KR102350387B1 - Apparatus and method for detecting fault line - Google Patents

Abstract

The present invention relates to an apparatus and method capable of detecting a section in which a failure occurs when a failure occurs in a single complex multi-track. For this, an apparatus for detecting a fault section when a fault occurs in a complex line including an overhead line and an underground line of the present invention for this purpose includes: a relay for detecting a current direction of active power; a sensor unit installed in the connection part of the overhead line and the underground line, and sensing the current flowing in the complex line; and calculating the phase value of the current sensed through the sensor unit, calculating the difference between the phase values of the current calculated before and after the failure when the failure occurs, based on the difference between the phase values of the calculated current and the current direction of the active power It is characterized in that it comprises a processing unit for determining the failure section.

Description

Fault section detection device and method {APPARATUS AND METHOD FOR DETECTING FAULT LINE}

The present invention relates to an apparatus and method for detecting a faulty section, and more particularly, to an apparatus and method capable of detecting a section in which a fault occurs when a fault occurs in a single complex multi-track.

Due to the rapid growth of the industrial economy in recent years, the demand for electricity is increasing year by year. Electricity consumption at the peak of summer is almost equal to the total supply of electric power supply facilities, and nationwide cooperation is required at the national level every year. In addition, the rapid increase in electric energy consumption caused by various small-scale industries, large buildings, and apartment complexes as well as the rapid overpopulation trend in cities is now demanding large-capacity transmission in downtown areas. As a result, the construction of underground transmission lines and complex lines with processing and underground is gradually increasing.

Most of the overhead line failures among these complex lines are temporary failures caused by temporary weakening of air insulation due to lightning strikes or tree contact. That is, in the case of an overhead line failure, in most cases, the cause of the failure is automatically removed after a certain period of time has elapsed. Accordingly, in the case of a failure of an overhead line, that is, a power transmission line, a method of repairing a failure on an overhead line by shutting off the line and re-inserting the circuit breaker after a predetermined time has elapsed is mainly adopted.

In addition, underground line failure that does not use air insulation has a high probability of permanent failure such as cable damage, so it is common not to apply automatic reclosing to prevent the spread of failure due to reclosing failure. Accordingly, the determination of permanent failure is determined by looking at the location of the failure in the complex line in which the overhead line and the underground line are mixed. In other words, a failure in the machining section is regarded as a temporary failure and automatic reclosing is performed, but a failure in the underground section is regarded as a permanent failure and automatic reclosing is not implemented. As such, for selective automatic reclosing in complex lines, it is necessary to identify whether the fault location is within the machining or underground section when the line breaks down.

In this regard, the conventional fault section identification method is largely classified into two types. First, there is a method using a distance relay. The method using the distance relay is a method of identifying the fault section based on the impedance between the substation and the fault point recognized by the distance relay when a line fault occurs. The fault section identification method using the distance relay has the advantage of no additional cost because it uses a pre-installed distance relay, but there is a problem that the fault section identification accuracy is low due to the error of the distance relay.

In addition, the second method of the conventional fault section identification method is a method using a current differential relay. The method of using a current differential relay is a method of installing CTs and differential relays at both ends of the section, and identifying internal failure by comparing the magnitude or phase of the current at both ends. While this method has the advantage of very high failure section identification accuracy, since CT and switchboard installations are required at both ends of the section, maintenance such as power supply is required, which requires high cost.

In this regard, there is Korean Patent No. 0699221 entitled "Failure determination system for protection of mixed transmission line and method therefor".

It is an object of the present invention to provide an apparatus and method for detecting a faulty section capable of detecting a section in which a fault occurs when a fault occurs in a single complex multi-track.

An apparatus for detecting a fault section when a fault occurs in a complex line including an overhead line and an underground line of the present invention for solving the above problems includes: a relay for detecting a current direction of active power; a sensor unit installed in the connection part of the overhead line and the underground line, and sensing the current flowing in the complex line; and calculating the phase value of the current sensed through the sensor unit, calculating the difference between the phase values of the current calculated before and after the failure when the failure occurs, based on the difference between the phase values of the calculated current and the current direction of the active power It is characterized in that it comprises a processing unit for determining the failure section.

Also, when it is determined that a failure has occurred in the underground line, the processing unit may generate a block signal for preventing reclosing of the underground line.

In addition, the sensor unit may be composed of at least one of a Rogowski coil CT (Current Transformer) and an optical CT.

In addition, the processor may calculate the phase value of the current over time by applying a fast Fourier transform (FFT) window to the current waveform acquired through the sensor unit.

The method of detecting a fault section when a fault occurs in a complex line including an overhead line and an underground line of the present invention for solving the above problems includes the steps of: detecting, through a relay, a direction of a current of active power; Sensing the current flowing in the complex line through the sensor unit installed in the connection portion of the overhead line and the underground line; calculating a phase value of the current sensed through the sensor unit by the processing unit; calculating, by the processing unit, a difference between phase values of currents calculated before and after the occurrence of a fault when a fault occurs; and determining, by the processing unit, a failure section based on the difference between the calculated current phase values and the current direction of the active power.

In addition, the failure section detection method of the present invention may further include, by the processing unit, generating a block signal for preventing reclosing of the underground line when it is determined that a failure has occurred in the underground line.

In addition, the sensor unit may be composed of at least one of a Rogowski coil CT and an optical CT.

In addition, in the calculating of the phase value of the current, the phase value of the current according to time may be calculated by applying a fast Fourier transform (FFT) window to the current waveform obtained through the sensor unit.

According to the device and method for detecting a fault section of the present invention, since the sensor unit only needs to be installed in one place of the terminal junction box at the processing-underground boundary, the implementation cost is low and the fault section determination accuracy is equal to that of the existing current differential method. .

Accordingly, when the device and method for detecting a failure section according to the present invention are applied to the selective automatic reclosing of a single-block complex line, automatic reclosing for permanent failures is implemented at a lower cost compared to the conventional method and prevention of failure propagation can contribute to

1 is a conceptual diagram of an apparatus for detecting a failure section according to an embodiment of the present invention.
2 is a block diagram of an apparatus for detecting a failure section according to an embodiment of the present invention.
3A, 3B, 4A, 4B, and 5 are conceptual diagrams for explaining a failure section detection method according to the present invention.
6 is a block diagram of a processing unit according to an embodiment of the present invention.
7A, 7B, 8A, 8B, 9A, and 9B are conceptual diagrams for explaining a failure section detection method according to the present invention.
10 is a flowchart of a method for detecting a failure section according to an embodiment of the present invention.

The present invention will be described in detail with reference to the accompanying drawings as follows. Here, repeated descriptions, well-known functions that may unnecessarily obscure the gist of the present invention, and detailed descriptions of configurations will be omitted. The embodiments of the present invention are provided in order to more completely explain the present invention to those of ordinary skill in the art. Accordingly, the shapes and sizes of elements in the drawings may be exaggerated for clearer description.

Hereinafter, an apparatus for detecting a failure section according to an embodiment of the present invention will be described. As mentioned above, when a failure occurs in a complex line including overhead lines and underground lines, it is important to find the location where the failure occurred. In this regard, conventionally, there has been a method using a distance relay or a current differential relay. However, as mentioned above, the method using the distance relay has a problem in that the detection accuracy is low, and the method using the current differential relay has high fault section detection accuracy, but the cost is high because CT and current differential relays must be installed at both ends of the section. There were many problems. Accordingly, it is an object of the present invention to provide an apparatus and method for detecting a failure section that is not expensive and has high detection accuracy, which overcomes the above-mentioned conventional problems.

1 is a conceptual diagram of an apparatus 100 for detecting a failure section according to an embodiment of the present invention. 2 is a block diagram of an apparatus 100 for detecting a failure section according to an embodiment of the present invention. As shown in FIG. 1 , the failure section detection apparatus 100 according to an embodiment of the present invention detects a failure section when a failure occurs based on the signal detected through the relay 30 and the measurement unit 110 . detect Here, the measurement unit 110 may be configured to include a Rogowski coil CT (Current Transformer). Of course, various sensors for detecting current, such as optical CT, may be applied to the measurement unit 110 . In addition, the measuring unit 110 is characterized in that it is installed in the connection portion of the overhead line and the underground line. The reason why the measuring unit 110 is installed in the connection part of the overhead line and the underground line will be described again below.

In addition, the relay 30 functions to detect the current direction of the active power. Accordingly, the failure section detection apparatus 100 according to an embodiment of the present invention is based on the information on the current direction of the active power collected from the relay 30 and the signal of the current detected from the sensor unit 110 . , characterized in that the fault section is detected. To this end, as shown in FIG. 2 , the failure section detection apparatus 100 of the present invention determines a failure section based on information collected and sensed from the relay 30 and the sensor unit 110 when a failure occurs. It may be configured to include the processing unit 120 .

First, with reference to FIGS. 3A, 3B, 4A, and 4B , a principle of detecting a failure section through the failure section detecting apparatus 100 of the present invention will be first described. First, refer to FIG. 3A. Figure 3a shows an example of the composite line before the failure occurs. In addition, Fig. 3a assumes that the current direction of the active power flows from the A substation to the B substation. And, the sensor unit 110 is installed in the connection portion of the overhead line and the underground line. Now, it is assumed that a failure occurs in the machining section with reference to FIG. 3B .

As shown in FIG. 3B , when a failure occurs in the machining section, the current I _{post _ false} flows to the failure point regardless of the previous type direction. On the other hand, before the failure, the current direction is determined according to the current direction of the active power. Therefore, if the current direction before the failure, that is, the direction of the current vector is known, it is possible to determine whether the failure direction is the left or right side of the sensor unit by looking at the difference from the direction of the current vector after the failure. In the case of the example of FIG. 3B , since a failure occurred in the machining section, the current (I _{post _ false} ) flows in the direction of the failure point, that is, the machining section. That is, when a failure occurs, based on the sensor unit 110, if the current (I _{post _ falut} ) flows to the left, a failure occurs in the overhead line, and when the current (I _{post _ falut} ) flows to the right, a failure occurs in the underground line can confirm.

Let's look at another similar example. 4A shows an example of a composite line before a failure occurs. In addition, Fig. 4a assumes that the current direction of the active power flows from the substation B to the substation A. And, the sensor unit 110 is installed in the connection portion of the overhead line and the underground line. Now, it is assumed that a failure occurs in the underground section with reference to FIG. 4B .

In the case of the example shown in FIG. 4B , like the example of FIG. 3B , when a fault occurs, the current I _{post _ falut} flows in the direction of the fault point. That is, in the example of FIG. 4B , the current I _{post _ falut} flows from the left to the right as opposed to FIG. 3B . Specifically, in the examples shown in FIGS. 3B and 4B, depending on the fault location, the direction of the current vector is reversed after the fault, and the phase change of the current vector after the fault according to the direction of the current before the fault is about 180° difference can fly Accordingly, when the sensor unit 110 is installed at the junction of the underground line and the overhead line, _{it is possible to detect the failure direction only in the direction of the current (I post _ falut} ), so the sensor unit 110 is the underground line and the overhead line. It is preferable to be installed at the junction of Referring back to FIG. 2 .

The processing unit 120 calculates a phase value of the current sensed by the sensor unit 110 . Here, the processing unit 120 may apply a fast Fourier transform (FFT) window to the waveform of the current sensed by the sensor unit 110 to calculate the phase value of the current. Here, the reason for calculating the phase value of the current is to determine the vector direction of the current, as mentioned above. See FIG. 5 .

5 shows a vector diagram of a current sensed through a sensor unit connected to a connection portion of an overhead line and an underground line. Specifically, FIG. 5A is a vector diagram of a current before the occurrence of a failure, FIG. 5B is a vector diagram when the failure point is in the left direction of the sensor unit, and FIG. 5C is a vector diagram when the failure point is in the right direction of the sensor unit. As shown in FIG. 5A , since the resistance component dominates the load current before the failure, the phase difference with the _{power supply voltage VA, pre-fault is small.} On the other hand, in case of a line failure, since the fault current is supplied to the line impedance, when viewed from the power source, the inductive reactance of the load becomes the main component, and has a phase difference of about 90° compared to the power supply voltage. _{In addition, I Load} and I _Fault in FIGS. 5A to 5C may be expressed as Equations 1 and 2 below.

Again, refer to FIG. 2 .

As mentioned above, the processing unit 120 calculates a current phase value according to time, detects a zero-crossing period of the calculated current phase, and converts it into a frequency.

Thereafter, the processing unit 120 determines whether a failure has occurred. Here, the determination of whether a failure has occurred through the processing unit 120 may be made based on the current flow of active power. Here, when it is determined that a failure has occurred, the processing unit 120 calculates the difference between the phase values of the calculated current before and after the failure occurs, and based on the difference between the calculated phase values of the current and the current direction of the active power to determine the fault section. As described above, when a failure occurs, the current flows to the failure point, and the phase of the current changes.

Specifically, as shown in FIGS. 3A, 3B, 4A and 4B, when a fault occurs in the line, if the fault location is within the right side (underground line) of the sensor unit 110, the fault current is from substation A Since the inductive reactance is supplied to the line, _{the phase of the fault current (I fault_BC} ) is about 90˚ behind the phase of the load current (I _{pre-fault ) before the fault.} If the fault location is on the left side of the sensor unit 110 (the overhead line), the fault current is supplied from the B substation to the line having the most inductive reactance, so _{the phase of the fault current (I fault_AB} ) is in the opposite direction of the load current before the fault ( -I _pre-fault ) is about 90˚ behind the phase. Therefore, the present invention utilizes the characteristic of knowing whether the fault location is on the left or right side of the sensor unit in the line between substations if the current flow direction of the composite line before the fault and the phase change value of the conductor current before and after the fault are known.

Accordingly, the processing unit 120 of the present invention may detect a failure section based on the current phase value and the current phase value before the failure, and the current phase value before the failure. Accordingly, the present invention requires less cost because only one CT needs to be installed compared to the conventional current differential method for comparing the magnitude (phase) of both ends of the section, and the fault point identification error is accurate compared to the distance relay method. It has the advantage of being able to detect a section.

In addition, the processing unit 120 of the present invention may further determine whether the fault section determined above is an underground line, that is, an underground section. As mentioned above, in a complex line including an overhead line and an underground line, when a failure occurs, most of the cases are temporary failures in the overhead line, but this is not the case in the underground line. Accordingly, when a failure occurs in the underground line, the processing unit 120 of the present invention may further generate a block signal for the automatic reclosing in order to prevent the automatic reclosing. Accordingly, the present invention can further have the effect of helping to perform an appropriate response according to the location of the failure.

6 is a block diagram of the processing unit 120 according to an embodiment of the present invention. As described above, the processing unit 120 according to an embodiment of the present invention determines whether or not there is a fault in the composite line based on the information on the current direction of the active power and the phase value of the current flowing in the composite line, and the failure Interval detection can be performed. To this end, the processing unit 120 according to an embodiment of the present invention includes a current direction detection module 121 , a current phase value calculation module 122 , a failure section determination module 123 , and a block signal generation module 124 . can be configured. Here, each component included in the processing unit 120 is divided to explain the functions performed by the processing unit 120 , and it is not actually necessary to be divided into the above components. In addition, in the following description, items overlapping with those described above will be omitted.

The current direction detection module 121 functions to detect the current direction of the complex line. As described above, the failure section detection method through the failure section detection apparatus 100 of the present invention is made based on the current direction and the amount of phase change of the current. Accordingly, the current direction detection module 121 detects the current direction of the active power based on the signal detected through the relay 30 .

The current phase value calculation module 122 functions to calculate the phase value of the current sensed through the sensor unit 110 . As described above, the sensor unit 110 may be installed in the connection portion of the overhead line and the underground line. In addition, the current phase value calculation module 122 may apply a fast Fourier transform (FFT) window to the waveform of the current sensed through the sensor unit 110 to calculate the phase value of the current. In addition, the current phase value calculation module 122 may calculate a current phase value according to time, detect a zero-crossing period of the calculated current phase, and convert it into a frequency.

The failure section determination module 123 determines whether a failure occurs based on the current direction of the active power detected through the above-mentioned current direction detection module 121 . In addition, when it is determined that a failure has occurred, the failure section determination module 123 determines the failure section based on the current flow direction of the active power and the phase value change of the current calculated through the current phase value calculation module 122 . do. Here, since the method for determining the failure section has been described in detail above, an additional description thereof will be omitted.

In addition, the failure section determination module 123 additionally determines whether the failure section is an underground section.

The block signal generating module 124 may further generate a block signal for the automatic reclosing in order to prevent automatic reclosing when it is determined that a failure has occurred in the underground section as a result of determination through the failure section determination module 123. can This is because, as described above, in complex lines, when a failure occurs, most of the cases are temporary failures in overhead lines, but this is not the case in underground lines. Accordingly, an automatic opening/closing path is formed when a failure occurs in an overhead line, and by preventing the automatic opening/closing path from being formed when a failure occurs in an underground line, more accurate failure recovery can also be performed.

Now, with reference to FIGS. 7A, 7B, 8A, 8B, 9A, and 9B, a description will be made for verification of an apparatus and method for detecting a failure section according to an embodiment of the present invention.

7a and 7b are composed of EMTP (Electro-Magnetic Transient Program), and when a ground fault occurs in each of the machining section (AB) and the underground section (BC), the detection current of the CT installed in the machining-underground boundary point cable is calculated. one result is shown.

Also, FIGS. 8A and 8B are the same as FIGS. 7A and 7B, but show a case in which only the power supply terminal and the reception terminal are changed. In the drawing, the direction of the phase change of the sensor installed at point B is reversed in case of a failure in section AB (F1 failure) and failure in section BC (F2 failure). As described with reference to FIG. 5 , it was confirmed as a result of EMTP calculation that the direction of the phase shift of the detected current after the failure was reversed according to the direction of the failure.

7A and 8A are the same fault conditions except that the current direction of the active power before the failure is different from the power end and the receiving end, that is, the sensor installed at the point B after the failure according to the direction of the current as shown in FIGS. 7B and 8B The direction of the phase change of the current detected in the negative is reversed. Therefore, if the direction of active power flow before the fault is known in advance, and the phase change of the current detected before and after the fault in the CT installed at point B when the line fault occurs, the location where the line fault occurred is either the AB section or the BC section. You can tell if it is within the range. In other words, if the CT is installed in the underground cable section where the Rogowski coil can be easily installed at the boundary junction of the overhead-underground mixed line, when a mixed line failure occurs, it is possible to identify whether the fault is in the overhead section or the underground section. In this way, if the failure section identification information is used as an automatic reclosing block signal in case of a breakdown in the underground section. It is possible to prevent automatic reclosing for permanent failure of the underground section of the mixed line and the resulting system shock and secondary failure.

9A and 9B are using the EMTP calculation model of FIGS. 7A, 7B, 8A and 8B, the detection current of the B-point sensor unit according to the failure of the underground/processing section, the magnitude of the current output through the sliding FFT window, and The following shows the case of detecting a fault signal in the underground section from the frequency (f=1/T) converted from the phase and zero crossing period (T) of the phase and the phase variation (=frequency variation) characteristics according to the location of the fault. 9a and 9b are each assuming the failure of the underground section and the processing section, and in the 3rd picture of FIG. 9a, the phase changes abruptly (the frequency increases rapidly in the 4th picture), and the 5th picture indicates the failure of the underground section can be seen to occur. On the other hand, in FIG. 9B , it can be seen that the time difference between zero points (=1/frequency) is not large due to the characteristic that the phase fluctuation is slightly stretched, so that no abrupt fluctuation is seen in the fifth figure.

10 is a flowchart of a method for detecting a failure section according to an embodiment of the present invention. Hereinafter, a method for detecting a failure section according to an embodiment of the present invention will be described with reference to FIG. 10 . Items overlapping with the above-mentioned parts will be omitted and description will be made.

First, the step (S110) of detecting the current direction of the active power through the relay is made, and the step (S120) of detecting the current flowing in the composite line through the sensor unit installed in the connection part of the overhead line and the underground line is performed. . As mentioned above, the sensor unit of the present invention is installed at the connection part of the overhead line and the underground line, and through the steps mentioned below, it is possible to detect a fault location on the left or right side based on the sensor unit. In addition, the sensor unit may be composed of at least one of a Rogowski coil CT and an optical CT.

After that, a step (S130) of calculating the phase value of the current sensed through the sensor unit by the processing unit is performed. As mentioned above, in step S130, the phase value of the current according to time may be calculated by applying a fast Fourier transform (FFT) window to the current waveform obtained through the sensor unit. In addition, in step S130, a process of detecting a zero-crossing period of the calculated current phase and converting it into a frequency may be further performed.

Thereafter, a step (S140) of determining whether a failure has occurred is performed by the processing unit. Specifically, step S140 may be made based on the current direction of the active power detected in step S110. If it is determined that a failure has occurred in step S140, control is transferred to step S110. Otherwise, control passes to step S150.

Step S150 is a step of determining a failure section. Specifically, step S150 calculates the difference between the phase values of the calculated current before and after the occurrence of the failure, and determines the failure section based on the difference between the calculated phase values of the current and the direction of the current of the active power. Here, since the method of determining the failure section through step S150 has been described in detail above, an additional description thereof will be omitted.

Thereafter, by the processing unit, the step (S160) of determining whether the fault location is an underground section is performed. As described above, in a complex line including an overhead line and an underground line, when a failure occurs, most of the cases are temporary failures in the overhead line, but this is not the case in the underground line. Through the determination process through step S160, it is determined which section the failure location is in, and a process of assisting failure recovery may be performed according to the determination result. As a result of the determination in step S160, if it is determined that an underground section failure has occurred, control is transferred to step S170, and in order to prevent automatic reclosing, a process of further generating a block signal for automatic reclosing is performed. Otherwise, control passes to the end block, causing automatic reclosing to be performed.

As described above, the best embodiment has been disclosed in the drawings and the specification. Although specific terms have been used herein, they are only used for the purpose of describing the present invention and are not used to limit the meaning or the scope of the present invention described in the claims. Therefore, it will be understood by those skilled in the art that various modifications and equivalent other embodiments are possible therefrom. Accordingly, the true technical protection scope of the present invention should be defined by the technical spirit of the appended claims.

100: fault section detection device 110: sensor unit
120: processing unit

Claims (8)

A device for detecting a faulty section when a fault occurs in a complex line including an overhead line and an underground line,
a relay for detecting the current direction of active power;
a sensor unit installed in the connection part of the overhead line and the underground line and sensing a current flowing in the complex line; and
Calculating the phase value of the current sensed through the sensor unit, and calculating the difference between the phase values of the current calculated before and after the fault occurs when a fault occurs,
A processing unit for determining a failure section based on the difference between the calculated current phase values and the current direction of the active power,
The processing unit calculates the phase value of the current over time by applying a fast Fourier transform (FFT) window to the current waveform obtained through the sensor unit,
When the overhead line is located on the left side of the sensor unit, and the underground line is located on the right side of the sensor unit,
If the fault location is the underground line on the right side of the sensor unit, the phase of the fault current is 90˚ behind the phase _{of the load current (I pre-fault ) before the fault,}
If the fault location is the overhead line on the left side of the sensor unit, the phase of the fault current is 90° behind the phase _{of the current in the opposite direction of the load current (-I pre-fault ) before the fault, the fault location} It is characterized in that it can be known whether is the left side or the right side of the sensor unit,
Failure section detection device. According to claim 1,
The processing unit,
When it is determined that a failure has occurred in the underground line, the failure section detection apparatus, characterized in that for generating a block signal for preventing reclosing of the underground line. According to claim 1,
The sensor unit,
Rogowski coil CT (Current Transformer) and characterized in that consisting of at least one of the optical CT, the failure section detection device. delete A method of detecting a faulty section when a fault occurs in a complex line including an overhead line and an underground line,
Detecting the current direction of the active power through the relay;
detecting a current flowing in the complex line through a sensor unit installed in a connection part of the overhead line and the underground line;
calculating a phase value of the current sensed through the sensor unit by the processing unit;
calculating, by the processing unit, a difference between phase values of currents calculated before and after the occurrence of a fault when a fault occurs; and
Comprising the step of determining, by the processing unit, a failure section based on the difference between the calculated current phase values and the current direction of the active power,
Calculating the phase value of the current comprises:
By applying a fast Fourier transform (FFT) window to the current waveform obtained through the sensor unit, the phase value of the current over time is calculated,
When the overhead line is located on the left side of the sensor unit, and the underground line is located on the right side of the sensor unit,
If the fault location is the underground line on the right side of the sensor unit, the phase of the fault current is 90˚ behind the phase _{of the load current (I pre-fault ) before the fault,}
If the fault location is the overhead line on the left side of the sensor unit, the phase of the fault current is 90° behind the phase _{of the current in the opposite direction of the load current (-I pre-fault ) before the fault, the fault location} It is characterized in that it can be known whether is the left side or the right side of the sensor unit,
How to detect a faulty section. 6. The method of claim 5,
When it is determined by the processing unit that a failure has occurred in the underground line, the method further comprising the step of generating a block signal for preventing reclosing of the underground line. 6. The method of claim 5,
The sensor unit,
Characterized in that it consists of at least one of Rogowski coil CT and optical CT, a fault section detection method.

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