JPH01116456A - Simple insulation resistance measurement for electric circuit - Google Patents

Abstract

PURPOSE:To achieve a higher measuring accuracy along with a reduction in measuring time by determining a initial value of a capacitor for adjustment, added to remove a measuring error due to an electrostatic capacitance, with an approximation to a value to be set finally. CONSTITUTION:A voltage shifted by 90 deg. in the phase from a voltage which is applied to an electric circuit with a connection line LINK not terminated by a capacitor Co to estimate a ground electrostatic capacitance from a DC component equivalent to a product of the voltage and a leakage current (i) with a frequency f1 in an output of a current transformer ZCT. Thereafter, the connection line LINK is set by inserting it with the capacitor Co almost equivalent to the ground electrostatic capacitance value estimated as initial value to reduce a value of ¦C-Co¦ in the initial state (namely, because of Capprox.=Co).

Description

[Detailed Description of the Invention] (Industrial Application Field) The present invention relates to a method for measuring insulation resistance of electrical circuits such as electrical wiring.
In particular, it relates to a simple method for measuring insulation resistance of electrical circuits that eliminates measurement errors due to ground capacitance.

(Prior art) It is necessary to monitor the insulation resistance of electric circuits such as electrical wiring to prevent accidents such as electric leakage, but the measurement method basically involves applying a low-frequency signal to the circuit under test. At the same time, the leakage component is extracted and the signal voltage /
Those that obtain electric current are common.

At this time, the leakage component level changes depending on the magnitude of the capacitance between the electric line and the ground or due to the load connected to the electric line, and if this value is large, a measurement error may occur.

The same applicant has already devised an effective method in Japanese Patent Application Laid-Open No. 12714/1983 as a method for accurately measuring insulation resistance values while eliminating the influence of capacitance.

In this method, as shown in Fig. 3, a ring-type injection transformer CT and a current transformer ZCT are coupled to the electrical circuits 1 and 2, both of which are grounded, and the injection transformer CT&C is connected to a low-frequency oscillator O.
8C, and a current transformer ZCT Ktl1 width sAMP, a bandpass filter/BPF, a rectifier circuit DET, and a leakage current detection circuit including a meter M, in an insulation resistance measuring device for an electrical circuit, in which the injection transformer CT and the transformer are connected. Flushware ZCT
Connect the connecting wire LIN so that it is in opposite phase to the electrical circuit.
A circuit is added that passes through K and is connected in a loop through capacitor CO.

Let me explain the operation of this insulation resistance measuring circuit.

Output signal voltage Vsi with frequency fl from oscillator O8C
nω1t (ωt = 2 w f l) is applied between the electric path 1.2 and the ground, and a leakage current i flows through the capacitance C and the insulation resistance R between them.

This leakage current is detected by the current transformer ZCT K in the absence of the connection line LINK, and is detected by the amplifier AMP and the frequency f.
A current i expressed by the following equation (1) &C is derived by the bandpass filter BPF K that passes only s.

1=(V/R)siaa+xt+a+tcVcosa+
xt =・= (1) This leakage current it-? By inputting the rectifier circuit DET Ic in stage 1, the DC component included in the right-hand side of Equation 11 is derived, but this also includes the component due to the capacitance C in the second term on the right-hand side. It is not possible to extract only the insulation resistance component.

Therefore, in this proposal, as described above, the connection line LINK in which the capacitor CO is inserted is interposed, and the capacitance CK
The leakage current due to the capacitor C.

The j%2 term on the right-hand side of the equation (1) is made to be zero by canceling the signal component flowing through the signal component.

That is, when the connection line LINK is inserted, the derived leakage current is is i 1 ” (V/R)sioω1t +a+t (C
-Co ) VCO3(131<・・・・・・・・・(
2) Therefore, when this is rectified, the output 1111 is l
is l =V ((1/R")+ω1" (C-Co
)"J" - (3).

Then, by adjusting the value of the capacitor Co, the meter M
If you monitor the indicated value, when C=Co, 1itl=v
/H is the minimum value, and this value is the reciprocal of the insulation resistance of the electrical circuit itself.

That is, by adjusting the capacitor CO using this method so that the indicated value of the meter M becomes the minimum value, the influence of the capacitance C can be removed and an extremely accurate insulation resistance value can be obtained.

The second factor is a diagram showing changes in the indicated value of the meter M when the capacitor CO is changed.

The purpose of this proposal mentioned above can be understood from this figure as well.

However, in the conventional method described above, the capacitor C
Busy and sequential C to adjust the value of O.

The value of the meter M had to be monitored while changing the value of the meter M, making it difficult to make quick adjustments. Especially when the difference between the values of CO and C is large, 1/R'' on the right side of equation (1) above.
ω5(C−Co)” is significantly larger than the term
There is a problem in that the time required for adjustment increases.

(Objective of the Invention) The present invention was made in order to understand the problems of the conventional method of measuring insulation resistance of electric circuits, etc. as described above, It is an object of the present invention to provide a method for measuring insulation resistance of electric circuits, etc., which enables accurate insulation resistance values to be obtained in a short time.

(Summary of the Invention) In order to achieve this object, the insulation resistance measuring method of the present invention uses a voltage that is 90 degrees phase-shifted from the voltage applied to the electrical circuit when the connection wire is not terminated with a capacitor Co. The ground capacitance is estimated from the direct current multiplied by the leakage current i of frequency f1 in the flowmeter output, and then the above connection line is connected to a capacitor Co which is equivalent to the above estimated ground capacitance value.
By inserting f as the initial value, Ic-
By setting the value of cOl to be small (ie, because of the 0-character Co), it is possible to further shorten the time required for adjustment and to enable highly accurate adjustment.

Also, if you insert a capacitor CO with a known value in advance and measure the ground capacitance using the above method, you will get the difference between C-Co, that is, the ground capacitance and the value of the capacitor Co. After obtaining an approximate value of C and setting the capacitor COK to this approximate value, the value of the capacitor Co is finely adjusted so that the leakage current at the detected frequency fl is the minimum KL,
The insulation resistance may be measured based on the magnitude of the leakage current at this time.

(Example) The insulation resistance measuring method of the present invention will be explained in detail based on an illustrated example.

FIG. 1 is a block diagram showing an embodiment of an apparatus for implementing the insulation resistance measuring method of the present invention, and the same symbols as in FIG. 3 have the same meanings.

In the same Figure 1, T is a transformer that converts high voltage electricity into low voltage, l and 2 are electrical circuits connected to the secondary coil of the transformer T, and a grounding wire Lm is connected to -12. has been done.

This embodiment shows an apparatus for measuring the insulation resistance of such an electric line.

2. Ring-shaped injection transformer C that penetrates both at once.
T, a current transformer ZCT, and a connecting line LINK that passes through both of them so that they are in opposite phases to each other, and this connecting line LINK is connected to an on/off switch SW and a variable capacitor CO.
Insert them in series and connect them in a ring shape.

Furthermore, the injection transformer CTK has two secondary windings Nl, N!
NIK is provided with a low frequency oscillator O8C, and the other N3 is connected with a series circuit consisting of a phase shifter PS, a multiplier MLILT, and low frequency filters LPF and MC.

In addition, a series circuit consisting of an amplifier AMP, a bandpass filter BPF, a second flow 1DBT, and a meter M is added to the secondary coil of the current transformer ZCT, and a part of the output of the bandpass filter BPF is compared with the multiplier MυLT. It is configured to be input as a signal.

The capacitance C and resistance R between the electric line 1 and the ground are schematic representations of the capacitance and insulation resistance between the electric line and the earth, respectively.

The operation in this configuration will be explained.

That is, in the measurement, first, the switch SW provided on the connection line LINK is set to the "off" state.

Oscillator O8C connected to winding N1 of injection transformer CT
A low frequency voltage V sinω of frequency f1 is applied to the stain path 1.2.
Apply lt'. Thus, the output of the current transformer ZCT is amplified by the amplifier AMP and the filter BP
If we extract the component of frequency fl by F, we can obtain filter BP
A leakage current corresponding to i in equation 11 is detected in the output of F.Also, the output voltage e s of the winding N! of the injection transformer CT
90 degree phase shifter ps inωIt! /c, the output will be 6cos(ωt t + (j), where 0 is the phase error, which also includes the phase error caused by the current transformer → amplifier → filter system. becomes.

If the output i of the filter BPF is applied to some inputs of the multiplier MTJLT and the output of the phase shifter PS is applied to the other input terminal, the output of the multiplier MUL'l' is 10)...・・・(
4) Input the multiplication output to the low pass filter LPF.

If we find the DC component of the multiplier output, we get So, if Iθ1 (1).

becomes. Therefore, the fJ42 term in equation (6) is generally sufficiently small, and if ωs, e, and V are constant values, it is possible to approximately estimate the ground capacitance from the value of the low-pass filter output.

That is, by displaying the low-pass filter D with the meter MC, the approximate ground capacitance is measured, and this value is expressed as C'
shall be.

Next, the value of the capacitor Co is set to an approximate value C' of the measured ground capacitance C. In addition, if the switch SW provided on the connection line LINK is turned on, a low frequency signal induced by the injection transformer CTK will flow through this connection line, but it will pass through the current transformer in the opposite phase to the electrical circuit, so it is connected. line LIN
Since the current ωIC'VCO5ω1t flows through K, the output il' of the bandpass filter BPF can be found by equation (2) and PQ41 to be lV.

i 1= 51ata l t+ωt (C-C'
)Vcosωtt・・・・・・・−・(7) Furthermore, the rectifier output 1 i1' I is υ, and by finely adjusting the value of the capacitor CO so that this value is minimized, the DC current related to the insulation resistance can be determined.

When adjusting the value of the busy capacitor Co as described above, if a value equal to fi'fcK is set as the initial value C', the value of the rectifier DBT can be adjusted to the minimum in an extremely short time and with high precision. can. As mentioned above, the minimum value of the meter M is a result that correctly represents the insulation resistance of the electric circuit.

Similarly, in the above explanation, the approximate value C' of the ground capacitance is displayed with a meter MC, etc., and the variable capacitor Co is adjusted to that value.
Although a case has been described in which the value is manually adjusted, it is not necessary to be limited to this when implementing the present invention, and an approximate value C' can be obtained from the output of the low-pass filter LPF while the switch SW is turned off for a predetermined period of time. It is within the skill of those skilled in the art to automatically adjust the variable capacitor Co electronically based on this value and finely adjust the value of the capacitor CO to KJ! so that the output of the 11 current circuit DET is minimized. It is easily achievable.

For example, a varicap diode may be suitable as the variable capacitor in this case.

Also, directly connect the capacitor Co'% without providing a switch SW:
It is also possible to detect capacitance while it is inserted.

That is, as is clear from the above explanation, the output D'u of the low-pass filter LPF is obtained when the switch SW is removed and the capacitor Co is directly inserted. When +61<1 (CO313"q1sSlaa-6 Therefore, as in the case of equation (6), the low-pass filter LP
The estimated value of capacitance C-co can be measured from the output D' of F. Since it is the set value of xCO company and is known, C
-Co to ground capacitance C7Ij! It is clear that the value of the capacitor Co may be changed so that the estimated partial pressure can be estimated, and further the value of the capacitor Co may be finely adjusted so that the display on the meter M indicates the minimum value. Naturally, C-Co takes both positive and negative values; when it is positive, C0 is increased, and when it is negative, Co is decreased.

Furthermore, although the above description has been made regarding the case of a single-phase, two-wire electrical circuit with one end grounded, measurements can be made in the same manner for electrical circuits such as single-phase, three-wire, three-phase, and three-wire electrical wiring.

Oka, furthermore, in the above explanation, the ground wire LINK is injected into the transformer,
The current transformer ZCT was simply passed through so that the phase was opposite to that of the electric circuit, but the connecting wire was wound N times with an injection transformer CT, and the current transformer ZCT was simply passed through so that the phase was opposite to that of the electric circuit. If one is wound N times, the value of the capacitor CO is isometrically C
The value of o/N may be used, and a variable capacitor that can be realized arbitrarily can be used. This method uses current transformers ZCT &
The same thing can be done with CN windings, or both may be wound with predetermined windings.

(Effects of the Invention) As explained above, the present invention eliminates measurement errors due to capacitance in a method of determining insulation resistance by detecting the leakage current of a low frequency signal applied to a trap or electric circuit. Since the initial value of the adjustment capacitor added for removal is determined to approximate the value that should be finally set, it is effective in shortening measurement time and improving measurement accuracy. .

[Brief explanation of the drawing]

FIG. 1 is a diagram showing an embodiment of an apparatus using the method of the present invention, FIG. 2 is a diagram showing the operation of the conventional method, and FIG. 3 is a diagram showing the conventional method. T......Power receiving transformer, CT...
・・・・・・Injection transformer, ZCT・・・・
·····Current transformer. O20...Oscillator, AMP...
・・・・・・Amplifier BPF・・・・・・Filter, DET・・・・・・Rectifier,
Mc, M......meter. PS・・・・・・・・・−・Phase shifter, MtJLT・
・・・・・・・・・Multiplier, LPF・・・・・・
...Low pass filter. Patent applicant: Toyo Tsushinki Co., Ltd.

Claims (1)

[Claims] 1. A core of a transformer that applies a low-frequency voltage to an electrical circuit and a current transformer that detects leakage current are combined, and a voltage whose phase is shifted by 90 degrees from the low-frequency voltage and the current transformer are combined. The estimated value of the ground capacitance of the electric line is measured by deriving the direct current component of the product of the product with the low frequency component in the output, and the core of the transformer and the current transformer are connected in opposite phase to the electric line. A new connecting line is provided that passes through the circuit, and a capacitor with a value equivalent to the estimated value of the ground capacitance measured above is inserted as an initial value into the connecting line of the electric circuit, and the value of the capacitor is further changed. A simple insulation resistance of an electrical circuit, characterized in that the insulation resistance is measured from the magnitude of the low frequency component after increasing or decreasing it so that the low frequency component contained in the output of the current transformer is minimized. Measuring method. 2. In claim 1, a connecting wire passing through the core of the transformer and the current transformer in a phase opposite to that of the electrical circuit is terminated with a capacitor, and the phase of the low frequency voltage is set to 9.
An estimated value of the difference between the capacitance to the ground and the capacitance of the capacitor is measured from the DC component of the product of the voltage phase shifted by 0 degrees and the low frequency component in the output of the current transformer, and from the estimated value, Calculate the estimated value of the capacitance, set the value of the capacitor by replacing it with the estimated value, and further adjust the value of the capacitor so that the low frequency component contained in the output of the current transformer is minimized. A simple method for measuring insulation resistance of an electric circuit, characterized in that insulation resistance is measured from the magnitude of the low frequency component after adjustment by increasing or decreasing. 3. Simple insulation of an electric circuit according to claims 1 and 2, wherein the connecting wire is wound around either the core of the transformer or the current transformer, or both. How to measure resistance.