JPH0363303B2 - - 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) Generally, in a power receiving room where a transformer that transforms high-voltage electricity into low-voltage electricity is installed, the insulation condition of the secondary circuit of the transformer is monitored, and the insulation condition is abnormal or abnormal conditions are detected. In such a case, a monitoring device generates an alarm signal, and this alarm signal is transmitted to an office or the like where a person is permanently stationed.

A method of transmitting such a signal is to apply a low frequency signal corresponding to the alarm signal, etc. to be transmitted to the low voltage secondary line of the transformer via the grounding wire of the second type grounding work on the line. In offices, etc. where manned monitoring is performed, the low frequency signal voltage induced between the electric line (mostly using a ground phase) and the ground line of type 3 construction or the ground is connected to an amplifier with high input impedance. However, in this case, the method of connecting the electric lines and the amplifier is to simply insert and connect a capacitor in series between these electric lines and the input terminal of the amplifier to derive the low frequency signal. It was hot.

(Problems to be Solved by the Invention) However, as described above, the conventional receiving method has the following drawbacks.

That is, in a receiving device installed in a manned office, etc., when detecting the low frequency signal voltage induced between the electric line and the third type grounding line or the earth, the electric line load is applied to the third type grounding line or the earth. There is a problem in that when impulsive noise currents generated from sources such as the like flow or are induced, they mix into the demodulated output of the receiver and cause malfunction. This is because an amplifier or the like having a high input impedance is connected between the electric line (ground phase) and the ground, and the amplifier becomes saturated with the above-mentioned impulsive noise.

(Means and effects for solving the problem) The present invention has been made to solve the problems of such conventional methods. In order to eliminate impulsive noise, when detecting the low frequency, terminate the electrical path and the third-class grounding wire or earth with a capacitor of the required value, and apply the voltage across the capacitor to an amplifier with high input impedance. By detecting the low frequency signal voltage, the impedance is made sufficiently low for pulse noises, thereby eliminating these pulse noises. As mentioned above, instead of the capacitor, an element having sufficiently high DC resistance and impedance that does not adversely affect the electric circuit may be used.

(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 is a transformer that transforms high voltage electricity into low voltage electricity, and 1, 2 and 3 are 3 for power.
It is a phase three-wire electric circuit, and 1 and 3 are low-voltage side non-grounded electric circuits, and 2 is a grounded electric circuit (earthed phase). The electric line 2 is grounded by a grounding line 4 which has undergone type 2 grounding work _E2 at the transformer, and a motor 15 is connected as a load on the extension thereof.

In this embodiment, the present invention is applied to such an electric line, and an alarm signal generated by, for example, an insulation monitoring device 5 installed near the transformer T is received by a receiver installed in an office or the like on an extension of the electric line. This shows the case where the data is transmitted to the device 6.

First, connect the output of the monitoring device 5 to the modulation device 7,
This modulates the output of the low frequency oscillator 8 as a carrier wave input to the section, and then inputs it to the transformer 9 coupled to the ground line 4 and applies it to the electric line via the ground line 4.

On the other hand, in the receiving device 6, the ground phase line 2
A capacitor 10 is used to terminate the connection between the capacitor 10 and the ground _E3 , and the above-mentioned low frequency signal induced across the capacitor 10 is connected to the input of the receiving circuit 11.
Capacitors 12 and 13 are inserted between the input terminal of the electrical circuit and the insulation resistance of the electrical circuit, so as not to affect the measurement when applying direct current using a megger or the like. It's for a reason.

In the receiving circuit 11, the low frequency voltage obtained through the capacitors 12 and 13 is received by, for example, a balanced amplifier, the output of which is passed through a filter, demodulated, and an alarm output is reproduced at its output terminal 14. This is what is output.

With this configuration, fluctuations in ground voltage or pulse noise due to noise generated by a load, such as the aforementioned motor, can be avoided by the capacitor 1.
0, the receiving circuit 11 is not affected by these, and the alarm signal can be reliably detected and demodulated.

Although the above embodiment shows a three-phase, three-wire case, the present invention is not limited to this in any way, and can be applied to a single-phase, three-wire case where one end of the secondary side is grounded, or to other electrical circuits. It is clear that you can also use
Furthermore, the capacitor 1 at the input end of the receiving circuit 11
0 may be replaced by another element, that is, one having a high impedance in terms of direct current but a low impedance against pulsed noise.

(Effects of the Invention) Since the present invention is configured and functions as described above, it is possible to accurately transmit alarm signals, etc. using electric circuits without being affected by load noise. It is extremely effective.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing one embodiment of the present invention. 1, 3...Ungrounded electric line, 2... Grounded electric line, 4...
...Grounding wire, 5...Monitoring device, 6...Receiving device, 7
...Modulation unit, 8...Low frequency oscillator, 9...Transformer, 10, 12 and 13...Capacitor, 11...
...Receiving circuit, T...transformer.

Claims (1)

[Claims] 1. A low-frequency signal modulated with an alarm signal to be transmitted obtained from a monitoring device, etc. is applied to the low-voltage secondary circuit through the grounding wire of a transformer that transforms high-voltage electricity into low-voltage electricity, and the By extension,
The alarm signal is output by terminating one of the low-voltage electric paths and the ground with a capacitor of a required value, and detecting and demodulating the low-frequency voltage induced across the capacitor. Features of a monitoring signal receiving device.