JPH1054863A - Method and apparatus for location of fault point - Google Patents

Abstract

PROBLEM TO BE SOLVED: To locate a fault point with a low-cost configuration, without being affected by a branch line or the like and with high accuracy in a fault detector which is used to locate the fault point in which the lightning, the ground fault or the like of a transmission line is generated. SOLUTION: From a transmitting apparatus A0 at an electric station A as a master station, optical pulses are radiated to an optical transmission line 13, laid in parallel with a transmission line 11, by a trigger circuit A7 and by an optical pulse generation circuit A8 when a surge voltage due to a fault is detected by an optical voltage sensor A5 and by a photoelectric conversion circuit A6. In response to the optical pulses, the surge voltage is detected by optical voltage sensors 85, C5 and by photoelectric conversion circuits B6, C6 in receiving apparatuses B0, C0 at electric stations B, C as slave stations, the optical pulses are detected by optical pulse receiving circuits B7, C7, the arrival time difference between both is measured by measuring circuits B8, C8, and the position of a fault point P is found by locating circuits B9, C9 on the basis of its measured result.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a transmission line,
The present invention relates to a fault point locating device called a fault locator for locating a fault point where a ground fault or a lightning strike has occurred, and a locating method thereof.

[0002]

2. Description of the Related Art In order to locate a fault point, a distance relay, which has been widely used, locates a fault point in one cycle based on a relationship between a voltage and a current, and activates a breaker in the next cycle. It is configured to trip. Therefore, for example, with a high-speed relay for 500 (kV), it takes 1.5 (cycles), that is, about 30 (msec) at 50 Hz, to locate a fault point and trip the circuit breaker.

Therefore, since it takes a long time, as a typical conventional example, for example, Japanese Patent Application No.
A fault locator such as that disclosed in Japanese Patent No. 3-259649 has been proposed.

In this prior art, a location is devised so as to perform high-speed orientation by utilizing a difference in propagation speed between a line wave and a ground wave due to a failure. However, this conventional technique has a problem that it is difficult to separate an interline wave and a ground wave. For this reason, a fault locator called a C type as shown in FIG. 7 has been proposed as another conventional technique.

FIG. 7 is a view for explaining the principle of fault locating of the C-type fault locator. The fault locator 1 is connected to a transmission line 3 via a capacity transformer 2 at an electric station a serving as a master station. The transmission line 3 connects between the electric station a and an electric station b serving as a slave station.
The electric stations a and b are substations and switchyards.

FIG. 8 is a voltage waveform diagram at the substation a side of the transmission line 3 for explaining the fault locating operation by the fault locator 1. As shown in FIG. When fault locator 1 detects a surge voltage due to a fault such as a lightning strike or a short circuit, time t
As shown by 0, a high-frequency impulse is transmitted to the transmission line 3. The high-frequency impulse propagates through the transmission line 3 and can observe reflected waves from a suspension point shown at times t1 and t2, a fault point p shown at time t3, and an electric station b at the end shown at time t4.

The time required for the reflected wave to arrive at the fixed reflection at the suspension point and at the end is known in advance, and therefore, the arrival time t3 of the reflected wave due to the fault point p from the transmission time t0 of the high-frequency impulse. 1 of the time to
/ 2 and the speed of the high-frequency impulse substantially equal to the speed of light of 3 × 10 ⁸ (m / s), the fault point p
Can be obtained from the substation a. In this manner, the fault locator 1 locates the fault point p on the transmission line 3.

[0008]

In the fault locator 1 as described above, it is necessary to transmit a high-frequency impulse to the transmission line 3, and it is difficult to electrically insulate the fault locator 1 from the transmission line 3. . Therefore, there is a problem that the fault locator 1 may be damaged by the surge voltage, and a power element or the like is required, which increases the cost.

Further, there is a problem that the location accuracy of the fault point is inferior for the following reasons. The high-frequency impulse needs to reach the fault point p before the fault is resolved, and it is necessary to output the high-frequency impulse immediately upon detecting the surge voltage, and a high response speed is required. The reflected wave is buried in the surge voltage,
In some cases, a reflected wave from the fault point p cannot be detected. Further, in order to remove the influence of noise or the like, a filtering process as shown by a broken line in FIG. 8 is required. In the case where the branch line is formed in the transmission line 3 as indicated by reference numeral 4 in FIG. 7, if the fault point p is located farther than the branch point r from the electric station a side, the branch line 4 It is not possible to determine on which path of the electric station c or the electric station b of the transmission line 3 the failure has occurred. In particular, in the case of lightning, if the fault is recovered until the high-frequency impulse reaches the fault point, for example, within several hundred μsec, the fault point cannot be detected.

It is an object of the present invention to provide a method and an apparatus for locating a fault point at low cost and with high accuracy.

[0011]

According to a first aspect of the present invention, there is provided a fault point locating method for locating a fault point in a transmission line connecting between electric substations. When detecting a surge current or voltage generated due to a failure in the electric wire, it emits an optical pulse to an optical transmission line laid in parallel with the power transmission line, and at the other electric station side,
Measuring the arrival time difference between the surge current or voltage and the light pulse, and using at least one of the electrical stations, the failure using the arrival time difference, the propagation speed of the surge current or voltage, and the propagation speed of the light pulse. It is characterized by locating points.

According to the above configuration, the master station is laid in parallel with a transmission line between electric stations such as a substation and a switchyard, and uses an optical transmission line used for communication between the electric stations. One of the substations emits an optical pulse in response to a surge current or a voltage, and one or more other substations serving as slave stations has an arrival time difference between the surge current or the voltage and the optical pulse, respectively. Is measured, and using this arrival time difference,
Since the propagation speed of the surge current or the voltage and the light pulse are substantially equal, the time from the detection of the surge current or the voltage, which is a known value, to the emission of the light pulse is subtracted from the arrival time difference. By dividing by 2, and further dividing by 2, the distance to the fault point can be obtained.

A branch path is formed by providing a plurality of the other electric stations, and when a branch path to each of the other electric stations has a failure, the branch path having a fault point is provided. Only at the substation side, the calculation result is the distance from one substation to the fault point, and the calculation result at the substation side of the remaining branch is the distance from the one substation to the base point of the branch. Becomes

Therefore, the fault point can be located with high accuracy only by using a low-cost configuration such as an optical pulse receiving / emitting circuit in the existing optical transmission line.

According to a second aspect of the present invention, there is provided a fault point locating apparatus for locating a fault point in a transmission line connecting between electric substations, wherein the optical transmission line is laid in parallel with the transmission line. And a first detecting means provided on one electric station side for detecting a surge current or a voltage generated due to a failure in the transmission line, and provided on one electric station side,
An optical pulse generating means for emitting an optical pulse to the optical transmission line in response to an output from the first detecting means; and a second detecting means provided on the other electric station side for detecting the surge current or voltage. A light pulse receiving means provided on the other electric station side for receiving the light pulse; and a light pulse receiving means provided on the other electric station side and responsive to an output from the second detecting means and the light pulse receiving means. Measuring means for measuring a difference in arrival time between the surge current or the voltage and the optical pulse; and at least one of the electrical stations, the measurement result of the measuring means, the propagation speed of the surge current or the voltage, Locating means for locating a fault point using the pulse propagation speed.

[0016] According to the above arrangement, when the electric current station serving as the master station detects the surge current or the voltage by the first detecting means, using the existing optical transmission line laid in parallel with the transmission line. And emitting an optical pulse from the optical pulse generating means to the optical transmission line. On the other hand, on the other electrical substation side serving as a slave station, the time from the time when the surge current or the voltage is detected by the second detecting means to the time when the optical pulse receiving means receives the optical pulse via the optical transmission line. Is measured by the measuring means, and in the orientation means, the response from the detection of the surge current or the voltage by the first detecting means to the generation of the light pulse by the light pulse generating means in response to the measurement result of the measuring means. After subtracting the delay time, the distance to the fault point can be obtained by dividing by the substantially same surge current, voltage and propagation speed of the light pulse and further dividing by 2.

Therefore, the fault point can be located with high accuracy simply by adding a low-cost configuration such as an optical pulse light receiving / emitting circuit using the existing optical transmission line.

[0018]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described.
The following is a description based on FIGS. 1 to 5.

FIG. 1 is a block diagram showing an electrical configuration of a fault locator which is a fault locating device according to an embodiment of the present invention. This fault locator is generally provided in a transmitting device A0 provided in an electric station A such as a power station or a substation serving as a master station, and in electric stations B and C such as a substation or a switching station serving as a slave station. It is provided with receiving devices B0 and C0 provided respectively. A bus A1 in the electric station A is connected to the transmission line 11 via a blocking coil A2. A bus B1 in the electric substation B is connected to the transmission line 11, and a bus C1 in the electric substation C is connected to a branch path 12 branched from the transmission line 11 at a branch point R.
An optical transmission line 13 is installed in advance between the electric stations A and B in parallel with the transmission line 11 for remote control and communication, and an optical transmission line 14 is also installed in the branch line 12 in parallel. Have been.

The transmitting device A0 connects the voltage dividing capacity A4 to the stray capacitance A3 of the conductor of the power transmission line 11, and takes in the divided voltage of the power transmission line 11 generated between the terminals of the voltage dividing capacity A4. The voltage between the terminals of the voltage dividing capacitor A4 is input to the optical voltage sensor A5. The optical voltage sensor A5 is realized by a photoelectric element such as a Pockels element, and the phase changes in accordance with the voltage between the terminals of the voltage dividing capacitor A4, and this changes the light amount. Therefore, the change in the amount of light returned by the optical voltage sensor A5 disposed on the optical axis between the light emitting and receiving elements is extracted as a voltage change by the photoelectric conversion circuit A6 implemented by a pair of light emitting and receiving elements.

The output from the photoelectric conversion circuit A6 is input to a trigger circuit A7. When the output from the photoelectric conversion circuit A6 exceeds a predetermined threshold value, the trigger output to the optical pulse generation circuit A8 is generated. Is derived. The optical pulse generation circuit A8 emits an optical pulse to the optical transmission line 13 in response to the trigger output. Therefore, when a surge voltage higher than a predetermined voltage level is detected on the transmission line 11 from the transmission device A0, an optical pulse is emitted to the optical transmission line 13.

In the receiving device B0, the transmitting device A0
Similarly to the above, the floating capacitor B3 is provided with the voltage dividing capacitor B4, and the change in the voltage between the terminals is converted into the change in the voltage level by the optical voltage sensor B5 and the photoelectric conversion circuit B6 to detect the surge voltage. The receiving device B0 has an optical transmission line 1
There is provided an optical pulse receiving circuit B7 for receiving an optical pulse via the optical pulse receiving circuit 3. The output from the optical pulse receiving circuit B7 and the output from the photoelectric conversion circuit B6 are input to a measurement circuit B8, and the measurement circuit B8
An arrival time difference from the arrival time of the surge voltage to the arrival time of the light pulse is measured. The output from the measurement circuit B8 is input to the orientation circuit B9, and as described later, it is determined whether or not the fault point P exists on the transmission line 11 and, if so, the distance to the fault point P. Can be.

In the receiving device C0, similarly to the receiving device B0, the voltage dividing capacitor C4 is connected to the stray capacitance C3, and the change in the voltage between the terminals is detected by the optical voltage sensor C5 and the photoelectric conversion circuit C4.
6, and the arrival time difference from the optical pulse received by the optical pulse receiving circuit C7 via the optical transmission line 14 is measured by the measuring circuit C8. Whether or not the point P exists on the branch road 12 and, if so, the distance to the failure point P are determined.

The measuring circuits B8 and C8 can be realized by, for example, a digital memory or the like, and store the arrival time of the surge voltage and the arrival time of the light pulse, respectively. Correspondingly, the locating circuits B9 and C9 are realized by a microprocessor or the like, calculate the arrival time difference from the time stored in the measuring circuits B8 and C8, and calculate the arrival time difference, the surge voltage and the propagation speed of the light pulse. From this, it is determined whether or not the fault point P is located on the local station side from the branch point R, and if it is on the local station side, the distance to the fault point P is located,
The orientation result is displayed on a printer or a screen. Note that the orientation result may be transmitted to the substation A via the optical transmission lines 13 and 14.

FIG. 2 is a waveform chart for explaining the fault locating principle of the fault locator configured as described above. However, the fault point P exists between the substation A and the branch point R, and for simplification of the description, a response delay time from when the transmitting device A0 detects the surge voltage to when the light pulse is generated. Is set to 0. Furthermore, each substation A, B,
The distance from C to the branch point R is xa, xb, xc, respectively.
And the distance from the electric station A to the failure point P is xp.

In FIG. 2, A, B, and C denote electrical stations A, B, and C, respectively.
, And α1, α2, α3 are electrical stations A, B, C
Represents the surge voltage waveform detected by. The time when the failure occurs is represented by t0, and as shown by times ta, tb, and tc, the time required for the line wave of the surge voltage to reach each of the electric stations A, B, and C depends on the speed of the surge voltage. If vp is used, it can be expressed by Expressions 1 to 3.

Ta = xp / vp (1) tb = {(xa-xp) + xb} / vp (2) tc = {(xa-xp) + xc} / vp (3) After detecting the surge voltage indicated by the reference symbol α1, the light pulse indicated by the reference symbol β1 is output at the time ta.
And substations B and C are referred to by reference numerals β2 and β3, respectively.
The time up to times tpb and tpc at which the optical pulse is received can be expressed by Equations 4 and 5, respectively, where the speed of the optical pulse is vc.

Tpb = (xp / vp) + (xa + xb) / vc (4) tpc = (xp / vp) + (xa + xc) / vc (5) Accordingly, the arrival time difference tΔ between the surge voltage and the light pulse.
b and tΔc can be obtained from Expressions 2 to 5 as shown in Expressions 6 and 7.

TΔb = tpb−tb = (xp / vp) + (xa + xb) / vc − {(xa−xp) + xb} / vp (6) tΔc = tpc−tc = (xp / vp) + (xa + xc) / Vc-{(xa-xp) + xc} / vp (7) Assuming that vp ≒ vc, the above equations 6 and 7 can be expressed by equations 8 and 9, respectively.

TΔb = 2 (xp / vp) (8) tΔc = 2 (xp / vp) (9) Therefore, xp = vp · tΔb / 2 = vp · tΔc / 2 (10) The difference in arrival time tΔb, tΔc is vp / 2
By multiplying by the distance xp.

Similarly, the measurement results of the distance to the fault point P on the substations B and C including the case where the fault point P exists on the transmission line from the branch point R to each of the substations B and C xpb,
Table 1 shows the relationship between xpc and the position of the fault point P.

[0032]

[Table 1]

FIGS. 3 and 4 are diagrams for explaining the principle of locating a fault on the branch path of the fault locator configured as described above. In these figures, there is another one.
A substation D serving as a slave station is added, a branch point from the transmission line 11 to the substation D is indicated by reference numeral Q, and a branch road is indicated by reference numeral 1.
Indicated at 5. In FIGS. 3 and 4, the path from the occurrence of the failure to the arrival of the light pulse at each of the electric stations B, C, and D is indicated by a broken line, and the path of the surge voltage is indicated by a two-dot chain line. ing.

The example of FIG. 3 shows a case where the fault point P exists on the branch 12 to the electric substation C. In this case, when the arrival path of the surge voltage is subtracted from the arrival path of the optical pulse from the fault point P to the electric stations B, C, and D, the equations 11 to 11 are respectively obtained.
It can be expressed by Equation 13.

(PA + AB) −PB = {(PR + AR) + (AR + RB)} − (PR + RB) = 2AR (11) (PA + AC) −PC = {PA + (PA + PC)} − PC = 2PA (12) (PA + AD) ) -PD = {(PR + AR) + (AR + RD)}-(PR + RD) = 2AR (13) Therefore, in the substation C on the route where the failure has occurred, the reach distance difference between the substation A and the substation A is as follows. While the distance PA is twice the distance PA from the failure point P, the difference between the remaining distances at the electric stations B and D on the remaining routes where no failure has occurred is due to the occurrence of the failure from the electric station A. The value is twice as long as the distance AR to the branch point R of the route. The distance AR is known, so that it is possible to determine on the electric stations B and D sides that a failure has occurred on the route of another station, and on the electric station C side that the own station has a failure. The distance PA from the electric power station A to the failure point P can be determined.

The example of FIG. 4 shows a case where a failure has occurred in the branch 15 to the electric substation D. In this case,
The reaching distance difference between the surge voltage and the light pulse measured at each of the electric stations B, C, and D is expressed by Expressions 14 to 16, respectively.

(PA + AB) -PB = {(PQ + AQ) + (AQ + QB)}-(PQ + QB) = 2AQ (14) (PA + AC) -PC = {(PQ + QR + AR) + (AR + RC)}-(PQ + QR + RC) = 2AR ... (15) (PA + AD) −PD = {PA + (PA + PD)} − PD = 2PA (16) Therefore, when viewed from the substation A side of the master station, the substation having the fault point P is the substation A. Distance P from the fault to the fault point P
Position A and the other substation's electrical stations indicate the distance from the master station to the known branch point to that electrical station. Thus, the branch paths 12 and 15 are formed, and the fault points P
, The orientation can be performed with high accuracy.

FIG. 5 is a flowchart for explaining the operation of the receiving devices B0 and C0. The example of FIG. 5 shows an example of the receiving device B0, and the operation of the receiving device C0 is the same. In step n1, the arrival time tb of the surge voltage is stored. In step n2, the arrival time tpb of the light pulse.
Is stored. In step n3, the arrival time difference tΔb is obtained from the equation (6). In step n4, the distance xpb between the electric substation B and the fault point P is obtained from the equation (10).

In step n5, it is determined whether or not the distance xpb is less than the distance xb. If so, the display output is performed in step n6.
In step n7, transmission to the substation A is performed. On the other hand, if the distance is equal to or longer than the distance xb in step n5, it is determined in step n8 that the transmission line on the other station is out of order, and the operation ends.

On the other hand, the measurement results from the electric stations B and C, which are the slave stations, are transmitted to the electric station A which is the master station.
When the orientation is performed on the side, the orientation operation is as shown in FIG. First, at step n11, each substation B,
The measurement results xpb and xpc at C are received. At step n12, it is determined whether or not the measurement results xpb and xpc are equal to each other. If so, it is determined that the fault point P is located closer to the electric station A than the branch point R, and the process proceeds to step n13. Transfer, distance xp between fault point P and substation A
Is substituted for the distance xpb or xpc.

On the other hand, in step n12, x
When pb = xpc is not satisfied, the process proceeds to step n14, where x
It is determined whether or not pc = xa. If so, it is determined that the fault point P exists between the electric substation B and the branch point R, and the process proceeds to step n15, where the distance xpb is changed to the distance xp.
Is assigned to Furthermore, when xpc = xa is not satisfied in step n14, the process proceeds to step n16.
It is determined whether or not xpb = xa, and if so, it is determined that the fault point P exists on the electric substation C side, and in step n17, the distance xp is added to the distance xp.
Is substituted, otherwise, in step n18, it is determined that the fault point P cannot be located. Steps n13, n15, n17 and n18 are followed by step n1.
Then, the display of the orientation result is performed.

As described above, in the fault locator according to the present invention, when the surge voltage is detected on the side of the electric station A, which is the master station, the light is transmitted to the optical transmission lines 13 and 14 juxtaposed with the transmission line 11 and the branch line 12. A pulse is output, and in each of the substations B and C, the fault point P is located based on the arrival time difference between the surge voltage and the light pulse. What is necessary is just to detect the first wave of the voltage,
With a simple configuration, high-accuracy orientation can be performed without being affected by components following the first wave or noise. Further, even if the branch paths 12 and 15 are formed, the orientation can be performed without any problem. Furthermore, since the optical pulse is used, the influence of the attenuation is small. Therefore, it is not necessary to use a large-capacity element for the power element of the optical pulse generating circuit A8, so that the cost can be reduced and the electric power station can be reduced. The path of the pulse from A to the electric stations B and C and the path of the surge voltage can be completely insulated, and damage to the pulse transmitting / receiving device due to the surge voltage can be prevented.

Although the orientation error depends on the characteristics of the circuits of the transmitting device A0 and the receiving devices B0 and C0, such characteristics can be corrected by performing a test once. Further, the speed vc of the optical pulse is theoretically 300 (m / μs), the speed vp of the surge voltage is 298 (m / μs) from the past test, and vp ≒ vc
Assuming that AD = 50 km and AP = 45 km in FIG. 4, for example, the orientation error is 45− (45/298 + 50 / 300−5 / 298) ×
298/2 = 0.166 (km). Therefore, by using vp = 299 (m / μs), the orientation error can be suppressed to about ± 100 m or less. Furthermore, a correction according to the distance, for example, AP = 50 km and +160 m may be performed.

The surge detection is not limited to the photovoltage sensor using the Pockels effect as described above, but a photocurrent sensor using the Faraday effect may be used.

[0045]

As described above, the fault locating method according to the first aspect of the present invention lays in parallel with a power transmission line in response to a surge current or a voltage on one of the electric stations, which is a master station. An optical pulse is emitted to the optical transmission line that is being sent, and at one or more other electrical stations that will be slave stations, the arrival time difference between the surge current or voltage and the optical pulse is measured, and this arrival time difference is used. Find the distance to the point of failure.

Therefore, the fault point can be located with high accuracy only by adding a low-cost configuration such as a light pulse receiving / emitting circuit using the existing optical transmission line.

Further, the fault locating device according to the second aspect of the present invention uses the existing optical transmission line laid in parallel with the power transmission line, as described above, on the side of the electric station serving as the master station. First
When a surge current or voltage is detected by the detecting means, an optical pulse is emitted from the optical pulse generating means to the optical transmission line, and on the other electric station side serving as a slave station, the surge current or the voltage is detected by the second detecting means. The time from when the light pulse is detected by the light pulse receiving means to the time when the light pulse is received by the light pulse receiving means is measured by the measuring means, and the distance to the failure point is obtained by the locating means using the measurement result.

Therefore, the fault point can be located with high accuracy only by adding a low-cost configuration such as a light pulse receiving / emitting circuit using the existing optical transmission line.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an electrical configuration of a fault locator according to an embodiment of the present invention.

FIG. 2 is a waveform chart for explaining a principle of fault locating in the fault locator.

FIG. 3 is a diagram showing a path of a surge voltage and an optical pulse for explaining a principle of locating a fault in a branch road.

FIG. 4 is a diagram illustrating a path of a surge voltage and an optical pulse for explaining a principle of locating a fault in a branch path.

FIG. 5 is a flowchart for explaining a fault point locating operation in a receiving device on the side of an electric station as a slave station.

FIG. 6 is a flowchart in a case where the fault point locating operation is performed at an electric station side of a master station.

FIG. 7 is a diagram for explaining the principle of fault locating of a conventional C-type fault locator.

FIG. 8 is a waveform diagram for explaining a fault point locating operation of the fault locator shown in FIG. 7;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 11 Transmission line 12 Branch line 13 Optical transmission line 14 Optical transmission line 15 Branch line A Electric station A0 Transmitting device A1 Bus A5 Optical voltage sensor (first detection means) A6 Photoelectric conversion circuit (first detection means) A7 Trigger circuit (Light pulse generation means) A8 Light pulse generation circuit (light pulse generation means) B Electric station B0 Receiver B5 Light voltage sensor (second detection means) B6 Photoelectric conversion circuit (second detection means) B7 Light pulse reception circuit (Light pulse receiving means) B8 Measurement circuit (Measurement means) B9 Orientation circuit (Orientation means) C Electric station C0 Receiver C5 Optical voltage sensor (Second detection means) C6 Photoelectric conversion circuit (Second detection means) C7 Light Pulse receiving circuit (optical pulse receiving means) C8 Measurement circuit (measuring means) C9 Location circuit (location means)

Claims (2)

[Claims] 1. A method for locating a failure point in a transmission line connecting between electric stations, comprising: detecting a surge current or a voltage caused by a failure in the transmission line; A light pulse is emitted to an optical transmission line laid in parallel with the above, at the other electric station side, the arrival time difference between the surge current or voltage and the light pulse is measured, and at least one of the electric stations side, A method of locating a fault using the arrival time difference, the propagation speed of a surge current or a voltage, and the propagation speed of an optical pulse. 2. An apparatus for locating a fault point in a transmission line connecting between electric stations, comprising: an optical transmission line laid in parallel with the transmission line; A first detecting means for detecting a surge current or a voltage generated by a failure in the electric wire; provided on one of the substations side; in response to an output from the first detecting means, an optical pulse is transmitted to the optical transmission line. Light pulse generating means for emitting light; second detecting means for detecting the surge current or voltage provided on the other electric station side; and optical pulse receiving means for receiving the light pulse provided on the other electric station side. Means for measuring the arrival time difference between the surge current or voltage and the light pulse in response to the outputs from the second detecting means and the light pulse receiving means, the measuring means being provided on the other electric station side; Together Provided at one of the electrical stations, the measurement result of the measuring means, the propagation speed of the surge current or voltage,
And a locating means for locating the failure point using the propagation speed of the light pulse.