KR101618627B1 - Method for cooperating operation of distance relay in power system, recording medium and system for performing the method - Google Patents

Abstract

A method of coordinating the operation of a distance relay in a power system using a directional distance relay and a superconducting fault current limiter installed at both ends of a transmission line, comprising the steps of: transmitting a signal detected by a distance relay to a counterpart; Comparing the signal detected at the distance relay and the signal received at the counterpart with each other to determine whether the fault is within the protection interval; And determining whether to send a carrier signal to the other end depending on whether the failure is within the protection zone or not, and sending or unloading the carrier signal. As a result, it is possible to secure a sufficient fault current limiting effect of the superconducting fault current limiter and secure the operation of a stable protective device, thereby protecting the power system.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of coordinating the operation of a distance relay in a power system, a recording medium and a system for performing the same,

The present invention relates to a method of coordinating the operation of a distance relay in a power system, a recording medium and a system for performing the same, and more particularly, to a distance relay capable of introducing a comparative relay system in a power system using a superconducting fault current limiter An operation cooperation method, and a recording medium and a system for performing the same.

With the recent development of Korea's industry, demand for electric power has been continuously increasing, which has led to an increase in the capacity of power generation facilities in the grid and the expansion of transmission and distribution lines. However, such an extension of the power system has an effect of reducing the impedance in the system to increase the size of the fault current in the event of a fault, which is exceeding the breaking capacity of the existing systematic circuit-breakers, .

Therefore, in order to solve such a problem, it is proposed to adopt a high impedance device, use a Hull Reactor, apply a system division method and replace with a large capacity circuit breaker as a method of reducing the fault current. However, these measures have disadvantages such as loss in normal times, decrease in stability of the system, and high cost due to replacement of the breaker. Therefore, the application of the superconducting fault current limiter, which is considered as the most ideal method for reducing the fault current, is attracting attention.

The superconducting fault current limiter has a characteristic of zero resistance at normal times by using the characteristics of a superconductor and has an operating characteristic of reducing a fault current by generating resistance due to a fault phenomenon at the time of fault occurrence. This has the advantage that it does not affect the system in a normal time as compared with other fault current reduction schemes, and an additional device is unnecessary. To this end, superconducting fault current limiter has been actively studied in the distribution system due to these advantages, and researches on the application in the transmission system have been progressed recently.

However, in a situation where the distance relay is widely used as one of various protection devices of the power system, the superconducting fault current limiter which operates to cope with the fault current affects the operation of the protection relay by changing the impedance.

If the impedance of the superconducting fault current limiter is limited to reduce the influence of the distance relay, the desired fault current limiting effect can not be obtained. If the protection relay is corrected assuming that the superconducting fault current limiter operates, A problem arises that creates a dangerous situation.

KR 10-2013-0053184 A KR 10-2013-0035295 A

SUMMARY OF THE INVENTION Accordingly, the present invention has been made keeping in mind the above problems occurring in the prior art, and it is an object of the present invention to provide a method of coordinating the operation of a distance relay for a stable protection operation of a power system.

It is another object of the present invention to provide a recording medium for performing a method of coordinating the operation of a distance relay in the power system.

It is a further object of the present invention to provide a system for performing a method of coordinating the operation of a distance relay in the power system.

In order to achieve the object of the present invention, a method of operating a distance relay in a power system using directional distance relays and a superconducting fault current limiter installed at both ends of a protection zone of a transmission line according to an embodiment, Transmitting the detected signal to the counterpart; Comparing the signal detected by the distance relay and the signal received from the counterpart with each other to determine whether the fault is within the protection interval; And determining whether to transmit a carrier signal to the counterpart depending on whether the failure is within the protection interval or not, and sending or unshipment the carrier signal.

In the embodiment of the present invention, the step of sending out or not delivering the carrier signal may enable the inside direction of the distance relay to be tripped at the counterpart by omitting the carrier signal at the time of an internal failure in the guard interval.

In the embodiment of the present invention, the step of sending out or not delivering the carrier signal may cause the carrier signal to be transmitted at the time of an external failure in the guard interval to stop the internal direction trip of the distance relay at the counterpart.

In the embodiment of the present invention, the step of sending out or not delivering the carrier signal may transmit the carrier signal in the normal transmission trip prevention mode.

According to another aspect of the present invention, there is provided a computer-readable storage medium storing a computer program for performing a method of coordinating the operation of a distance relay in the power system described above.

According to another aspect of the present invention, there is provided a system for performing an operation cooperation method of a distance relay in a power system, the system comprising: relay; A superconducting fault current limiter connected to the outgoing point of the transmission line to sense and limit a fault current generated in the power system; And a controller connected to each of the distance relays to transmit a signal sensed by the distance relay to a counterpart, compare the received signals with each other, determine whether the fault is within the protection interval, And a blocking circuit.

In an exemplary embodiment of the present invention, the trip inhibiting circuit may enable the internal direction trip of the distance relay at the counterpart by not sending the carry signal at the time of an internal failure in the guard interval.

In an embodiment of the present invention, the trip inhibiting circuit may send the carry signal in the event of an external failure in the guard interval, so as to prevent an internal trip of the distance relay at the counterpart.

In an embodiment of the present invention, the superconducting fault current limiter includes a superconducting element in which an electric resistance is zero in a steady state of the power system, and a resistance due to the fault current occurs when a fault occurs; A circuit breaker connected in series with the superconducting device to cut off current flowing to the superconducting device when the fault current is equal to or greater than a threshold value; And a current-limiting element connected in parallel to the superconducting element and the breaker, for energizing the fault current when the circuit breaker performs a shut-off operation.

In an embodiment of the present invention, the trip inhibiting circuit can transmit the carrier signal in a normal transmission trip prevention mode.

According to the present invention, when a superconducting fault current limiter is applied to a power system, the problem of a distance relay whose operating co-ordination varies depending on the impedance changed by the operation of the superconducting fault current limiter is applied to a comparative relay method, Can be solved. Accordingly, the superconducting fault current limiter can maintain the impedance necessary for restricting the fault current, while securing the operation characteristics of the protection relay, thereby stabilizing the power system.

1 is a configuration diagram of a superconducting fault current limiter used in a transmission system.
2 is a waveform diagram showing the operating characteristics of the superconducting fault current limiter of FIG.
3 is a view showing a protection region of the mho-type distance relay.
4 is an operation diagram of the distance relay in case of a 1-line ground fault.
5 is a view showing an impedance trajectory when a superconducting fault current limiter is applied.
FIG. 6 is a waveform diagram showing a failure current of the distance relay according to the malfunction phenomenon of FIG. 5;
7 is a waveform diagram showing a fault current of the distance relay in case of an internal fault;
FIG. 8 is a block diagram of a motion coordination system of a distance relay according to an embodiment of the present invention. Referring to FIG.
FIG. 9 is a waveform diagram showing a failure current of the distance relay in the case of the internal failure of FIG. 8; FIG.
10 is a waveform diagram showing a failure current of the distance relay in the case of the external failure in FIG.
11 is a flowchart of a method of coordinating the operation of a distance relay in a power system according to an embodiment of the present invention.

The following detailed description of the invention refers to the accompanying drawings, which illustrate, by way of illustration, specific embodiments in which the invention may be practiced. These embodiments are described in sufficient detail to enable those skilled in the art to practice the invention. It should be understood that the various embodiments of the present invention are different, but need not be mutually exclusive. For example, certain features, structures, and characteristics described herein may be implemented in other embodiments without departing from the spirit and scope of the invention in connection with an embodiment. It is also to be understood that the position or arrangement of the individual components within each disclosed embodiment may be varied without departing from the spirit and scope of the invention. The following detailed description is, therefore, not to be taken in a limiting sense, and the scope of the present invention is to be limited only by the appended claims, along with the full scope of equivalents to which such claims are entitled, if properly explained. In the drawings, like reference numerals refer to the same or similar functions throughout the several views.

Hereinafter, preferred embodiments of the present invention will be described in more detail with reference to the drawings.

At present, in Korea power system, distance relays are widely used to protect 154kV, 345kV, and 765kV transmission lines. The distance relay has a function to select and stop the fault within the set distance through the measurement ratio of the voltage and the current, from the point where the relay is installed to the high point. If such a distance relay causes a malfunction due to a certain problem, it may not be possible to shut down the fault section but may also block the healthy section, which causes a serious problem in the stability of the power system.

Accordingly, the present invention confirms the operating characteristics of a distance relay when a superconducting fault current limiter is applied to a superconducting fault current limiter in a transmission system, analyzes the malfunction phenomenon thereof, and proposes a solution thereof.

1 is a configuration diagram of a superconducting fault current limiter used in a transmission system. 2 is a waveform diagram showing the operating characteristics of the superconducting fault current limiter of FIG.

Referring to FIG. 1, a superconducting fault current limiter (SFCL) 50 for reducing a fault current generated when a fault occurs in a transmission system is composed of a superconducting device (HTSC), a breaker CB and a current limiting device do. The HTSC and the breaker CB are connected in series to the line and the current limiting device CLR is connected in parallel to the superconducting device HTSC and the breaker CB.

The current (i _SFCL ) flowing through the superconducting fault current limiter 50 flows only through the superconducting element (HTSC) in the transmission system. However, when a fault occurs, the resistance of the superconducting element (HTSC) is generated due to the inductance phenomenon, and a part of the current flowing in the superconducting fault current limiter 50 according to the magnitude of the resistance is generated by the current- RTI ID = 0.0 > (i _CLR ). ≪ / RTI > And has a characteristic of restricting the fault current by the current-limiting device (CLR) by interrupting the current flowing to the superconducting element (HTSC) by using the breaker CB connected in series to the superconducting element (HTSC) after a predetermined time.

Accordingly, the superconducting device (HTSC) detects a fault current at an early stage of a fault and plays a role in minimizing a burden on a large fault current in the transmission system.

Referring to FIG. 2, operational waveforms of the superconducting fault current limiter 50 are shown. The operation specifications of the superconducting fault current limiter 50 are based on the case of a transmission-class superconducting fault current limiter under study. The resistance of the superconducting element HTSC is 8 [Omega], and the impedance of the current-limiting element CLR is 6 [Omega].

2, a resistance R _SC is generated in the superconducting element (HTSC) when the current i _SC flowing through the superconducting element (HTSC) exceeds 8.7 [kA]. This value is converged to 8 [ do. Thus, the magnitude of the current (i _SFCL ) flowing through the superconducting fault current limiter 50 is reduced. After the breaker CB is operated, the fault current flowing through the superconducting element (HTSC) becomes 0 [A], so that the resistance of the superconducting element (HTSC) has zero resistance.

Also, it can be confirmed that the current flowing in the superconducting fault current limiter 50 flows only to the current limiting device CLR, and the fault current is reduced by the value of the current limiting device CLR.

On the other hand, the power transmission system is more affected by the failure propagation than the power distribution system, so that the operation of the protection relay is required to be faster in operation and higher in reliability than the protection relay system used in the power distribution system. In Korea, the distance relay is widely used as a protection device for the transmission system. The distance relay is a protection relay system that detects and protects the fault through the impedance calculated by the voltage and current measured from the relay installation point in the transmission line. It is also called an impedance relay.

The distance relay used in the present invention is a mno-type distance relay, which is a distance relay indicated by a circle passing through the origin. The name mho is a reciprocal number of the impedance (OHM), that is, admittance unit (MHO) Is a name to be attached because it is a relay operating when the magnitude of the component with respect to a certain angle of the reference angle is greater than or equal to a predetermined value.

FIG. 3 is a view showing the protection area of the mho-type distance relay through RX coordinates. In the simulation transmission line circuit, the Zone 1 protection area is 75% of the protection zone line, the Zone 2 is 150% 225% area. However, the protection range and operating time of the protective relay may be subject to the correction instructions in accordance with the fault situation.

FIG. 4 is a diagram showing the operation of the distance relay in case of a 1-line ground fault. FIG. 4 conceptually illustrates the operating range and operating time of the distance relay in the case of a ground fault applied to the model transmission circuit.

When the impedance of the superconducting fault current limiter is a reactance component, the effect on the distance relay is greatly affected because the reactance component is larger than the resistance due to the characteristics of the power system. Therefore, a malfunction of the distance relay was confirmed when the impedance of the superconducting fault current limiter was a reactance component.

5, the impedance trace of the distance relay of the internal fault section is enlarged to the R-X coordinate when the IR element impedance of the superconducting fault current limiter is a reactance component. It can be seen that the impedance trajectory of the distance relay moves upward in the direction of the reactance as the reactance component of the current limiting element increases in the limit region of Zone 1. As a result, it can be confirmed that the impedance trajectory moves out of the operation region of Zone 1 and moves to the operation region of Zone 2, thereby causing a malfunction phenomenon.

6 (b) is a malfunction phenomenon as shown in FIG. 5, and is a reactance component of a current limiting element of the superconducting fault current limiter in the zone limit of Zone 1, and FIG. 6 It is the fault current.

Referring to FIG. 6 (a), the fault current has an instantaneous shutdown time within the zone 1 operation time of 5 [Hz] because the impedance trajectory of the distance relay stays in the limit region of Zone 1 when the superconducting fault current limiter is not used.

However, referring to FIG. 6 (b), since the impedance trajectory deviates from the operation region of Zone 1 and remains in the operation region of Zone 2 when applying the SFCL having the reactance component, Of the delay time. This indicates an underrelease phenomenon, which is one of the malfunctions of the distance relay, and the operating range of the distance relay does not reach the correction range. This underrun phenomenon is caused by the fact that the electric distance of the distance relay is increased due to the reactance of the superconducting fault current limiter, which causes malfunction.

7 (a) and 7 (b) are waveform diagrams showing the fault currents of the distance relays at both ends of the guard interval in the guard interval, respectively, and showing the fault currents of the distance relay in the guard interval when the comparison relay method is not yet used.

7 (a), when the fault current is reduced due to the influence of the superconducting fault current limiter and when the superconducting fault current limiter, which is a malfunction phenomenon, is applied, the instantaneous shutdown within 5 [Hz] 2 delay time of 20 [Hz].

In the present invention, as a method for solving the malfunction phenomenon caused by the application of the superconducting fault current limiter, the operation cooperation of the distance relay is simulated by using the normal transmission trip prevention method among the direction comparison relay methods.

FIG. 8 is a block diagram of a motion coordination system of a distance relay according to an embodiment of the present invention. Referring to FIG.

Referring to FIG. 8, the operation coordination system 1 of the distance relay according to an embodiment of the present invention includes distance relays 10 and 30 installed at both ends of a guard interval of a power system to a transmission line, A superconducting fault current limiter 50 for detecting and restricting a fault current generated in the power system and tripping circuits 15 and 35 for supplementing the operation of the distance relays 10 and 30 in a direction comparative relaying method .

The distance relays 10 and 30 are directional distance relays that detect and protect the fault through the impedance calculated by the voltage and current measured from the relay installation point in the transmission line. The distance relays 10 and 30 are mho-type distance relays and have been described above with reference to Figs. 3 and 4.

The superconducting fault current limiter 50 is connected to a drawing point of the transmission line to detect and limit a fault current generated in the power system. The superconducting fault current limiter 50 includes a superconducting device (HTSC), a circuit breaker CB and a current limiting device (CLR) as described with reference to FIG. 1, and the operation characteristics have been described with reference to FIG.

The trip inhibiting circuits 15 and 35 are connected to the respective distance relays 10 and 30 to transmit signals sensed by the distance relays 15 and 35 to a counterpart, It is determined whether or not there is a failure in the section and it is determined whether or not the carrier signal is transmitted to the opposite end.

In the direction comparative relay method, information obtained by a directional relay installed at each end of a transmission line is transmitted to a counterpart by a communication device, and the transmitted signals are compared with each other to discriminate a fault within the protection interval. To determine whether the guard interval is within or outside the guard interval. The directional comparison relaying method includes a normal transmission transmission stopping method in accordance with a carrier signal transmission method and a transmission stopping method in case of a failure.

In one embodiment, the trip-inhibiting circuits 15 and 35 use a transmission-trip blocking method at all times, and the operating characteristics of the trip-blocking circuits 15 and 35 are such that a carrier signal is transmitted when an external fault occurs using signals between relays, trip, and does not send a carrier signal in case of an internal fault, so that it is possible to trip by an inward directional relay operation at the other end.

Specifically, the trip inhibiting circuits 15 and 35 are tripped under the condition that the inward directional element for measuring a high advantage operates and the trip stop command signal is not received from the counterpart. The inward elements (In) of the trip inhibiting circuits (15, 35) use Zone 2 and Zone 3 elements, and the outward direction elements (Out) are elements for measuring a backward failure at a distance relay installation point.

Each of the trip inhibiting circuits 15 and 35 includes an internal signal IS, an external signal OS, a transfer signal TS and a received signal RS signal.

If the current transmission line is normally operated without failure, the internal directional signal terminal (IS) and the external directional signal terminal (OS) at both ends do not operate and signal transmission to the other terminal is not performed. However, when a failure occurs at the rear end (bus side) of the trip-inhibiting circuit 15, the distance relay 35 operates the internal directional signal IS if the fault point is within the protection range, The external signal terminal (OS) of the relay 15 also operates and sends a signal to the transmission signal terminal TS to send a trip blocking signal to the other terminal. Therefore, the output signal of the receiving signal terminal (RS) of the distance relay 35 is outputted, and the output of the AND circuit is blocked.

On the contrary, in case of an internal failure in the guard interval, the carry signal is not outputted and the internal direction trip of the distance relay is enabled at the counterpart.

On the other hand, since the operating time of the inward directional signal IS and the outward directional signal OS are similar (15 to 20 ms), the time delay of the transmission signal terminal TS and the reception signal terminal RS The IS signal of the distance relay 15 may be tripped immediately and malfunctioned. In order to prevent such a malfunction, it is possible to make the internal signal stage IS operate and to trip when the signal is not received even if the delay time of the signal from the counterpart (communication device delay time) is exceeded. ).

The communication device used in the direction comparison trip prevention method is applicable to a device that uses a power line carrier, an optical communication device, or the like and is capable of outputting a contact signal from a protection relay to a contact signal in a receiver of a counterpart communication device . In the case of power line transfer, it is possible to use the On-Off contact method in which the contact signal of the protection relay is converted into a frequency signal in the range of 30 kHz to 600 kHz and transmitted and received. In the case of using optical communication, Can be converted and transmitted / received.

FIG. 9 shows a fault current of the distance relay in the internal fault section in FIG. 8, and a waveform of the fault current in the distance relay in the protection section when the transmission trip protection mode is always applied.

Fig. 9 (a) is the fault current of the left distance relay 10 of Fig. 8, and Fig. 9 (b) is the fault current of the right distance relay 30 of Fig. Referring to Figure 9 (a), can identify equal regardless of Figure 7 (a) the blocking time of the fault current of the i ₁₃ malfunction developing superconducting fault current limiter application which appeared in.

FIG. 10 shows a fault current of the distance relay in the external fault section in FIG. 8, and a waveform of the fault current in the distance relay in the protection section when the transmission trip protection mode is always applied. Referring to FIG. 10, it can be confirmed that there is no influence by the application of the normal transmission trip blocking method.

According to the present invention, when a superconducting fault current limiter is applied to a power system, a problem of a distance relay whose operating co-ordination varies depending on an impedance changed by the operation of a superconducting fault current limiter is applied to a comparative relay method, I can solve the problem. Accordingly, the superconducting fault current limiter can maintain the impedance necessary for restricting the fault current, while securing the operation characteristics of the protection relay, thereby stabilizing the power system.

11 is a flowchart of a method of coordinating the operation of a distance relay in a power system according to an embodiment of the present invention.

The operation cooperation method of the distance relay in the power system according to the present embodiment can be carried out in substantially the same configuration as the operation cooperation system 1 of the distance relay of Fig. Therefore, the same components as those of the operation cooperative system 1 of the distance relay of Fig. 8 are denoted by the same reference numerals, and repeated descriptions are omitted.

11, a method of coordinating the operation of a distance relay in a power system using directional distance relays and a superconducting fault current limiter installed at both ends of a protection zone of a transmission line according to the present embodiment, (Step S10).

A signal detected in the distance relay and a signal received in the counterpart are compared with each other to determine whether the fault is within the protection interval (step S30).

In step S50, it is determined whether or not a carrier signal is to be transmitted to the opposite end according to whether the failure is within the protection interval determined in step S30. If it is an internal failure in the guard interval, the carrier signal is not transmitted and the internal directional trip of the distance relay is enabled at the counterpart (step S70). On the other hand, if it is an external failure in the guard interval, the carrier signal is transmitted to stop the internal direction trip of the distance relay at the counterpart (step S90).

The carrier signal can be transmitted in a normal transmission trip blocking mode.

In the power system according to the present invention, the method of coordinating the operation of the distance relay may be implemented in the form of program instructions that can be executed through various computer components and recorded in a computer-readable recording medium. The computer-readable recording medium may include program commands, data files, data structures, and the like, alone or in combination.

The program instructions recorded on the computer-readable recording medium may be ones that are specially designed and configured for the present invention and are known and available to those skilled in the art of computer software.

Examples of computer-readable recording media include magnetic media such as hard disks, floppy disks and magnetic tape, optical recording media such as CD-ROMs and DVDs, magneto-optical media such as floptical disks, media, and hardware devices specifically configured to store and execute program instructions such as ROM, RAM, flash memory, and the like.

Examples of program instructions include machine language code such as those generated by a compiler, as well as high-level language code that can be executed by a computer using an interpreter or the like. The hardware device may be configured to operate as one or more software modules for performing the processing according to the present invention, and vice versa.

It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the spirit or scope of the present invention as defined by the following claims. You will understand.

The method and system for coordinating the operation of a distance relay according to the present invention is applied to a power system to not only interrupt the fault current but also stably maintain the operation characteristics of the protection relay, thereby protecting the power system, And the economic effect of reducing labor force and the like.

1: Operation Relay System of Distance Relay
10, 30: Distance relay
15, 35: Trip stop circuit
50: Superconducting fault current limiter

Claims (10)

A method of coordinating the operation of a distance relay in a power system using directional distance relays and superconducting fault current limiters installed at both ends of a transmission line,
Transmitting a signal sensed by the distance relay to a counterpart;
Comparing the signal detected by the distance relay and the signal received from the counterpart with each other to determine whether the fault is within the protection interval;
Operating one of an inward direction signal terminal and an outward direction signal terminal connected to the distance relay depending on whether the fault is within the protection interval;
Transmitting a carrier signal to the counterpart when the counterpart is operating; And
Wherein if the internal signal terminal is operated, the broadcast signal is not transmitted to the counterpart, and if the carrier signal is not received from the counterpart within a predetermined delay time, the internal directional trip of the distance relay is enabled, And allowing both of the distance relays provided at both ends to make an internal direction trip.
The method as claimed in claim 1, wherein the step of enabling all of the distance relays provided at both ends of the guard interval to trip inward,
Wherein the control unit is configured to enable the tripping of the distance relay in the counterpart by not sending out the carrier signal when the protection zone has an internal failure.
The method as claimed in claim 1, wherein when the outward signal terminal is operated,
And transmits the carrier signal when an external failure occurs in the guard interval to stop the trip of the distance relay in the counterpart from the counterpart.
The method as claimed in claim 1, wherein the step of delivering or not delivering the carrier signal comprises:
And the carrier signal is transmitted in a normal transmission trip prevention mode.
A computer-readable recording medium having recorded thereon a computer program for performing a method of coordinating the operation of a distance relay in a power system according to any one of claims 1 to 4.
A distance relay installed at both ends of the protection section of the power system to the transmission line and having directionality;
A superconducting fault current limiter connected to the outgoing point of the transmission line to sense and limit a fault current generated in the power system; And
A signal detected by the distance relay is transmitted to a counterpart, and the received signals are compared with each other, and it is determined whether there is a failure within the protection interval, and one of an inner direction signal terminal and an outer direction signal terminal connected to the respective distance relays Wherein when the outside directional signal terminal is operated, a carrier signal is transmitted to the opposite terminal, and when the inside directional signal terminal is operated, the carrier signal is not transmitted to the opposite terminal and within a predetermined delay time And a trip inhibiting circuit that enables internal disturbance of the distance relay to be enabled so that all the distance relays provided at both ends of the guard interval can be tripped inward if no carrier signal is received from the counterpart, Cooperative system.
7. The apparatus according to claim 6, wherein the trip-
Wherein the control unit is configured to enable the tripping of the distance relay in the counterpart at the counterpart by not sending out the carrier signal when the guard interval fails.
7. The apparatus according to claim 6, wherein the trip-
And transmits the carrier signal when an external failure occurs in the guard interval to stop an internal direction trip of the distance relay at the counterpart.
7. The superconducting fault current limiter according to claim 6,
A superconducting element in which electric resistance is zero in a steady state of the power system and resistance is generated by a fault current when a fault occurs;
A circuit breaker connected in series with the superconducting device to cut off current flowing to the superconducting device when the fault current is equal to or greater than a threshold value; And
And a current-limiting element connected in parallel to the superconducting element and the breaker, the current-limiting element conducting the fault current when the breaker performs a shut-down operation.
7. The apparatus according to claim 6, wherein the trip-
And transmits the carrier signal in a normal transmission trip prevention mode.

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