JP4248627B2 - Ground fault inspection device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a ground fault inspection apparatus that inspects a ground fault of an electric circuit such as a power transmission line.
[0002]
[Prior art]
Electric lines such as power transmission lines and telephone lines installed in underground wiring grooves often cause ground faults, and inspection that can easily and quickly detect the location where the ground fault occurs (ground fault position) A device is sought. In order to easily and promptly detect the ground fault position, it is desirable to inspect in a state where current is flowing in the electric circuit (hereinafter referred to as a live line state) without removing the electric circuit from the connection portion.
[0003]
In a conventional inspection apparatus that inspects a ground fault of an electric circuit in a live line state, a low frequency signal of about 10 Hz is applied between one end of the electric circuit to be inspected and a ground line. Next, a current transformer is brought close to the circuit to be inspected to detect the low frequency signal. When the current transformer is moved along the circuit to be inspected, the detected value of the low-frequency signal changes significantly before and after the ground fault position. The ground fault position can be detected based on the change in the detected value.
[0004]
[Problems to be solved by the invention]
In the conventional inspection apparatus, when the length of the electric circuit to be inspected is several tens of meters or more, the low-frequency signal is attenuated due to the stray capacitance between the electric circuit and the ground, and the detection level by the current transformer is lowered. It becomes difficult to detect the entanglement point. In addition, many various electric wires such as power transmission lines and data transmission lines are often disposed in the wiring groove, and noise in a wide frequency band is generated from these electric wires. Therefore, these noises are induced in the circuit to be inspected, and a large error occurs in the inspection value of the current transformer, making it difficult to detect the ground fault point.
[0005]
An object of this invention is to provide the ground fault inspection apparatus which test | inspects the position of the ground fault which generate | occur | produced in a part of long electric circuit in a hot-line state, without being influenced by noise etc.
[0006]
[Means for Solving the Problems]
In the ground fault inspection apparatus of the present invention,
Conductive wires placed along the live electrical circuit to be inspected,
A pulse generator connected between one terminal of the conductive line and a ground line, and applying a pulse signal to the conductive line for inducing an induced current in the circuit under test;
A magnetic sensor for detecting a magnetic field generated by an induced current induced in the circuit under test by electromagnetic induction of a pulse signal applied to the conductive wire from the pulse generator; and
A display device for displaying a waveform of a detection output of the magnetic sensor;
With
The polarity of the waveform of the detection output of the magnetic sensor displayed on the display device is reversed on both sides of the ground fault point of the electric circuit to be inspected.
[0007]
Due to the electromagnetic induction of the pulse signal applied to the conductive wire, an induced current having a waveform corresponding to the time constant of the circuit to be inspected is generated in the circuit to be inspected. Since there is a stray capacitance between the circuit to be inspected and the ground, the pulse width of the induced current is wider than the pulse width of the pulse signal supplied by the pulse generator, and the polarity is on both sides of the ground fault position of the circuit to be inspected. Is the opposite. The ground fault position can be detected by moving the magnetic sensor along the circuit to be inspected and looking for a place where the polarity of the induced current changes.
[0008]
DETAILED DESCRIPTION OF THE INVENTION
A preferred embodiment of the present invention will be described below with reference to FIGS.
"Example"
FIG. 1 is a configuration diagram of the ground fault inspection apparatus according to the present invention in use. In the figure, an inspected electric circuit 1 is, for example, a power transmission line, a data transmission line, or the like, and is connected to a predetermined device 10 at a terminal 1A. A transmission current or a current for transmitting data flows through the circuit 1 to be inspected, and this state is hereinafter referred to as a hot line state. It is assumed that a ground fault occurs at the position indicated by the arrow 14 in the circuit 1 to be inspected, and the insulation between the circuit 1 to be inspected and the ground (hereinafter referred to as the ground G) is lowered. Hereinafter, the position of the arrow 14 is referred to as a ground fault point 14. There is a stray capacitance between the circuit 1 to be inspected and the ground G as indicated by a dotted line.
[0009]
The conductive wire 2 is a very general electric wire in which a copper wire is covered with an insulator, and is disposed along the electric circuit 1 to be inspected. The distance between the circuit 1 to be inspected and the conductive wire 2 is preferably 0.5 to 3 m. The length of the conductive wire 2 is adjusted to the length of the electric circuit 1 to be inspected in the range of 5 to 50 m. One terminal 2 </ b> A of the conductive wire 2 is connected to one output terminal of the pulse generator 3. The other terminal of the pulse generator 3 is connected to the ground G. When the length of the conductive line is as short as 5 to 15 m, a capacitor 11 of about 0.1 μF is connected between the other terminal 2B of the conductive line 2 and the ground G. When the length of the dielectric wire is as long as 20 to 50 m, the stray capacitance is large and the capacitor 11 does not need to be connected.
[0010]
The magnetic field sensors 4A and 4B that detect a magnetic field incorporate a three-axis magnetic sensor capable of detecting a three-dimensional magnetic field by bridge-connecting a plurality of magnetic thin film elements. As the three-axis magnetic sensor, a commercially available standard product (for example, HM-1000 model manufactured by Honeywell, USA) can be used. The three-axis magnetic sensor of the magnetic field sensors 4A and 4B is configured such that one output signal is obtained by synthesizing the three-axis detection outputs. The magnetic field sensors 4A and 4B have a built-in power source such as a battery, and are connected to the ground fault determiner 12 by an optical fiber 8 having a length of 2 to 5 m. The ground fault determination device 12 includes a display unit 5 using a cathode ray tube or a liquid crystal plate. The magnetic field sensors 4A and 4B are rods having a diameter of about 3 to 4 cm and a length of about 20 cm, and can be brought close to an arbitrary position of the electric circuit 1 to be inspected.
[0011]
Next, a procedure for detecting a ground fault using the ground fault inspection apparatus will be described. For example, the pulse generator 3 applies a positive pulse signal having a peak value of 500 V and a pulse width of 20 microseconds (μS) to the conductive wire 2 at intervals of 3 seconds. Due to the electromagnetic induction of this pulse signal, a pulse current is induced in the circuit 1 to be inspected, and an induced current flows. This induced current generates a magnetic field around the circuit to be inspected 1, and this magnetic field is detected by the magnetic field sensors 4 </ b> A and 4 </ b> B that are close to the circuit to be inspected 1. FIG. 2 shows a waveform of a pulse signal generated by the pulse generator 3 and a detection waveform in an experimental example in which this pulse signal is applied to the conductive wire 2 having a length of 30 m extended along the circuit 1 to be inspected. The detected waveform indicates the detected value of the magnetic flux density by the magnetic field sensors 4A and 4B. The detected value of the magnetic flux density was a mountain-like waveform having a steep rise and a gentle fall, the peak value was 100 milligauss (mG), and the time width was about 100 μS.
[0012]
In FIG. 1, the detected waveform of the magnetic field sensor 4A brought close to the electric circuit 1 to be inspected between the terminal 1A and the ground fault point 14 becomes a positive waveform as shown by the waveform p in FIG. In FIG. 1, the detected waveform of the magnetic field sensor 4B brought closer to the electric circuit 1 to be inspected on the right side from the ground fault point 14 becomes a negative waveform as shown by the waveform n in FIG. That is, the polarities of the detected values of the magnetic flux density detected by the magnetic field sensors 4A and 4B are reversed with respect to the ground fault point 14.
[0013]
The ground fault detection operation is performed as follows, for example. One worker has the ground fault discriminator 12 and the magnetic field sensor 4A, and the other worker has the magnetic field sensor 4B. Both workers move their magnetic field sensors 4A and 4B close to the electric circuit 1 to be inspected and move in a certain direction while maintaining a separation distance of several meters from each other. Since the magnetic field sensors 4A and 4B detect a three-dimensional magnetic field by a three-axis magnetic sensor, the magnetic field can be detected regardless of the posture of the magnetic field sensors 4A and 4B close to the electric circuit 1 to be inspected. When the ground fault point 14 is not between the magnetic field sensors 4A and 4B, the polarities of the detection waveforms of the magnetic field sensors 4A and 4B displayed on the display unit 5 are the same. When the ground fault point 14 enters between the two magnetic field sensors 4A and 4B, the polarities of the detected waveforms are opposite to each other as described above. By gradually reducing the distance between the two magnetic field sensors 4A and 4B in this state, The ground fault point 14 can be specified. Visibility can be improved if the display colors of the display unit 5 are different from each other according to the sign of the detected waveform.
If the detection waveform is notified by a method exemplified below instead of displaying the positive / negative of the detected waveform on the display unit 5 using a cathode ray tube or the like, the operation becomes easier and the cost of the apparatus is reduced. Can do.
(1) The positive / negative sign of the detected waveform is reported with sounds having different frequencies or intermittent sounds having different repetition frequencies.
(2) The positive / negative of the detected waveform is displayed by turning on the indicator lights of different colors.
[0014]
It is not always necessary to use two magnetic field sensors 4A and 4B, and only one magnetic field sensor 4A can be moved by one operator and the ground fault point 14 can be detected. The electric circuit 1 to be inspected in the above experimental example was an AC 200V power supply wiring, and the current was 10A. Since the magnetic field sensors 4A and 4B also detect a magnetic field due to an AC 200V current, a detected value of a magnetic flux density due to an AC 200V current is superimposed on the detected value. In this example, the peak value (not shown) of the detection waveform due to the AC 200 V current was about 30 mG, which was about one third of the peak value of the detection waveform due to the applied pulse. Therefore, the value of the magnetic flux density by the applied pulse can be detected even when the detection current by AC200V is superimposed.
[0015]
【The invention's effect】
According to the present invention, as is apparent from the description of the above embodiment, a magnetic flux density of a magnetic field caused by an induced current induced in a circuit to be inspected by applying a high-voltage pulse signal to a conductive line arranged along the circuit to be inspected. Is detected by a magnetic field sensor. Since the polarities of the detected values of the magnetic flux density are opposite to each other on both sides of the ground fault point of the circuit to be inspected, the ground fault point can be detected. Since the magnetic field of the circuit to be inspected is detected by a magnetic field sensor, the work can be performed in a non-contact manner, and by using a high voltage pulse signal, the level of the induced current is large and the S / N ratio is high. The detection of the entanglement point can be performed accurately and easily.
[Brief description of the drawings]
FIG. 1 is a block diagram showing the configuration of an embodiment of the present invention. FIG. 2 is a waveform diagram of applied pulse voltage and induced current in the embodiment.
DESCRIPTION OF SYMBOLS 1 Circuit to be inspected 2 Conducting wire 3 Pulse generator 4A, 4B Magnetic field sensor 5 Display part 8 Optical fiber 10 Equipment 11 Capacitor 12 Ground fault discriminator 14 Ground fault point

Claims (2)

Conductive wires placed along the live electrical circuit to be inspected,
A pulse generator connected between one terminal of the conductive line and a ground line, and applying a pulse signal to the conductive line for inducing an induced current in the circuit under test ;
By electromagnetic induction of a pulse signal applied to the conductive wire from the pulse generator, the magnetic sensor for detecting the magnetic field generated Ri by the induction current induced in the inspection path, and the detection output of the waveform of the magnetic sensor Display device,
Equipped with a,
The ground fault inspection apparatus , wherein the polarity of the waveform of the detection output of the magnetic sensor displayed on the display device is reversed on both sides of the ground fault point of the circuit to be inspected.   The ground fault inspection apparatus according to claim 1, wherein the magnetic sensor is a three-axis magnetic sensor that detects a three-dimensional magnetic field.

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