JPH0713647B2 - Insulation resistance measuring device phase adjustment method - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for adjusting temperature change or circuit constant secular change in an apparatus for measuring the insulation resistance of an electric circuit or the like in a live state.

(Prior Art) Conventionally, in order to detect a trouble in an electric circuit such as an electric leakage at an early stage, it is general to monitor the electric circuit condition by using an insulation resistance measuring method of the electric circuit as shown in FIG. 5, for example.

This is the second type ground wire of the power receiving transformer T having a load of Z.
To L _E, inserting the transformer OT connecting the measurement low frequency signal oscillator OSC comprising a frequency ₁ of the commercial power source frequency and another differences or, or the ground line L _E on or the insert connecting the oscillator OSC in series By applying a low-frequency voltage for measurement to the electric lines 1 and 2 by penetrating the electric lines 1 and 2 into the toroidal core transformer to which the oscillator is connected, and by using the zero-phase current transformer ZCT that penetrates the ground line L _E. , The leakage current of the low frequency signal for measurement that is returned to the ground line through the insulation resistance R _O existing between the electric line and the ground and the stray capacitance C _O to the ground is detected, and the leakage current is amplified by an amplifier AMP and then filtered. Only the component of frequency ₁ is selected by FIL and this is
The insulation resistance of the electric circuit is measured by synchronously detecting with the multiplier MULT using the output signal of SC and detecting the effective component (OUT ₁ ) in the leakage current component (that is, the component in phase with the applied low frequency voltage). It was configured as follows.

The theory of measurement will be further explained to help understanding of the present invention.

Assuming that the measurement signal voltage applied to the ground line L _{E is} , for example, a sine wave of V _sin ω _1t (ω ₁ = 2π ₁ ), the ground point E
The leakage current I of frequency ₁ which returns to the ground line L _E via If a value proportional to the component of the same phase as the applied AC voltage, that is, the component of the first term on the right side of equation (1) above is detected by means such as synchronous detection, this value is reversed to the insulation resistance R _O. Since it is proportional, the insulation resistance value of the electric path can be obtained. However, in the conventional method in which the leakage current returning to the ground line is detected by the zero-phase current transformer ZCT and the leakage current component of frequency ₁ contained in this is selected and output by the filter FIL, the zero-current transformer is normally used. Since the phase of the leakage current at frequency ₁ shifts in the system of device → amplifier → filter, it is necessary to compensate for this phase shift in order to obtain a value inversely proportional to R _O from these coherent detection outputs. For this reason, conventionally, as shown in the same figure, by inserting a phase shifter PS at the first input end of the synchronous detector MULT or at the second input end, the phase shift is corrected and the two are synchronized with each other. . That is, by providing this phase shifter PS, there is no stray capacitance C _O to the ground (C _O = 0)
Therefore, it was set in advance so that the phase difference between the voltages applied to the first and second input terminals of the synchronous detector becomes zero.

However, in the conventional method as described above, the zero-phase current transformer ZCT,
Since the phase characteristics of the filter FIL, phase shifter PS, etc. fluctuate due to changes in temperature or secular changes in the characteristics of the parts used, as a result, a phase error with the first adjustment value occurs, and it is not possible to provide correct measurement results there were. In order to deal with these problems, the effect of the phase error was conventionally minimized by adopting an extremely high-quality zero-phase current transformer or filter with less characteristic fluctuation, but the effect should still be completely eliminated. Was difficult.

(Object of the Invention) The present invention has been made in order to eliminate the drawbacks of the conventional insulation resistance measuring method as described above, and always corrects the phase shift of the measurement signal inexpensively without requiring expensive parts. However, it is an object of the present invention to provide a phase adjustment method for an insulation resistance measuring device that can always provide accurate measurement results.

(Summary of the Invention) In order to achieve this object, the present invention is, in principle, forcibly inserting a reactance element (for example, a capacitor or the like) of a predetermined value between the measured circuit and the ground, and the low frequency voltage and 90 ° phase Different currents, and this current is repeatedly connected and disconnected randomly at a constant period T or a predetermined interval T, and the frequency component of frequency 1 / T contained in the output of the first synchronous detector and the leakage of the frequency ₁ The product of the current component and the frequency component of frequency 1 / T contained in the output obtained by synchronously detecting by the second synchronous detector with a voltage whose phase is shifted by 90 ° from the low frequency voltage The phase of the voltage, which is a 90 ° phase shift from the low frequency voltage applied to the first synchronous detector and the low frequency voltage applied to the second synchronous detector, is automatically adjusted so that the minute approaches zero. What you configure to adjust A.

(Example) First, before explaining the measuring method according to the present invention, the conventional method and its drawbacks will be described in a little more detail in order to help understanding thereof.

If the leakage current component I of frequency ₁ shown in the equation (1) passes through the system of the zero-phase current transformer ZCT, the amplifier AMP, and the filter FIL, and the phase shift is θ, the filter FIL output I ₁ becomes And this is applied to the first input of the synchronous detector MULT.

If the voltage applied to the second input terminal of the synchronous detector is, for example, a _O sin (ω _1t + θ ₁ ) of constant amplitude, the output of the synchronous detector, that is, the effective component D is Therefore, the output D _O when θ = θ ₁ is Since V and a _O are constant, a value inversely proportional to the insulation resistance R _O can be measured. Therefore, the phase shift θ−θ
The error E of D with respect to D _O when ₁ is not zero is Becomes

Now, for example, when θ−θ ₁ = 1 (degrees), ₁ =
In _{25Hz, R O = 20KΩ, 1} ω when the _{C O = 5μF C O R O} 1
Since it is 5.7, the error ε is 27.4%, and it can be seen that the measurement error is significantly large.

The present invention proposes a method for suppressing the occurrence of an error due to the above-mentioned phase shift as much as possible.

FIG. 1 is a circuit diagram showing an embodiment of an insulation resistance measuring device according to the present invention. As in the case of FIG. 5, a low-impedance transformer OT coupled with a low-frequency generating oscillator OSC having a frequency of ₁ is inserted in series with the ground line L _E so that the voltage V A low-frequency signal which is applied to the ground line L _E and is fed back to the ground line L _E from the leakage signal of the low-frequency signal to the ground line L _E by the zero-phase current transformer, the filter FIL, and the first synchronous detector. The in-phase (effective) component inversely proportional to the insulation resistance is extracted, but in the present embodiment, the following device is further added.

That is, a series circuit of a capacitor C and a switch SW is inserted between the connection point of the ground line L _{E with} the electric path 2 and the ground point E of the ground, and the switch SW is turned on at a required period T-. O
FF. Further, when a part of the output of the low frequency oscillator OSC is applied to the synchronous detector MULT1, it is replaced by the phase shifter PS and is performed via the automatic phase shift control circuit PC, and the synchronous detector MULT1 The output D ₁ is input to one input terminal of the multiplier MULT2 via the bandpass filter BP1 which passes only the frequency 1 / T.

Further, the input of the synchronous detector MULT1, that is, a part of the output of the filter FIL is used as one input of the second synchronous detector MULT3,
A direct current obtained by passing the output of the multiplier MULT2 to the other input of the multiplier MULT2 through the second bandpass filter BP2 passing the 1 / T frequency and passing the output of the multiplier MULT2 through the low pass filter LF _1. The automatic phase shift control circuit PC is controlled by a component signal, and a part of the automatic phase shift control circuit PC is connected to the second synchronous detector MUL via a 90 ° phase shifter PSS.
It is configured to be connected to the other input of T3.

The operation of the insulation resistance measuring apparatus of the electric circuit constructed in this way, particularly the phase adjusting method, will be described in detail below.

In the figure, the switch SW is connected in parallel with the ground line L _E.
When ON is turned on, a current of ω ₁ CV _cos ω _1t flows additionally to the ground line L _E, and the leakage current Io of the applied low frequency component flowing in the ground line at this time is Becomes Therefore, considering the phase shift generated in the system of zero-phase current transformer ZCT, amplifier AMP and filter FIL, the filter F
The output I ₂ of IL is calculated from the relationship of equation (2). And the output D ₁ of the synchronous detector MULT1 at this time is
From the relationship of equation (4) Becomes

Now, switch SW is synchronized T When turned on and off, the C term contained in the second term of equation (9) repeats existence / non-existence at the period T, so that the output D ₁ of the synchronous detector MULT1 has a frequency 1 / T component. (As can be seen from the expression (9), when θ = θ ₁ , the second term becomes zero, so that the frequency 1 / T component does not occur). If the output of the synchronous detector MULT1 is applied to the filter BP1 that extracts only the frequency 1 / T, the output A of the filter BP1 is expressed by the following equation (10).

Here, k is a constant, and is a phase determined from filter characteristics and the like.

On the other hand, the output branched from the output of the filter FIL is the second
Of it is input to the synchronous detector MULT _3, in the synchronization signal to the site is the signal a _O sin (ω relative to the first synchronous detector MULT1
_{Since 1t} + θ ₁ ) is obtained by passing the 90 ° phase shifter PSS, it becomes a _O cos (ω _1t + θ ₁ ). Therefore, the output of the second synchronous detector MULT3, that is, the invalid component D ₂ is D ₂ = I ₂ × a _O cos (ω _1t + θ ₁ ) ... (11) In addition, in this equation, the above (3) Angular frequency ω
Means removing _one or more components, so that As described above, the term of C in this equation is the period T
Since the presence / absence is repeated at, if the output of the synchronous detector MULT3 is applied to the filter BP2 that extracts only the frequency 1 / T component,
The output B of the filter BP2 is It can be expressed as. Here, k, is the same as the relation in Eq. (10). Bandpass filter BP2 obtained in this way
When the output B (13) of the above equation and the output A (10) of the bandpass filter BP1 are applied to the input terminals of the multiplication circuit MULT2, the output D ₃ of the multiplication circuit MULT2 becomes Becomes Therefore, the DC component D ₄ obtained by applying the output of the multiplication circuit MULT2 to the low-pass filter LF is Can be expressed as

Therefore, the synchronization reference signal a _O sin to be input to the two synchronization detectors MULT1 and MULT3 by the automatic phase control circuit PC
The phase θ ₁ of (ω _1t + θ ₁ ) and a _O cos (ω _1t + θ ₁ ) is adjusted so that the low-pass filter LF output D ₄ becomes zero, that is, θ
= Θ ₁ , the second term in D of the output OUT2 of the first synchronous detector MULT1 represented by the equation (4) becomes zero and an accurate detection signal can be obtained. it can.

In addition, in the automatic phase adjustment circuit PC required here, the closed loop in FIG. 1, that is, the first synchronous detector MULT1, the first bandpass filter BP1, the multiplier MULT2, and the lowpass filter LF are moved by 90 °. The low component which is supplied to the two synchronous detectors so that the DC component D ₄ obtained through the phase detector PSS, the second synchronous detector MULT3, the second bandpass filter BP2, the multiplier MULT2 and the lowpass filter LF becomes zero It is only necessary to automatically adjust the phase of the output signal of the frequency oscillator OSC. Since this automatic phase adjustment circuit can be easily realized by existing technology, its explanation is omitted.

Furthermore, in the above description, the capacitor C is simply turned on and off in the cycle T, but the phase control method is also applied when the value of the capacitor C is continuously (eg, sinusoidally) changed in the cycle T. In this case, a variable capacitance element may be used instead of the capacitor C at this time.

Further, the phase adjustment may be performed for a certain period of time and θ ₁ may be fixed when θ−θ ₁₀ is reached, or the above-mentioned phase adjustment may be performed intermittently such that the phase adjustment is performed randomly after a certain period of time. .

Further, in the above description, the case where the capacitor C is inserted between the ground electric line and the ground has been described, but the present invention is not limited to this, and may be inserted between the non-ground electric line and the ground, for example. However, in this case, since the commercial power is applied to the capacitor C, the current flowing through the capacitor C and the switch SW becomes remarkably large, so that it is necessary to use one that can withstand this.

In reality, the capacitor C inserted between the electric line and ground
In this case, some resistance may be inserted in series due to the influence of the connection line, etc. In this case, the current flowing through the capacitor C does not exactly 90 ° phase shift with respect to the applied low frequency voltage, so there is a slight error. However, this error is generally so small that it does not hinder the measurement.

FIG. 2 is a block diagram showing a modified embodiment of the present invention, which shows another embodiment of the method for inserting a series circuit of a capacitor and a switch connected between the electric line and the ground.

In this embodiment, instead of the transformer OT used for applying a low frequency signal to the ground line L _E , an OT ′ having a secondary winding is provided.
A series circuit of a capacitor C and a switch SW is connected to the secondary winding so that a part of the series circuit penetrates through the zero-phase current transformer ZCT.

According to this example, it is not necessary to directly connect the capacitor C and the switch S to the ground line L _{E as} in the embodiment shown in FIG. 1, so that the installation work can be simplified.

The operation is exactly the same as that described in FIG.

FIG. 3 shows another embodiment of the same part, in which a circuit in which a capacitor C and a switch SW are connected in series is used as a transformer OT for applying a low frequency to the ground line L _E.
It is connected to the primary side of. At this time, when the voltage on the primary side is higher than the voltage on the secondary side, the operation can be made the same as that shown in FIG. 1 and its description by reducing the capacity of the capacitor C by the ratio.

Although the voltage applied to the capacitor C is set to V in the equation (7), it is not limited to this in the practice of the present invention and other voltages will not cause any problem in operation.

In addition, two synchronous detectors MU are connected from the automatic phase control circuit PC.
The sync signals input to LT1 and MULT3 are adjusted in advance so that they are exactly 90 ° out of phase with each other, and the output of the low-pass filter is zero, which is caused by subsequent temperature changes or aging changes. If the phase shift is compensated by the above-described automatic phase control method, the phase synchronization period can be shortened.

In the above description, a capacitor element is used to flow a current having a 90 ° phase difference from the low frequency voltage for measurement, but the present invention is not necessarily limited to this, and another circuit network (for example, an inductance and a capacitor may be used). Obviously, a combination of circuits) may be used. Further applied low frequency voltage and 90 °
In order to generate currents having different phases, a voltage with a 90 ° phase shift may be generated by the oscillator OSC, and the voltage may be supplied to the zero-phase current transformer at a cycle T via a resistor or the like.

Further, in the above description, the phase of the signal applied to the second input of the synchronous detector is adjusted in adjusting the phase, but the phase of the signal applied to the first input of the synchronous detector is adjusted. It is clear that the same result can be obtained by adjusting.

FIG. 4 is a block diagram showing another modified embodiment of the present invention. As a means for applying a 90 ° phase-shifted low frequency signal to the leakage current detection system that returns to the ground line, it is directly connected from the low frequency oscillator OSC. The 90 ° shifted signal is derived, inserted into the switch SW, and applied to the signal line penetrating the zero-phase current transformer ZCT. Further, the automatic phase control circuit PC is further connected to the first phase.
It is configured to be inserted into the input terminal of the synchronous detector MULT1 of.

With this configuration as well, if the automatic phase control circuit PC is controlled so that the output of the low-pass filter LF becomes zero as in the case shown in FIGS. Can be measured.

In the above description, the low-frequency signal voltage has been described as a sine wave, but the present invention is not limited to this, and may be, for example, a rectangular wave or its fundamental wave component or higher harmonic wave component.

Further, in the above description, the case where the 90 ° phase shift signal applied to the leakage signal deriving system is interrupted at the cycle T has been described, but various methods can be considered for this interrupting timing.

The first method is a method of constantly repeating this interruption, and a method of constantly monitoring the direct current component of the low-pass filter LF and causing the automatic phase control circuit to function so that it becomes zero or minimum, the second method is A method of doing this intermittently at a predetermined interval, or a method of repeating the above-mentioned phase adjustment operation by repeating the intermittent operation at a random interval containing the frequency component 1 / T, etc., but other methods are used. It will be obvious that it is okay.

In the above embodiment, the case of the single-phase two-wire type electric circuit has been shown, but the present invention can be similarly applied to the single-phase three-wire type electric circuit and the three-phase three-wire type electric line whose one end is grounded.

(Effect of the Invention) As described above, the present invention is configured to automatically adjust the phase characteristic variation of the insulation resistance measuring circuit, and therefore, in order to realize an insulation resistance measuring device that is extremely stable and accurate at all times. It is very effective.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention, FIG.
3 and 4 are partial block diagrams showing another embodiment of the present invention, and FIG. 5 is a block diagram showing a conventional method for measuring insulation resistance. T …… transformer, 1,2 …… electric circuit, L _E …… ground wire, E …… ground point, ZCT …… zero-phase current transformer, AMP …… amplifier, FIL …… filter, MULT1, and MULT3 …… Synchronous detector, MULT3 …… Multiplier, P
C …… Automatic phase control circuit, BP ₁ , BP ₂ …… Filter, DET ……
Rectifier circuit, PSS ... 90 ° phase shifter.

Claims (5)

[Claims] _{1. A} low frequency signal voltage having a frequency of ₁ different from a commercial frequency is applied to an electric line through a ground wire of a transformer and the effective component of the low frequency signal which is fed back to the ground wire is extracted to extract the effective component. In the method of measuring the insulation resistance between the electric line and the ground, the low frequency signal applied to the electric line and 90 °
A signal whose phase has been shifted is fed back to the ground line and is applied to a circuit for detecting a leakage current of a low frequency signal continuously at a cycle T or at predetermined intervals or at random intervals including a frequency component 1 / T. Along with the component of frequency 1 / T contained in the effective component and the reference signal used to extract the effective component, extracted from the leak current of the fed back low frequency signal based on the 90 ° phase-shifted signal. The phase of the reference signal used to extract the effective component and the ineffective component so that the direct current component in the product output is zero and the product with the frequency component of frequency 1 / T included in the ineffective component is obtained. A phase adjusting method for an insulation resistance measuring device, characterized by being adjusted manually or automatically. 2. A means for applying the 90 ° phase-shifted signal to a circuit for detecting a leakage current component of a low-frequency signal returned to the ground line inserts a variable reactance between the electric line and the ground, 2. The insulation resistance measurement according to claim 1, wherein the value of the variable reactance is changed continuously in a cycle T, or at a predetermined interval or at random intervals including a frequency component 1 / T. Phase adjustment method for equipment. 3. A circuit comprising fixed reactance and switching means is inserted in place of the variable reactance,
3. The phase adjusting method for an insulation resistance measuring apparatus according to claim 2, wherein the switching means is opened / closed continuously in a cycle T or at predetermined intervals or at random intervals. 4. The zero-phase current transformer when the means for detecting the leakage current component of the low-frequency signal returned to the ground line is performed through the zero-phase current transformer connected to the ground line. 4. The phase adjusting method for an insulation resistance measuring apparatus according to claim 1, 2 or 3, wherein the variable reactance element or the circuit consisting of the fixed reactance and the switching means is inserted into the signal line which is penetrated. 5. A leakage current of a low frequency signal fed back to the ground line instead of adjusting the phase of a reference signal for extracting the effective component and the ineffective component by means for making the direct current component in the product output zero. The phase adjusting method in the insulation resistance measuring device according to any one of claims 1 to 4, wherein the phase of the component is adjusted.