JP2961418B2 - Indicator for exploring ground fault points - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] According to the present invention, in a state attached to a power generation line, a current of a signal for searching for a ground fault point sent from a transmitter flows through a distribution line at the attachment point. The present invention relates to a ground fault point exploration indicator for detecting and displaying a case.

[Conventional technology]

Conventionally, this type of display is configured as follows. That is, a resonance circuit that resonates at the frequency of the search signal is attached to the core for detecting the search signal flowing in the distribution line.
A display device that performs a display operation by receiving an output signal from the resonance circuit is connected to the resonance circuit. The operating sensitivity of the display device is an operating current or a current when the display is operated in an operating current-frequency characteristic as shown in FIG. The frequency indicates the frequency of the search signal during the operation. Therefore, ambient temperature is 20 (℃), 40 (℃), -20 (℃)
Operating current of the display when the
Explaining the relationship between the peripheral numbers, if the temperature is 20 (° C), 150mA, 180Hz (operation), 175mA, 170Hz (operation), 160m
A, 175Hz (operation), 160mA, 185Hz (operation), 175mA, 190
Hz (operation), and 130 mA, 180 Hz (non-operation), 190 mA, 160 Hz (non-operation), 150 mA, 170 Hz (non-operation). When the temperature is 40 (℃)
140mA, 160Hz (operation), 170mA, 150Hz (operation), 150m
A, 155Hz (operation), 149mA, 160Hz (operation), 165mA, 168
Hz (operation), 130 mA, 160 Hz (non-operation)
Indicates 150mA, 180Hz (non-operating) and -20
(℃) 165mA, 215Hz (operation), 167mA, 212Hz
(Operation), 170, 210Hz (operation), 150m
A, 220 Hz (non-operating), 180 mA, 200 Hz (non-operating). In the case of operation, however, a curved point in the figure is shown, and in the case of non-operation, an appropriate point located below the curve is shown.

That is, as shown in the operating current-frequency characteristics of FIG. 13, the display (conventional type) does not operate unless the operating current is large and the frequency is high as the temperature decreases, and conversely, the temperature increases. It shows that the operation current is small and the operation is performed even when the frequency is low. The operation sensitivity of the display is determined based on the sensitivity current (200mA) of the ground fault relay installed in the substation for detecting an accident. It is set to operate reliably. Further, if the value of the operating current is too small, the above-mentioned value is determined because, for example, malfunction occurs due to charging current with respect to the earth capacitance of the distribution line.

In such an indicator, when the current of the search signal from the transmitter flows through the distribution line, it is detected by the core, and the resonance circuit produces an output. If it is equal to or higher than the operation sensitivity of the display device, the display device performs the display operation. As a result, an appropriate display is made.

However, if the temperature of the installation location of the display changes depending on, for example, the season, the resonance frequency of the resonance circuit changes. That is, the operating current-frequency characteristic changes as shown in FIG. Therefore, conventionally, the frequency of the search signal from the transmitter is changed correspondingly, and P2 in FIG.
The operation of the display is performed at around ℃, operating current 140 mA, resonance frequency 162 Hz or P3, that is, around ambient temperature −20 ° C., operating current 160 mA, resonance frequency 215 Hz.

[Problems to be solved by the invention]

By the way, recently, an indicator which operates only with a search signal of a certain frequency is further provided on a distribution line. Then, it is required that the existing display and the new display be operated with one search signal, for example, 180 Hz and 150 mA. In this case, the frequency of the search signal must be fixed. That is, the frequency cannot be changed. Then, there is a problem in that the conventional display cannot be operated at the point where the temperature has changed, for example, at points P2 and P3 in FIG.

The present invention has been made in view of the above points, and an object of the present invention is that even when an exploration signal of a fixed frequency is transmitted under a condition in which an ambient temperature changes, the search signal is transmitted to the signal. It is an object of the present invention to provide a ground fault point exploration indicator which performs an accurate operation in response.

[Means for solving the problem]

In order to achieve the above object, the present invention employs the means described in the claims, and the operation is as follows.

[Action]

When a search signal arrives at the distribution line, the signal is detected by the core. When the output of the resonance circuit based on the signal exceeds the operation sensitivity of the display device, the display device performs the display operation, and does not perform the operation in the following cases. Even if the ambient temperature changes and the resonance frequency of the resonance circuit deviates from the frequency of the search signal, an output corresponding to the strength of the search signal can be obtained from the resonance circuit. As a result, the display device operates normally.

〔Example〕

Hereinafter, drawings showing an embodiment of the present application will be described. FIG. 1 shows a display circuit. In the figure, A
Is a detection unit for detecting a signal flowing through the distribution line. A display device B performs a display operation in response to an output signal of the detection unit A. C is a suppression circuit for suppressing the operation of the display device when the signal is weaker than a predetermined value. D is a return signal detection unit for detecting a return signal flowing through the distribution line. E denotes a return operation control unit which causes the display device B to perform a return operation in response to a signal from the detection unit D. F is a short-circuit display control unit. When a short-circuit current flows through the distribution line,
This is a part for causing the display device B to perform the display. Next, the detection unit A will be described. Reference numeral 1 denotes a CT (current transformer) on the ground fault detection side, which is composed of a split type core 3 and a first detection coil 4 wound around the core, as shown in FIG. The core 3 is made of ferrite having a high magnetic permeability in order to increase the sensitivity. Reference numeral 5 denotes a resonance capacitor which is connected to the coil 4 in parallel. The detection coil 4
The capacitor 5 and the capacitor 5 form a parallel resonance circuit 7 that resonates at 180 Hz of the search signal from the transmitter. The search signal of the transmitter is not limited to 180 Hz, but is set to an appropriate frequency within a range of, for example, 150 Hz to 250 Hz. The resonance frequency of the resonance circuit 7 is adjusted to the frequency. Next, the display device B will be described. This display device comprises a display control circuit B1 and a display B2 shown in FIG. First, the display control circuit B1 will be described.
The circuit B1 includes a display operation unit and a return operation unit. The display operation part is a part for performing the display operation of the display B2,
8, 16, 19, and 23 to 29. The return operation unit is a part for returning the display B2 to a return operation, and is constituted by members indicated by reference numerals 8, 16, 23, 29 to 31. Further, a sensitivity setting device 15 for setting the operation sensitivity of the display device is commonly provided. Hereinafter, these members will be described. Reference numeral 8 denotes a full-wave rectifier circuit connected to the output side of the resonance circuit, and the sensitivity setting device 15 is configured with a variable resistor so as to limit a current flowing through a display capacitor 16 and a load resistor 17 to be described later. Is used to set the circuit current, that is, the sensitivity. Reference numeral 16 denotes a display capacitor for storing an input signal (a search signal), and an electrolytic capacitor is suitable for use as the capacitor. 19 is a first switching element, which uses an SCR. 19a is an anode, 19b is a cathode, and 19c is a gate. Reference numeral 23 denotes a zener diode, which prevents the input side of the voltage detection element from being input with a predetermined voltage, for example, 8 V or more. Reference numeral 24 denotes a second voltage detecting element, the input terminal 24a of which has a predetermined voltage of, for example, 2 V (however, 10 V
When the signal reaches v), a signal is output from the output terminal 24b. Reference numeral 25 denotes a differentiating circuit comprising a capacitor 26 and a resistor 27. The output signal from the voltage detecting element 24 is converted into a pulse by the same circuit, and further, the trigger is applied to the gate 19c of the first switching element 19 through the protective resistor 28. It is designed to be input as a signal. Reference numeral 29 denotes a capacitor for storing the current flowing through the zener diode 23, and for setting the input terminal 30a of the third voltage detecting element 30 to a predetermined voltage, for example, 4V. Reference numeral 31 denotes a second switching element, which is made conductive by a signal from the output terminal 30b of the third voltage detecting element 30, and is made conductive at the time of recovery, and uses, for example, an SCR. 31a is the anode,
31b indicates a cathode, and 31c indicates a gate.

Next, the display B2 will be described. Reference numeral 21 denotes a display body driving coil including a display coil 20 and a return coil 22. One end 20a of the display coil 20 and one end 22a of the return coil 22 are connected and integrated. An electromagnet 38 shown in FIG. 3 is formed by winding the coil 21 around an iron core. 39
Is a permanent magnet having N and S poles as shown in FIG.
39a makes it rotatable. Reference numeral 36 denotes a display attached to the shaft 39a, which is painted differently as shown in the drawing so that display and non-display can be distinguished depending on the rotation position.

Next, the suppression circuit C shown in FIG. 1 will be described. Reference numeral 17 denotes a load resistor connected in parallel to the output side of the detection unit A via the rectifier circuit 8. Reference numeral 18 denotes a first voltage detection element, and an input terminal 18a
Is connected to the plus side, and the ground terminal 18c is connected to the ground side. The sensing element 18 and the load resistor 17 form an equivalent circuit shown in FIG. The detection element 18 includes a detection unit 18e having a higher impedance than the load resistance 17, and when the voltage level of the input terminal 18a reaches a predetermined voltage, for example, 2v, the output terminal 18b is input from the connection state to the ground terminal 18c. The state is switched to the connection state to the terminal, and the load resistance 17 is short-circuited by this switching, and the resistance is separated from the output terminal of the rectifier, that is, both ends of the first detection coil 4 by opening the contact 18d. become.

Next, the return signal detection unit D in FIG. 1 includes a current transformer (CT) 2. The current transformer 2 is, as shown in FIG.
It is constituted by the core 3 and a second detection coil 32 wound therearound.

Next, the return operation control unit E of FIG. 1 will be described. 33
Is a discrimination circuit for discriminating a return signal, for example, a 50 Hz commercial current, and is constituted by a filter circuit. Reference numeral 34 denotes a third switching element, which comprises a transistor.

Next, the short-circuit display control unit F will be described. Reference numerals 9 and 10 denote Zener diodes connected in parallel to the output terminals of the rectifier 8 in order to limit the generated voltage at the output terminals of the rectifier 8 when an excessive current such as a short-circuit current flows through the high-voltage distribution line 103. The one with a Zener voltage of 2 V is used between B and R, and the one with 24 V is used between R and R. 12 is protection resistance, 11
Is a fourth switching element, and when a current flows through the protection resistor 12, the voltage drop across the resistor is added to the ard 11a and the gate 1
This is applied between 1b and is switched by it, and a programmable unijunction transistor (PUT) is used. Reference numeral 14 denotes a fifth switching element whose base 14a is connected to the cathode 11c of the fourth switching element (PUT) via a protection resistor 13. The protection resistor 13 is used to prevent an excessive signal from being input from the fourth switching element 11 when a short-circuit current flows through the high-voltage distribution line 103. 35 is a capacitor for setting the voltage of the base 14a to a predetermined voltage.

In the display having the above-described circuit configuration, first, the valley of the operating current-frequency characteristic as shown in FIG.
Operating sensitivity position (position corresponding to 150 mA in the figure)
A core having a magnetic permeability that is deeper than that of the core is used. That is, the output of the resonance circuit is increased by increasing the inductance, and thereby the position of the operation sensitivity is deepened as described above. As a result, the search signal transmitted from the transmitter, ie, the operating current (150 mA), has a wider frequency bandwidth in the display operation area.

Second, if the valley of the operating current-frequency characteristic is deeper than the operating sensitivity of the display device as described above, the display device may malfunction there. Therefore, the display operation is suppressed by the suppression circuit C there. For example, when the current value of the search signal flowing through the distribution line is 150 mA or less, the voltage at the input terminal 18a of the first voltage detection element 18 is suppressed low by the load resistor 17 connected in parallel to the output terminal of the resonance circuit. Is kept in a non-operating state. On the other hand, when the current value of the search signal is 150 mA or more, the voltage detection element 18 is operated by a voltage drop due to the circuit current flowing through the load resistor 17, whereby the load resistor 17
Is disconnected from the output terminal of the resonance circuit 7. As a result, the display capacitor 16 connected in parallel to the resonance circuit is charged at once, and its voltage is detected by another voltage detection element 24 (second voltage detection element) connected in parallel to the capacitor 16, and the voltage is detected in the subsequent stage. A circuit current is applied to the display coil 20 to operate the display 36.

That is, as for the point of the core 3 of the first resonance circuit 7, one having an operating current-frequency characteristic as shown by I and I 'in FIG. 5 is selected and used. In other words, if the current (sensitivity) of the exploration signal at which the operation is performed is set to 150 mA, when the ambient temperature is 20 ° C., the operable frequency band is 150 Hz to 2 Hz.
The frequency bandwidth can be increased to 40 Hz. The operating current (current of the exploration signal) and the frequency characteristics when the ambient temperature is 40 ° C and when the ambient temperature is -20 ° C are respectively
II, III. However, II and III have characteristics I 'of 150 mA or less.
Are not shown in the drawing.

From the above, the ambient temperature at which the display is used is -20 to
These common frequency bandwidths are in the 40 ° C range.
f1 to f2 (160Hz to 240Hz), so if the frequency to be transmitted from the transmitter is set within the above range, for example,
If the search signal is transmitted at a fixed frequency of 180 Hz, the display performs a display operation regardless of the ambient temperature.

As shown in the characteristic diagrams I and I ', it cannot be used as it is. In other words, the above characteristics are 150mA that should be in the non-operating region due to the increased sensitivity.
It shows that the following currents also malfunction before and after the resonance frequency. Therefore, the above-described suppression circuit C is provided so that the operation is not performed unless the search signal (operation current) is 150 mA or more.

That is, as described in the second point, the load resistor 17 is connected in parallel to the output terminal of the resonance circuit 7. The load resistance 17 is determined by the current (exploration signal) flowing through the high-voltage distribution line.
In the case of 0 mA or less, the output of the resonance circuit is suppressed by the same resistance, and its value is limited to 2 V or less of the operating voltage of the first voltage detecting element 18. On the other hand, when the current of the search signal is 150 mA or more, the voltage detecting element 18 is operated by the voltage drop across the load resistor 17, thereby disconnecting the resistor 17 from the output terminal of the resonance circuit 7. As a result, the display capacitor 16 is charged all at once to a predetermined voltage of, for example, 10 V at the output of the resonance circuit, and this is detected by the second voltage detecting element 24. After the detection, the charge of the display capacitor 16 is discharged. Display coil 20
And the display 36 is operated.

That is, the operating characteristics of the display are the frequency-operating current characteristics I, II, and III of FIG. 5, the operating current (the current of the search signal flowing through the high-voltage distribution line) is 150 mA, and the ambient temperature range is -20. When the temperature is between ℃ and 40, the operable frequency band is f1
.About.f2 (160 Hz to 240 Hz). Therefore, if the transmitter transmits a search signal including the above-described current and a frequency in this band, the display device can reliably perform a display operation.

Next, a description will be given of an operation method and an operation in the case of performing a search operation for a ground fault point using the display having the above circuit configuration.

[Search for ground fault points]

In FIGS. 6 to 8, when a ground fault occurs in a high-voltage distribution line, the fault-to-ground fault section I is set by an accident section detection device installed in a substation (sales office) and an automatic section switch of the distribution line. Is detected. In the section I where the ground fault detection is performed, the closing of the automatic segment switches S1 and S2 is locked, and the power is cut off.

The high-voltage distribution line 103 has a number of indicators 100, 1
00 'are attached in a suspended manner at appropriate intervals.
When the accident section I is detected, the transmitter 101 is carried by a vehicle or the like to the detected accident section I and the high-voltage distribution line 103 is detected.
And the ground E. In this case, each terminal of the distribution line in the section I is grounded to the ground in three phases.

When the transmission preparation is completed in this way, the transmitter transmits a search signal a having a predetermined frequency, for example, 180 Hz and a maximum generated voltage (peak value) of 10 kv for, for example, 35 seconds.

Then, the exploration signal flows through the circuit that returns to the transmitter 101 → the high-voltage distribution line 103 → the ground fault resistance Rg at the fault point → the ground E → the transmitter 101. As a result, the indicator 100 mounted between the accident point and the transmitter 101 detects this exploration signal (current) i flowing through the high-voltage distribution line 103 and operates to determine that there is a ground fault. indicate. Also, the indicator 100 'mounted at a location other than the above does not operate because the current does not flow. In other words, it can be determined that the accident point exists between the activated indicator 100 and the inactivated indicator 100 '.
For example, if this indicator is attached to each distribution line 103 of each electric pole 102 as shown in FIG. 8, a specific accident point can be found at an early stage.

The operation of the display in the above case is as follows.
That is, in the display, a signal flows through the path shown by the thick line in FIG. 9 and the display B2 performs the display operation. That is, the current transformer 1
, The signal is detected, and the signal output from the coil 4 is rectified by the rectifier circuit 8. This current is stored in the display capacitor 16 via the variable resistor 15. The signal (current) also flows to the load resistor 17 via the variable resistor 15. In this case, the voltage drop across the load resistor 17 is a predetermined voltage (for example, 2
When v) is reached, that is, when the input terminal 18a of the element 18 reaches a predetermined voltage, the voltage is output from the output terminal 18b. As a result, the load resistor 17 is disconnected from the output terminal of the current transformer 1. As a result, all the signals are applied to the display capacitor 16, and the electric charge is immediately stored to reach a predetermined voltage, for example, 10V.

In this way, the Zener diode 23 has a predetermined voltage of 8 V
When the voltage of the capacitor 29 becomes the predetermined voltage of 2V, the input terminal 24a of the second voltage detecting element 24 becomes 2V and an output is generated from the output terminal 24b. This output signal is
The pulse is shaped into a pulse-like waveform by 5, and is input to the gate 19c of the first switching element 19 via the protection resistor 28.
The element is rendered conductive by this trigger signal. Then, a discharging circuit on the + side of the display capacitor 16 → the display coil 20 → the first switching element 19 → the − side of the display capacitor 16 is formed, and the above-mentioned electric charge stored in the display capacitor 16 is discharged. .

That is, a current flows through the display coil 20, and the magnetic body 38 (for example, tomenda (trade name)) in FIG. 3 is magnetized. Due to this magnetization, the permanent magnet 39 disposed in the vicinity of the magnetic body repels and rotates, and the display 36 rotates, and the display indicates the ground fault state. The magnetic body 38 has such a characteristic that it keeps being kept magnetized once and keeps the state when a current flows in the reverse direction.

The reason why the exploration signal is set to 180 Hz in the above description is to make it easier to determine the commercial frequency of 50 Hz, and if the frequency is too high, the influence of the ground capacitance of the distribution line becomes large, the ground impedance decreases, and the charging current decreases. This is determined by the fact that the range of the search for the fault point becomes narrower, and the power that the display unit can receive per unit time is increased.

(Return operation of display unit)

Reconnect the output terminal on the transmitter side to the return terminal side and connect to the two wires of the high voltage distribution line. In addition, the terminal is grounded in three phases at a time.

In this state, a return signal is transmitted to the distribution line 103. The maximum generated voltage is, for example, 60 V, and the duration is, for example, 12
Seconds. In this case, a current of 7.2 A flows due to the above voltage. When the return signal of 50 Hz flows through the high-voltage distribution line 103 as described above, the signal flows on the path indicated by the thick line in FIG. 10 and the display B2 returns. That is, the return signal is detected by the current transformer 2 on the return side. This detected signal is 50Hz
A positive signal flows through the filter circuit 33 through the diode 49 and flows into the base 34a of the third switching element 34.
Therefore, the element is turned on.

Further, since the current value of the return signal is larger than the search signal at the time of the ground fault, the signal is also detected in the current transformer 1.
As a result, the same operation as that during the ground fault display is performed, and the output signal of the second voltage detection element 24 is output through the differentiating circuit 25. However, in this case, as described above, the potential to the point is lowered low because the third switching element 34 has already been turned on.
19 remains OFF. And Zener diode 2
The current flowing through 3 flows into the capacitor 29 and is stored,
When the voltage reaches a predetermined voltage 4v, the voltage is output from the output terminal of the voltage detection element 30 to the gate 31c of the second switching element 31, and the second switching element 31 is turned on by the trigger signal. This forms a discharge path on the + side of the display capacitor 16 → the return coil 22 → the second switching element 31 → the − side of the display capacitor 16. Accordingly, the magnetic body 38 magnetized at the time of the above display is magnetized to the opposite polarity, so that the permanent magnet 39 is attracted by this, and the display body 36 returns from the display state to the original state.

[Operation when short-circuit current flows]

In the distribution line, an interphase short circuit or the like occurs for some reason, and an excessive current flows through the high-voltage distribution line 103. Then, in the display, a signal flows through a path shown by a thick line in FIG. 11, and the display B2 performs a display operation. That is, this current (signal) is detected by the current transformer 2 and further a 50 Hz filter circuit
It passes through 33 and then through diode 49.

In this case, a signal detected by the current transformer 1 and rectified by the rectifier circuit 8 due to an excessive input signal exceeds the Zener voltage 24 V of the Zener diode 10. Further, when both ends of the Zener diode 9 reach the Zener voltage 2V, the resistor 12
Is applied to the anode of the fourth switching element 11
The element 11 is conducted between the gate 11b and the gate 11b. Second
The signal input to the integration circuit 50 via the switching element 11 is input to the base 14a of the fifth switching element 14 via the protection resistor 13, whereby the element 14 becomes conductive.
Then, the output of the diode 49 is connected to the collector 14 of the element 14.
b, falls through the emitter 14c to the ground circuit, and the third switching element 34 is kept in the OFF state.

Accordingly, in the other circuits, the same operation as that of the ground fault display is performed, and the magnetic body 38 of the display B2 is magnetized in the same direction as that at the time of the ground fault. As a result, the display 36 also rotates in the same direction, and enters the display state.

Next, FIG. 12 shows another embodiment of the display device of the present invention, which differs from the above embodiment in the following points. A large wattage limiting resistor R1 is provided on the output side of the current transformer 1e to limit the input signal caused by a large load current (not a short-circuit current but a constantly flowing load current) flowing through the high-voltage distribution line. To suppress output.

Further, a differentiating circuit 2 on the output end side of the second voltage detecting element 24e.
A Miller integrating circuit 43 including a transistor 41 and a capacitor 42 is provided between 5e and the gate 19ce of the first switching element 19e. Further, in connection with the above, a field effect transistor (FET) 44 is used as a third switching element connected to the output side of the filter circuit 33e, and the diode 49e is turned in the opposite direction to set the gate 44a of the transistor 44 to a high voltage. When a current of 50 Hz is flowing through the distribution line, a negative potential is applied to turn on the field effect transistor 44, thereby turning off the transistor 41 connected to the drain 44b of the transistor via the resistor 45. It is. By these circuit changes, the gate characteristics of the first switching element 19e are stabilized, and the accuracy of discriminating between the return operation and the display operation is further improved.

In addition, functionally considered to be the same or equivalent to those in the previous figure, the same reference numerals as those in the previous figure denote the same parts as in the previous figure.
And duplicated description is omitted.

[Effect of the Invention] As described above, in the present invention, the transmitter 1
When the current of the search signal output from 01 flows, not only the display device B can be operated for display by a signal obtained in the resonance circuit 7 but also the magnetic permeability of the core 3 due to a change in the ambient temperature at the installation location. And the resonance frequency of the resonance circuit 7 changes from the predetermined frequency of the search signal, the resonance circuit 7 has a U-shaped valley of the operating current-frequency characteristic that is lower than the operation sensitivity of the display device. It is designed to be deeper and to suppress the display operation of the display device B in a part where the operating sensitivity is deeper, so that when a search signal of a predetermined frequency is sent to the distribution line 103, In addition, an output for appropriately operating the display device B in accordance with the strength, that is, an operating current-frequency characteristic can be obtained, and a normal display without erroneous display can be performed. This means that outside of the display 100,
In order to operate other types of display devices with one search signal, there is utility that the display device can be used without any trouble even in a site where a search signal having a fixed frequency is transmitted.

[Brief description of the drawings]

The drawings show an embodiment of the present invention. FIG. 1 is a circuit diagram of a display, FIG. 2 is an equivalent circuit diagram showing a connection state between a first voltage detecting element and a load resistor, and FIG. FIG. 4 is a schematic diagram of the structure of the detection unit, FIG. 5 is an operating current-frequency characteristic diagram of the display, FIG. 6 is a schematic explanatory diagram showing a use state of the search device, FIG. The figure shows a front view of the operation status of the display at the time of a ground fault, FIG. 8 shows the plan view of FIG. 7, FIG. 9, FIG. 10, and FIG. FIG. 12 is a circuit diagram showing a different embodiment, and FIG. 13 is an operating current-frequency characteristic diagram in a conventional display. A: detection unit, B: display device, C: suppression circuit, 3 ...
... core, 4 ... coil, 5 ... capacitor for resonance, 7 ...
... Resonant circuit, 15 ... Sensitivity setting device.

Continued on the front page (72) Inventor Ryosaku Nakata 35 Fukamama, Nagakusa-cho, Obu City, Aichi Prefecture Japan High Voltage Electric Co., Ltd. (72) Inventor: Norifumi Hotta 35, Fukamama, Nagagusa-cho, Obu-shi, Aichi Japan High-Tech Electric Research Laboratory (56) References JP-A-55-134365 (JP, A) JP-A-55 -89762 (JP, A) (58) Field surveyed (Int. Cl. ⁶ , DB name) G01R 31/08

Claims (1)

(57) [Claims] 1. A core for transmitting a search signal different from a commercial power supply to a distribution line in a power failure state by a transmitter, and detecting a magnetic field induced in the surroundings by the search signal flowing in the distribution line.
It has a resonance circuit that resonates at the frequency of the search signal detected by the core, a display device configured to perform a display operation by an output signal of the resonance circuit, and a sensitivity adjuster for setting operation sensitivity of the display device. In the display for detecting a ground fault, the sensitivity adjuster and the core of the resonance circuit are provided with an operating current −
The valley of the frequency characteristic is determined to be smaller than the sensitivity current of the ground fault relay of the substation of the display device, and is deeper than the position of the operation sensitivity that does not operate with the charging current with respect to the earth capacitance of the distribution line. And a suppression circuit for suppressing the display operation of the display device in a portion where the valley of the operating current-frequency characteristic is deeper than the position of the operation sensitivity of the display device. A ground fault display.