JPH0418634B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an electrical circuit insulation monitoring device. Conventionally,
As a method of monitoring the insulation condition of the low-voltage circuit on the secondary side of a transformer that transforms high-voltage electricity into low-voltage electricity, a low-frequency voltage different from the power supply frequency (monitoring signal ) is applied, and this voltage causes a current to flow through the impedance between the low-voltage line connected to the transformer and the earth, and this current flows to the grounding wire of the transformer's type 2 grounding work, so this current is Changes in the ground impedance of the electrical circuit were determined by detecting the signal from the grounding wire using a CT (current transformer), passing it through a filter, etc., and monitoring this value.

Furthermore, by comparing the phases of the monitoring signal and the current based on the monitoring signal detected by CT and extracting the voltage component of the current that is in phase with the monitoring signal, the impedance between the electrical circuit and the ground can be determined. Of these, judgments were also made based on resistance.

These devices (insulation detection devices) that monitor the impedance between the electric circuit and the ground are generally placed near the transformer, and the person who operates or monitors the insulation detection device is responsible for the location of the transformer. If the device is permanently stationed in a location (office, etc.) that is different from the power receiving room (power receiving room), install a separate signal wire for transmitting the signal output from the insulation detection device between the power receiving room and the office, etc. It was necessary to place it.

For this reason, when newly installing signal wires in a building that was already completed, a lot of time and money was required for the wiring work. To compensate for this, the conventional method of transmitting signals between the power receiving room and offices, etc. is to superimpose a high-frequency electrical signal modulated with the signal to be transmitted on the power wiring for the lights, and separate this high-frequency signal. A method of transmitting the necessary signals by receiving and demodulating them at a location (Lightline carrier method)
It was hot.

However, since the conventional method described above uses power wiring for lighting, the signal may not be transmitted sufficiently depending on changes in the lighting load, and the length of the power wiring for lighting, load, etc. The drawback was that it could not be put to practical use unless it was restricted to the following conditions.

The present invention has been made in order to eliminate the drawbacks of conventional insulation monitoring devices, and provides for signal transmission between a power receiving room in which the insulation detection device is installed and an office where a person monitoring the device is located. In order to achieve this, power wiring is used, and as a signal transmission means, the insulation detection device uses a monitoring signal added to the grounding wire of the transformer's type 2 grounding work. , there is no need for construction work for the arrangement of signal wires, and the device that sends out signals on the power receiving room side can be manufactured at low cost because it uses an insulation detection device.Furthermore, monitoring signals can be widely monitored from every corner of the electrical circuit. It is an object of the present invention to provide an insulation monitoring device that is emitted at a low frequency with low internal resistance, has low attenuation, and is capable of sufficiently reliably transmitting a signal over a relatively long distance.

The present invention will be described in detail below based on illustrated embodiments.

FIG. 1 is a block diagram showing one embodiment of the present invention. In this figure, reference numeral 1 indicates a low-voltage side winding of a transformer that transforms high-voltage electricity into low-voltage electricity, and in the case of this embodiment, it indicates a single-phase three-wire electric circuit. 2 and 3 indicate two of the low-voltage electrical lines connected to the transformer, and the electrical line 2 is subjected to type 2 grounding work with the ground wire 4 at the transformer.

8 is an oscillation unit that oscillates at a frequency different from the power supply frequency, and an injection transformer 6 applies a monitoring signal to the ground line 4. In this example, the frequency is 25Hz voltage
2.5V (rms) is applied to the ground wire.

5 is for detecting the current flowing through the grounding wire 4.
The current detected by CT5, which is a CT (current transformer), is compared in phase with the oscillation voltage of 8 in the judgment section 7,
When the current in phase with the oscillation voltage reaches a certain value, an alarm signal is sent to the output terminal 13 of the determining section 7.

Reference numeral 9 denotes a modulation section, which stops the oscillation of 8 when an alarm signal is output to the judgment section output 13.

When 9 sends a signal different from 13 that needs to be transmitted, it can also have the function of continuing the oscillation of 8 by separating it at certain time intervals and sending out a signal different from 13.

In this embodiment, the device consisting of components 5 to 9 and 13 is referred to as an insulation detection device. Note that the increase in the impedance of 4 due to the connection of 5 and 6 should not affect the grounding resistance of the required type 2 grounding work. (In the case of the example, it is 1 or less)
10 is a capacitor connected to one wire of the electrical circuit where the insulation detection device is installed, and 11 is a grounding wire that is grounded to the earth.

The monitoring signal coming on the electric line 2 is received as a voltage between 11 and 11 through 10, and the receiving section 12 receives it as a voltage between it and 11.
This device separates and amplifies the monitoring signal and generates an alarm when the monitoring signal is a signal modulated by 9.

10 prevents the electrical circuit and the ground from being connected in a direct current manner by 12, and 10 to 11
The monitoring signal current flowing through the insulation detection device is kept small enough to not affect the current that the insulation detection device is trying to detect.

In addition, 12 is in order to issue an alarm in a safe direction.
When the monitoring signal applied to 2 can no longer be detected, an alarm is generated.

When the monitoring signal emitted from the insulation detector installed in the power receiving room has a frequency of 25 Hz and a voltage of 2.5 V, the attenuation is very small.We conducted tests in many locations in which a receiving device consisting of 10 to 12 pieces was installed at the end of the electrical circuit. I tried both, and they all detected and worked correctly.

Therefore, by using this device, the alarm signal of the insulation detection device can be sent to a receiving device in another remote office connected to the same transformer circuit with sufficient reliability by using the ground side circuit of the power wiring. be able to.

In the insulation detection device, since 5 to 8 are technologies that have already been used, it can be manufactured at low cost by just adding 9, and the receiving section also detects, separates, and amplifies low frequency signals, so it is relatively simple. Since it can be manufactured at low cost, the insulation monitoring device used in combination with the insulation detection device of the present invention and a receiving device for detecting the low frequency signal emitted by the insulation detection device is practical and can be widely used.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing one embodiment of the present invention. 1...Low voltage side winding of the transformer, 2 and 3...Low voltage electrical line connected to the transformer, 4...Grounding wire, 5...
... CT (current transformer), 6 ... Injection transformer, 7 ... Judgment section, 8 ... Oscillation section, 9 ... Modulation section, 10 ... Capacitor, 11 ... Grounding wire, 12 ... Receiving section, 1
3...Alarm signal output.

Claims (1)

[Scope of Claims] 1. Monitoring signal oscillation means for applying a monitoring signal of a low frequency different from the frequency of the power source to a grounding wire connected between a low-voltage circuit of a transformer that converts a high-voltage power source to a low-voltage power source and the ground. and detecting means for detecting the insulation state of the low voltage electrical circuit by comparing the current flowing back into the grounding wire and the monitoring signal oscillated from the monitoring signal oscillating means; and a detection output of the detecting means. a modulating means that applies a predetermined modulation to the supervisory signal generated from the supervisory signal oscillating means; An insulation monitoring device comprising: means for generating an alarm when the monitoring signal is a signal to which the predetermined modulation has been applied.