JPS631982A - Insulation monitor apparatus - Google Patents

Abstract

PURPOSE:To reduce the number of necessary transformers, by mixing measuring low frequency AC voltage and a carrier wave modulated by the output signal from an insulation monitor apparatus before applying the same to the injection transformer connected to an earth wire. CONSTITUTION:The middle electric circuit 2 of the low voltage electric circuits 1-3 connected to the secondary winding of a transformer T is earthed through an earth wire 4. A zero phase transformer 7 detects the current flowing to the earth wire 4 and the detected current is sent to a discrimination part 8. In this constitution, an adder-amplifier 15 is inserted between a measuring low frequency oscillator 5 and an injection transformer 6 for injecting the output thereof in the earth wire 4 and the output of a modulator 10 is connected to one of the input terminals of the amplifier 15. By this constitution, since both of measuring low frequency voltage and a carrier wave modulated on the basis of information obtained from a monitor apparatus can be applied to the electric circuits by the same transformer 6, one expensive large transformer can be saved. By this method, the miniaturization and cost reduction of the apparatus can be achieved.

Description

[Detailed description of the invention] (Industrial application field) The present invention relates to an electrical circuit insulation monitoring device. .

(Prior Art) Conventionally, as a method for monitoring the insulation state of the low voltage line on the secondary side of a transformer that transforms high voltage electricity into low voltage electricity, the secondary side of the transformer is A low-frequency voltage (monitoring signal) different from the power supply frequency is applied to the secondary electric line, and this voltage causes the second electric current to flow through the impedance due to insulation resistance or stray capacitance between the secondary low-voltage electric line and the ground. The in-phase component of the low-frequency AC voltage is detected from the signal flowing back to the grounding wire during grounding work through a zero-phase current transformer and filter connected to the grounding wire, and by monitoring this value, Determining changes in ground impedance is being carried out.

Furthermore, in addition to insulation monitoring, the current derived by the zero-phase current transformer, that is, the monitoring signal, is synchronously detected with the measurement low-frequency AC signal, and the voltage component and in-phase component of the monitoring signal are detected, and the necessary calculations are performed. Among the impedances between the electric circuit and the ground, the insulation resistance value is also calculated by applying .

However, these devices (insulation detectors) that monitor the impedance between the electrical circuit and the ground are placed near the transformer.
This is because the transformer is generally installed in a place where no one is permanently present.

It is necessary to transmit these monitoring results to the place where the office equipment is resident, and for this purpose, conventionally, a carrier wave of several kHz is modulated according to the monitoring result, and this is transmitted to the second By applying it to the grounding wire of the construction site, the carrier wave signal is propagated to the secondary electrical circuit and detected between the grounding phase electrical circuit and the ground in an office or the like where the electrical circuit is installed, and the monitoring result is received. was.

However, in the conventional method described above, when propagating the carrier wave modulated by the output of the insulation monitoring device installed near the transformer into the electric line, an injection transformer is required to apply the carrier wave to the ground wire, and - generally large-sized Since three of these expensive transformers were used, including a transformer for injecting a low frequency signal for measurement and a zero-phase current transformer for extracting a reflux signal, there was a drawback that the apparatus was expensive and large.

(Object of the Invention) The present invention was made to eliminate this drawback, and an object of the present invention is to provide an insulation monitoring device that can be made smaller and lower in price by reducing the number of transformers required. do.

(Summary of the Invention) In order to achieve this object, the present invention adds an addition mixing means to an injection transformer coupled to a ground line for applying the measurement low frequency signal to the electric path, and The low frequency wave for measurement and the carrier wave modulated by the output signal from the nuclear insulation monitoring device are mixed and then applied to the injection transformer.

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

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

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-voltage electric lines connected to the secondary winding of the transformer, and the middle line 2 is the It is grounded with grounding wire 4 of type 2 construction. Reference numeral 5 denotes an oscillator which oscillates a frequency 9 different from the power supply frequency, for example 10 to 30 H7, which is applied to the electric path via a transformer 6 for applying a low frequency coupled to the ground line 4. Reference numeral 7 denotes a zero-phase current transformer for detecting the current flowing in the grounding wire, and from the current detected by this, only the monitoring signal is separated in the discriminator 8, and synchronously detected by the output of the low frequency oscillator 5. When the current in phase with the oscillation voltage reaches a certain value, an alarm signal is generated at the output terminal 9 of the discrimination section 8. A carrier wave of, for example, 1 to 5 KHz is modulated by the output of the discriminator 8, and the modulated signal is sent to the low voltage power line 1 via a transformer 11 for carrier wave injection and a grounding wire 4 of type 2 construction. , 2.3.

Further, 12 is a receiving unit installed in an office or the like where a part of the electric line is installed, and its input is derived between one of the electric lines, for example, the grounded center wire 2 and the grounding point 13. In this system, a reproduced carrier wave is input, demodulated at the core, and transmitted cable monitoring information is detected.

Similarly, a DC blocking capacitor 14 is inserted between the input terminal of the receiving section and the electric line 2 to measure the insulation of the electric line using a megger or the like.

As described above, the conventional insulation monitoring device requires both the transformer 6 for injecting a low frequency signal for measurement and the transformer for injecting a carrier wave, and therefore has the disadvantage of being large and expensive.

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

For the sake of simplicity, explanation of the same parts will be omitted and only the differences between the two will be explained as follows.

The second difference between this embodiment and the conventional one is that a summing amplifier 15 is inserted between the measurement low-frequency oscillator 5 and an injection transformer 6 for applying this output to the ground line, and the summing amplifier 15 is The configuration is such that the output of the modulator 10 is connected to the other input terminal.

With this arrangement, 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 circuit by the same injection transformer, thereby eliminating the need for a single expensive and large transformer. You can save money.

Furthermore, as shown in FIG. 1 (bl), if an injection transformer with two windings on the secondary side or an injection transformer 16 of a two-man power type with an intermediate tap is used instead of the injection transformer 60, the summing amplifier is not necessary. It can be made smaller and cheaper.

(Effects of the Invention) Since the present invention is constructed as described above, an injection transformer required for transmitting information obtained from an insulation monitoring device, etc. to a remote location via an electric line is used for applying low frequency voltage for measurement. It can also be used as a transformer, which is effective in reducing the size and cost of the device.

[Brief explanation of the drawing]

FIG. 1 (al is a block diagram showing one embodiment of the present invention, FIG. 1 (bl is a partial block diagram showing a modified embodiment of the present invention, and FIG. 2 is a block diagram showing a conventional insulation monitoring device. Yes. T......Transformer, 1, 2 and 3...
・・・・・・Secondary side low voltage circuit, 4・・・・・・
...Grounding wire. 5...Low frequency oscillator for measurement, 6.
11 and 16... Injection transformer,
7...Zero-phase current transformer, 8...-
...discrimination section. 10...Modulator, 12...
...Receiving section.

Claims (2)

[Claims] (1) A low-frequency AC voltage different from the power supply frequency is applied via an injection transformer to the ground wire of the Type 2 construction of a transformer that transforms high-voltage electricity into low-voltage electricity, and the low-frequency AC voltage is used to transform the above-mentioned In a device that monitors the insulation of an electrical circuit by detecting a component in phase with the low-frequency AC voltage from the leakage current that returns to the grounding wire of Type 2 construction, a carrier wave modulated by a signal representing the insulation state of the electrical circuit is used. and the low frequency AC voltage for measurement are added and mixed, and then applied to the electric line via the injection transformer, and the modulated carrier wave is derived and demodulated at any point on the extension of the electric line. An insulation monitoring device characterized by: (2) Claims characterized in that the injection transformer is configured such that the secondary side of the injection transformer has two windings or is provided with an intermediate tap, so that the addition mixing is performed in the injection transformer. The insulation monitoring device according to item 1.