JPH0740058B2 - Probing device for ground fault of electric wire - Google Patents

Description

TECHNICAL FIELD The present invention relates to a device for finding a ground fault point of an electric wire, such as an electric wire passed through a conduit, which cannot be seen from the outside.

<Prior art> When a ground fault occurs in an electric wire, the AC test signal is conventionally applied to this wire and a magnetic sensor is installed along the wire in order to find the ground fault location without touching the wire. A method of moving and checking how far the test signal can be detected was taken.

This will be described with reference to FIG. 7. An AC signal source 51 is connected to one end of an electric wire D to be tested, a magnetic sensor (pickup coil) 52 is moved along the electric wire, and a signal generated by electromagnetic induction is examined. Reference numeral 53 is a ground fault point, and a leak current flows in the electric wire from the signal source 51 to the ground fault point 53, and a signal can be detected by the sensor during this period. But,
After passing the ground fault point 53, there is no reaction. From this,
The position of the ground fault can be specified.

<< Problems to be Solved by the Invention >> By the way, an electric wire to be tested may be routed in a complicated path, and the situation may not be visible from the outside. For example, an antifreeze heating wire that is wound around a complicatedly branched water pipe and is covered with a heat insulating material together with the water pipe, and a heating wire that is buried in a road to melt snow. When applying the above-mentioned conventional exploration method to such an electric wire, when there is no response to the magnetic sensor, it is not possible to determine whether it is due to a ground fault or because the electric wire does not pass near it. It was

An object of the present invention is to provide a device that can easily detect a ground fault location even with an electric wire whose installation route cannot be seen from the outside.

<< Means for Solving the Problems >> The ground fault detection device for an electric wire according to the present invention comprises a transmitter, a terminal, and a receiver. The transmitter alternately sends two AC signals having different frequencies, that is, a pilot signal and a search signal, to the electric wire to be tested. The terminating end terminates the end of the wire to the ground when the pilot signal is sent, and opens the end of the wire when the probe signal is sent. The receiver is configured to detect a pilot signal and a probe signal from a magnetic sensor that is moved along the wire.

<Operation> When the transmitter sends a probe signal to the wire, the terminal opens the end of the wire, so if there is a ground fault in the wire, there will be a leakage current in the wire from the transmitter to the ground fault point. There is current, but no current flows from the ground fault point to the end of the wire. Therefore, when the magnetic sensor is moved along the electric wire, the search signal can be detected up to the ground fault point, but the search signal cannot be detected thereafter. In this way, the ground fault point can be found.

If the wire path is not visible, pay attention to the pilot signal as well. When the transmitter is sending the pilot signal,
The terminal end terminates the end of the wire on the ground. Therefore, since the electric current flows through the electric wire to the end, the pilot signal can be detected anywhere by moving the magnetic sensor along the electric wire.

In other words, if the pilot signal can be detected, the electric wire runs near the sensor. When the pilot signal can be detected, but the exploration signal cannot be detected, it indicates that there is a ground fault location in front of it (on the transmitter side).

<Embodiment> First, regarding the transmission unit, FIG. 2 shows the output timing of the transmission unit, in which a pilot signal of 2 KHz and a search signal of 500 Hz are alternately sent out about every 2 seconds. Both the pilot signal and the search signal are sine waves. Fig. 1 is a block diagram of the transmitter A. The reference signal generated by the oscillator 1 is divided by the frequency divider 2 to generate 2KHz and 500Hz.
Pulse signal is taken out. These signals have their operation intervals controlled by the gate circuits 3a and 3b, and then the low-pass filter 4
Enters a and 4b and becomes a sine wave tone burst signal. Further, these signals are mixed by the mixer 5, amplified by the AMP 6, and then sent out from the transformer 7.

FIG. 3 is a block diagram of the terminal section B. The signal detected by the current transformer 11 is amplified by the AMP 12, passes through the 2 KHz bandpass filter, and is waveform-shaped by the Schmitt circuit 14, and then the first and second ones. Shot multi vibrator
15a, 15b, their outputs enter the EX-OR circuit 16,
The output drives the relay 17. Reference numeral 18 is a terminating resistor, which is turned on / off by the contact 17a of the relay. Termination resistor 18
Should be as small as possible so as not to place a burden on the transmitter, and is 750Ω in the embodiment.

The operation of the terminating portion B will be described with reference to FIG. 4. When a 2 KHz pilot signal is received, the first and second one-shot multivibrators 15a and 15b each output a pulse of a unique width, and the EX- The OR is driven and the relay is driven. That is, when the 2 KHz pilot signal is sent, the relay contact 17a is turned on (termination), and when the search signal of 500 HZ is sent, it is turned off (open).

As shown in FIG. 5, the receiver C receives the output from the magnetic sensor 21 by the transformer 22, amplifies it by the AMP 23, extracts the signals of 500 Hz and 2 KHz through the band pass filters 24a, 24b, and outputs the peak hold circuit 25a, At 25b, the peak value of the signal is displayed on the meters 26a, 26b.

When using, as shown in FIG. 6, the output of the transmitter A is connected to the electric wire D to be tested, the end B is connected to the electric wire D at a location distant from the transmitter, and the magnetic sensor 21 of the receiver C is connected. Move along the wire D. In the figure, reference numeral 31 is a ground fault point, and reference numeral 32 is a ground fault resistance.

When the probe signal is sent from the transmitter A to the electric wire D, the relay 17 at the terminal end is turned off. In this state, a leak current flows from the transmitter A to the ground through the wire D and the ground fault resistance 32, and no current flows to the wire D between the ground fault point 31 and the terminal end. Therefore, when the magnetic sensor 21 is moved along the electric wire D, the search signal can be detected up to the ground fault point 31, but the search signal cannot be detected before that (on the terminal side). That is, when the search signal suddenly cannot be detected while moving the magnetic sensor 21 along the electric wire D, that point is the ground fault point 31.

When the route of the electric wire is visible, it is possible to find the ground fault point by paying attention only to the search signal in this way.

When the pilot signal is applied to the electric wire D to be tested, the relay at the terminating end is turned on, and the electric current flows from the transmitter A through the electric wire D and the terminating resistor 18 to the ground. Therefore, when the magnetic sensor 21 is moved along the electric wire D, the pilot signal can be detected anywhere in the electric wire except for the case of a complete ground fault (that is, the value of the ground fault resistance 32 is almost zero).

Therefore, when the route of the electric wire is not known from the outside, the route of the electric wire can be known by paying attention to the pilot signal.
When the pilot signal cannot be detected, the sensor is moving away from the wire.

When the magnetic sensor was moved along the electric wire and both the pilot signal and the search signal could be detected until now, but after passing a certain point, only the pilot signal can be detected, that point is the ground fault location.

<< Effects of the Invention >> The present invention applies a pilot signal and a search signal alternately to an electric wire to be tested, and terminates the end of the electric wire to the ground only when the pilot signal is applied, while the magnetic sensor is applied to the electric wire. By moving along, the pilot signal and the search signal are detected, and the ground fault point can be searched depending on to what point the search signal can be detected while tracing the laying route of the electric wire using the pilot signal as a clue. In this way, even for electric wires whose laying route cannot be seen from the outside,
It is possible to easily detect a ground fault.

[Brief description of drawings]

1 is a block diagram of the transmitter, FIG. 2 is an output waveform diagram of the transmitter, FIG. 3 is a block diagram of the terminal, FIG. 4 is a timing diagram of the terminal, and FIG. 5 is a block diagram of the receiver. , FIG. 6 is an illustration of use of the exploration device, and FIG. 7 is an illustration of a conventional ground fault exploration method. A: transmitter, B: terminal, C: receiver D: electric wire, 21: magnetic sensor

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Keiichi Endo, No. 1 Maejima, Daigasakihama, Shichigahama-cho, Miyagi-gun, Miyagi Prefecture Tohoku Electric Power Co., Inc. Sendai Thermal Power Station (72) Masahiro Hashimoto Maejima, Masakijima, Shichigahama-machi, Miyagi-gun, Miyagi Prefecture No. 1 Tohoku Electric Power Co., Inc. Sendai Thermal Power Station (72) Inventor Jiro Sato No. 1 Maejima, Daigasakihama, Shichigahama-cho, Miyagi-gun, Miyagi-gun Miyagi Prefecture No. 1 Sendai Thermal Power Station, Tohoku Electric Power Co., Inc. (72) Kazuo Takahashi Shichigahama, Miyagi-gun, Miyagi Prefecture Machishiro Gasakihama Maejima No. 1 Tohoku Electric Power Co., Inc. Sendai Thermal Power Plant (72) Inventor Koichi Konno 1-1-11, Koutorihonmachi, Taishiro-ku, Sendai-shi, Miyagi Inventor Hiroki Wada Izumi-ku, Sendai-shi, Miyagi 6-18-33 Nankodai

Claims (1)

[Claims] 1. An electric wire to be tested has two different frequencies at one end.
One AC signal, that is, a transmitter that alternately sends a pilot signal and a search signal, and terminates the end of the wire to the ground when the pilot signal is sent, and the end of the wire when the search signal is sent. A ground fault detecting device for an electric wire, which comprises an open end portion and a receiving portion for detecting a pilot signal and an exploration signal from a magnetic sensor moved along the electric wire.