JPH0218009B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method of transmitting an alarm signal obtained by monitoring the insulation condition of an electric circuit.

(Prior art) In general, in a transformer that transforms high-voltage electricity into low-voltage electricity, the insulation condition of the secondary low-voltage circuit is monitored, and in the event of an abnormality in the insulation resistance value, this can be quickly detected and immediate countermeasures taken. Various monitoring devices will be installed at required locations to ensure a stable supply of power.

This method of monitoring the status of electrical circuits generally involves installing a detector on the type 2 grounding wire of the transformer, and detecting commercial power leakage through impedance (insulation resistance or capacitance component, etc.) existing between the low-voltage electrical circuit and the ground. In order to measure the power supply component or the state of the circuit, it is common to apply a signal with a frequency different from the commercial power supply frequency to the circuit, and then detect the component leaking through the impedance.

Therefore, these monitoring devices are naturally installed near the transformer.

However, since the power receiving room where the transformer is installed is constructed in a place where no one is normally stationed due to the high voltage power transmission lines entering and pushing into the power receiving room, It is necessary to transmit alarm signals etc. to an office or control center where a person is permanently stationed.

Conventionally, the method for transmitting this monitoring signal was to install a new monitoring signal transmission line between the monitoring equipment and the office, but it was not possible to install this transmission line in an existing building. It took a lot of time and money to do so. To reduce this burden,
A high frequency transmission signal modulated with the signal to be transmitted is superimposed on the existing power wiring for electric lights between the power receiving room and the office etc., and this high frequency signal is received at the office etc.
There was a method (power line transmission method) that transmitted the necessary monitoring signals by demodulating them.

Another method is to use a transformer secondary low-voltage line instead of the above-mentioned power line, that is, a grounding line for type 2 grounding work for power transmission, which corresponds to the alarm signal that should be transmitted to the line. In the office or the like where a low frequency signal is applied and manned monitoring is performed, the low frequency signal voltage or current between the electric line (ground phase) and the third type grounding line is detected, and the presence or absence of an alarm signal is detected. There was a way to identify the type.

(Problems to be Solved by the Invention) However, all of the conventional alarm signal transmission methods as described above have various drawbacks.

In other words, since the former electric light line transportation method uses electric power wiring for electric lights, signal transmission may not be carried out sufficiently due to changes in the electric light load. However, the latter method using power transmission lines has the disadvantage that it cannot be put to practical use unless it is constrained by the above-mentioned type 3 grounding work. Since the voltage at the ground point rises to the line voltage, the reception circuit becomes saturated and becomes difficult to receive the transmitted signal, even if a monitoring signal indicating that the impedance between the line and the ground has dropped abnormally is being transmitted. This had the disadvantage that it could not be reproduced in the receiving section.

(Means and effects for solving the problem) The present invention has been made to solve the problems of the conventional method, and is to solve the problems of the conventional method. It detects this and forcibly outputs an alarm signal to the receiving output, making it possible to reliably detect abnormalities in the electrical circuit from the receiving output.

In addition, when applying the transmission signal to the grounding wire of Type 2 construction, by using a low frequency signal with low internal resistance, attenuation is small and reliable transmission is possible without being affected by load even over long distance cable lines. The purpose of this invention is to provide a device that can achieve this goal.

(Example) The present invention will be described in detail below based on an illustrated example.

FIG. 1 is a block diagram showing one embodiment of the present invention. In the same figure, T indicates a transformer that transforms high-voltage electricity into low-voltage electricity. In this case, it is a single-phase three-wire type, and 1 and 3 are ungrounded lines on the low voltage side, and 2 is a grounded line (grounded phase). Show each. The electric line 2 is subjected to type 2 grounding work using a grounding wire 4 at the transformer.

In this embodiment, the present invention is applied to such an electric line, and an alarm signal generated by a monitoring device 5 attached to an insulation resistance measuring device etc. installed near the transformer T is transmitted to an office located on an extension of the electric line. This shows a case where the signal is transmitted to an alarm signal receiving device 6 installed in a room or the like.

First, the output of the insulation monitoring device 5 and the modulation device 7
are connected by a terminal 8, and the insulation monitoring device 5
The monitoring signal generated by the carrier wave is modulated or code-converted in the modulation unit 7, and then injected into the transformer 9 coupled to the ground line 4, thereby converting the ground line to the ground line. It is applied to the electric circuit 2 via.

On the other hand, the alarm signal receiving device 6 connects this to the ground via a connecting wire 10 provided in the ground phase circuit 2.
The above-mentioned modulated carrier low frequency signal induced between E ₃ and the grounding line 11 that has undergone type 3 grounding work is derived to the demodulation circuit 12. At this time, the electric line 2 and the demodulation circuit 1
A capacitor 14 is connected to the connection line 10 provided between the
Insert it so that it does not affect the insulation resistance value when measuring insulation resistance with DC voltage using a megger, etc.

The input terminal of this demodulation circuit is designed to have a sufficiently high impedance with respect to the load connected to the electric line, thereby preventing the alarm signal receiving device 6 from having an adverse effect on the commercial power of the electric line.

The modulated carrier signal derived in this way is
Inside the receiving device 6, the commercial power supply frequency component and its harmonic components are removed and demodulated, and the transmitted alarm signal is detected and its type is identified.

Furthermore, a ground fault detection circuit 13 is connected in parallel with this demodulation circuit between the ground phase electric line 2 and the third type grounding line 11, so that the voltage rises above a certain level due to a ground fault in the electric line. It is configured to detect the commercial power supply voltage and notify that fact, or it is connected so that the output of the receiver 6 is controlled to receive an alarm signal regardless of the result of detection of the modulated carrier signal.

Naturally, the input impedance of the ground fault detection circuit 13 at this time is also configured to have a high impedance with respect to the commercial power supply.

It would also be effective to take into consideration that the demodulation circuit outputs an alarm in a safe direction so that an alarm is generated when the transmission signal cannot be received.

As is clear from the above explanation, if a device configured in this manner is used, the alarm signal of the insulation monitoring device can be transmitted to an office connected to the same transformer far away by using the ground wire of the power wiring. It can be transmitted reliably to the receiving end.

Furthermore, although the above embodiments have been shown in the case of a single-phase three-wire system, the present invention is not limited to this in any way, and can also be applied to, for example, a three-phase system with one end of the secondary side grounded, or a single-phase system. That is clear.

Furthermore, various configurations of these devices are conceivable in addition to the above-mentioned embodiments, such as a device in which the insulation resistance measurement function of the electrical circuit and the above-mentioned alarm signal transmission function are combined in the same device, or It is clear that any modulation method may be used when superimposing the alarm signal on the carrier wave.

(Effects of the Invention) Since the present invention is constructed and operated as described above, the alarm signal is not interrupted even when an accident such as a ground fault occurs in the electric line, and the alarm signal is accurately transmitted. It has an extremely large effect on this.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing one embodiment of the present invention. 1, 3...Ungrounded electrical circuit, 2...Grounded electrical circuit, 4 and 11...Grounding wire, 5...Insulation resistance etc. monitoring device,
6... Receiving device, 7... Modulator, 9... Injection transformer, 10... Connection line, 12... Demodulation circuit, 13
...Ground fault detection circuit.

Claims (1)

[Claims] 1. Transmission of low-frequency waves modulated by alarm signals, etc. to be transmitted obtained from insulation monitoring equipment, etc., to the low-voltage secondary circuit via the grounding wire of the second-class grounding work of the transformer that transforms high-voltage electricity to low-voltage electricity. By applying a signal and at the same time detecting and demodulating the low frequency voltage induced between the earth and the grounding line of the low voltage line on which the second type grounding work has been carried out on the extension of the line. The monitoring system is characterized in that, in addition to outputting the transmitted signal such as an alarm, an alarm signal is forcibly output when the commercial frequency voltage between the grounding cable and the earth exceeds a predetermined value. Signal transmission equipment.