A power taking circuit for a current transformer power taking device

Abstract

The application relates to a power taking circuit for a current transformer power taking device, which comprises a protection and load relief circuit, an impedance matching circuit, a power conversion circuit and an energy storage circuit, wherein the power taking current transformer is connected with the protection and load relief circuit, the protection and load relief circuit is connected with the impedance matching circuit, the impedance matching circuit is connected with the power conversion circuit, the power conversion circuit is connected with the energy storage circuit, and a special controller is connected with the impedance matching circuit, the power conversion circuit and the energy storage circuit respectively. Through the joint action of the impedance matching circuit, the power conversion circuit and the energy storage circuit, the power taking circuit can still stably output full power in the case of small current. Compared with the prior art, the power density of the power taking device is improved, and the direct current power output is more stable.

Description

Technical Field

[0001] This invention relates to the field of inductive power harvesting technology for power transmission lines, and in particular to a power harvesting circuit for a current transformer power harvesting device. Background Technology

[0002] Monitoring the real-time operating status of transmission lines is a crucial measure to ensure the safe and stable operation of the power system. However, the power supply problem for online monitoring equipment has always been a factor restricting its development. Current transformer induction power supply technology, due to its advantages of low cost, practicality, and wide applicability, is expected to become the most effective power supply method.

[0003] However, most current inductive power extraction devices can only meet the needs of power transmission lines with an current of 50A or more, and there are problems such as power supply dead zone, power extraction power limited by size, and easy saturation of high current magnetic cores.

[0004] The current method to solve the core saturation problem is to open the air gap in the CT core to reduce its equivalent permeability. This method can effectively improve the anti-saturation capability of the CT power supply device, but it also reduces the power supply effect at low current. If the required power output can be achieved in low current scenarios, the core volume needs to be increased, which cannot meet the requirements of lightweight design.

[0005] While installing two sets of windings for power extraction and auxiliary windings on the core of the power extraction CT, or using a dual-CT structure with a damped CT equipped with a resonant matching capacitor and a power extraction CT with a shunt line, can achieve stable power output over a wide current range, this method makes the power extraction CT structure and control system more complex, with high customization requirements, small demand, and limited practicality.

[0006] High permeability materials such as nanocrystals or ferrites are used to solve the problem of insufficient power output of CT under low current. However, high permeability materials generally have the disadvantage of low saturation magnetic flux density, which makes the CT easily enter the saturation state during power output, resulting in serious heating of the CT core and endangering system safety.

[0007] In summary, current methods for addressing core saturation and improving energy harvesting power, such as opening an air gap, lead to poor power harvesting performance of the inductive power harvesting device under low current conditions. If the power harvesting performance under low current conditions is considered, a small air gap will generate voltage spikes. On the other hand, using a dual-CT structure with a wide current range results in a complex structure and high cost. The use of high permeability materials leads to severe heating of the CT core and poor safety performance. Summary of the Invention

[0008] The purpose of this invention is to overcome the defects of the prior art by providing a power extraction circuit for a current transformer power extraction device. It adopts a protection and load relief circuit to reduce peak voltage while ensuring that the air gap is not too large. Combined with an impedance matching circuit, a power conversion circuit and an energy storage circuit, it effectively improves the power extraction power.

[0009] The objective of this invention can be achieved through the following technical solutions:

[0010] A power extraction circuit for a current transformer power extraction device includes: a protection and load relief circuit, an impedance matching circuit, a power conversion circuit, and an energy storage circuit.

[0011] The current transformer is connected to the protection and unloading circuit. The live wire CTL_OUT and neutral wire CTN_OUT of the protection and unloading circuit are connected to the impedance matching circuit. The live wire L and neutral wire N of the impedance matching circuit are connected to the power conversion circuit. The negative voltage DC- of the power conversion circuit is connected to the energy storage circuit. The dedicated controller is connected to the impedance matching circuit, the power conversion circuit and the energy storage circuit respectively.

[0012] The protection and unloading circuit is connected to the current transformer via wires CTL_IN and CTN_IN. The protection and unloading circuit includes:

[0013] A resistor and a capacitor connected in series;

[0014] A series-connected varistor and lightning rod assembly;

[0015] Transient suppression diode;

[0016] A resistor and a capacitor connected in series;

[0017] Resistors connected in series;

[0018] The above 5 component groups are connected in parallel between the wires CTL_IN and CTN_IN;

[0019] A bidirectional thyristor is connected in parallel across the resistor and capacitor in series. The capacitor and resistor are connected in parallel, and the series resistor and bidirectional thyristor are connected between the capacitor and the bidirectional thyristor.

[0020] Furthermore, the impedance matching circuit includes a common-mode inductor, a fuse, a matching capacitor, and a relay.

[0021] The live wire CTL_OUT and the neutral wire CTN_OUT are connected to the first and second inductors of the common-mode inductor, respectively. The first inductor is connected to one end of the fuse, and the other end of the fuse is connected to one end of the matching capacitor and the live wire L. The other end of the matching capacitor is connected to the normally closed contact of the relay. The matching capacitor and the relay are connected between the live wire L and the neutral wire N. The second inductor is connected to the neutral wire N. The matching capacitor is connected in parallel with the excitation inductance of the current-taking electromagnetic core of the current transformer for resonance.

[0022] Furthermore, the relay coil is connected to the negative voltage DC- of the rectifier bridge of the power conversion circuit and the KM terminal of the dedicated controller, respectively.

[0023] Furthermore, the power conversion circuit includes a MOSFET, a rectifier bridge, and a transformer. The L-terminal of the rectifier bridge is connected to the live wire L, and the N-terminal of the rectifier bridge is connected to the neutral wire N. Capacitor C4 is connected between the positive voltage terminal DC+ and the negative voltage terminal DC- of the rectifier bridge.

[0024] The primary winding of the transformer serves as the main winding, with its same-name terminal connected to the positive voltage DC+ and its opposite-name terminal connected to the anode of the diode. The secondary winding of the transformer serves as the auxiliary winding, with its opposite-name terminal connected to the negative voltage DC-.

[0025] The source of the MOSFET is connected to the negative voltage DC- through a resistor. A capacitor and a resistor are connected in series between the source and drain of the MOSFET. A resistor and a capacitor are connected between the gate of the MOSFET and the negative voltage DC-. The resistor and capacitor are connected in parallel.

[0026] The cathode of the diode is connected to the wire P+. A capacitor and a capacitor are connected in parallel between the wire P+ and the negative voltage DC-, as well as a resistor and a resistor in series. The series group of resistors and resistors is connected in parallel with the capacitors and capacitors. The resistor, capacitor, and Zener diode are connected in parallel.

[0027] The output power between the conductor P+ and the negative voltage terminal DC- is the final DC power obtained from the power supply.

[0028] Furthermore, the BstC port of the dedicated controller is connected to the gate of the MOSFET, and the CS port of the dedicated controller is connected to the source of the MOSFET.

[0029] Furthermore, the Auxl port of the dedicated controller is connected to the same-name terminal of the secondary coil of the transformer, and the INV port of the dedicated controller is connected to the cathode of the Zener diode.

[0030] Furthermore, the INV port is internally connected to the positive input of the dual operational amplifier in the dedicated controller, the inverting input of the dual operational amplifier is connected to the reference voltage, and the output of the dual operational amplifier controls the gate potential of the MOS transistor.

[0031] Furthermore, the energy storage circuit consists of two supercapacitors connected in series. One end of the two supercapacitors is the CG port, and the other end is connected to the negative voltage DC-. A MID port is provided between the two supercapacitors.

[0032] Furthermore, the CG port of the dedicated controller is connected to the CG port of the energy storage circuit, and the MID port of the dedicated controller is connected to the MID port of the energy storage circuit.

[0033] Furthermore, there are two sets of series-connected varistor and lightning rod groups: one consisting of a series-connected varistor and lightning rod, and the other consisting of a series-connected varistor and lightning rod.

[0034] Compared with the prior art, the present invention has the following beneficial effects:

[0035] (1) The protection and load relief circuit adopted in this invention reduces peak voltage while ensuring that the air gap is not too large. Once a peak voltage occurs, the bidirectional thyristors Q1 and Q2 will automatically conduct to achieve the purpose of load relief. At the same time, the power supply device is hung in the air and is easily struck by lightning in thunderstorms. Therefore, a varistor and a lightning rod are added to the protection and load relief circuit to protect the circuit from damage by lightning.

[0036] (2) This invention combines an impedance matching circuit, a power conversion circuit, and an energy storage circuit. An induced voltage is generated in the secondary coil of the electromagnetic core. After noise suppression by a common-mode inductor, the capacitor and the excitation inductor of the electromagnetic core resonate in parallel, reducing the shunting effect of the excitation branch and allowing more current to flow to the load side, which can effectively improve the power extraction. The compensation AC voltage output by the impedance matching circuit is used as the input of the power conversion circuit. After being rectified by the rectifier bridge, it is converted into the initial DC voltage and stored in the energy storage circuit. In the above process, a dedicated controller coordinates and controls the working state of the impedance matching circuit, the power conversion circuit, and the energy storage circuit. A simple CT structure and control system are adopted, resulting in high output power and high power density. Attached Figure Description

[0037] Figure 1 This is the overall circuit diagram of the present invention;

[0038] Figure 2 This is a circuit diagram illustrating the protection and load dissipation functions of the present invention.

[0039] Figure 3 This is the impedance matching circuit diagram of the present invention;

[0040] Figure 4 This is a power conversion circuit diagram of the present invention;

[0041] Figure 5 This is the energy storage circuit diagram of the present invention;

[0042] Figure 6 This is a structural diagram of the dedicated controller of the present invention;

[0043] Figure 7 This is a structural diagram of a dual operational amplifier connected to the internal INV port of the dedicated controller of the present invention;

[0044] Among them, common mode inductor 1, fuse 2, matching capacitor 3, electrical appliance 4, rectifier bridge 5, resistor R1, resistor R2, resistor R3, resistor R4, resistor R5, resistor R6, resistor R7, resistor R8, resistor R9, resistor R10, capacitor C1, capacitor C2, capacitor C3, capacitor C4, capacitor C5, capacitor C6, capacitor C7, capacitor C8, capacitor C9, varistor Y1, surge protector DT1, varistor Y2, surge protector DT2, transient voltage suppressor diode TVS1, bidirectional thyristor Q1, bidirectional thyristor Q2, first inductor L1, second inductor L2, transformer T1, MOSFET Q3, diode D1, Zener diode Z1. Detailed Implementation

[0045] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments. These embodiments are based on the technical solution of the present invention and provide detailed implementation methods and specific operating procedures. However, the scope of protection of the present invention is not limited to the following embodiments.

[0046] This invention proposes a power supply circuit for a current transformer power supply device, the circuit diagram of which is shown below. Figure 1 As shown, the circuit includes: a protection and load relief circuit, an impedance matching circuit, a power conversion circuit, and an energy storage circuit. The current transformer is connected to the protection and load relief circuit, which in turn is connected to the impedance matching circuit. The impedance matching circuit is connected to the power conversion circuit, which is then connected to the energy storage circuit. A dedicated controller is connected to each of the impedance matching circuit, power conversion circuit, and energy storage circuit. Through the combined action of the impedance matching circuit, power conversion circuit, and energy storage circuit, the power supply circuit can still stably output sufficient power even under low current conditions.

[0047] The technical solution of this invention is applied to a high-power-density CT power supply device, the volume of which does not exceed 1800 cm². 3 By coordinating the operation of the impedance matching circuit, power conversion circuit, and energy storage circuit through a dedicated controller, the current of the transmission line can be above 15A, with a rated power of 2W and a maximum power of 2.5W for inductive power output. This invention has the advantages of small size, light weight, high output power, and high power density.

[0048] The protection and load relief circuit serves to protect against lightning strikes and voltage spikes. The circuit diagram of the protection and load relief circuit is shown below. Figure 2As shown. The protection and load relief circuit consists of resistors, capacitors, lightning rods, bidirectional thyristors, and transient suppression diodes. The power-operated current transformer (CT) is connected to the protection and unloading circuit via wires CTL_IN and CTN_IN; resistors R1 and C1 are connected in series between wires CTL_IN and CTN_IN; varistor Y1 and surge diode DT1 are connected in series between wires CTL_IN and CTN_IN; varistor Y2 and surge diode DT2 are connected in series between wires CTL_IN and CTN_IN; transient voltage suppressor diode TVS1 is connected between wires CTL_IN and CTN_IN; resistors R2 and C2 are connected in series between wires CTL_IN and CTN_IN; bidirectional thyristor Q1 is connected in parallel across the series resistors R2 and C2; resistors R4 and R5 are connected in series between wires CTL_IN and CTN_IN; capacitor C3 is connected in parallel with resistor R5; bidirectional thyristor Q2 and resistor R3 are connected in series between bidirectional thyristor Q1 and capacitor C3.

[0049] like Figure 2 As shown, when current flows through a transmission line, it generates alternating magnetic flux, which induces a voltage in the secondary coil of the current collector (CT) core. When the transmission line current is large, due to the saturation effect of the ferromagnetic material in the CT core, a voltage spike will be induced on the secondary side. To address this, materials with high saturation magnetic density and an air gap are used. However, considering the power extraction effect at low currents, the air gap cannot be too large, which may still result in voltage spikes on the secondary side. Therefore, a dual voltage spike protection circuit is added to the protection and load relief circuit to protect the power extraction system. Once a voltage spike occurs, the bidirectional thyristors Q1 and Q2 automatically conduct to achieve load relief. In addition, the power extraction device is suspended high in the air and is susceptible to lightning strikes during thunderstorms. Therefore, a varistor and a lightning rod are added to the protection and load relief circuit to protect the circuit from damage caused by lightning strikes.

[0050] Impedance matching circuits compensate for the initial AC voltage obtained by the current collector (CT) from the power transmission cable, thus obtaining a compensated AC voltage. The circuit diagram of an impedance matching circuit is shown below. Figure 3 As shown. The impedance matching circuit consists of a common-mode inductor 1, a fuse 2, a matching capacitor 3, and a relay 4. The normally closed contact of the matching capacitor 3 and the relay 4 are connected together, and the two are connected between the live wire L and the neutral wire N; the first inductor L1 of the common-mode inductor is connected to the live wire CTL_OUT on one side and to the live wire L on the other side; the second inductor L2 of the common-mode inductor is connected to the neutral wire CTN_OUT on one side and to the neutral wire N on the other side; the fuse 2 is connected in series between the L1 inductor and the matching capacitor.

[0051] like Figure 3As shown, an induced voltage is generated in the secondary coil of the CT magnetic core. After noise is suppressed by the common-mode inductor, the capacitor and the excitation inductor of the magnetic core are connected in parallel to resonate by properly matching the capacitor parameters. This reduces the shunting effect of the excitation branch and allows more current to flow to the load side, which can effectively improve the power extraction.

[0052] The power conversion circuit rectifies and regulates the aforementioned compensated AC voltage to output the final DC power. The circuit diagram of the power conversion circuit is shown below. Figure 4 As shown. The power conversion circuit consists of a rectifier bridge 5, a transformer T1, a MOSFET Q3, diodes, resistors, and capacitors. The L port of the rectifier bridge is connected to the live wire L, and the N port is connected to the neutral wire N; capacitor C4 is connected between the DC+ and DC- terminals of the rectifier bridge; the primary winding of transformer T1 serves as the main winding, with its same-name terminal connected to DC+ and its opposite-name terminal connected to the anode of diode D1; the secondary winding of transformer T1 serves as the auxiliary winding, with its opposite-name terminal connected to DC-; the drain of MOSFET Q3 is connected to the anode of diode D1, the source of the MOSFET is connected to DC- through resistor R7, and capacitor C6 is connected in series between the source and drain of MOSFET Q3. With resistor R8, resistor R6 and capacitor C5 are connected between the gate of MOSFET Q3 and DC-, and resistor R6 and capacitor C5 are connected in parallel; the cathode of diode D1 is connected to the wire P+; capacitors C7 and C8 are connected between P+ and DC-, and capacitors C7 and C8 are connected in parallel; resistors R9 and R10 are connected between P+ and DC-, and resistors R9 and R10 are connected in series; capacitor C9 and Zener diode Z1 are connected in parallel across resistor R10; the output power between P+ and DC- is the final DC voltage.

[0053] like Figure 4 As shown, the compensated AC voltage is used as the input of the power conversion circuit. It is converted into the initial DC voltage through the rectifier bridge. By turning on and off the MOSFET Q3, the voltage between P+ and DC-, i.e. the final DC voltage, is controlled at 75V.

[0054] The energy storage circuit serves as a backup power source for the power extraction system. When the current in the transmission line is less than 15A, the energy storage circuit activates to supply power to the system. The circuit diagram of the energy storage circuit is shown below. Figure 5 As shown. The energy storage circuit consists of two supercapacitors connected in series. One end is connected to wire CG, the other end is connected to wire DC-, and the two capacitors are connected by wire MID.

[0055] like Figure 5 As shown, two supercapacitors are connected in series to form an energy storage circuit, which, together with a dedicated controller, enables equal-voltage charging and discharging.

[0056] The power extraction circuit of this invention also includes a control circuit, which automatically adjusts the operating state of the capacitor-compensated power conversion circuit according to the changes in current in the transmission line to obtain stable power output. The control circuit includes a dedicated controller, model KZ7525. The dedicated controller is connected to the gate of MOSFET Q3 in the power conversion circuit via wire BstC, to the source of MOSFET Q3 via wire CS, to the same-name terminal of the auxiliary coil of transformer T1 via wire AuxL, and to the cathode of the Zener diode via wire INV; the dedicated controller is connected to the relay coil via wire KM; the dedicated controller is connected to the CG port of the energy storage circuit via wire CG, and to the MID port of the energy storage circuit via wire MID. Figure 6 The diagram shows the controller's structure. The dedicated controller is connected to the impedance matching circuit, power conversion circuit, and energy storage circuit via seven wires. The Auxl signal is the voltage zero-crossing detection signal, the CS signal is the power conversion circuit current sampling signal, the BstC signal is the gate control signal of MOSFET Q3, the INV signal is the voltage feedback signal, the KM signal is the relay control signal, the CG signal is the energy storage circuit control signal, and the MID signal is the supercapacitor voltage equalization signal of the energy storage circuit.

[0057] Figure 7 This diagram shows the structure of a dual operational amplifier connected to the INV port inside the dedicated controller. The dedicated controller integrates a dual operational amplifier, which is based on the INV voltage feedback signal U. INV It is compared with the reference voltages REFA and REFB, and then compared by an operational amplifier. According to the magnitude of different voltage values, the gate potential of MOSFET Q3 is changed, thereby changing the switching state of MOSFET Q3.

[0058] When the INV voltage feedback signal UINV < 30V, the energy storage circuit enters the discharge mode, and the supercapacitor powers the system. When the INV voltage feedback signal UINV ≥ 30V, the control circuit controls the impedance matching circuit and the power conversion circuit to work simultaneously. When the INV voltage feedback signal UINV ≥ 70V, the control circuit controls the impedance matching circuit to work, the power conversion circuit to not work, and the energy storage circuit enters the charging mode. When the INV voltage feedback signal UINV ≥ 100V, the control circuit controls both the impedance matching circuit and the power conversion circuit to not work, and the energy storage circuit enters the charging mode.

[0059] The preferred embodiments of the present invention have been described in detail above. It should be understood that those skilled in the art can make numerous modifications and variations based on the concept of the present invention without creative effort. Therefore, all technical solutions that can be obtained by those skilled in the art based on the concept of the present invention through logical analysis, reasoning, or limited experimentation on the basis of existing technology should be within the scope of protection defined by the claims.

Claims

1. A power extraction circuit for a current transformer power extraction device, characterized in that, The circuit includes: Protection and load dissipation circuits, impedance matching circuits, power conversion circuits, and energy storage circuits, among which, The current transformer is connected to the protection and unloading circuit. The live wire CTL_OUT and neutral wire CTN_OUT of the protection and unloading circuit are connected to the impedance matching circuit. The live wire L and neutral wire N of the impedance matching circuit are connected to the power conversion circuit. The negative voltage DC- of the power conversion circuit is connected to the energy storage circuit. The dedicated controller is connected to the impedance matching circuit, the power conversion circuit and the energy storage circuit respectively. The protection and unloading circuit is connected to the current transformer via wires CTL_IN and CTN_IN. The protection and unloading circuit includes: A resistor (R1) and a capacitor (C1) connected in series; A series-connected varistor and lightning rod assembly; Transient voltage suppressor diode (TVS1); A resistor (R2) and a capacitor (C2) connected in series; Resistors (R4) and (R5) connected in series; The above 5 component groups are connected in parallel between the wires CTL_IN and CTN_IN; A bidirectional thyristor (Q1) is connected in parallel across the series connection of resistor (R2) and capacitor (C2). A capacitor (C3) is connected in parallel with resistor (R5). The series resistor (R3) and bidirectional thyristor (Q2) are connected between capacitor (C3) and bidirectional thyristor (Q1).

2. The power supply circuit for a current transformer power supply device according to claim 1, characterized in that, The impedance matching circuit includes a common-mode inductor (1), a fuse (2), a matching capacitor (3), and a relay (4). Among them, the live wire CTL_OUT and the neutral wire CTN_OUT are respectively connected to the first inductor (L1) and the second inductor (L2) of the common mode inductor (1). The first inductor (L1) is connected to one end of the fuse (2). The other end of the fuse (2) is connected to one end of the matching capacitor (3) and the live wire L. The other end of the matching capacitor (3) is connected to the normally closed contact of the relay (4). The matching capacitor (3) and the relay (4) are connected between the live wire L and the neutral wire N. The second inductor (L2) is connected to the neutral wire N. The matching capacitor (3) is connected in parallel with the excitation inductance of the current transformer core.

3. The power supply circuit for a current transformer power supply device according to claim 2, characterized in that, The coil of the relay (4) is connected to the negative voltage DC- of the rectifier bridge (5) of the power conversion circuit and the KM terminal of the dedicated controller.

4. A power supply circuit for a current transformer power supply device according to claim 2, characterized in that, The power conversion circuit includes a MOSFET (Q3), a rectifier bridge (5), and a transformer (T1). The L port of the rectifier bridge (5) is connected to the live wire L, and the N port of the rectifier bridge (5) is connected to the neutral wire N. The capacitor C4 is connected between the positive voltage DC+ and the negative voltage DC- of the rectifier bridge (5). The primary winding of transformer (T1) serves as the main winding, with its same-name terminal connected to the positive voltage DC+ and its opposite-name terminal connected to the anode of diode (D1). The secondary winding of transformer (T1) serves as the auxiliary winding, with its opposite-name terminal connected to the negative voltage DC-. The source of the MOSFET (Q3) is connected to the negative voltage DC- through a resistor (R7). A capacitor (C6) and a resistor (R8) are connected in series between the source and drain of the MOSFET (Q3). A resistor (R6) and a capacitor (C5) are connected between the gate of the MOSFET and the negative voltage DC-. The resistor (R6) and the capacitor (C5) are connected in parallel. The cathode of diode (D1) is connected to the wire P+. A capacitor (C7) and a capacitor (C8) are connected in parallel between the wire P+ and the negative voltage DC-, as well as a resistor (R9) and a resistor (R10) connected in series. The series connection of resistor (R9) and resistor (R10) is connected in parallel with capacitor (C7) and capacitor (C8). Resistor (R10) is connected in parallel with capacitor (C9) and Zener diode (Z1). The output power between the conductor P+ and the negative voltage terminal DC- is the final DC power obtained from the power supply.

5. A power supply circuit for a current transformer power supply device according to claim 4, characterized in that, The BstC port of the dedicated controller is connected to the gate of the MOSFET (Q3), and the CS port of the dedicated controller is connected to the source of the MOSFET (Q3).

6. A power supply circuit for a current transformer power supply device according to claim 5, characterized in that, The Auxl port of the dedicated controller is connected to the same-name terminal of the secondary coil of the transformer (T1), and the INV port of the dedicated controller is connected to the cathode of the Zener diode (Z1).

7. A power supply circuit for a current transformer power supply device according to claim 6, characterized in that, The INV port is connected to the positive input of the dual operational amplifier inside the dedicated controller. The inverting input of the dual operational amplifier is connected to the reference voltage. The output of the dual operational amplifier controls the gate potential of the MOS transistor (Q3).

8. A power supply circuit for a current transformer power supply device according to claim 1, characterized in that, The energy storage circuit consists of two supercapacitors connected in series. One end of the two supercapacitors is the CG port, and the other end is connected to the negative voltage DC-. There is a MID port between the two supercapacitors.

9. A power supply circuit for a current transformer power supply device according to claim 8, characterized in that, The CG port of the dedicated controller is connected to the CG port of the energy storage circuit, and the MID port of the dedicated controller is connected to the MID port of the energy storage circuit.

10. A power supply circuit for a current transformer power supply device according to claim 1, characterized in that, There are two sets of series-connected varistor and lightning rods: one is series-connected varistor (Y1) and lightning rod (DT1), and the other is series-connected varistor (Y2) and lightning rod (DT2).

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