CN214335110U

CN214335110U - Instantaneous grounding current injection method line selection device for medium-voltage power grid

Info

Publication number: CN214335110U
Application number: CN202023040546.XU
Authority: CN
Inventors: 张致良
Original assignee: Anhui Haowo Power Technology Co ltd
Current assignee: Anhui Haowo Power Technology Co ltd
Priority date: 2020-12-17
Filing date: 2020-12-17
Publication date: 2021-10-01
Anticipated expiration: 2030-12-17

Abstract

The utility model discloses an instantaneous ground connection injection current method route selection device to middling voltage electric wire netting, including the intelligent route selection main control unit WHDX-ZK that inserts the distribution network system respectively, isolator GL, high impedance grounding transformer WH-JDB, single-phase quick circuit breaker WH-DSKG and current transformer LH, the bus connection of wire and bat point net system is passed through to high impedance grounding transformer WH-JDB's input, the utility model relates to an electrical engineering technical field. The line selection device adopting the instantaneous grounding injection current method for the medium-voltage power grid can effectively reduce the probability of two-phase different-place short circuit or interphase short circuit formed by the system due to grounding, avoid system accidents, have remarkable economic benefit and effectively reduce the equipment insulation pollution flashover accident rate. After the system is grounded, the voltage is increased, so that the development of surface discharge of the pollution equipment is accelerated under the action of overvoltage, the occurrence of pollution flashover accidents is accelerated, a fault loop can be cut off quickly, the system is recovered, and the system operates normally.

Description

Instantaneous grounding current injection method line selection device for medium-voltage power grid

Technical Field

The utility model relates to an electrical engineering technical field specifically is an instantaneous ground connection injection current method route selection device to middling pressure electric wire netting.

Background

According to the current research and application situations at home and abroad, the low-current grounding grid ground fault line selection basically adopts a low-current line selection method, which is called as a passive line selection method.

The passive line selection method is further classified into a steady-state component method and a transient component method. The steady state component method is mostly researched by a fifth harmonic method and a negative sequence current method, due to the development of an electronic information technology, the fault signal transient component can be obtained, and due to the fact that the transient component contains richer fault information, methods for researching how to use the transient component to select lines include a wavelet method and an energy method.

(1) 5 th harmonic method

The main principle of the 5 th harmonic method is: the compensation effect of the arc suppression coil on the 5 th harmonic is small, compared with 1/25 of a steady-state power frequency component, the zero sequence 5 th harmonic current of the fault circuit is opposite to the zero sequence 3 th harmonic current of the rest non-fault circuits in the main direction and the amplitude of the zero sequence 5 th harmonic current is maximum. But the 5 th harmonic wave is inherently small (only one-fiftieth of the fault-steady-state zero-sequence current) and is highly susceptible to the cost of the fifth harmonic wave in the load and the current transmitter.

(2) Negative sequence current method

The main idea of the negative sequence current method is as follows: the negative sequence fundamental current of the fault line is opposite to the negative sequence fundamental current of all the non-fault lines in direction and has the largest amplitude, so that line selection can be carried out by comparing the magnitude and the direction of the negative sequence current of each outgoing line. The negative sequence current method has strong adaptability to overcurrent resistance, but unstable earth faults are difficult to detect, and a large negative sequence current exists in a line and the acquisition of the negative sequence current is difficult due to operation.

(3) Wavelet method

After wavelet transformation is proposed by Gabor, the wavelet transformation technology is more and more mature, the application range of the wavelet transformation technology is wider and wider, many scholars at home and abroad introduce a wavelet analysis method into fault detection, and utilize the wavelet transformation to process fault signals and extract fault characteristics, such as modulus maximum, phase relation of fault lines and non-fault lines under characteristic frequency, relation of wavelet entropy of the fault lines and the non-fault lines, and the like. However, since the results obtained by the wavelet analysis are different depending on the small basis functions used, and the so-called frequency of the transient component of the signal is not a certain value due to the uncertainty of parameters and the like when a single-phase ground fault occurs in an actual system, there is no theoretical basis for selecting a line based on the so-called characteristic frequency.

(4) Energy method

The energy method is the integral of the product of zero sequence current and zero sequence voltage, i.e. the active component method. Since the energy of the non-fault line after the single-phase earth fault occurs is equal to the sum of the energy of all the non-fault lines and the energy of the arc suppression coil, and the polarity of the energy is opposite to that of the energy on the fault line, the fault line and the non-fault line can be judged by comparing the direction and the magnitude of the energy. The method is not influenced by loads and transient processes, but because the proportion of active components is small, the transient signals are not fully utilized, and the integral function is easy to generate accumulated errors, the actual application effect of the method does not reach an ideal state.

In summary, in combination with the current situation faced by enterprises in China, the accuracy of line selection by using the low-current line selection method does not reach the range permitted by the enterprises and the power system.

The utility model discloses combine the characteristics of undercurrent route selection, adopt the initiative route selection method, heavy current route selection promptly.

In recent years, with the development of a power distribution network, most users adopt a cable line as a main connection mode for a 3-35kV system, and meanwhile, the capacity of the users is continuously increased, the length of a cable feeder line is also continuously increased, so that the single-phase grounding capacitance current of a power system is also continuously increased, and the single-phase grounding hazard is also increased, so that the characteristics of the single-phase grounding fault of the power grid are researched, a fault line selection method with high sensitivity and good reliability is developed, and the method has important theoretical significance and high practical value for improving the power supply safety and the power supply continuous reliability.

Meanwhile, aiming at the demand of intelligent power diversification development of a power system, the requirement of the intelligent power grid on accurate positioning of the single-phase earth fault is not solved all the time, the intelligent power grid technology is actively developed in China at present, and one important content of the intelligent power grid is automatic positioning and cutting of the fault and normal power supply without influencing a sound line. And current large-scale electric power enterprise electric power system can not in time find earth fault return circuit has become the very big puzzlement of current user, seriously influences the reliability and the security of supplying power that lasts of enterprise, is directed to the utility model discloses an implement, find a quick, effectual route selection mode for electric power system and enterprise user and provide a reasonable solution.

SUMMERY OF THE UTILITY MODEL

Technical problem to be solved

The utility model provides a not enough to prior art, the utility model provides a to instantaneous ground connection injection current method route selection device of middling pressure electric wire netting can effectively reduce the probability of the double-phase strange land short circuit or alternate short circuit that the system formed because of ground connection. Avoid because system ground connection back, cause the voltage to rise, exist insulating weak point in the electric wire netting to cause the insulating weak point of electric wire netting to be punctured and take place the short circuit accident, simultaneously the utility model discloses the method of implementing does not receive system ground current's size, does not receive influences such as trouble phase place and arc suppression coil factor, directly rushes into the current signal of certain size, and the size to current signal simultaneously, time is controlled, in order to reach the pristine condition that does not influence the ground point.

(II) technical scheme

In order to achieve the above purpose, the utility model discloses a following technical scheme realizes: the instantaneous grounding injection current method line selection device for the medium-voltage power grid comprises an intelligent line selection main controller WHDX-ZK, an isolating switch GL, a high-impedance grounding transformer WH-JDB, a single-phase quick breaker WH-DSKG and a current transformer LH which are respectively connected into a power distribution grid system, wherein the input end of the high-impedance grounding transformer WH-JDB is connected with a bus of a tapping grid system through a wire, the output end of the high-impedance grounding transformer WH-JDB is connected with the input end of the single-phase quick breaker WH-DSKG through a wire, the output end of the single-phase quick breaker WH-DSKG is connected with the input end of the current transformer LH through a wire, and the wiring end of the intelligent line selection controller WHDX-ZK is in control connection with the high-impedance grounding transformer WH-JDB through the isolating switch GL.

Preferably, the high-impedance grounding transformer WH-JDB is a three-phase three-pole structure, each phase coil is composed of two sub-coils (1#, 2# coils, see the drawing i), the two sub-coils form an electromagnetic balance group, and each sub-coil is axially arranged (whereas the common grounding transformer is concentrically arranged in the radial direction).

Preferably, the power distribution network system comprises n groups of outgoing line loops.

Preferably, the single-phase fast circuit breaker WH-DSKG is a single-phase fast permanent magnet eddy current electromagnetic switch, and the operating principle thereof is an electromagnetic action principle.

Preferably, the single-phase fast circuit breaker WH-DSKG comprises a vacuum arc-extinguishing chamber, a bistable mechanism, an opening energy-storage capacitor, a closing energy-storage capacitor and a control switch, wherein the bistable mechanism is respectively connected with the opening energy-storage capacitor, the closing energy-storage capacitor and the control switch through wires.

Preferably, the bistable mechanism is composed of an opening coil, an eddy current disc and a closing coil respectively.

In a second aspect, the present invention further provides a method for implementing an instantaneous ground injection current method line selection device for a medium voltage power grid, comprising the steps of:

s1, when the system has single-phase earth fault, firstly selecting and storing each branch current by the principle of small current line selection;

s2, then the instantaneous grounding injection current method line selection device grounds the high-impedance grounding transformer WH-JDB by starting the single-phase quick circuit breaker WH-DSKG, at the moment, a grounding transformer is used for actively injecting current signals into the system, and because the injected current can be transmitted along a grounding loop and finally flows into a grounding fault point, the instantaneous grounding injection current method line selection device collects and stores current signals of zero sequence current transformers LH of all branches of the loop again;

and S3, comparing the previous data with the next data by the line selection device of the instantaneous grounding injection current method, and automatically selecting the grounding loop by the line selection device of the instantaneous grounding injection current method according to the characteristics that the current signal of the ungrounded loop is not changed and the current signal of the grounding loop is changed.

Preferably, the primary branch current selection determination time in step S1 is 20 ms.

Preferably, in step S2, the instantaneous ground injection current method line selection device starts the single-phase fast circuit breaker WH-DSKG, injects 50-200A (optional) of fault point by high impedance ground direction change, resamples each loop current by the instantaneous ground injection current method line selection device, and selects a fault loop, where the switch closing time is 13.1ms, the switch opening time is 4.08ms, and the current injection ground point time is not greater than 20 ms.

Preferably, in step S3, the maximum increment line selection is performed by the instantaneous ground injection current line selection device, and the loop with the largest zero sequence current change is determined by combining the loop current values sampled by the first fusion method and the loop current values sampled by the second injection method.

(III) advantageous effects

The utility model provides an instantaneous ground connection injection current method route selection device to middling pressure electric wire netting. Compared with the prior art, the method has the following beneficial effects:

(1) according to the line selection device for the medium-voltage power grid by the instantaneous grounding injection current method, after the system is grounded, the device is accurately selected to be connected to a fault loop, so that the probability of two-phase different-place short circuit or interphase short circuit formed by the system due to grounding can be effectively reduced, the system is prevented from accidents, remarkable economic benefits are achieved, and the phenomenon that the voltage is increased due to the fact that the system is grounded, and the insulating weak point exists in the power grid, so that the insulating weak point of the power grid is broken down to cause short circuit accidents is avoided.

(2) The instantaneous grounding current injection method line selection device for the medium-voltage power grid can effectively reduce the insulation pollution flashover accident rate of equipment. After the system is grounded, the voltage is increased, so that the development of surface discharge of the pollution equipment is accelerated under the action of overvoltage, and the occurrence of pollution flashover accidents is accelerated.

(3) The instantaneous grounding current injection method line selection device for the medium-voltage power grid can rapidly cut off a fault loop, so that the system is recovered and normally operates.

Drawings

FIG. 1 is a circuit diagram of the structure of the present invention connected to a power distribution grid system;

FIG. 2 is a circuit diagram of the structure of the present invention;

fig. 3 is a schematic structural diagram of the single-phase fast circuit breaker of the present invention;

fig. 4 is a schematic diagram of the structure of the grounding transformer coil of the present invention;

fig. 5 is a schematic diagram of the structure of the high impedance grounding transformer coil of the present invention.

In the figure, a vacuum arc extinguish chamber 1, a bistable mechanism 2, a switching-off coil 21, an eddy current disc 22, a switching-on coil 23, a switching-off energy storage capacitor 3, a switching-on energy storage capacitor 4 and a control switch 5 are arranged.

Detailed Description

The technical solutions in the embodiments of the present invention will be described clearly and completely with reference to the accompanying drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments in the present invention, all other embodiments obtained by a person skilled in the art without creative work belong to the protection scope of the present invention.

Referring to fig. 1-5, an embodiment of the present invention provides a technical solution: the utility model provides an instantaneous ground connection injection current method line selection device to medium voltage electric network, including the intelligent line selection main control ware WHDX-ZK of inserting the distribution network system respectively, isolator GL, high impedance grounding transformer WH-JDB, single-phase quick circuit breaker WH-DSKG and current transformer LH, the input of high impedance grounding transformer WH-JDB passes through the wire and is connected with the bus of clap net system, and the output of high impedance grounding transformer WH-JDB passes through the wire and is connected with the input of single-phase quick circuit breaker WH-DSKG, the output of single-phase quick circuit breaker WH-DSKG passes through the wire and is connected with the input of current transformer LH, and the impedance grounding transformer WH-JDB of intelligent line selection controller WHDX-ZK carries out the control connection through isolator GL and high impedance grounding transformer WH-JDB.

As shown in fig. 4 and 5, in the embodiment of the present invention, the high impedance grounding transformer WH-JDB is a three-phase three-column structure, each phase coil is composed of two sub-coils, i.e. 1# coil and 2# coil, two sub-coils form an electromagnetic balance group, each phase of sub-coils is arranged axially, and the common grounding transformer is arranged concentrically in the radial direction.

In the embodiment of the utility model, the high impedance grounding transformer WH-JDB is mainly used in the ungrounded power grid of the neutral point of 6KV to 35KV and is used for fault branch line selection and trip protection; preventing the fault from further propagating. When a single-phase earth fault occurs, the high-resistance variable zero-sequence reactor bears system phase voltage so as to output zero-sequence short-circuit current to the fault branch, and the current is used for determining the fault branch or tripping and cutting off the fault branch in a relay protection mode.

The structure is characterized as follows:

(1) and an iron core structure: a three-phase three-column core structure;

(2) and a coil structure: the three-phase and each-phase double coils are axially arranged in a sectional and staggered manner. The zigzag asymmetric connection method of the wiring group;

the performance characteristics are as follows:

1) the neutral point of the high-impedance grounding transformer WH-JDB can be directly grounded, and when a single-phase grounding fault occurs

The high impedance grounding transformer WH-JDB outputs zero sequence current to the fault branch, and the current can be used for determining the fault branch or tripping and removing the fault branch in relay protection.

2) The zero sequence impedance of the common grounding transformer is generally from a few ohms to tens of ohms; the zero-sequence impedance of the high-impedance grounding transformer WH-JDB can reach hundreds of ohms to thousands of ohms.

3) The high-impedance grounding transformer WH-JDB can resist the single-phase short circuit impact of a system and cannot damage a knot structure. The neutral point of a common grounding transformer must be grounded through resistance or impedance, otherwise, the structure is damaged and the coil is burnt out due to single-phase short circuit impact.

4) The high-impedance grounding transformer WH-JDB can replace a small-resistance grounding protection system (a common grounding transformer neutral point is grounded through a small resistance) which is widely applied at present; the cost is low, no active loss and no heat are generated, and the installation is convenient and the occupied space is small.

The principle outline of the high-impedance grounding transformer WH-JDB is as follows:

the zero-sequence impedance X0 of the grounding transformer is proportional to the square of the turns W of each phase coil, the area Dr of the leakage of the coil and the inverse proportion of the reactance height Hk of the coil; and the area Dr of the coil drain is proportional to the coil's radial dimension a. After the capacity and voltage of the grounding transformer are determined, the section of an iron core and the number of turns of a coil are basically determined, so that the size of the zero sequence impedance is determined by the magnetic leakage area and the reactance height of the coil, and the attached figures 4 and 5 show that the coil of the common grounding transformer is in a radial concentric arrangement structure, the magnetic leakage width is the radial size, the reactance height is the axial height of the coil, the reactance height is far larger than the radial size of the coil, the radial magnetic leakage width is small, the reactance height of the axial coil is high, and the zero sequence impedance cannot be made into high impedance. Each phase coil balance group of the high-impedance grounding transformer WH-JDB is of an axial arrangement structure, the magnetic leakage width is the axis height of the coil, and the reactance height is the full-phase width of the coil, so that the magnetic leakage area is greatly increased, the reactance height is greatly reduced, zero-sequence impedance is greatly increased, and the axial coil arrangement structure can be made into the high-impedance grounding transformer WH-JDB.

In fig. 4 and 5, R1 is the average radius of 1 good coil, R12 is the average radius of magnetic leakage air channel, R2 is the average radius of No. 2 coils, a1 and a2 are the radial size of No. 1 coil and No. 2 coil respectively, a12 is the width between No. 1 coil and No. 2 coil, a is the total radial width of coil (the magnetic leakage width of coil), Hk is the reactance of coil, R is the average radius of coil.

The embodiment of the utility model provides an in, distribution network system includes n group's return circuit of being qualified for the next round of competitions.

By fig. 3, in the embodiment of the utility model, single-phase quick circuit breaker WH-DSKG adopts a single-phase quick permanent magnetism vortex electromagnetic switch, and its theory of operation is to adopt the electromagnetic action principle, single-phase quick circuit breaker WH-DSKG includes vacuum interrupter 1, bistable mechanism 2, separating brake energy storage electric capacity 3, combined floodgate energy storage electric capacity 4 and control switch 5, bistable mechanism 2 pass through the wire respectively with separating brake energy storage electric capacity 3, combined floodgate energy storage electric capacity 4 and control switch 5 are connected, bistable mechanism 2 is respectively by separating brake coil 21, vortex dish 22 and combined floodgate coil 23 are constituteed.

The embodiment of the utility model provides a still provide a method of carrying out instantaneous ground connection injection current method route selection device to medium voltage electric wire netting, specifically include following step:

s1, when the system has single-phase earth fault, firstly, selecting and storing each branch current according to the principle of small current line selection, and judging the time for selecting each branch current for one time to be 20 ms;

s2, then the instantaneous grounding injection current method line selection device grounds the high impedance grounding transformer WH-JDB by starting the single-phase fast breaker WH-DSKG, at the moment, the grounding transformer is used for actively rushing in current signals to the system, because the injected current can be propagated along the grounding loop and finally flows into the grounding fault point, the instantaneous grounding injection current method line selection device collects and stores the LH current signals of each branch zero sequence current transformer of the loop again, the instantaneous grounding injection current method line selection device starts the single-phase fast breaker WH-DSKG, 50-200A is injected into the high impedance grounding direction change fault point, the actual current magnitude can be freely selected according to the actual situation, the instantaneous grounding injection current method line selection device resamples each loop current to select the fault loop, the switch closing time is 13.1ms, the switch opening time is 4.08ms, the current is injected into the grounding point for no more than 20 ms;

s3, comparing the previous data with the next data through the instantaneous grounding injection current method line selection device, automatically selecting a grounding loop through the instantaneous grounding injection current method line selection device according to the characteristic that the ungrounded loop current signal is unchanged and the grounding loop current signal is changed, performing maximum increment line selection through the instantaneous grounding injection current method line selection device, and judging a loop with the maximum zero sequence current change by combining the current values of the loops sampled by the first fusion method and the current values of the loops sampled by the second injection method.

The utility model discloses not influenced by the size of system ground current, not influenced by trouble phase place and arc suppression coil factor etc. directly rush into the current signal of a certain size, to current signal's size, the time is controlled simultaneously to reach the pristine condition that does not influence the ground point.

As shown in fig. 1, the embodiment of the present invention is implemented as follows:

1. for the first time, when a certain line (as follows) of the line is grounded, the controller controls and collects the zero sequence currents of all loops as follows:

I_A、I_B、I_C、I_D、I_E、I_F······n。

2. secondly, the line selection device adopting the instantaneous grounding injection current method is started, and at the moment, the line selection device adopting the instantaneous grounding injection current method injects zero-sequence current into the system through the grounding transformer and the vacuum circuit breaker, the current only passes through the grounding point,

I_a、I_b、I_c、I_d、I_e、I_f······n。

3. by a second time it can be concluded that the fault point current becomes large, i.e. I_FChange of I_fAnd I is_f＝I_F+I_{Injection of}Only the current at the fault point changes, the basic point does not change, I_fAnd I_{Injection of}The currents are relatively close.

4. Stopping judging and selecting I_fThe loop is a ground loop.

5. Main controller WHDX-ZK, isolating switch GL, high impedance grounding transformer WH-JDB, single-phase quick circuit breaker WH-DSKG and current transformer LH

The embodiment of the utility model provides an in, after distribution network system F return circuit takes place ground connection, the utility model discloses main control unit WHDX-ZK gathers, operates, votes each return circuit zero sequence current of system to it is the biggest to reach F return circuit current, promptly: i is_F＝I_A+I_B+I_C+I_D+I_EAfter the determination, the utility model is put into the device and injected with current I_KAnd then the utility model discloses main control unit WHDX-ZK gathers, operates, votes each return circuit zero sequence current of system once more and reachs each return circuit current to it is the biggest to reachs F return circuit zero sequence current, promptly: i is_f＝I_a+I_b+I_c+I_d+I_e+I_KFinally, the utility model discloses main control unit WHDX-ZK compares every return circuit's zero sequence current once more, adornsBefore putting into and after throwing into to compare, judge the biggest return circuit of variable quantity at last, promptly: IA. IB, IC, ID, IE are unchanged, and IF changes are greatest.

And finally, selecting a grounding loop according to the combination of the three judgments.

The utility model discloses can realize accurate route selection, the utility model discloses a fusion method, current injection method, the biggest increment method principle accomplish 100% accuracy and elect the fault circuit, through adopting high-pressure quick switching technique, realize that the electric current pours into fast, instantaneous breaking away from, to the no disturbance of system, the utility model discloses a high impedance ground of three-phase five-column structure principle becomes, and this ground connection becomes the zero sequence current excitation path who utilizes self, realizes high impedance ground. Device high impedance ground connection becomes direct ground connection operation, the utility model discloses select dress arc extinguishing device can realize the arc extinguishing function, combines full voltage monitoring data to realize the record analysis to fault information simultaneously.

And those not described in detail in this specification are well within the skill of those in the art.

It is noted that, herein, relational terms such as first and second, and the like may be used solely to distinguish one entity or action from another entity or action without necessarily requiring or implying any actual such relationship or order between such entities or actions. Also, the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus.

Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that changes, modifications, substitutions and alterations can be made in these embodiments without departing from the principles and spirit of the invention, the scope of which is defined in the appended claims and their equivalents.

Claims

1. The utility model provides a to instantaneous ground connection injection current method route selection device of medium voltage electric wire netting which characterized in that: the intelligent line selection system comprises an intelligent line selection main controller WHDX-ZK, an isolating switch GL, a high-impedance grounding transformer WH-JDB, a single-phase quick circuit breaker WH-DSKG and a current transformer LH which are respectively connected into a power distribution network system, wherein the input end of the high-impedance grounding transformer WH-JDB is connected with a bus of the dotting network system through a wire, the output end of the high-impedance grounding transformer WH-JDB is connected with the input end of the single-phase quick circuit breaker WH-DSKG through a wire, the output end of the single-phase quick circuit breaker WH-DSKG is connected with the input end of the current transformer LH through a wire, and the wiring end of the intelligent line selection controller WHDX-ZK is in control connection with the high-impedance grounding transformer WH-JDB through the isolating switch GL.

2. An instantaneous earth injection current method line selection device for a medium voltage network according to claim 1, characterized in that: the high-impedance grounding transformer WH-JDB is of a three-phase three-column structure, each phase coil is composed of two branching coils, the two branching coils form an electromagnetic balance group, and each phase branching coil is axially arranged.

3. An instantaneous earth injection current method line selection device for a medium voltage network according to claim 1, characterized in that: the power distribution network system comprises n groups of outlet loops.

4. An instantaneous earth injection current method line selection device for a medium voltage network according to claim 1, characterized in that: the single-phase fast breaker WH-DSKG adopts a single-phase fast permanent magnet eddy current electromagnetic switch, and the working principle of the single-phase fast breaker WH-DSKG adopts an electromagnetic action principle.

5. An instantaneous earth injection current method line selection device for a medium voltage network according to claim 4, characterized in that: the single-phase quick circuit breaker WH-DSKG comprises a vacuum arc extinguish chamber (1), a bistable mechanism (2), a switching-off energy storage capacitor (3), a switching-on energy storage capacitor (4) and a control switch (5), wherein the bistable mechanism (2) is respectively connected with the switching-off energy storage capacitor (3), the switching-on energy storage capacitor (4) and the control switch (5) through wires.

6. An instantaneous earth injection current method line selection device for a medium voltage network according to claim 5, characterized in that: the bistable mechanism (2) is composed of a switching-off coil (21), an eddy current disc (22) and a switching-on coil (23).