JPS58127173A - Measurement of insulation resistance for electric line - Google Patents

Abstract

PURPOSE:To enable a highly accurate measurement of insulation resistance under a hot-line condition in a wide range utterly irrelevant to stray capacity with a simple method. CONSTITUTION:Outputs of a 90 deg. phase sifter PS and a buffer BA are applied to a multiplier MULT1, the output of which is applied to a low pass filter LPF1 to obtain a DC component D=(omega0CV0/2)V2. The output of the LPF1 is multiplied constant times with a coefficient device CF and inputted into a multiplier MULT3. The output of the multiplier MULT3 and the output of the buffer BA are added with an adder AD, the output of which is inputted into a multiplier MULT2. The input is multiplied by an output from an oscillator OSC with a multiplier MULT2 to extract the DC component thereof with a low pass filter LPF2, which provides V0V2/R at the output thereof LPF2. This is a value reversely proportional to the insulation resistance, utterly irrelevant to the capacitance C. It should be noted that an applied voltage is put at V=V0sinomega0t and a voltage obtained when this voltage V is applied to a 90 deg. phase shifter at V2cosomega0t.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for precisely measuring insulation carry-over in live electrical circuits.

When measuring the insulation condition of a live electrical circuit, normally all zero-phase current transformers (hereinafter abbreviated as ZCT) are used to detect leakage current. In addition to the component due to ground capacitance (hereinafter referred to as insulation resistance),
It also includes components that flow due to floating @do (hereinafter referred to as floating @do). In general, the current due to stray capacitance is significantly larger than that due to insulation resistance, so the measurement error in insulation resistance is significant.

These currents also vary depending on the presence or absence of a load. In online monitoring of disconnected live circuits, etc., the measurement system cannot be adjusted each time, so the measurement system is not marked @
Reorganization is required. Moreover, you can rest assured that all fluctuations in insulation resistance over a wide range that occur due to insulation deterioration can be accurately and stably measured.

The present invention relates to a useful device that makes it possible to measure insulation resistance over a wide range under live wire conditions, completely independent of stray capacitance.

The present invention will be described in detail below with reference to the drawings.

Figure 1 shows an embodiment of the present invention, in which a zero-phase current transformer Z is connected to the ground wire.
Frequency i while passing through CT.

It penetrates the transformer T connected to the oscillator O8C that oscillates a low frequency or the core of an oscillation transformer that oscillates a low frequency. If the total voltage of frequency fo applied to the electric path is Y, then leakage current due to the commercial frequency component and the applied low frequency voltage component is used sideways in the output of the zero-phase current transformer. Filter F that selects only the low-frequency at-pressure acid component to which the zero-phase current transformer output is applied
If the voltage is applied to 1 g of output, the insulation resistance R to be measured is
A current IB flowing through the floating capacitance iC and a current i flowing through the floating capacitance iC are included.

1, the low frequency voltage V applied to the circuit (voltage between the circuit and the ground) f V=VosinωOt (ωo=2'rf
o) By setting 12 becomes 1g=iH+ic. This current is obtained by applying the output of the zero-phase current transformer ZCT to the filter F, and this Ig is amplified by the buffer amplifier BP.

By the way, ia (first term of equation 0) and ic (second term of equation 0)
Comparing the sizes of , IR is generally a much smaller value than ic. Therefore, when trying to increase the sensitivity of the measuring device, errors occur due to the influence of jc. Also (1
) If the second term in the equation is not small, there is a possibility that a total error will occur during detection using counterfeit money synchronous detection, etc., which is proportional to the first term.

The device of the present invention solves this problem as follows. That is, the voltage V2ω56Jot obtained by passing the voltage ■ applied to the above electric circuit through a 90° phase shifter, and the current i of amplitude a by reversing the polarity =--B CO5ωo
A correction signal t is obtained. Adding this to Ig in equation (1) yields. By the way, if we take the ``element'' of the word ``port'' and the above ■2cOδωot, we get igxV.
2cosωot. As for the DC component on the right side of equation (3), the second term of equation (2) approaches zero. In other words, Autumn 1 above
By adjusting the value of a in proportion to the DC component of g×■2CoSωot, the invalid component included in S g + 1 can be made sufficiently small.

In the embodiment of FIG. 1, the output of filter F is added to buffer amplifier BA to obtain 1g-5= of equation (1). On the other hand, a voltage V2sinωat is obtained from the output of the low frequency voltage oscillator O8C. The output of the oscillator O8C is applied to a 90 degree phase shifter ps to shift the phase by 90 degrees to obtain 2CoSωof.

It is further input to the polarity inverting circuit INV to obtain -v2ωSωot at its output, and the output of INV is added to one input of the multiplier MULT3.

The buffer amplifier BA output is applied to one input terminal of the multiplier MLILT1, and the output of the previous phase shifter ps V2CO3
ωot is added to the other input of the multiplier MULTI. Therefore, a signal expressed by equation (3) is obtained at the output of MULTI. This MUL'l "output of 1" is applied to the other input end of the DC molecule 3 by being applied to the low-pass filter LPFl. Thus the multiplier M
A signal corresponding to one ωoCVocoSωot is obtained at the output of TJ LT 3. By calculating the sum of the output of the multiplier MUL'r3 and the output of the Vanofa AMBU BA in the adder ADD, a signal in which the second term of equation (2) is sufficiently small is obtained at the output of the adder ADD. Therefore, the adder ADI
) and the voltage Vzsinωot, the multiplier MI
The DC component taken by JLT2 becomes an amount proportional to low. Note that in this automatic adjustment, since the component caused by the IC in the A1) output is minute, the same result can be obtained even if the output of A1)D is fully rectified.

In the above embodiment, a zero phase flow device ZCT was installed at the ground.
It is clear that the same result can be obtained even if the electric line vCZC'l'2 is passed through. Similarly, the same result can be obtained even if the transformer T is passed through the electric path.

Further, although this embodiment has been described in the case of a single-phase two-wire system, it is similarly applicable to a single-phase three-wire system, a three-phase system, etc. Low frequency voltage application transformer all grounded 1j! You can also cut them and insert them in series. The industrial value of the present invention, which enables accurate measurement of insulation resistance with a simple circuit, is high.

[Brief explanation of the drawing]

FIG. 1 shows an embodiment of the insulation resistance measuring device of the present invention. Z C'I"...Zero phase current transformer T...
・Transformer O8C・・・Low frequency oscillator BA・・
...Buffer amplifier MUL'["2, M[JL
'I'3... Multiplier ZL... Load
C... Stray capacitance 1 (,,,,,,,
Insulation resistance ps・・・90 degree phase shifter IN
V...Polarity inversion circuit CF...Coefficient unit AD
D... Adder LPFI, LPF2... Low pass filter patent applicant Toyo Tsushinki Co., Ltd.

Claims (1)

[Claims] A low-frequency voltage, which is a measurement signal, is applied to the live electrical circuit through the grounding wire by electromagnetic induction or series coupling, and the leakage current or current that returns to the grounding wire is detected by a zero-phase current transformer. In a device that measures the total insulation resistance of the electrical circuit by detecting an effective component due to insulation resistance in the low frequency component contained in the output of the zero-phase current transformer, After obtaining the DC component of the product of the voltage of the low frequency component and the voltage whose phase differs by 900 from the applied low frequency voltage, we calculate the DC component of the nuclide multiplied by a factor and the applied low frequency voltage. is a voltage whose phase differs by 90°.By taking the frequency frost, the effective component due to the insulation resistance in the current can be precisely measured by the direct current component of the voltage and the leakage of the low frequency component. Insulation resistance measuring device # as a percentage.