JPS60186765A - Compensating method of measuring device for insulation resistance - Google Patents

Abstract

PURPOSE:To measure insulation resistance, etc., regardless of temperature variation, secular change, etc., by providing the same characteristics to a circuit which generates a signal for detection, and the zero-phase device, amplifier, filter, etc., of a measuring circuit. CONSTITUTION:A low-frequency signal voltage for measurement with a frequency f1 different from the commercial frequency is applied to the cable run of a receiving transformer T with a load Z through a dual earth line LE by an oscillator OSC. Then, a component of frequency f1 in a leak current is detected by measuring circuit such as the zero-phase device ZCT, amplifier AMP, filter FIL1, etc., and supplied to a multiplying circuit MULT for synchronous detection. This circuit MULT is supplied with a detection signal from the circuit consisting of a zero-phase device ZCT1, amplifier AMP1, filter FIL1, phase shifter PS, etc., having the same characteristics with the phase device ZCT, etc., of the measuring circuit, so that temperature variation and secular change of each circuit element are canceled. Then, the insulation resistance, etc., of the cable run are measured from the leak current value without reference to temperature variation and a secular change.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method of compensating for temperature changes or secular changes in circuit constants of a device that measures the insulation resistance and ground stray capacitance of electric circuits etc. in a live line state.

Conventionally, it has been common to use a method of measuring the insulation resistance of an electrical circuit as shown in Figure $1 for early detection of troubles in electrical circuits such as electrical leakage.

This is the second step of grounding i of the receiving transformer T with a load Z.
! l! LE'c The electric circuit can be connected by passing it through the transformer OT connected to the measuring low frequency signal oscillator O8C with a frequency f+ different from the commercial power supply frequency, or by cutting the grounding wire and connecting the oscillator in series with it. A full low-frequency voltage for measurement is applied to L1 and the electric line L2, and the zero-phase current transformer zc'r passes through the grounding line LE2, and the voltage is applied through the insulation resistance R・0 and the stray capacitance to ground Cof that exist between the electric line and the ground. All leakage currents returning to the ground line are detected and sent to the amplifier AM.
After amplifying with P, only the component of frequency f1 is selected in addition to the filter FIL.

The effective component in the leakage current (that is, the component in phase with the applied low-frequency voltage for measurement) is detected, and this is synchronously detected by a multiplier MTJLT using, for example, the output of the oscillator 08C, thereby insulating the electrical circuit. It was configured to measure resistance.

To further explain the measurement theory, the grounding wire L B
Es
If 1nω1t (ω, =2πf+).

The leakage current of frequency f1 that returns via the ground point Ei is Therefore, the component is in phase with the applied AC voltage.

That is, if a value proportional to the first term component on the right side of the above equation (1) is detected by means such as synchronous detection, the insulation resistance R.

It was possible to obtain a measurement value that was inversely proportional to , and from this the insulation resistance value of the electrical circuit could be determined.

However, if the leakage current that returns to the grounding wire is detected by the zero-phase current transformer ZCT, and the leakage current component of frequency fl included in the output of the zero-phase current transformer is selectively outputted by the filter FIL, the zero-phase In the system of current transformer → amplifier → filter, the leakage current of frequency f1 always has a phase shift, so in order to synchronize them, it is necessary to compensate for this phase shift. For this purpose, the first input of the synchronous detector A phase shifter P86 was inserted at the end or the second input end, thereby compensating for the phase shift and achieving mutual synchronization.

That is, by providing this phase shifter PS, the stray capacitance to ground C
o (Co=O), the first . The phase difference between the voltages applied to the second input terminal was set in advance to be zero and fixed.

However, in the conventional method as described above, the zero-phase current transformer ZC
If the phase characteristics at frequency fl of T, filter FIL, etc. fluctuate due to temperature changes or secular changes in the characteristics of used parts, a phase error with the initial adjustment value will occur, making it impossible to provide accurate measurement results. In order to deal with these problems, it has conventionally been necessary to use an extremely high quality zero-phase current transformer or filter with little variation in characteristics.

Even if these are adopted, there is a shadow of phase error! # It was difficult to get rid of wo.

The present invention has been made to solve these drawbacks, and when detecting a leakage signal, the oscillator output is applied to the second input terminal of a synchronous detector via the oscillator O8C → phase shifter PS. An object of the present invention is to provide a complete compensation method for an insulation resistance measuring device which is connected through a circuit having characteristics similar to those of the zero-phase current transformer, filter, and amplifier used in the present invention.

First, before explaining the measuring method according to the present invention, the drawbacks of the conventional method will be explained in some detail to help understand the method.

The leakage current component (■) at frequency f1 shown in equation (1) is zero-phase current transformer ZCT, amplifier AMP, and filter FIL.
If the phase shift occurring in the O system is θ, the filter FIL output Il is as follows: (2) This is applied to the first input terminal of the synchronous detector MULT.

Further, the voltage applied to the second input terminal of the synchronous detector is set to, for example, a constant amplitude a. 5in (ω1t+01), the DC component obtained from the output of the synchronous detector is D=11x ao
sin (O1 is 10+) -... Output DO Hatona') +V+
Since aO is constant, a value that is inversely proportional to insulation resistance R·O can be measured. Therefore, the above is true when the phase shift θ−θ is not zero.

The error E of D is = l −cos (θ−θ1)−ωIC0R1Osi
n (0-01)...(6).

Now 1. For example, when θ-01=1 (degrees), in equation (6), fl
=25Hz, R,o=20Ω, Co=5 iiF
It can be seen that the error ε is 27.4%, which means that the measurement error becomes significantly large.

Also, temperature fluctuation of zero-phase current transformer ZCT, e.g. -10 to 60°C
The phase variation characteristic for f1=25H2 reaches as much as ±1 degree, which increases the measurement error.

The present invention proposes a method for minimizing the occurrence of errors due to the above-mentioned phase shift.

FIG. 2 is a circuit diagram showing an entire embodiment of the insulation resistance measuring method according to the present invention, and the same symbols as in FIG. 1 have the same meanings.

In the figure, an oscillator O8C for generating a low frequency of frequency f1 is connected in series to the ground line Lx via a transformer OT, and a voltage of voltage (2) is applied to the ground line Lx.

At this time, the innovidance of the transformer inserted in series with the grounding wire is selected to be sufficiently low. By passing the entire frequency f1 component of the zero-phase current transformer ZCT output and applying it to the filter FIL that removes the commercial frequency component, an output corresponding to equation (2) is obtained, and this is applied to the first filter of the synchronous detector MtJLT. input end 1 of
to be applied.

On the other hand, for example, a resistor R is placed on the output side of the transformer for applying low frequency signals.
・If all connections are made and a constant current i is applied, ■ i =] "sin"Jxt °°H"H+"' (7)
becomes. This current i is detected by a second zero-phase current transformer zc'r1, which has the same characteristics as the zero-phase current transformer ZC'[', and is applied to a second amplifier AMP1, which has the same characteristics as the amplifier AMP. , the second filter has the same characteristic sound as the filter FIL.
If the voltage is applied to the filter FIL1 of the filter F I L
The way l comes out 11 is V i , = −π−5in (ω1t+θ′) −−−
-----(81. Here, θ' is the zero-phase current transformer zc'
It is the phase shift at frequency f1 from t''i to the output of filter FIL1, and is generally θ' in θ.
! : This is because the characteristics of the AMP and the filters FIL1 and FIL are the same. Also, a is the gain of these systems.

Therefore, by adding the fill FILI to the phase shifter PS and setting it so that θ=θ', and applying the output of the phase shifter PS to the second input terminal of the synchronous detector MULT, synchronous detection can be performed. The output 0UT2 of the device MULT can be obtained from a calculation similar to the relationship in equation (3). Since (2) and a are constant here, the insulation resistance can be measured by knowing the value of the output OUT. To explain in detail the history of these relationships, the phase θ included in equation (2) due to temperature fluctuations, etc.
changes to θ+ε, and the phase θI included in equation (8) becomes θ
/+, /, these phase differences become θ+ε, -(θl+ε')=θ-θ'+ε1-ε', but the phase shifter PS is used so that θ-θ'=0. However, as mentioned above, if both systems use circuits with almost the same characteristics and are selected so that ε1 and ε' fluctuate almost equally, ε , -ε' are significantly small, and the occurrence of errors can be ignored.

Similarly, if all filters FIL whose phase characteristics vary little due to temperature can be used, the filter FTLI-
It is economical because there is no need to insert it.

In this case, it is clear that the fixed phase shift of the filter FIL can be adjusted by the phase shifter PS.

As explained above, according to the method of the present invention, the zero-phase current transformer Z
Since the zero-phase current transformer ZCT1 has the same characteristics as the CT→filter FIL system and is installed in the filter F'ILI, the temperature of the total phase shift of each group.

Since the fluctuations due to aging can be made relatively the same, by making only the phase shifter PS have a small fluctuation, it is possible to cancel each fluctuation.

Note that a highly stable phase shifter can be easily realized by connecting multiple stages of phase shifters with low phase shifts, and even if there is a phase shift due to constant variations of the components of each phase shifter (not shown in the figure), Fluctuations in the overall phase characteristics can be made extremely small.

In the examples, a single-phase, two-wire case is shown for ease of explanation, but the present invention is not necessarily limited to this, and a single-phase, three-wire case is shown.
It is clear that the same principle can be used even in the case of a helical type or three-phase three-wire type.

In the above embodiment, the grounding wire was cut and inserted when applying the low frequency signal to the town.

It may be passed through the transformer connected to the oscillator, -1
However, by shifting the phase of the voltage applied to the second input terminal of the synchronous detector M [JLT by 90 degrees more than in the above embodiment, it is possible to obtain a value proportional to the ground stray capacitance in the synchronous detector output. This makes it possible to measure the floating capacitance of electrical circuits to the ground.

Although not shown in this embodiment, (the absolute value of the output 11 of the filter FIL expressed by equation 21 11+1=V, /
1. + ((dt..) 2K Separately installed with rectifier circuit O ← At the same time as detecting light, the phase difference S between the output of filter FIL and the output of filter FILI is completely detected 1111ωSS
By performing the calculation, it is possible to obtain a value proportional to the reciprocal of the insulation resistance R,o, so it can also be used as a method of compensating for circuit phase fluctuations in insulation resistance measurement, similar to the method described above. be able to.

Fig. 3 is a circuit diagram showing another embodiment in which the measurement signal voltage is detected by a zero-phase current transformer. The current is detected by a zero-phase current transformer ZCT1.

Furthermore, FIG. 4 is a circuit diagram showing another embodiment of the present invention, in which a separate winding provided in the transformer OT passing through the grounding line Lg2 is terminated with a resistor R, and the current flowing therein is detected.

In the above explanation, the zero-phase current transformer ZCTQ is used to detect the zero-phase current, but the present invention is not limited to this in any way. It is obvious that a low-phase current transformer ZCT in the embodiment shown in FIG.
It is sufficient to remove ZCTI and leave only the filters FIL and FIL1.

Further, although the measurement signal voltage has been described as a sine wave, it is not limited to this, and it may be a rectangular wave, for example, and its fundamental wave component or high frequency component may be used.

As explained above, the present invention relates to insulation resistance of electric circuits.

The measurement signal obtained through a similar circuit having the same characteristics as the amplifier, filter, etc. used in the leakage component detection circuit of the applied signal of the measurement signal voltage in the circuit for measuring stray capacitance or circuit resistance, etc. The device is configured to carry out the various measurements using the circuit, and since changes in the characteristics of the measurement circuit due to changes in temperature or aging of the parts used cancel each other out, it is possible to measure the characteristics of the electric circuit accurately at a very low cost. It is very effective.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing a conventional method for measuring total insulation resistance. FIG. 2 is a block diagram showing one embodiment of the present invention, and FIG.
and FIG. 4 are block diagrams showing another embodiment of the present invention. Patent applicant: Toyo Tsushinki Co., Ltd.

Claims (1)

[Claims] A first step for detecting a leakage current of the frequency f+ included in the output of the first zero-phase current transformer by passing the commercial frequency and grounding wires to the all zero-phase current transformer ZCTΦ in the electrical circuit via the grounding wire of the transformer. A second zero-phase current transformer having the same characteristic sound as the first zero-phase current transformer detects the current flowing to the load connected to the measurement signal voltage. By detecting the frequency f1 component with a second filter having the same characteristics as the first filter, the phase change current gain can be reduced to zero by measuring the entire insulation resistance using the first and second filter outputs. A compensation method for an insulation resistance measuring device characterized by suppressing the influence of phase characteristic fluctuations due to fluctuations in circuit constants of phase current transformers and filters.