CN117833086A - Monitoring system and method for power frequency overvoltage flexible inhibition protection device - Google Patents

Abstract

The invention relates to a monitoring system and a method of a power frequency overvoltage flexible inhibition protection device, wherein the monitoring system comprises a cabinet body; the isolation handcart is arranged on the inner wall of the cabinet body, is used as an isolation switch for the high-voltage part to withdraw and put into operation, is rocked in or out by a handcart rocking handle, and is opened or closed by a door in the cabinet body; and a primary bus as a common power source for the main circuit of the system; and the lightning arrester is arranged at the bottom end of the inner wall of the cabinet body, a movable/static contact is connected to the lightning arrester through a wire, one end of the movable/static contact is electrically connected to the primary bus, and the lightning arrester is opened or closed by the rear door of the cabinet body. The lightning arrester in the overvoltage protection device adopts a method of combining and collocating the SiC valve plate and the ZnO valve plate, utilizes the nonlinear characteristic of ZnO to play a role in limiting voltage and damping oscillation, and jointly absorbs arc energy, thereby playing an important role in effectively inhibiting arc reignition.

Description

Monitoring system and method for power frequency overvoltage flexible suppression protection device

Technical Field

The present invention relates to the technical field of overvoltage protection systems, and in particular to a monitoring system and method for a power frequency overvoltage flexible suppression protection device.

Background technique

Electricity is an important energy source for modern civilization production and life, and human beings are increasingly dependent on electricity. In the operation of the power system, the two main destructive factors that affect the quality, safety and reliability of power supply and use are nothing more than: overcurrent and overvoltage, but they have always been very common in the operation of the system. If there are no effective preventive measures, overvoltage and overcurrent may cause serious harm to the operation of the power system at any time.

There are many reasons for overvoltage in the power grid, which can be mainly divided into: resonant overvoltage, cut-off overvoltage, operating overvoltage and lightning overvoltage, etc. Once the overvoltage in the system occurs, if it cannot be effectively suppressed, it will cause insulation damage to electrical equipment at the least, or cause large-scale power outages, or even fires or explosions, causing significant economic losses to people's lives, production and society.

At present, the overvoltage protection methods adopted by domestic power generation and distribution systems are almost all arc suppression coils and metal oxide lightning arresters, which cannot fully and reliably protect the normal operation of the power system. For example, when the arc suppression coil is used to compensate for the circuit capacitance, since the circuit capacitance value changes at any time when the power supply system is running, the inductance of the arc suppression coil cannot change accordingly. Once the inductance and capacitance values in the circuit are equal, a resonant overvoltage will be generated. The neutral point grounding through the arc suppression coil can only reduce the probability of arc grounding overvoltage, and cannot eliminate the arc grounding overvoltage and its amplitude, thereby reducing the safety of the circuit system. In addition, the existing lightning arrester for overvoltage protection has a limited current carrying capacity, often explodes and is damaged, and has a high risk factor. Moreover, when the lightning arrester with a discharge gap is used for overvoltage protection, due to the existence of its discharge gap, it cannot play the role of damping resonance and suppressing resonant overvoltage during operation, which is not conducive to the promotion and application of the device. For another example, when a lightning arrester with a fuse is used, its protection function is immediately lost when the fuse is blown. If the function is to be restored, it must be shut down for manual operation, which makes the manual operation cumbersome, time-consuming and labor-intensive.

Summary of the invention

The purpose of the present invention is to provide a monitoring system and method for a power frequency overvoltage flexible suppression protection device to solve the problems of the prior art.

The object of the present invention can be achieved by the following technical solution: A monitoring system for a power frequency overvoltage flexible suppression protection device comprises:

Cabinet;

An isolation trolley is arranged on the inner wall of the cabinet. The isolation trolley is used as an isolating switch for withdrawing and putting the high-voltage part into operation. The trolley is cranked in or out by the trolley crank handle, and the isolation trolley is opened or closed by the cabinet middle door.

A primary bus, which serves as a common power source for the main circuit of the system;

A lightning arrester, which is installed at the bottom of the inner wall of the cabinet, and is connected to a moving/static contact through a wire, one end of the moving/static contact is electrically connected to the primary bus, and the lightning arrester is opened or closed by the cabinet rear door;

A data acquisition terminal and an operator, wherein the data acquisition terminal is used to collect electrical signals from electrical components in the cabinet and transmit them to the operator, and the operator is used to calculate and convert the electrical signals and transmit them to the processor;

Among them, the data acquisition terminal, the operator, the industrial computer touch screen, and the control buttons/indicator lights are integrated into the control and microcomputer board. The data acquisition terminal and the operator are located in an isolation cavity together, and a shielding cover is provided on the inner wall of the cabinet outside the isolation cavity. The isolation cavity is opened or closed by the cabinet door.

Furthermore, the arrester is provided with an overvoltage protection circuit connected to the moving/static contacts, the overvoltage protection circuit includes a switch connected to the power line, the switch is connected in parallel with a first resistor R1 and a light bulb and a first capacitor C1 connected in series, the first resistor R1 is connected in parallel with a second resistor R2 and a third resistor R3 for grounding protection.

Furthermore, the first resistor R1 is a PTC device, the second resistor R2 is a high-energy SiC valve plate, the third resistor R3 is a high-energy/low-field-strength ZnO valve plate, and the field strength of the ZnO valve plate is 25 V/mm.

Furthermore, one end of the trolley crank handle is connected to a screw shaft extending to the inner wall of the cabinet, and a screw nut fixed to the isolation trolley is spirally transmitted on the screw shaft. As the trolley crank handle rotates, the isolation trolley enters or separates from the cabinet.

Further, the data acquisition terminal includes a three-phase loop equivalent wiring circuit connected to the primary bus, and the three-phase loop equivalent wiring circuit includes a first AC signal source, a second AC signal source and a third AC signal source connected to the neutral point in a Y0-type manner;

Among them, the first AC signal source is connected in parallel with a first inductor L1 and a second capacitor C2, the second AC signal source is connected in parallel with a second inductor L2 and a third capacitor C3, the second AC signal source is connected in parallel with a third inductor L3 and a fourth capacitor C4, and one output end of the first AC signal source, the second AC signal source and the third AC signal source are commonly grounded for protection.

Furthermore, the first AC signal source, the second AC signal source and the third AC signal source generate a first electromotive force correspondingly. , the second electromotive force/> and the third electromotive force/> .

The monitoring method of the power frequency overvoltage flexible suppression protection device is applied to the monitoring system of the power frequency overvoltage flexible suppression protection device, and comprises the following steps:

S1. The working resistor on the arrester can be connected in three ways. The first way is to directly connect the SiC valve plate to the arrester and measure the current/voltage change value of the silicon carbide valve plate. The second way is to directly connect the ZnO valve plate to the arrester and measure the current/voltage change value of the SiC valve plate. The third way is to connect the first resistor R1 in parallel to the second resistor R2 and the third resistor R3, and at the same time connect the first resistor R1 to the power line through a switch, and measure the current/voltage change value of the valve plate of the above parallel component;

S2. The inductance of the first inductor L1, the second inductor L2 and the third inductor L3 in the equivalent wiring circuit is kept the same, and the capacitance of the second capacitor C2, the third capacitor C3 and the fourth capacitor C4 is kept the same;

S3. Measure the first electromotive force in the equivalent wiring circuit , the second electromotive force/> and the third electromotive force/> , and measure the displacement voltage Uo of the neutral point between the three. The calculation formula is as follows:

;

In the formula, 、/> 、/> is the equivalent admittance in the three-phase circuit;

During normal operation, =/> =/> , because/> +/> +/> =0, so Uo=0, that is, the neutral point of the power supply is at zero potential. When Uo≠0, that is, the neutral point of the power supply is at non-zero potential, it means that the circuit is in a fault state.

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

1. The lightning arrester in the overvoltage protection device of the present invention adopts a method of combining SiC valve discs and ZnO valve discs, using the nonlinear characteristics of ZnO to limit the voltage and SiC to damp the oscillation, and the two together absorb the arc energy, which plays a significant role in effectively suppressing the reignition of the arc;

2. The overvoltage protection device of the present invention uses a PTC device and a high-energy, low-field strength ZnO high-energy valve plate as a self-recovering current-limiting fuse, which no longer requires power outages and manual processing, reduces power outages and labor costs, and meets the requirements of unmanned intelligence. The positive temperature coefficient characteristics of the PTC device are used to play an automatic current limiting role. At the same time, due to the nonlinear characteristics of ZnO, its voltage value does not increase with the increase of current, which plays a voltage limiting role. During normal operation, the PTC device can compensate for the negative resistance characteristics of the ZnO valve plate, and there is no need to consider the charge rate problem of ZnO, which truly plays a protective role of intelligent voltage limiting. Through the mutual compensation adjustment of the two, the circuit can have an effective current limiting and voltage limiting effect;

3. In order to monitor the three-phase voltage to ground of the system and perform circuit protection, an electromagnetic voltage transformer with Y0 connection is installed on the circuit bus. In addition to the ground capacitance C2, C3 and C4 of the power equipment and lines, the system ground parameters also include excitation inductance L1, L2 and L3. During normal operation, the excitation impedance of the voltage transformer is very large, so the impedance of each phase to ground is capacitive, the three phases are basically balanced, and the displacement voltage of the system neutral point O is very small, which can effectively detect whether there is overvoltage in the system.

BRIEF DESCRIPTION OF THE DRAWINGS

In order to facilitate understanding by those skilled in the art, the present invention is further described below with reference to the accompanying drawings.

FIG1 is a schematic structural diagram of a power frequency overvoltage flexible suppression protection device according to the present invention;

FIG2 is a side view of the power frequency overvoltage flexible suppression protection device of the present invention;

FIG3 is an enlarged view of point A in FIG1 of the present invention;

FIG4 is a wiring diagram of an overvoltage protection circuit of the present invention;

FIG5 is a wiring diagram of a three-phase loop equivalent wiring circuit of the present invention;

FIG6 is a schematic diagram of a characteristic curve of a high-energy silicon carbide valve plate of the present invention;

FIG7 is a schematic diagram of a characteristic curve of a high energy/low field strength zinc oxide valve plate of the present invention;

FIG8 is a schematic diagram of the characteristic curve of the high-energy silicon carbide and high-energy/low-field-strength zinc oxide valve plate parallel assembly of the present invention.

In the figure: 1. Cabinet; 2. Isolation trolley; 3. Trolley handle; 4. Cabinet middle door; 5. Primary bus; 6. Lightning arrester; 7. Moving/static contacts; 8. Cabinet rear door; 9. Data acquisition terminal; 10. Calculator; 11. Industrial computer touch screen; 12. Control button/indicator light; 13. Cabinet upper door; 14. Screw shaft; 15. Screw nut.

Detailed ways

The technical solution of the present invention will be clearly and completely described below in conjunction with the embodiments. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

Referring to Figures 1 to 8, the monitoring system of the power frequency overvoltage flexible suppression protection device includes: a cabinet 1; an isolating trolley 2 arranged on the inner wall of the cabinet 1, the isolating trolley 2 is used as an isolating switch for withdrawing and putting the high-voltage part into operation, is shaken in or out by the trolley handle 3, and the isolating trolley 2 is opened or closed by the cabinet middle door 4; a primary bus 5, the primary bus 5 serves as a common power supply for the main circuit of the system; a lightning arrester 6, the lightning arrester 6 is installed at the bottom end of the inner wall of the cabinet 1, and the lightning arrester 6 is connected to a moving/static contact 7 through a wire, one end of the moving/static contact 7 is electrically connected to the primary bus 5, and the lightning arrester 6 is opened or closed by the cabinet rear door 8.

The data acquisition terminal 9 and the operator 10 are used to collect the electrical signals of the electrical components in the cabinet 1 and transmit them to the operator 10. The operator 10 is used to calculate and convert the electrical signals and transmit them to the processor; wherein the data acquisition terminal 9, the operator 10, the industrial computer touch screen 11, and the control button/indicator light 12 are integrated into a control and microcomputer board. The data acquisition terminal 9 and the operator 10 are together in an isolation cavity, and a shielding cover is provided on the inner wall of the cabinet 1 outside the isolation cavity, and the isolation cavity is opened or closed by the cabinet upper door 13.

The above-mentioned structures and modules are all in an independent isolation space and are provided with corresponding explosion-proof pressure relief channels, which can shield the electromagnetic interference of strong electric fields and implement reliable insulation isolation between high and low voltages. One end of the trolley crank handle 3 is connected to a screw shaft 14 extending to the inner wall of the cabinet 1, and a screw nut 15 fixed to the isolation trolley 2 is spirally transmitted on the screw shaft 14. As the trolley crank handle 3 rotates, the isolation trolley 2 enters or separates from the cabinet 1. In addition, the isolation trolley 2, as an isolating switch, can rotate the trolley crank handle 3 to rotate the screw shaft 14, so that the isolation trolley 2 can enter or separate from the inside of the cabinet 1 through the action of the spiral transmission.

From the perspective of the physical product, it has a scientific and reasonable structural layout: highly integrated, each functional unit is independently divided and arranged, electromagnetic shielding and isolation between high and low voltages are completely achieved, safety and reliability are extremely high, and the isolation trolley 2 is cleverly used to replace the traditional upper isolation switch, which reduces the volume, improves practicality and reliability, and realizes modularization; the integrated modular structure design is very convenient for the neat installation and coordination of the device and system equipment, which greatly facilitates operation management and maintenance.

Referring to Figures 1, 4, 6, 7 and 8, the lightning arrester 6 is provided with an overvoltage protection circuit connected to the moving/static contact 7, the overvoltage protection circuit includes a switch connected to the power line, the switch is connected in parallel with a first resistor R1 and a bulb and a first capacitor C1 connected in series, the first resistor R1 is connected in parallel with a second resistor R2 and a third resistor R3 and grounding protection is performed, the first resistor R1 is a PTC device, the second resistor R2 is a high-energy SiC valve plate, the third resistor R3 is a high-energy/low-field strength ZnO valve plate, and the field strength of the ZnO valve plate is 25V/mm.

The arrester 6 of the present invention adopts a nonlinear functional device made of nano-level new materials to enable the device to achieve very high electrical performance and parameters. The arrester 6 uses two valve plates, high-energy silicon carbide and high-energy, low-field strength zinc oxide, and is scientifically combined in series and parallel, so that the nonlinear curve is located at the inflection point. When the current increases several times or dozens of times very quickly, the voltage change is still very small. Therefore, it can play a key role in strongly damping oscillation and clamping voltage in the circuit.

At present, most of the 6-66kV power grids in my country are operated in an ungrounded neutral point mode. The operation practice of such power grids has proved that in an ungrounded neutral point system, on the one hand, there are many ferromagnetic resonance overvoltages caused by the saturation of the voltage transformer core. Although many measures have been taken to limit the resonance overvoltage, such as: harmonic elimination lamps, harmonic elimination devices, lightning arresters and line selection devices, grounding transformers and arc suppression coils, etc., these methods are too old, too low in standard, and complex grounding methods, and cannot effectively suppress the resonance overvoltage and operation overvoltage. Burning of the equipment itself, fuse melting and other phenomena continue to occur; on the other hand, when the system has a single-phase metallic direct grounding, the voltage of the non-fault phase to the ground will rise to the line voltage, the three-phase line voltage value remains unchanged, and the three phases are still symmetrical, the operation of the three-phase electrical equipment is not affected, and thus does not affect the normal transmission of electric energy.

Foreign countries adopt the method of direct neutral grounding for 6-66kV power grids, and a few areas in China also adopt the method of grounding through small resistors. Although the arc grounding overvoltage is suppressed and the problems of arc suppression coils are overcome, the reliability of power supply to users is sacrificed. When a single-phase grounding occurs in this system, the short-circuit current is artificially increased to cause the circuit breaker to operate. Regardless of the nature and importance of the load, the fault line is cut off without exception, and it is impossible to distinguish between metallic grounding and arc grounding, so that the metallic grounding fault line that does not have the hazard of arc grounding overvoltage is also cut off, expanding the scope and time of power outages. Due to the increase in fault current, arc grounding aggravates the burning of the fault point.

In the existing lightning arrester 6, the charge rate of the ZnO valve plate increases with the increase of the overvoltage at both ends of the lightning arrester 6. Excessive charge rate will damage the ZnO valve plate, and even cause an explosion. ZnO has poor current sharing characteristics. In order to avoid excessive current in a branch, a fuse is used in the lightning arrester 6 to protect it. After the fuse is blown, it cannot be restored by itself, and power outage and manual processing are required.

The overvoltage protection device of the present invention uses PTC devices and high-energy/low-field-strength ZnO valve plates as self-recovering current-limiting fuses, which no longer require power outages and manual processing, reducing power outages and labor costs and meeting the requirements of unmanned intelligence. The principle is: when the loop current increases, due to the positive temperature coefficient characteristics of the PTC device, its resistance value also increases, thereby playing a role in automatic current limiting; at the same time, due to the nonlinear characteristics of the high-energy/low-field-strength ZnO valve plate, its voltage value does not increase with the increase of current, playing a role in voltage limiting. During normal operation, the PTC device can compensate for the negative resistance characteristics of the high-energy/low-field-strength ZnO valve plate, without considering the charge rate problem of the high-energy/low-field-strength ZnO valve plate, and truly plays a protective role in intelligent voltage limiting.

The arc suppression coil can compensate for the capacitance in the power supply system and reduce the overvoltage level that may occur when a single-phase grounding fault occurs. However, since the capacitance value of the loop changes at any time when the power supply system is running, the inductance of the arc suppression coil cannot change accordingly. Once the inductance and capacitance values in the loop are equal, a resonant overvoltage will be generated. The neutral point grounding through the arc suppression coil can only reduce the probability of arc grounding overvoltage, but cannot eliminate the arc grounding overvoltage and its amplitude. As is known to all, unidirectional intermittent arc grounding overvoltage is one of the common internal overvoltage phenomena, mainly caused by arc reignition. The overvoltage protection device of the present invention adopts a combination of high-energy SiC valve disc and high-energy/low-field-strength ZnO valve disc, and utilizes the nonlinear characteristics of the high-energy/low-field-strength ZnO valve disc to play a voltage limiting role, and the high-energy SiC valve disc to play a damping oscillation role, and the two absorb the arc energy together, which plays a very effective role in suppressing arc reignition.

The arrester 6 uses a new type of nano-composite material, so the current carrying capacity is increased several times and the residual pressure is greatly reduced by as much as 90%. As a result, the system protection voltage amplitude setting can be reduced by as much as 50%, which greatly improves the safety and reliability of the system equipment operation, integrates the required traditional functions and equipment and devices into one, realizes one machine with multiple functions, and the parameter indicators have been greatly upgraded, avoiding complicated equipment installation and inconvenient operation and maintenance, which can greatly save equipment investment, installation costs and space occupancy.

1 and 5 , the data acquisition terminal 9 includes a three-phase loop equivalent wiring circuit connected to the primary bus 5 , and the three-phase loop equivalent wiring circuit includes a first AC signal source, a second AC signal source, and a third AC signal source connected to the neutral point in a YO type;

The first AC signal source is connected in parallel with a first inductor L1 and a second capacitor C2, the second AC signal source is connected in parallel with a second inductor L2 and a third capacitor C3, the second AC signal source is connected in parallel with a third inductor L3 and a fourth capacitor C4, and one end of the output of the first AC signal source, the second AC signal source and the third AC signal source is grounded together for protection, and a first electromotive force is generated correspondingly on the first AC signal source, the second AC signal source and the third AC signal source. , the second electromotive force/> and the third electromotive force/> .

The monitoring method of the power frequency overvoltage flexible suppression protection device is applied to the monitoring system of the power frequency overvoltage flexible suppression protection device, and comprises the following steps:

S1. The working resistor on the arrester 6 can be connected in three ways. The first way is to directly connect the SiC valve plate to the arrester 6 and measure the current/voltage change value of the silicon carbide valve plate. The second way is to directly connect the ZnO valve plate to the arrester 6 and measure the current/voltage change value of the SiC valve plate. The third way is to connect the first resistor R1 in parallel to the second resistor R2 and the third resistor R3, and at the same time connect the first resistor R1 to the power line through a switch, and measure the current/voltage change value of the valve plate of the above parallel component;

S2. The inductance of the first inductor L1, the second inductor L2 and the third inductor L3 in the equivalent wiring circuit is kept the same, and the capacitance of the second capacitor C2, the third capacitor C3 and the fourth capacitor C4 is kept the same;

S3. Measure the first electromotive force in the equivalent wiring circuit , the second electromotive force/> and the third electromotive force/> , and measure the displacement voltage Uo of the neutral point between the three. The calculation formula is as follows:

;

In the formula, 、/> 、/> is the equivalent admittance in the three-phase circuit;

During normal operation, =/> =/> , because/> +/> +/> =0, so Uo=0, that is, the neutral point of the power supply is at zero potential. When Uo≠0, that is, the neutral point of the power supply is at non-zero potential, it means that the circuit is in a fault state.

When the system receives interference, the core of the voltage transformer becomes saturated. For example, the potential of phases A and B increases, and the inductive current of L1 and L2 increases. This may cause the admittance of phases A and B to ground to become inductive admittance, that is, and/> is the inductive admittance, and /> is the capacitive admittance. Due to the mutual cancellation of capacitive admittance and inductive admittance, /> +/> +/> The voltage at the neutral point of the system is significantly reduced, which in turn causes a significant increase in the displacement voltage at the neutral point of the system.

Claims (7)

1. Monitoring system of flexible suppression protector of power frequency overvoltage, its characterized in that includes:

a cabinet body (1);

the isolation handcart (2) is arranged on the inner wall of the cabinet body (1), the isolation handcart (2) is used as an isolation switch for withdrawing and putting into operation of a high-voltage part, the isolation handcart is rocked in or out by the handcart rocking handle (3), and the isolation handcart (2) is opened or closed by the door (4) in the cabinet body;

a primary bus (5), wherein the primary bus (5) is used as a common power supply of a main loop of the system;

the lightning arrester (6) is arranged at the bottom end of the inner wall of the cabinet body (1), the lightning arrester (6) is connected with a moving/static contact (7) through a wire, one end of the moving/static contact (7) is electrically connected to the primary bus (5), and the lightning arrester (6) is opened or closed by the cabinet body back door (8);

the device comprises a data acquisition end (9) and an arithmetic unit (10), wherein the data acquisition end (9) is used for acquiring and transmitting an electric signal of an electric component in the cabinet body (1) to the arithmetic unit (10), and the arithmetic unit (10) is used for calculating, converting and transmitting the electric signal to a processor;

the data acquisition end (9), the arithmetic unit (10), the industrial personal computer touch screen (11) and the control button/indicator lamp (12) are integrated into a control and microcomputer plate, the data acquisition end (9) and the arithmetic unit (10) are jointly located in an isolation cavity, a shielding cover arranged on the inner wall of the cabinet body (1) is arranged outside the isolation cavity, and the isolation cavity is opened or closed by the upper door (13) of the cabinet body.

2. The monitoring system of the power frequency overvoltage flexible inhibition protection device according to claim 1, wherein an overvoltage protection circuit connected with a movable/static contact (7) is arranged on the lightning arrester (6), the overvoltage protection circuit comprises a switch connected with a power line, a first resistor R1, a bulb and a first capacitor C1 which are connected in series are connected in parallel on the switch, and a second resistor R2 and a third resistor R3 are connected in parallel on the first resistor R1 and are grounded.

3. The monitoring system of the power frequency overvoltage flexible inhibition protection device according to claim 2, wherein the first resistor R1 is a PTC device, the second resistor R2 is a high-energy SiC valve sheet, the third resistor R3 is a high-energy/low-field-strength ZnO valve sheet, and the ZnO valve sheet field strength is 25V/mm.

4. A monitoring system of a power frequency overvoltage flexible inhibition protection device according to claim 3, characterized in that one end of the handcart rocking handle (3) is connected with a screw shaft (14) extending to the inner wall of the cabinet body (1), a screw nut (15) fixed on the isolation handcart (2) is screwed on the screw shaft (14), and the isolation handcart (2) enters or separates in the cabinet body (1) along with the rotation of the handcart rocking handle (3).

5. The monitoring system of the power frequency overvoltage flexible suppression protector according to claim 4, characterized in that the data acquisition end (9) comprises a three-phase loop equivalent wiring circuit connected with the primary bus (5), and the three-phase loop equivalent wiring circuit comprises a first alternating current signal source, a second alternating current signal source and a third alternating current signal source which are connected with a neutral point YO type;

the first alternating current signal source is connected with a first inductor L1 and a second capacitor C2 in parallel, the second alternating current signal source is connected with a second inductor L2 and a third capacitor C3 in parallel, the second alternating current signal source is connected with a third inductor L3 and a fourth capacitor C4 in parallel, and the output ends of the first alternating current signal source, the second alternating current signal source and the third alternating current signal source are jointly grounded.

6. The system of claim 5, wherein the first, second and third ac signal sources are configured to generate a first electromotive forceSecond electromotive force->And a third electromotive force->。

7. The monitoring system of the power frequency overvoltage flexible suppression protection device according to claim 6, wherein the monitoring method comprises the following steps:

s1, connecting working resistance cards on a lightning arrester (6) in three modes, wherein the first mode is to directly connect a SiC valve block on the lightning arrester (6) and measure the current/voltage change value of a silicon carbide valve block, the second mode is to directly connect a ZnO valve block on the lightning arrester (6) and measure the current/voltage change value of the SiC valve block, and the third mode is to connect a first resistor R1 in parallel with a second resistor R2 and a third resistor R3, and simultaneously connect the first resistor R1 to a power line through a switch and measure the current/voltage change value of the valve block of the parallel assembly;

s2, keeping the inductance of a first inductor L1, a second inductor L2 and a third inductor L3 in the equivalent wiring circuit the same, and keeping the capacitance of a second capacitor C2, a third capacitor C3 and a fourth capacitor C4 the same;

s3, measuring first electromotive force in equivalent wiring circuitSecond electromotive force->And a third electromotive force->And measuring the displacement voltage Uo of the neutral point among the three, wherein the calculation formula is as follows:

；

in the method, in the process of the invention,、/>、/>is the equivalent admittance in the three-phase loop;

in the normal course of operation of the device,=/>=/>due to->+/>+/>=0, so uo=0, i.e. the power supply neutral is at zero potential, and when uo+.0, i.e. the power supply neutral is at non-zero potential, it means that the circuit is operating in a fault state.