JPH07119785B2 - Insulation monitoring device - Google Patents

Description

TECHNICAL FIELD The present invention relates to an insulation monitoring device for electric circuits.

(Prior Art) Conventionally, as a method of monitoring the insulation state of a low piezoelectric path on the secondary side of a transformer that transforms high-voltage electricity into low-voltage electricity, the transformer 2 is installed through a grounding wire of the second type construction of the transformer. A low-frequency voltage (monitoring signal) different from the power supply frequency is applied to the secondary circuit, and this voltage causes the second current among the currents flowing in the impedance due to the insulation resistance or the stray capacitance existing between the secondary low-piezoelectric path and the ground. The low-frequency AC voltage and the in-phase component are detected from the signal flowing back to the grounding wire of the seed grounding work through a zero-phase current transformer and a filter that are coupled to the grounding wire, and this value is monitored to monitor the value of the electric circuit. Judgment of changes in ground impedance is performed.

Further, in addition to the insulation monitoring, the current derived by the zero-phase current transformer, that is, the monitoring signal is synchronously detected by the low-frequency AC signal for measurement, the voltage component of the monitoring signal and the in-phase component are detected, and required calculation is performed. It is also performed to calculate the insulation resistance value of the impedance between the electric circuit and the ground.

However, these devices (insulation detectors) that monitor the impedance between the electric line and ground are located near the transformer, and
Since the transformer is usually installed in a place where people are not resident, it is necessary to transmit these monitoring results to a place where people are resident, such as an office. Modulate a carrier wave of several KHZ and apply this to the ground wire of the second type construction through a transformer for carrier injection so that it propagates to the secondary electric line and is grounded in the office where the electric line is laid. The carrier signal detected between the phase electric circuit and the ground was demodulated and the monitoring result was received.

However, in the above-mentioned conventional method, an injection transformer for applying the carrier wave to the ground line is required when the carrier wave modulated by the output of the insulation monitor installed near the transformer is carried in the electric line. Since these three transformers are used in combination with the measuring low-frequency signal injecting transformer and the return signal extracting zero-phase current transformer, there is a drawback that the device becomes expensive and large.

(Object of the Invention) The present invention has been made in order to eliminate this drawback, and an object of the present invention is to provide an insulation monitoring device that can reduce the size and cost of the device by reducing the number of transformers required. To do.

(Summary of the Invention) In order to achieve this object, the present invention adds a summing / mixing means to an injection transformer coupled to a ground wire for applying the low frequency signal for measurement to an electric line, and in the section, the above-mentioned mixing / mixing means is added. The measuring low frequency and the carrier wave modulated by the output signal from the insulation monitoring device are mixed and then applied to the injection transformer.

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

Before that, in order to facilitate understanding of the present invention, a conventional insulation monitoring device will be briefly described.

That is, FIG. 2 is a block diagram showing a conventional insulation monitoring device.

In this figure, T is a transformer that transforms high-voltage electricity into low-voltage electricity, and 1, 2 and 3 indicate low-piezoelectric paths connected to the secondary windings of the transformer, of which the middle line 2 is the It is grounded by the grounding wire 4 of type 2 construction. An oscillating unit 5 oscillates a frequency different from the power supply frequency, for example, 10 to 30 Hz, and is applied to the electric path through a low frequency applying transformer 6 coupled to the ground line 4. Reference numeral 7 is a zero-phase current transformer for detecting the current flowing through the ground line, and the current detected by this is separated by the discriminator 8 into a monitoring signal only, which is synchronously detected by the output of the low-frequency oscillator 5. When the current for the same phase as the oscillation voltage reaches a constant value, an alarm signal is generated at the output terminal 9 of the discriminator 8. Reference numeral 10 is a modulator, and a carrier of 1 to 5 KHz is modulated by the output of the discrimination unit 8 and the modulated signal is transmitted through the transformer 11 for carrier injection and the ground wire 4 of the second kind construction to the low piezoelectric path 1 , 2,3 are applied.

Reference numeral 12 is a receiver installed in an office or the like where a part of the electric line is laid, and its input is led between one of the electric lines, for example, a grounded middle wire 2 and a grounding point 13. The above-mentioned carrier wave is input and at the same time, demodulation is carried out in the section to detect the transmitted electric line monitoring information.

A DC blocking capacitor 14 is inserted between the input end of the receiving section and the electric line 2 for measuring the electric line insulation by a megger or the like.

As described above, the conventional insulation monitoring device has the drawback of being large and expensive because it requires both the measuring low-frequency signal injection transformer 6 and the carrier injection transformer.

FIG. 1 (a) is a block diagram showing an embodiment of the present invention, and the same reference numerals as those in FIG. 1 denote the same parts.

For simplification of description, the description of the same parts will be omitted and only the differences between the two will be described as follows.

That is, this embodiment is different from the conventional one in that a summing amplifier 15 is inserted between the measuring low frequency oscillator 5 and the injection transformer 6 for applying this output to the ground line, and That is, the output of the modulator 10 is connected to one input end.

With this configuration, both the low-frequency voltage for measurement and the carrier wave modulated by the information obtained from the monitoring device can be applied to the electric line by the same injection transformer, so that one expensive and large transformer is saved. be able to.

Further, as shown in FIG. 1 (b), if the injection transformer 6 is replaced by an injection transformer having two windings on the secondary side or an injection transformer 16 having a two-input type with an intermediate tap, the summing amplifier is used. Can be eliminated and the size and cost can be further reduced.

(Advantages of the Invention) Since the present invention is configured as described above, an injection transformer required for transmitting information obtained from an insulation monitoring device or the like to a remote place through an electric line is used for measuring low frequency voltage application. Since it can be used as a transformer, it is effective in far reducing the size and cost of the device.

[Brief description of drawings]

1 (a) is a block diagram showing an embodiment of the present invention, FIG. 1 (b) is a partial block diagram showing a modified embodiment of the present invention, and FIG. 2 is a block showing a conventional insulation monitoring device. It is a figure. T …… Transformer, 1, 2 and 3 …… Secondary side low piezoelectric path, 4 …… Ground wire, 5 …… Low frequency oscillator for measurement, 6, 11 and 16 …… Injection transformer, 7 …… Zero phase change Sink, 8 …… Discriminating part, 10 …… Modulator, 12…
… Receiver.

 ─────────────────────────────────────────────────── ─── Continuation of front page (56) Reference JP-A-60-176415 (JP, A) JP-A-60-216274 (JP, A) JP-A-60-216275 (JP, A) JP-A 61- 233375 (JP, A) JP-A-60-241710 (JP, A)

Claims (2)

[Claims] 1. A low-frequency AC voltage different from the power-supply frequency is applied to a ground wire of the second-class construction of a transformer that transforms high-voltage electricity into low-voltage electricity through an injection transformer, and the low-frequency AC voltage is applied. In a device for monitoring insulation of an electric line by detecting a component in phase with the low-frequency AC voltage from a leakage current returned to the grounding wire of the above-mentioned type 2 construction, modulation by a signal indicating the insulation state of the electric line The mixed carrier wave and the measuring low-frequency AC voltage are added and mixed, and then applied to the electric line through the injection transformer, and the modulated carrier wave is derived and demodulated at an arbitrary point on the extension line of the electric line. An insulation monitoring device characterized by being configured. 2. The injection transformer is configured to perform the additive mixing by forming the secondary side of the injection transformer into two windings or providing an intermediate tap. Insulation monitoring device according to claim 1.