JPS63268096A - Warning signal transmitter having ground impedance compensated - Google Patents

Abstract

PURPOSE:To compensate automatically a drop in received signal voltage by increasing a transmission output for a specific time when the leak current of a low frequency signal larger than a specific value is detected. CONSTITUTION:A voltage induced between a cable run 1 and a grounding point (E2) by applying a sent signal of low frequency to the cable run is denoted as (e) and the received voltage of a receiver 7 is denoted as V. Then this received voltage V becomes lower because of increases in grounding resistance (r) and electrostatic capacity (c) to the ground and a decrease in ground insulation resistance R. Further, a feedback current (i) based upon the low-frequency signal voltage (e) fed back to a grounding line 1 increases as a leak current (i) as the parallel impedance of the ground insulation resistance R and electrostatic ground capacity decreases. Consequently, the output of a current transformer which passes through the grounding line 1 is applied to a detecting circuit 10 and applied to the system consisting of a filter F, a rectifying circuit DET, and a comparing circuit COMP for a reference value i0; when the output (i) of the filter F increases above the specific value i0, the transmission output is increased to compensate the drop in the received voltage.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a transmission device for alarm signals obtained by monitoring the insulation state of electrical circuits.

(Prior art) As a method of monitoring the insulation condition of the secondary low-voltage line of the power receiving transformer and transmitting various alarm signals from the power receiving room where the monitoring device is installed to offices where people are permanently stationed, The transmission device shown in the figure is used. That is, by applying the output voltage of the transmitter 4 to which the alarm signal 6 is input to the injection transformer 5 passing through the grounding wire 1 of the transformer T, a modulated voltage e is generated between the electrical line 3 and the grounding point 82. Apply a low frequency signal voltage.

A receiver 7 installed on the extension of the electric line 3 connects to the earth E3 via the electric line 3 and a capacitor Co (Co is a DC voltage used to protect the receiver when measuring the insulation resistance of the electric line in annual inspections, etc.). It detects the signal voltage between the
It was intended to play and output. However, the electric line 3.
As shown in the figure, there are ground insulation resistances Rt and Rx and ground capacitances C1 and C2 between the electric path 2 and the ground. Further, a grounding resistance r exists at the grounding point E2. Therefore, even if the input terminal impedance of the receiver is sufficiently high, alarm signals and the like are attenuated due to the influence of these ground impedances, resulting in a situation in which signals cannot be received correctly.

(Object of the Invention) The present invention provides a device that can correctly obtain a received signal even if the impedance existing between the electric line and the ground becomes low.

(Summary of the Invention) In order to compensate for the attenuation of the received signal voltage when the impedance between the ground and the ground becomes low, the present invention reduces the frequency component of the transmitted signal that returns to the ground line by the low frequency transmitted signal voltage applied to the electric line. A leakage current is detected, and when the impedance decreases, the leakage current increases.If the leakage current of the low frequency signal is detected to be greater than a predetermined value, the transmission signal is transmitted for a predetermined period of time. By increasing the voltage, the drop in received signal voltage is automatically compensated for.

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

FIG. 1 is a diagram showing an embodiment of the present invention, and the same symbols in this figure as in FIG. 3 have the same meanings. By applying a low frequency transmission signal to the electric line, the stain line 1 and the ground point (
E2) Let e be the voltage induced between. Assuming that the received voltage of the receiver 7 is V (the input impedance of the receiver is selected to be sufficiently high), the signal transmission system in Fig. 1 has the voltage V in Fig. 2.
Increase in ground resistance r and ground capacitance C.

It can be seen that the received voltage decreases as the ground insulation resistance R decreases. On the other hand, the feedback current i due to the low frequency signal voltage e that returns to the grounding wire 1 is +2... Leakage current i will increase.

Therefore, the output of the current transformer 8 passing through the grounding wire 1 is applied to the detection circuit 10 (FIG. 3 shows the details of the detection circuit),
Transmission signal frequency band filter F, rectifier circuit DET reference value i. and a comparator circuit COMP, and in the comparator circuit, the output i of the filter F becomes a predetermined value i. When this happens, the control circuit C0NT operates for a predetermined period of time to increase the gain of the amplifier 11 for applying the low frequency signal voltage to the injection transformer 5, thereby increasing the applied voltage e. In this way, the leakage current i also increases, but the receiving voltage (2) is not high, and it is possible to receive the signal correctly.

Furthermore, after a predetermined period of time, the gain of the amplifier 11 is returned to the original gain under the control of the control circuit CON'I'.

This is because there is a possibility that the ground impedance of the electric line becomes high during this time.

Further, if the output i is a predetermined value of 10 or more, the same operation is repeated. Fi does not increase the applied voltage e from the beginning,
This takes into consideration the adverse effect on load equipment connected to the stain path due to electromagnetic field radiation in the electric path due to the applied voltage eK.
, various alarm signals 6 are input to the input of the transmitter 9 as in FIG. 4, and are modulated by the transmission processing device 9 and applied to the amplifier 11. The operation of the receiving circuit is basically the same as that shown in FIG.

As described above, an important function of an alarm signal transmission device is to transmit an alarm signal to a receiver even in a state where insulation deterioration occurs and R becomes extremely low (a state close to a ground fault). You can expect a significant effect in achieving your goals.

In the above explanation, the gain of the amplifier was controlled in steps, but
The invention is not necessarily limited to this, and depending on the magnitude of the leakage current exceeding a predetermined value, the above example shows a case of a single-phase two-wire system, but even a single-phase three-wire system or a three-phase three-wire system may be used. It is clear that it does not matter. The current transformer 8 may also be used for an insulation detector (not shown).

[Brief explanation of the drawing]

Fig. 1 is a diagram showing an embodiment of the present invention, Fig. 2 is a diagram showing a circuit of the signal transmission system, Fig. 3 is a diagram showing a detection circuit, and Fig. 4 is a diagram showing an example of the present invention.
The figure shows an example of a conventional device. 1......Grounding wire, 2,3...
...Electric circuit. 4......Transmitter, 5...
・・Injection transformer 6・・・・・・Alarm signal,
7......Receiver, 8...-...
...Current transformer, 9......Transmission processing device, 10......Detection circuit. F・・・・・・Filter, DET・−・
・・・・・・Rectifier circuit, COMP・・・・・・
...Comparison circuit. C0NT・・・・・・・Control circuit. Patent applicant: Toyo Tsushinki Co., Ltd. Part Z

Claims (1)

[Claims] A low-frequency transmission signal voltage modulated by an alarm signal to be transmitted obtained from an insulating device, etc. is applied to the low-voltage secondary electric line via the low-voltage side grounding wire of the power receiving transformer, and at the same time, on the extension of the electric line, In a transmission device that outputs the transmitted alarm signal etc. by detecting and demodulating the low-frequency received signal voltage induced between a grounding cable and the earth, the low-frequency signal is returned to the grounding line. An alarm that compensates for ground impedance, characterized in that when the component current exceeds a predetermined value, the low frequency signal voltage is increased for a predetermined period of time to compensate for a drop in received signal voltage due to a drop in ground impedance. Signal transmission equipment.