JP2543699B2 - Warning signal transmission method compensating for ground impedance - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method of transmitting an alarm signal obtained by monitoring the insulation state of a circuit.

(Prior art) Monitoring the insulation state of the secondary low-voltage path of the power receiving transformer,
As a method of transmitting various alarm signals from a power receiving room in which a monitoring device is installed to an office where people are resident, the transmission device shown in FIG. 4 has been conventionally used. That is, by applying the output voltage of the transmitter 4 which receives the alarm signal 6 to the injection transformer 5 penetrating the ground wire 1 of the transformer T, the modulated low voltage e between the electric line 3 and the ground point E ₂ is obtained. The frequency signal voltage is applied.

In the receiver 7 provided on the extension of the electric line 3, via the electric line 3 and a capacitor C ₀ (C ₀ is a DC voltage for protecting the receiver when measuring the insulation resistance of the electric line in an annual inspection etc.) Earth E ₃
The signal voltage between them is detected, demodulated, and a predetermined alarm signal AL is reproduced and output. However, as shown in the drawing, there are ground insulation resistances R ₁ and R ₂ and ground capacitances C ₁ and C ₂ between the electric lines 3 and ₂ and the ground. A ground resistance r exists at the ground point E ₂ . Therefore, even if the input impedance of the receiver is sufficiently high, the alarm signal and the like are attenuated by the influence of these ground impedances, and there is a drawback that the signal cannot be received correctly.

(Object of the Invention) The present invention provides a method for correctly obtaining a received signal even if the impedance existing between the electric line and the ground becomes low.

(Summary of the Invention) The present invention compensates for the attenuation of the received signal voltage when the impedance between the ground and the ground becomes low. Therefore, in order to compensate for the low frequency transmitted signal voltage applied to the electric line, The leakage current is detected, and when the impedance decreases, the leakage current increases and is detected. When a leakage current of the low frequency signal having a magnitude greater than a predetermined value is detected, the transmission signal is transmitted for a predetermined time. By increasing the voltage, the drop in the received signal voltage is automatically compensated.

(Example) Hereinafter, the present invention will be described in detail based on an illustrated example.

FIG. 1 is a diagram showing an embodiment of the present invention.
The same symbols as in the figure have the same meanings. Let e be the voltage induced between the electric line 1 and the ground point (E ₂ ) by applying a low-frequency transmission signal to the electric line. When the reception voltage of the receiver 7 is V (the input impedance of the receiver is selected to be sufficiently high), the signal transmission system of FIG. 1 can be represented by the equivalent circuit of FIG. In Figure 2 Corresponds to C = C ₁ + C ₂ . Therefore, the received voltage V is Therefore, it can be seen that the reception voltage becomes low due to the increase of the ground resistance r, the electrostatic capacitance c to the ground, and the decrease of the insulation resistance R to the ground. On the other hand, the feedback current i due to the low-frequency signal voltage e fed back to the ground line 1
Is here Therefore, the leakage current i increases as the parallel impedance of the ground insulation resistance R and the ground capacitance decreases.

Therefore, the output of the current transformer 8 penetrating the ground wire 1 is applied to the detection circuit 10 (FIG. 3 shows the details of the detection circuit), and the filter F of the transmission signal frequency band and the rectification circuit DET reference value i ₀ It is applied to the system composed of the comparison circuit COMP, and when the output i of the filter F exceeds the predetermined value i ₀ in the comparison circuit, the control circuit
The CONT operates for a predetermined time, and the applied voltage e is increased by increasing the gain of the amplifier 11 for applying the low frequency signal voltage to the injection transformer 5. Thus, the leakage current i also becomes large, but the reception voltage V becomes high, and correct signal reception is possible.

After a predetermined time, the gain of the amplifier 11 is returned to the original gain under the control of the control circuit CONT. This is because there is a possibility that the ground impedance of the electric path is high during this period.

Further, if the output i is a predetermined value i ₀ or more, the same operation is repeated. The reason why the applied voltage e is not increased from the beginning is that the load device connected to the electric line by the electromagnetic field radiation in the electric line due to the applied voltage e. It takes into account the adverse effects of.

As in FIG. 4, various alarm signals 6 are input to the transmitter 9, which are modulated by the rapid signal processing device 9 and applied to the amplifier 11. The operation of the receiving circuit is basically the same as that of FIG.

As described above, transmitting the alarm signal to the receiver even in the state where the insulation deterioration occurs and R becomes extremely low (a state close to the ground fault) is important in the transmission of the alarm signal. A significant effect can be expected in achieving it.

In the above description, the gain of the amplifier is controlled in steps. However, the present invention is not limited to this, and a single-phase two-wire system is shown in the above embodiment due to the magnitude of the leakage current above a predetermined value. It is clear that a three-wire system or a three-phase three-wire system electric circuit may be used. The current transformer 8 may also be used as an insulation detector (not shown).

[Brief description of drawings]

1 is a diagram showing an embodiment of the present invention, FIG. 2 is a diagram showing an equivalent circuit of a signal transmission system, FIG. 3 is a diagram showing a detection circuit, and FIG.
The figure shows an example of a conventional device. 1 ... Ground wire, 2, 3 ... Electric line, 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, CONT …… control circuit.

Claims (1)

(57) [Claims] 1. A low voltage 2 through a low voltage side ground wire of a power receiving transformer.
A low-frequency transmission signal voltage modulated by an alarm signal or the like to be transmitted obtained from an insulating device or the like is applied to the next electric line, and the low frequency induced between the ground electric line and the ground on the extension line of the electric line. In the transmission method of outputting the transmitted alarm signal or the like by detecting and demodulating the received signal voltage of, when the current of the low frequency component fed back to the ground line becomes a predetermined value or more, the A method for transmitting an alarm signal that compensates for ground impedance, characterized by compensating for a decrease in received signal voltage due to a decrease in ground impedance by increasing a low-frequency signal voltage for a predetermined time.