitude and duration of the voltage detection module both reach preset thresholds, it determines that the overvoltage type is a steady-state overvoltage and triggers the discharge gap circuit switch to achieve the purpose of discharge gap discharge. By setting multiple thresholds, it is possible to identify steady-state overvoltages of different amplitudes and effectively achieve active breakdown of the discharge gap. At the same time, through the design of multiple thresholds, the problem that some steady-state overvoltages with low amplitudes cannot trigger the discharge gap discharge can be effectively solved, further improving the reliability of the protection device.

[0027] In summary, this invention integrates a filtering module, an isolation transformer, a charging / discharging module, and a digital control unit, achieving accurate identification of the type of overvoltage at the transformer neutral point. Specifically, under steady-state overvoltage, a controllable gap actuates to release the overvoltage; under transient overvoltage, a surge arrester actuates to release the overvoltage. By accurately identifying the type of overvoltage at the transformer neutral point, it solves the problems of high malfunction rates and transformer damage associated with existing neutral point devices. Simultaneously, the digital control unit and gap discharge unit, through the setting of multiple thresholds for voltage and duration, can achieve reliable and stable breakdown of the discharge gap after low-amplitude steady-state overvoltages. Attached Figure Description

[0028] Figure 1 This is a schematic diagram of the transformer intelligent enclosed neutral point protection device of the present invention.

[0029] Figure 2 This is a circuit diagram of the intelligent enclosed neutral point protection device for transformers according to the present invention.

[0030] Attached diagram labels: A - Transformer neutral point, S - Maintenance switch, MOA - Surge arrester, C1 - Capacitor No. 1, C2 - Capacitor No. 2, C3 - Capacitor No. 3, C4 - Capacitor No. 4, R1 - Resistor No. 1, R2 - Resistor No. 2, R3 - Resistor No. 3, R4 - Resistor No. 4, T1 - Isolation transformer, T2 - Pulse transformer, D1 - Rectifier bridge, V - Voltage detection module, K1 - Pulse-triggered controllable switch, U1 - Power supply, CT - Current transformer, G - Enclosed discharge gap, J - Trigger electrode, GND - Ground. Detailed Implementation

[0031] The present invention will now be further described with reference to the accompanying drawings.

[0032] like Figure 1 As shown, the intelligent enclosed neutral point protection device for transformers of the present invention mainly includes a maintenance switch, a surge arrester, a capacitor voltage divider, a filter module, an isolation transformer, a charging and discharging module, a voltage detection module, a gap discharge unit, and a digital control unit.

[0033] The maintenance switch, surge arrester, capacitor voltage divider, and gap discharge unit are connected in parallel and are respectively connected to the neutral point A of the transformer. The filter module is connected between the output terminal of the capacitor voltage divider and the primary side of the isolation transformer. The charging and discharging module is connected to the secondary side of the isolation transformer T1, and the output terminal of the charging and discharging module is connected to a voltage detection module. The digital control unit is connected to the voltage detection module, the maintenance switch, and the gap discharge unit.

[0034] In the above-described apparatus, preferably, such as Figure 2 As shown, one end of the maintenance switch S is grounded to GND, and the other end is connected to the transformer neutral point A. During equipment maintenance, the maintenance switch S is used to provide a reliable grounding point to avoid injury to workers. One end of the surge arrester MOA is grounded to GND, and the other end is connected to the transformer neutral point A.

[0035] In the above-described device, the capacitive voltage divider is used to divide the overvoltage signal at the neutral point A of the transformer. Preferably, the capacitive voltage divider consists of a first capacitor C1 and a second capacitor C2 connected in series. Specifically, one end of the first capacitor C1 is connected to the neutral point A of the transformer, and the other end is grounded to GND via the second capacitor C2. The first capacitor C1 acts as the high-voltage arm capacitor, and the second capacitor C2 acts as the low-voltage arm capacitor. The series connection of the first capacitor C1 and the second capacitor C2 serves to divide the voltage at the neutral point A of the transformer, ensuring that the voltage across the second capacitor C2 drops to approximately 220V.

[0036] In the above-described device, the filtering module is used to filter the voltage signal flowing into the isolation transformer T1 after being divided by the capacitor voltage divider. This effectively removes high-frequency signals (i.e., transient overvoltage signals) and retains the 50Hz power frequency or its multiples (i.e., steady-state overvoltage signals, mostly over 100ms). This solves the magnetic saturation problem of the isolation transformer T1 and also distinguishes between transient and steady-state overvoltage signals from a frequency perspective. Preferably, the filtering module consists of a resistor R1 and a capacitor C3. One end of resistor R1 is connected to the high-voltage side of capacitor C2, and the other end is grounded to GND via capacitor C3. By setting the parameters of resistor R1 and capacitor C3, the signal input to the isolation transformer T1 can be filtered, removing high-frequency signals and retaining the power frequency or its multiples, while simultaneously preventing magnetic saturation of the isolation transformer T1.

[0037] In the above device, the two terminals of the primary side of the isolation transformer T1 are respectively connected to the two ends of the third capacitor C3, with a transformation ratio of 1:1. This isolates the unit module (primary element) on the primary side from the unit module (secondary element) on the secondary side, preventing the primary side signal from affecting the subsequent module on the secondary side and thus protecting the secondary element.

[0038] In the aforementioned device, the charging and discharging module can be composed of resistor R2 (number 2), resistor R3 (number 3), capacitor C4 (number 4), and rectifier bridge D1. Resistor R2 and capacitor C4 form the charging circuit, resistor R3 and capacitor C4 form the discharging circuit, and rectifier bridge D1 is used to rectify the voltage signal. Its main function is: the signal from the secondary side of isolation transformer T1 is converted into a DC signal by rectifier bridge D1; this signal then passes through the charging circuit of resistor R2 and capacitor C4, charging capacitor C4 and thus creating a voltage across capacitor C4. Specifically, in the charging and discharging module, one end "a" of the AC signal of rectifier bridge D1 is connected to one terminal of the secondary side of isolation transformer T1 via resistor R2 (number two). The other end "b" of the AC signal of rectifier bridge D1 is connected to the other terminal of the secondary side of isolation transformer T1. The negative terminal "c" of the DC signal of rectifier bridge D1 is grounded to GND, and the positive terminal "d" of the DC signal of rectifier bridge D1 is grounded to GND via resistor R3 (number three). Capacitor C4 (number four) is connected in parallel across resistor R3. By setting the parameters of resistor R2 (number two) and capacitor C4 (number four), the charging time constant t is set. c The purpose is that, since the resistance of rectifier bridge D1 is extremely small when it is in the conducting state, the time constant t c=RC. By setting the parameters of resistor R2 and capacitor C4, the charging time of the voltage across capacitor C4 can be controlled, enabling the differentiation between steady-state overvoltages and residual low-frequency transient signals. Specifically, by adjusting the parameters of resistor R2 and capacitor C4, the charging time will be lower for low-frequency transient signals (less than 10ms), and higher for steady-state overvoltage signals (mostly longer than 100ms). For long-lasting steady-state overvoltages, a stable voltage can be formed across capacitor C4 and last for a long time; for short-lasting transient overvoltages, a stable voltage cannot be formed across capacitor C4. This forms a second layer of identification logic for steady-state and transient overvoltages.

[0039] In the above device, the voltage detection module V can be a voltmeter with data transmission function, connected in parallel across capacitor C4. The voltage detection module is used to detect the voltage amplitude and duration across capacitor C4, and transmits the detection data as an input signal to the digital control unit in real time.

[0040] In the above-mentioned device, the gap discharge unit includes a pulse transformer T2, a pulse-triggered controllable switch K1, a power supply U1, a fourth resistor R4, a closed discharge gap G, and a current transformer CT. The closed discharge gap G includes a section of enclosed busbar filled with insulating gas, which can be an SF6 gas insulation structure. A high-voltage terminal G1 and a low-voltage terminal G2 are arranged opposite each other within the enclosed busbar, with a gap between them. The high-voltage terminal G1 is connected to the transformer neutral point A, and the low-voltage terminal G2 is grounded to GND via the current transformer CT. One terminal of the primary side of the pulse transformer T2 is connected to the positive terminal of the power supply U1 via the pulse-triggered controllable switch K1, and the other terminal of the primary side of the pulse transformer T2 is connected to the negative terminal of the power supply U1 via the fourth resistor R4. One terminal of the secondary side of the pulse transformer T2 is connected to a trigger electrode J, which is embedded in the low-voltage terminal G2 of the closed discharge gap G. The other terminal of the secondary side of the pulse transformer T2 is grounded to GND via the current transformer CT.

[0041] The pulse-triggered controllable switch K1 is controlled by the digital control unit. By controlling the opening and closing of the pulse-triggered controllable switch K1, the discharge of the closed discharge gap G is controlled. The power supply U1 provides voltage to the closed discharge gap G. The fourth resistor R4 acts as a current-limiting resistor to prevent excessive current in the primary circuit of the pulse transformer T2 from burning out the transformer. The pulse transformer T2 isolates the primary and secondary equipment while providing power to the trigger electrode J. The current transformer CT acts as a zero-sequence current detection unit for the transformer neutral point, providing zero-sequence current data for the background relay protection. The logic of the gap discharge unit is as follows: when the pulse-triggered controllable switch K1 is closed, the power supply U1 provides voltage to the primary side of the pulse transformer T2. Then, after the voltage is induced at the secondary side of the pulse transformer T2, the trigger electrode J and the low-voltage terminal G2 break down first, generating plasma, which in turn causes the closed discharge gap G to break down (the high-voltage terminal G1 and the low-voltage terminal G2 actively break down), thereby releasing the overvoltage at the transformer neutral point A.

[0042] In the aforementioned device, the digital control unit comprises a TM32F10X series MCU and other components. The digital control unit is connected to the voltage detection module V, the pulse-triggered controllable switch K1, and the maintenance switch S. The digital control unit reads data from the voltage detection module V in real time, compares the detected data with a preset threshold, and controls the pulse-triggered controllable switch K1 to open or close based on the comparison result, thereby controlling the discharge of the closed discharge gap G. When the detected voltage amplitude and duration match the preset threshold, a pulse trigger command is issued to close the pulse-triggered controllable switch K1, achieving the purpose of controlling the discharge of the closed discharge gap G. Through various threshold designs, the problem of low steady-state overvoltage amplitude preventing the discharge gap from being triggered can be effectively solved, further improving the reliability of the protection device. Simultaneously, the digital control unit uploads the voltage data across capacitor C4 to the main control backend in real time, achieving real-time monitoring. Furthermore, the digital control unit also remotely controls the opening and closing of the maintenance switch S by controlling its power supply.

[0043] Although the functions and working processes of the present invention have been described above in conjunction with the accompanying drawings, the present invention is not limited to the specific functions and working processes described above. The specific embodiments described above are merely illustrative and not restrictive. Those skilled in the art can make many other forms under the guidance of the present invention without departing from the spirit and scope of the claims, and all of these are within the protection scope of the present invention.

Claims

1. A transformer intelligent enclosed neutral point protection device, comprising a surge arrester (MOA), a capacitive voltage divider, an isolation transformer (T1), and a charging / discharging module, wherein the surge arrester (MOA) and the capacitive voltage divider are respectively connected to the transformer neutral point (A), the primary side of the isolation transformer (T1) is connected to the output terminal of the capacitive voltage divider, and the secondary side is connected to the input terminal of the charging / discharging module, wherein the charging / discharging module is composed of a second resistor (R2), a third resistor (R3), a fourth capacitor (C4), and a rectifier bridge (D1), characterized in that, The transformer neutral point (A) is also connected to a maintenance switch (S) and a gap discharge unit. The gap discharge unit includes a pulse transformer (T2). The primary side of the pulse transformer (T2) is connected in series with a pulse-triggered controllable switch (K1), a power supply (U1), and a fourth resistor (R4). One terminal of the secondary side of the pulse transformer (T2) is connected to a trigger electrode (J). The trigger electrode (J) is embedded in the low-voltage terminal connector of the closed discharge gap (G). The other terminal of the secondary side of the pulse transformer (T2) and the low-voltage terminal connector of the closed discharge gap (G) are both grounded through a current transformer (CT). The high-voltage terminal connector of the closed discharge gap (G) is connected to the transformer neutral point (A). A filter module is connected between the output terminal of the capacitor voltage divider and the primary side of the isolation transformer (T1). The filter module is used to filter the voltage signal flowing into the isolation transformer (T1) after voltage division by the capacitor voltage divider, remove high-frequency signals, retain the power frequency or its multiples, and realize the distinction between transient overvoltage signals and steady-state overvoltage signals. The output terminal of the charging and discharging module is connected to a voltage detection module (V). The voltage detection module (V) is used to detect the voltage amplitude and continuous charging time across capacitor C4 and transmit the detection data to the digital control unit in real time. The digital control unit uploads the detection data to the main control backend in real time. At the same time, the digital control unit compares the detection data with a preset threshold and controls the pulse-triggered controllable switch (K1) to open or close based on the comparison result, thereby controlling the discharge of the closed discharge gap (G). In addition, the digital control unit is also used to control the opening and closing of the maintenance switch (S).

2. The intelligent enclosed neutral point protection device for transformers according to claim 1, characterized in that, The neutral point (A) of the transformer is grounded (GND) via a maintenance switch (S). During equipment maintenance, the maintenance switch (S) is used to provide a reliable grounding point.

3. The intelligent enclosed neutral point protection device for transformers according to claim 1, characterized in that, One end of the surge arrester (MOA) is connected to the transformer neutral point (A), and the other end is grounded (GND).

4. The intelligent enclosed neutral point protection device for transformers according to claim 1, characterized in that, The capacitor voltage divider consists of a first capacitor (C1) and a second capacitor (C2) connected in series. One end of the first capacitor (C1) is connected to the neutral point (A) of the transformer, and the other end is grounded (GND) through the second capacitor (C2).

5. The intelligent enclosed neutral point protection device for transformers according to claim 1, characterized in that, The filter module consists of a resistor (R1) and a capacitor (C3). One end of the resistor (R1) is connected to the high-voltage side of the capacitor (C2), and the other end is grounded (GND) through the capacitor (C3). The capacitor (C3) is connected to the primary side of the isolation transformer (T1).

6. The intelligent enclosed neutral point protection device for transformers according to claim 1, characterized in that, The isolation transformer (T1) has a turns ratio of 1:1 and is used to isolate the unit modules at its primary and secondary ends.

7. The intelligent enclosed neutral point protection device for transformers according to claim 1, characterized in that, The charging and discharging module consists of resistor No. 2 (R2), resistor No. 3 (R3), capacitor No. 4 (C4), and rectifier bridge (D1). One end of the AC signal of rectifier bridge (D1) is connected to one terminal of the secondary side of isolation transformer (T1) through resistor No. 2 (R2), and the other end of the AC signal of rectifier bridge (D1) is connected to the other terminal of the secondary side of isolation transformer (T1). The negative terminal of DC signal of rectifier bridge (D1) is grounded (GND), and the positive terminal of DC signal of rectifier bridge (D1) is grounded (GND) through resistor No. 3 (R3) and capacitor No. 4 (C4) connected in parallel.

8. The intelligent enclosed neutral point protection device for transformers according to claim 1, characterized in that, The voltage detection module (V) uses a voltmeter with data transmission function, which is connected in parallel across capacitor C4.

9. The intelligent enclosed neutral point protection device for transformers according to claim 1, characterized in that, The closed discharge gap (G) includes a closed busbar filled with insulating gas, and a high-voltage terminal connector (G1) and a low-voltage terminal connector (G2) are arranged opposite to each other inside the closed busbar.

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