JP3316431B2 - Fault detector for transmission and distribution lines - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fault point detecting device for detecting a fault point of a transmission / distribution line installed on a support such as a tower or a power distribution pole, and more particularly to a fault point of a ground fault or a short circuit accident. The present invention relates to a fault detection device for transmission and distribution lines.

[0002]

2. Description of the Related Art Conventionally, this type of device is provided with explosives and, for example, a red cloth inside, and when a fault current is detected, explosives are exploded to remove a part of the exterior, and the cloth is removed therefrom. There was a flashing indicator that hanged down to indicate the point of failure. Further, as a device for detecting a section of a ground fault, there is one described in JP-A-1-123169.
An electromagnetic coil detects a fault current generated in the event of a ground fault of a power cable laid in a tunnel (tunnel), and when the fault current exceeds a predetermined value, operates an arithmetic unit for a predetermined time, The output signal was output only when the output value of the microhorn during that time was equal to or higher than the background noise.

[0003]

However, since the fault current flows to the surrounding steel tower via the overhead ground wire, the explosion may occur even with a plurality of flashing indicators installed on the steel tower. Failure point determination becomes complicated,
Since the flash indicator is disposable, there is a problem that the installation cost is increased.

The conventional example described in Japanese Patent Application Laid-Open No. 1-123169 is based on the assumption that sound propagates in a tunnel of an underground line. Various dark noises such as wind noise, lightning strike noise, rain noise, and corona noise generated by the surface discharge of the electric wire and the insulator are generated. Also, there is no direct lightning strike in the cave,
Lightning can hit the transmission and distribution lines installed on the ground directly. For this reason, even if the above-described conventional example is applied to the detection of a fault point in a transmission and distribution line, there are the following problems.

That is, on the ground, dark noise such as wind noise, rain noise and corona noise is generated even when an electrical failure does not occur. Other than the above, the detection device malfunctions. Lightning can not occur in the tunnel, but there are lightning strikes in the transmission and distribution line facilities and their surroundings.In this case, if the potential fluctuations due to the lightning strike are small, an electrical fault such as a ground fault or short circuit may not occur. is there. However, in the conventional example, the magnetic field generated in the power cable is detected by the electromagnetic coil, and the arithmetic device is activated by comparing the voltage generated by the electromagnetic coil with the comparator.
When applied to transmission and distribution line equipment, the electromagnetic coil detects the magnetic field generated by the lightning current due to the lightning strike on the equipment and its vicinity, activates the arithmetic unit, and reduces the sound of the lightning strike following the lightning current. The horn detects and outputs an output signal indicating a failure even though the failure is not an electrical failure.

Further, an electromagnetic coil for detecting a magnetic field is mounted on the ceiling of a tunnel, but in the detection of a fault point of a transmission / distribution line, a fault current flows through the transmission / distribution line in the air and is supported by the transmission / distribution line. There is also a case where the electromagnetic coil flows along an object, an overhead ground line, the ground, and the like around the place where a failure occurs, and it is not possible to determine where and how to install the electromagnetic coil. The present invention has been made in view of the above problems, and provides a transmission line and distribution line fault point detection device capable of accurately detecting an electrical fault point in a transmission and distribution line installed on the ground without malfunction due to dark noise or lightning strike. The purpose is to do.

[0007]

In order to achieve the above object, according to the present invention, transmission and distribution lines are provided at predetermined intervals.
Installed at or near multiple supports to be installed
Fault point detection device that is set to carry lightning current
Support (for example, several tens μS to several hundred μS) or more
Current detection means for detecting a flowing current as a fault current;
Occurs with the occurrence of the fault current and propagates in the air
A flash sound detecting means for detecting a flash sound; and detecting the fault current.
From the time of departure, set in relation to the distance between adjacent supports
If the flashing sound is detected within the set time,
Detects that a failure has occurred in the support on which the ejection device is installed
And a fault detecting device for a transmission / distribution line, comprising:

That is, of the currents measured by the current sensor, a fault current after a lapse of a set time in which a lightning current flows is detected by a current detection circuit, and a sound generated when an electric fault is measured by a sound wave sensor is detected. Of these, the flash (short) sound separated by the filter circuit is detected by the sound wave detection circuit, and if the detected fault current and the flash sound are detected within a preset time, the failure determination circuit fails. And the display circuit can display the fault point.

Further, the filter circuit has a frequency band of 2 kHz or less, a frequency band of 10 kHz or less, or 20 kHz.
It is preferable to use a high-pass filter that removes the following frequency bands to reduce the effect of background noise on fault current. The filter circuit has a frequency band of 2 kHz or more and 10 kHz or less, 10 kHz and 20 kHz.
frequency band below kHz or above 20 kHz and 4
It is preferable to reduce the influence of background noise on the fault current by using a band-pass filter that passes a frequency band of 0 kHz or less.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An apparatus for detecting a fault in a transmission and distribution line according to the present invention will be described with reference to FIGS. FIG. 1 is a configuration diagram showing the configuration principle of the fault point detection device according to the present invention. In the case of a ground fault due to a lightning strike or the like, the shunt current (fault current) from the transmission and distribution lines passes through supports such as steel towers and pillars, and overhead ground wires and grounds installed on the supports. Then, it flows to the generator (power supply) that is the power station. Further, in the case of an electrical failure due to a short circuit due to contact between transmission and distribution lines, the shunt current returns to the power supply by folding back at one of the contacted transmission and distribution lines. The shunt current from the transmission and distribution line does not flow directly to the support, the overhead ground wire, and the ground, but the current flowing in the transmission and distribution line causes the induced current (fault current) to flow to the support, the overhead ground wire, and the ground. I have. The present invention detects these fault currents using a fault point detecting device.

In FIG. 1, a fault point detecting device 10 includes a current sensor 11 comprising a current transformer (CT) or an electromagnetic coil, a lightning current removing circuit 12, a current detecting circuit 13, and a timer circuit 1.
4. It is composed of a sound wave sensor 15, a frequency component classification circuit 16, a sound wave detection circuit 17, a failure determination circuit 18 and a display circuit 19. There are multiple distributions.

The current sensor 11 measures a fault current shunted to a support or an overhead ground wire. Lightning current elimination circuit 12,
The current detection circuit 13 and the timer circuit 14 are current detection means according to the present invention, and the lightning current elimination circuit 12 transmits the lightning current from the measured fault current through the current after the lapse of time during which the lightning current flows. Has been removed. The current detection circuit 13 activates the timer circuit 14 when the current value of the input current exceeds a preset current value (threshold). The timer circuit 14 outputs a signal for a time set in advance by a signal from the current detection circuit 13.

[0013] The lightning current is generally several tens to several hundreds from the time of the lightning strike, as is also known by the JEC-212 (1.2 / 50 μs or 8/20 μs) standard. It flows for a time of μs (see FIG. 2). Then, if an electrical failure occurs, as shown in FIG. 2, even after 10 ms from the time of the lightning strike, the failure current flows to the support, the overhead ground wire, and the ground. The fault current flows for 2 to 10 cycles (40 to 200 ms) until the circuit breaker of the power plant operates and stops power transmission. Also, if only lightning strikes and no electrical fault has occurred, it means that no lightning current and no fault current have occurred within a few ms after the time of the lightning strike.

As described above, since the fault current flows even after 10 ms from the lightning strike time, the lightning current removing circuit 12 performs, for example, several ms to 10 m from the lightning strike time.
The current sensor output after s is output to the current detection circuit 13, and the current detection circuit 13 activates the timer circuit 14 when the sensor output exceeds the threshold value. Next, the timer circuit 1
The time setting of No. 4 will be described. For example, in the case of the overhead power transmission line shown in FIG. 3, the ground height of the tower 1 as a support is usually about 100 m or less, so that the fault point A
It is assumed that the distance between the fault point detecting device 10 and the fault point detecting device 10 is 100 m, and the fault point detecting device 10 is installed under the leg of the steel tower 1. In the figure, 2 is an overhead ground wire, 3 is a transmission line, 4 is an insulator, and 5 is an arc horn.

In this case, if an electrical failure (ground fault) occurs due to a lightning strike or the like in the tower 1, a potential difference between the tower 1 and the transmission line 3 increases, causing a flash between the protective arc horn 5 of the insulator 4. A fault current flows through the tower 1 and the overhead ground wire 2 due to a short circuit (or a reverse flash). The current flowing through the tower 1 is a current sensor 11
The flashing sound is generated at any point in the steel tower 1. In this case, the time difference from the detection of the current to the detection of the flashing sound is detected by the sound wave sensor 15 within about 0.3 seconds, assuming that the sound speed is 340 m / s.

When an electric fault occurs in a tower adjacent to the tower 1, a fault current is generated via an overhead ground line or the ground.
The current sensor 11 detects a fault current flowing through the tower 1 on which the fault point detection device 10 is installed. However, since the current tower 11 is usually several hundred meters away from the adjacent tower, the fault is detected when an electrical fault occurs in the tower 1. As compared with the flashover detection time, a failure occurs in the adjacent tower, and the time from the detection of the fault current in the tower 1 to the detection of the flashover is longer. Usually, the distance between the towers is about 400 m, so that the time taken for the flash detection sound generated in the adjacent tower to be detected by the failure detection device 10 is about 1.2 seconds.

As described above, when a failure occurs in the tower 1, the time difference between the detection of the current and the detection of the flashing sound is within 0.3 seconds.
The signal output time Td is set to 0.3 seconds in advance,
It eliminates the detection of flashing noise when a fault occurs at an adjacent tower. On the other hand, the sound wave sensor 15 is composed of, for example, a microphone and measures a sound generated at the time of the failure.

The frequency component discriminating circuit 16 is a frequency detecting means according to the present invention, and is a band-pass filter (hereinafter referred to as "BP").
F ”) or a high-pass filter (hereinafter“ HPF ”)
), And a sound of a predetermined frequency is detected from the measured sounds. For example, a flashing sound generated by a ground fault or short circuit failure and a dark noise (a sound wave sensor 15)
The frequency characteristics of the wind sound when the wind hits the wind, the rain sound when the sound wave sensor 15 hits the rain, and the corona noise generated from the transmission and distribution lines and insulators) are as shown in FIG. Become.

In FIG. 4, the horizontal axis represents the frequency of various sounds [k
Hz], and the vertical axis represents the sound pressure level [dBV] measured by the sound wave sensor. Here, the flash sound has a characteristic in a frequency band of 0 to 60 kHz or more. Also,
The corona noise has a frequency characteristic similar to that of the flashing sound, but has a lower sound pressure level than that of the flashing sound. The wind noise is 0
It shows frequency characteristics up to 20 kHz, especially 0 to 20 kHz.
It has a large sound pressure level in a low frequency band of about 3 kHz. Rain noise has a frequency characteristic up to about 40 kHz, but has a lower sound pressure level than the corona noise.

As described above, since the sound pressure level relatively changes depending on the positional relationship between the sound source and the sound wave sensor, in the present invention, the sound wave sensor is used to distinguish the flashing sound from other background noise. In addition to measuring the magnitude of the measured sound pressure level, the signal obtained by the acoustic wave sensor is selected by the frequency component separation circuit 16 to select a signal of a specific frequency, and only the flash sound is selected and separated.

Referring to FIG. 4, for example, a frequency band having a large sound pressure level due to background noise is 2 kHz, preferably 3 kHz or less. It is conceivable to remove them so that they are not detected. Further, for example, when a radio or a stereo emits a so-called audible sound in the vicinity of the sound wave sensor, a sound component up to an audible sound band of 20 kHz is detected by a frequency component classification circuit 16 composed of an HPF so as not to detect the audible sound. Is removed and the flash sound has 2
It is also conceivable to detect a frequency component of 0 kHz or more. In addition, the peak value of the flashing sound is 10 kHz or more and 20 k or more.
Since the frequency component exists in the frequency band of not more than Hz or not less than 20 kHz and not more than 40 kHz, it is conceivable that only this component is detected by the frequency component classification circuit 16 composed of the BPF.

The sound wave detecting circuit 17 is a sound detecting means according to the present invention. Among the sounds of a predetermined frequency detected by the frequency component separating circuit 16, a randomly generated dark sound such as a wind sound, a rain sound and a corona noise. Removes noise. As is apparent from FIG. 4, when the frequency exceeds about 3 kHz, the sound pressure level of the background noise is greatly reduced, and the sound pressure of the flashlight and the background noise (for example, the corona noise which is the highest among the background noises) is reduced. The difference between the levels increases. Therefore, in the present invention, the threshold value of the sound detected by the sound wave detection circuit 17 is set to a level higher than the sound pressure level of the above-mentioned dark noise per 3 kHz, and the dark noise generated at random is removed.

The failure judging circuit 18 is a judging means according to the present invention, while the signal from the timer circuit 14 is being output.
It is determined whether the sound wave detection circuit 17 has detected a sound of a predetermined frequency, and the result of the determination is output to the display circuit 19. That is, the failure determination circuit 18
The signal is output to the display circuit 19 when the output signal of No. 4 and the output signal of the sound wave detection circuit 17 are simultaneously generated.

The display circuit 19 is a holding means and a display means according to the present invention, holds the determination result from the failure determination circuit 18 and displays a failure point based on the determination result.
FIG. 5 is a configuration diagram illustrating an example of a specific configuration of the fault point detection device illustrated in FIG. 1, and FIGS. 6 to 8 are waveform diagrams illustrating output waveforms of each unit illustrated in FIG. 5. In FIG. 5, parts having the same names as those in FIG. 1 are given the same numbers.

The current flowing under the overhead ground wire or under the steel tower leg is detected by the current sensor 11, and the waveform is shaped by the rectifying / smoothing circuit 21. A current comparison circuit (comparator) 22 and a gate (logical product) circuit 23 constitute a current detection circuit 13,
Delay circuit 24 composed of one-shot multivibrator
And the NOT (inverting) circuit 25 constitute the lightning current elimination circuit 12. In the current comparison circuit 22, a threshold value of the current to be detected (for example, 10 A) is set in advance. When the current input from the rectification / smoothing circuit 21 exceeds the threshold value, a trigger signal is sent to the gate circuit 23 and the delay circuit 24. Output.

The delay circuit 24 is, for example, several milliseconds to 10 milliseconds, which is a time that elapses a sufficient time of a lightning current, for example, from the rising of the input trigger signal (current comparison circuit output).
A trigger signal having a pulse width delayed by about
The trigger signal is inverted by the NOT circuit 25 and input to the gate circuit 23. As a result, the gate circuit 23 can open the gate after the delay time of the trigger signal (time during which the lightning current is generated) and output the current comparison circuit output to the timer circuit 14. The signal is output to the AND circuit 26 constituting the failure determination circuit 18 for 0.3 seconds preset by the output from the gate circuit 23.

On the other hand, the flash sound at the time of the occurrence of the electrical failure is detected by the sound wave sensor 15 and further amplified by the amplifier 27, and then the filter circuit 2 constituting the frequency component classification circuit 16 is formed.
Enter 8 The filter circuit 28 is a HPF that removes a frequency band of 2 kHz or less, a frequency band of 10 or less or a frequency band of 20 kHz or less, or a frequency band of 2 kHz or more and 10 kHz or less, a frequency band of 10 kHz or more and 20 kHz or less. B that passes a frequency band of 20 kHz or more and 40 kHz or less
The amplified flashing sound is output to the sound wave comparing circuit 29 as the set frequency component.

The sound wave comparison circuit (comparator) 29 constituting the sound wave detection circuit 17 is set in advance with a threshold value of a sound volume to be detected (for example, a sound pressure level of -30 dBV). When the threshold value is exceeded, a signal is output to the AND circuit 26. When there is a signal output from the sound wave comparison circuit for 0.3 seconds set by the timer circuit 14, the AND circuit 26 outputs the signal to the latch circuit (latching relay) 30.

The latch circuit 30 and the LED display circuit 31
The display circuit 19 is configured, and when a signal is input from the AND circuit 26, the latch circuit 30 holds the signal,
The signal is output to the LED display circuit 31 and another device to be described later as a contact output. The LED display circuit 31 displays an electrical fault point based on the signal. Here, as shown in FIG. 6, for example, when a lightning strike due to a lightning strike occurs on a steel tower on which the failure point detection device 10 is installed and the current sensor 11 measures a failure current following the lightning current, the operation time T of the timer circuit 14 is calculated.
A signal is output from the sound wave comparison circuit 29 to the latch circuit 30 via the logical product circuit 26 in d, and the LED display circuit 31 displays an electrical fault point.

When an electric fault occurs in another tower, as shown in FIG.
Since a signal is output from the sound wave comparison circuit 29 to the AND circuit 26 at a time later than d, the output of the AND circuit 26 remains at the low level, and it is not determined that a failure has occurred. Also,
For example, as shown in FIG. 8, when there is only a lightning strike due to a lightning strike on a steel tower on which the fault point detection device 10 is installed, and no electric fault occurs, a fault current does not flow through the steel tower. Reference numeral 22 detects a trigger signal caused only by the lightning current from the current sensor 11. As a result, the trigger signal is removed by the delay circuit 24, and the timer circuit 14 does not operate.
Remains at low level, and it is not determined that a failure has occurred.

The output terminal of the AND circuit 26 is connected to the latch circuit 3
0, and when there is an output from the AND circuit 26, the latch circuit 30 holds the state, and
The signal is output to the D display circuit 31 or, for example, a communication unit or the like connected to the contact. Further, if the latch circuit 30 is in the holding state, for example, if the observer presses the reset switch 30a, a reverse current flows through the latch circuit to return the holding state to the original state, the failure can be detected again. .

As shown in FIG. 9, the fault point detecting device 10 is held and installed on the side of the pylon by a current sensor 11 wound around the pylon 1. The LED display circuit 31 has an operation state confirmation switch 31a provided near the center of the failure point detection device frame, and red and blue LED elements 31b and 31c.
Is a switch for confirming the operation state of the battery / storage battery as a power supply. When the switch 31a is pressed, for example, when the latch circuit 30 is in the above-mentioned holding state,
The red LED element 31b is turned on, and when no electrical failure is detected, the blue LED element 31c is turned on. In the figure, a sound wave sensor 15 is provided above the frame so as to be able to detect spatially propagated sound.
a is provided in the lower part. The sound wave sensor can be provided at a position other than the upper portion of the frame, as long as the sound can detect the spatially propagated sound.

As described above, in the present embodiment, a fault current that exceeds a predetermined volume level in a predetermined frequency band and flows after a lapse of a set time in which a lightning current flows is detected, so that wind noise, rain noise, corona noise, etc. It is possible to accurately detect an electrical fault point in a transmission and distribution line installed on the ground without malfunction due to dark noise or lightning. In the present embodiment, the case where the fault point detecting device is installed below the leg of the steel tower has been described. However, the present invention is not limited to this. For example, as shown in FIG. It is also possible to install at the lower part, middle part, upper part of the steel tower 1 or the overhead ground wire 2.

When the fault detecting device is installed above the steel tower as described above, it may be difficult for the observer to recognize the trouble by the display using the LED element as the display means.
Instead of the D display circuit, for example, a configuration in which a red cloth is hung as a banner is also possible. In this case, a weight is attached to the tip of the cloth wound in the device, the weight is supported by a hinge, and when a fault current is detected, the support of the hinge is released to weight the cloth. Then, it is conceivable to use a structure that hangs outside.

Further, in the above-mentioned display means, when the confirmation is completed, it is necessary for the observer to climb the steel tower and return the hanging curtain to the inside of the failure point detecting device. Therefore, for example, the operation of the latch circuit 30 shown in FIG. When a wireless data transmission device is connected to the contact and the latch circuit is in a holding state, a contact output can be output to the transmission device to transmit a signal.
In this case, when a monitor having a wireless data receiving device passes nearby, a signal from the transmitting device is received by the receiving device, and an identification number or the like preset for each transmitting device is displayed by an LED. By doing so, it becomes possible to recognize the fault point.

Further, in this embodiment, detection of a fault point of a transmission line has been described. However, a fault point can be detected in the same manner as described above in the case of a distribution line installed on a column.

[0037]

As described above, according to the present invention, the predetermined
Multiple supports with transmission and distribution lines installed at intervals of
Fault detection devices installed at or near the object
And supported for longer than the set time for lightning current to flow
Current detection means for detecting a current flowing through an object as a fault current
And propagated in the air due to the occurrence of the above fault current
Flashing sound detecting means for detecting flashing sound
From the point of detection of
When the flashing sound is detected within the specified time,
Failure of the support on which the point detection device is installed
Determining means for detecting the flash sound,
Detection of flash sound by filter circuit of detection means
In addition, the flash sound detection means can perform
Detect flashing sound more reliably by detecting the upper sound
Therefore, it is possible to accurately detect an electrical failure point in a transmission and distribution line installed on the ground without malfunction due to dark noise or lightning. Also, when a failure is detected,
By providing means for displaying and / or notifying,
The failure point can be notified to the supervisor.

The frequency detecting means may be a frequency band of 2 kHz or less, a frequency band of 10 kHz or less, or a frequency band of 20 kHz or less.
Since there is a filter circuit for removing a frequency band equal to or lower than z, a fault current can be detected in a frequency band where the influence of background noise is small. The frequency detecting means is a frequency band of 2 kHz or more and 10 kHz or less, 10 kHz
And a filter circuit that passes a frequency band of 20 kHz or less or a frequency band of 20 kHz or more and 40 kHz or less, so that the fault current can be detected in a frequency band where the influence of background noise is small.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing the configuration principle of a fault point detection device according to the present invention.

FIG. 2 is a waveform chart showing waveforms of a lightning current and a fault current generated by a lightning strike.

FIG. 3 is a diagram showing an installation example when the fault point detection device according to the invention is installed on a transmission line.

FIG. 4 is a characteristic diagram showing characteristics of frequencies and sound pressure levels of various sounds detected by the failure point detection device according to the present invention.

FIG. 5 is a configuration diagram illustrating an example of a specific configuration of the fault point detection device illustrated in FIG. 1;

FIG. 6 is a waveform diagram showing output waveforms of respective parts of the fault point detection device shown in FIG. 5 when a fault current occurs in the installed steel tower.

FIG. 7 is a waveform diagram showing output waveforms of respective parts of the apparatus when a fault current occurs in a tower other than the installed tower.

FIG. 8 is a waveform chart showing output waveforms of respective parts of the device when only a lightning current is generated.

FIG. 9 is a diagram showing a state of attachment of the fault point detection device shown in FIG. 5;

FIG. 10 is a view showing a mounting position of a fault point detecting device in a steel tower.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 steel tower 2 overhead ground wire 3 transmission line 4 insulator 5 arc horn 10 fault point detection device 11 current sensor 12 lightning current removal circuit 13 current detection circuit 14 timer circuit 15 sound wave sensor 16 frequency component classification circuit 17 sound wave detection circuit 18 failure judgment circuit 19 Display circuit

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-62-124467 (JP, A) JP-A-1-123169 (JP, A) JP-A 8-17895 (JP, A) JP-A-3- 46577 (JP, A) JP-A-61-45976 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G01R 31/08 H02H 7/26

Claims (5)

(57) [Claims] 1. Transmission and distribution lines are installed at predetermined intervals.
Installed at or near multiple supports
A fault point detection device, which is used to detect a voltage flowing through a support for a set time or more during which a lightning current flows.
Current detecting means for detecting a current as a fault current; and a current generated by the fault current and propagated in the air.
A flash-sound detecting means for detecting a flash-sound, and a distance between adjacent supports from a point of time when the fault current is detected.
The flashover is detected within the time set in relation to
Failure occurs in the support on which the failure point detection device is installed.
And a judging means for detecting as being generated.
A fault detection device for transmission and distribution lines. 2. The fault detection of a transmission / distribution line according to claim 1.
When a failure is detected in the device, it is further indicated and / or
Transmission / distribution line failure characterized by means for notifying
Point detector. 3. The method according to claim 1, wherein said flash sound detecting means is a sound wave sensor.
2 kHz or less, 10 kHz or less,
Or a filter that removes the frequency band below 20 kHz
Detecting flash sound propagating in the air with a circuit
The fault detection of the transmission and distribution line according to claim 1 or 2,
apparatus. 4. The method according to claim 1, wherein said flash sound detecting means is a sound wave sensor.
2 kHz or more and 10 kHz in the detected signal
The following frequency band, 10 kHz or more, and 20 kHz
The following frequency band, or more than 20kHz and 40k
Equipped with a filter circuit to pass the frequency band below Hz
To detect flashing sound propagating in the air
Item 3. The fault detecting device for transmission and distribution lines according to Item 1 or 2. 5. The method according to claim 1, wherein said flash sound detecting means detects a sound of background noise or more.
The transmission according to any one of claims 1 to 4, wherein the transmission is detected.
Fault detector for distribution lines.