JPS6146113A - Insulating resistance measuring method - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention] (Industrial application field) The present invention relates to a method for measuring insulation resistance, etc. of an electric circuit.

(Prior art) Conventionally, in order to detect troubles in electrical circuits such as power transmission lines at an early stage, insulation resistance of electrical circuits is constantly monitored and abnormalities are detected quickly to prevent damage such as burnout due to deterioration of insulation resistance. is being carried out.

Various methods have been devised to measure the insulation resistance of such electrical circuits, but the second example is
There is one shown in the figure.

That is, in the figure, it is a power receiving transformer, and the overvoltage secondary circuits 2 and 3 thereof are connected to a load Z, and one of these circuits, for example, circuit 3, is generally grounded by a grounding wire 4. , furthermore, the ungrounded circuit 2 has insulation resistance R and ground static.
It is connected to the ground by capacitance C. Note that insulation resistance and ground capacitance also exist in the ground conductor, but they will be omitted below to simplify the explanation.

In order to measure the insulation resistance R of such an electric path,
As shown in the figure, a low-frequency signal generator for measurement (OSC) and a zero-phase current transformer (2CT) are inserted and connected to the grounding wire 4 to apply a low-frequency signal (f) for measurement to the electrical circuit and also to The leakage current component of the measurement low-frequency signal f1 flowing back to the ground line via the resistor R and ground capacitance c=2 is detected by the zero-phase current transformer ZCT, and is detected by the synchronous detection circuit MUL.
A component in phase with the low frequency voltage applied at T.

That is, the effective component is derived to obtain a signal that is inversely proportional to the insulation resistance R.

(Problems to be Solved by the Invention) However, in the conventional measuring method as described above, when the ground capacitance is large, the current due to the ground capacitance in the leakage current at frequency f1 is larger than the current due to the ground capacitance.

Since the current is larger than that due to the insulation resistance, there is a problem in that the effective component cannot be detected correctly due to errors in the synchronous detector.

(Means for Solving Problems) The present invention has been made to solve the problems of the conventional method of measuring insulation resistance of electric circuits, etc., and in order to provide a measuring device with a simple and inexpensive configuration, the following steps are taken. We provide methods such as:

That is, a measurement rectangular wave signal containing a large number of harmonic components or a two-frequency measurement low-frequency signal "f" having different frequencies but synchronized with each other in phase is applied to an electric line, and the insulation resistance of the electric line or Detecting the plurality of high frequency components in the measurement rectangular wave signal or the two-frequency measurement low frequency signal flowing back to the grounding line via the capacitance t, and detecting the respective frequencies ft and fz (fz
>ft) Detecting the voltage difference between the signal obtained by converting the frequency of one of the signals, for example, the reflux component of fz, so that it becomes equal to the other signal f, and the reflux component of the f1. so as to obtain an output inversely proportional to the insulation resistance R. Further, by detecting the voltage that is the sum of the two voltages, it is also possible to obtain an output proportional to the ground capacitance C of the electric circuit.

However, any method may be used to convert the detected measurement signal f or fz to the other frequency.1For example, a simple method may be used, such as frequency shifting using an amplitude modulator. You can achieve your goals through configuration.

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

'W, Figure 1 is a block diagram showing one embodiment of the present invention.

In the figure, T is a power receiving transformer, 2 and 3 are secondary circuits,
4 is a grounding wire, ZCT and 5 are transformers coupled to a zero-phase current transformer and an oscillator OSC inserted into the grounding wire, as in the above @2 diagram.

In this embodiment, a rectangular wave oscillator containing a high frequency component is used as the measurement signal oscillator, and the circuit for detecting the leakage current flowing back into the ground wire 4 is constructed as follows.

That is, the zero-phase current transformer ZCT output passing through the grounding wire 4 is branched via the amplifier AMP@ to two band Φ pass filters BPF2 and BPF3 having different frequencies, and the output of one of them, for example, BPF 3, is guided to the modulator MOD. After the output is applied to a low-pass filter LPF for frequency conversion, the output is input to the subtraction circuit SUB 2 via a phase shifter PS.

On the other hand, the modulation signal input terminal of the modulator MOD is input with the output obtained from a part of the circuit of the rectangular wave oscillator 0802 applied to the electric circuit, and the other input terminal of the subtraction circuit 5UB2 is input with the band pass signal. - The output of the filter BPF 2 is input, and the output of the subtraction circuit SUB 2 is input to the detection circuit DET, so that a signal inversely proportional to the insulation resistance R of the electric circuit is obtained at its output terminal.

The operation of the measuring circuit configured as described above will be explained below using mathematical expressions.

That is, the voltage applied to the oscillator is set to ■[Porto J, its duty ratio is 50%, and the commercial power supply voltage of the secondary circuit is Vo(
Volt], its frequency is f.

Then, the leakage current i flowing back to the grounding wire 4 is j = (Vo/R,) 5iIIωOt + ω6c
V□ CO5ω(Ij+ (V +/R・) sinω
It + (V3/R1) cos3 ω, t +・
・-+ CωIV1CO56J 1 t + 3 Cω
It is expressed as IV3 CO53 (+J1 t+...... (1). However, Vl, V3...... are the harmonic components of the rectangular wave signal applied to the electric circuit. It is voltage.

An output corresponding to this current i is obtained at the output end of the amplifier AMP via the zero-phase current transformer ZCT.

Passage frequency f of each subsequent filter BPF and BPF
If f is 1 and 3ft, the output χl of each filter is
and z3 becomes.

The output χ3 of the filter BPF 3 is applied to one input of the amplitude modulator MOD, and the frequency f1t- is applied to the other input of the MOD.
A low-pass filter □ is installed at the output of the splitter before the output oscillator and at the output of the modulator.

A = hill sin (3-4). 1t+3CJV3eJ)5
(3-4) (dttR・= −usinωtt+3CωIV3ωSωIt・
...... (4) R. The phase shifter PS installed at the low-pass filter output is
The phase shift in fill BPF 3 and low pass filter LPP is compensated, and the signal y expressed by equation (4) is
It was established to obtain the following.

By the way, voltage V9 frequency f 11 duty ratio 50'%
If we expand the square wave into a 7-lier series, we get 3v3==v,
Therefore, the second term of equation (2) and the second term of equation (4) are equal, so the difference between equations (2) and (4) is calculated by subtracter 5LJB.
Then, the output of SUB is v1+v3, χ1− y = 7 suωt t −°= (5)
becomes. Therefore, the output of the subtracter is rectified DETV, +V
.

If rectified by R, the output OUT can be inversely proportional to R, that is, the insulation resistance.

Also, in the calculation χl-y of the difference between equations (2) and (4), (
2) When the components of the second term in equation (4) and the second term in equation (4) are extremely large and are not equal to each other with the accuracy of the nine circuits, a cancellation residual occurs and χsY provides a voltage that is correctly inversely proportional to the insulation resistance. However, in this case, by synchronously detecting χ1-y with the applied low-frequency voltage, it is possible to eliminate the influence of the above-mentioned residual component whose phase differs by 90 degrees from the applied voltage.

Also, the sum of χ1 and y is similarly 3V'3=V1.

z, -1-y == 2 CωIV1cosa+1
t ・-= (6) and fk This is the capacitance, 1ct
Since the equation includes -, the capacitance 1i:t- of the electric circuit can be calculated by obtaining a voltage proportional to the ground capacitance.

In the above embodiment, the frequency g is used as the measurement frequency signal.
! Although the components of l f t and 3 f 1 are used, the present invention is not necessarily limited to this in any way, and similar results can be obtained even if two-frequency signals of frequencies fn and fm are used as the applied low-frequency voltage. The gains are clear. It is also clear that it is not necessary to limit the applied voltage to a rectangular wave; for example, two measurement signal oscillators may be provided to carry out similar measurements.9 The method of the present invention can be expanded and used.

(Effects of the Invention) Since the present invention is configured and operates as described above, it is extremely effective in measuring the insulation resistance and capacitance of an electric circuit in a live line state using an extremely simple method. .

In the above-mentioned embodiment, only the case of a two-phase, two-wire electric circuit was illustrated for the sake of simplicity, but the present invention is not limited to this, and it is unnecessary to explain that the present invention can be applied to, for example, a three-phase, three-wire electric circuit. .

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of the present invention. FIG. 2 is a block diagram showing a conventional method for measuring insulation resistance of an electric circuit. T...-...Power receiving transformer, 2 and 3...
......-Electric circuit, 4......Grounding wire, AMP......Amplifier,
ZCT・・・・・・Zero phase current transformer. BPF,,BPl,'□,BPF3・・・・・・・・・
Bandpass fill, MOD...
・Modulator. LPF・・・・・・・・・Low pass filter, P
S... Phase shifter, 5TJB...
...Subtractor, DET...Detection circuit, OSC, and 08C2...
・Oscillator.

Claims (1)

[Claims] 1. Apply a low-frequency signal voltage for measurement containing at least two frequencies f_1 and f_2 different from the commercial frequency to the electrical circuit via the grounding wire of the transformer, etc. by electromagnetic induction or series coupling, etc., and couple it to the grounding wire, etc. The low-frequency signal voltage f_ for measurement that flows back to the ground line by the zero-phase current transformer
After detecting the leakage current components f_1 and f_2 and separating them with a filter, the leakage current component f_2 is converted to f_
An insulation resistance measuring method characterized in that an output inversely proportional to the insulation resistance of an electric circuit is obtained by using a level difference between a signal obtained by frequency conversion to the same frequency as 1 and the leakage current component f_1.