JPS6366473A - Phase adjustment of insulation resistance measuring apparatus - Google Patents

Abstract

PURPOSE:To measure insulation resistance accurately, by automatically adjusting variations in phase characteristic of an insulation resistance measuring circuit. CONSTITUTION:A capacitor C and a switch SW are provided between an electric circuit 2 to be measured and the earth E and opened or closed at a specified cycle T. An output of a low frequency oscillator OS is applied to a synchronous detector MULT1 through an automatic phase shift control circuit PC and an output of the detector MULT1 is inputted into a multiplier MULT2 through a BPF-BP1 adapted to pass 1/T frequency alone. Furthermore, a part of an input of the detector MULT1 is supplied to a synchronous detector MULT3, an output of which is inputted into a multiplier MULT2 via a BPF-BP2 adapted to pass 1/T frequency. An output of the multiplier is passed through an LPF-LF1 to obtain a DC component signal, by which the circuit PC is controlled. Thus, variations are automatically adjusted with the circuit PC in the phase of a low frequency voltage to be applied to the detector MULT1 and of a voltage to be applied to the detector MULT3 as shifted by 90 deg. from the low frequency voltage through a 90 deg. phase shifter PSS thereby enabling stable and accurate measurement of the insulation resistance.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method of adjusting a device for measuring insulation resistance of an electrical circuit or the like in a live line state against temperature changes or secular changes in circuit constants.

(Prior Art) Conventionally, it has been common practice to monitor the condition of an electrical circuit using a method of measuring the insulation resistance of the electrical circuit, as shown in FIG.

This is the second type grounding wire LE ic of the power receiving transformer T with a load Z, and the transformer O connected to the measuring low frequency signal oscillator O8C with a frequency fx different from the commercial tl1 frequency.
T, or by inserting and connecting the oscillator O8C in series with the ground f@Lv, or by passing the electric line 1.2 through the toroidal core transformer connected to the oscillator, the electric line L and the electric line are connected. A zero-phase current transformer ZCT in which a constant low frequency voltage is applied to 2 and the grounding wire LE is passed through it.
Therefore, the leakage current of the measurement low frequency absorption signal that returns to the ground line via the insulation resistance RO and the ground stray capacitance Co existing between the electric path and the ground is detected, and this is detected by the amplifier AM.
After being amplified by P, the frequency f1 is
Select only the component and synchronously detect it with the multiplier MULT using the output signal of the oscillator O8C, for example, to obtain the effective component (01)Tl in the leakage current (i.e., the component in phase with the applied low frequency voltage) ) was detected, the insulation resistance of the electrical circuit was measured from K.

To help understand the present invention, the measurement theory thereof will be further explained.

If the measurement signal voltage applied to the grounding line LK is, for example, a sine wave and Vsiaω11 (ω1 = 2πfl), then the leakage current of frequency f1 that returns to the grounding line LEK via the grounding point E is expressed as: A component that is in phase with the applied AC voltage.

In other words, if a value proportional to the first term on the right side of equation (1) above is detected by means such as synchronous detection, this value will be inversely proportional to the insulation resistance RO, and this will determine the insulation resistance value of the electrical circuit. can be found.

However, in the conventional method in which the leakage current returning to the ground wire is detected by the zero-phase current transformer ZCT, and the leakage current component of the frequency f1 included in this is selected and outputted by the filter FIL, 9 normal zero-phase current transformers Since the phase of the leakage current at frequency f1 is shifted in the system of amplifier→amplifier→filter, it is necessary to compensate for this phase shift in order to obtain a value inversely proportional to RO from these synchronous detection outputs. For this purpose, conventionally, as shown in the figure, a phase shifter PS was inserted into the first input terminal or the second input terminal of the synchronous detector MLILT to correct the phase shift and achieve mutual synchronization. . That is, this phase shifter P
By providing S, there is no floating capacity tCO to the ground (C
.

= 0), the first . It is set in advance so that the phase difference between the voltages applied to the input terminal of yIJ2 is zero.

However, in the conventional method as described above, the zero-phase current transformer ZC
Since the phase characteristics of T, filter FIL, phase shifter PS, etc. fluctuate due to temperature changes or secular changes in the characteristics of the parts used, this results in a phase error with the initial adjustment value.
There was a drawback that accurate measurement results could not be provided. Conventionally, to deal with these problems, the influence of phase errors has been minimized as much as possible by using extremely high-quality zero-phase current transformers or filters with little characteristic variation, but even so, it has not been possible to completely eliminate the influence. It was difficult to do so.

(Object of the Invention) The present invention has been made to eliminate the drawbacks of the conventional insulation resistance measurement method as explained above, and is capable of constantly correcting the phase shift of the measurement signal at low cost 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, in principle, forcibly inserts an actuator element (such as a capacitor) with a predetermined value between the electrical circuit to be measured and the ground, so that the low frequency voltage ° While flowing currents with different phases, this current is randomly connected and disconnected at a constant period T or a predetermined interval T, and the frequency component of the frequency 1/T included in the output of the synchronous detector of the cabinet 1,
Leakage of said frequency f=1! The product of the current component and the frequency component of frequency 1/T included in the output obtained by synchronously detecting the current component with a voltage whose phase is shifted by 90 degrees from the low frequency R voltage with a second synchronous detector is calculated. Automatically adjust the phase of the voltage with 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 so that the DC component approaches zero. It is configured to adjust to.

(Example) First, before explaining the measuring method according to the present invention, the conventional method and its drawbacks will be explained in some detail to help the understanding.

The leakage first flow component of the frequency f1 shown in equation (1) is zero-phase current transformer ZCT, amplifier AMP, and filter FIL.
If the phase shift that occurs when passing through the system is set to 0, the filter FIL output crab 1 becomes
is applied to the first input terminal of.

Further, the voltage applied to the second input terminal of the synchronous detector is set to, for example, a constant amplitude a. 5in(ωt t-Ht ), the output of the synchronous detector, that is, the effective component, is D = I t
xaosin(ωxt+θ1) ・−・・−・(31
(□ means to remove components with an angular frequency of 01 or more) ・・・−・・・・・・(4) Therefore, when 0=01, the output DO is # v# Since aQ is constant, it is isolated It is inversely proportional to the resistance RO, and the hypothetical value can be measured. Therefore, the above is true when the phase shift θ−θl is not zero.

The error E of D for
1) --------(6).

Now 1. For example, when θ−θl=1 (degrees), in equation (6), f
When t=25Hz, Ro=20, Ω, and Co:5#F, ωtCoRo=15.7, so the error e is 27.
It can be seen that the measurement error becomes 4 yen, and the measurement error becomes significantly large.

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

The first part is a circuit diagram showing an embodiment of the insulation resistance measuring device according to the present invention. This can be done by inserting a low impedance transformer/transfer OT coupled with an oscillator O8C for generating a low frequency of one frequency fl in series in the grounding line LE, as shown in FIG. (2) A low frequency signal of
The purpose is to extract an in-phase (effective) component that is inversely proportional to the insulation resistance of the path, and in this embodiment, the following device is additionally added.

That is, a series circuit of a capacitor C and a switch SW is inserted between the connection point of the grounding line Lm with the electric circuit 2 and the grounding point E, and the switch SWg is turned 0N-OFF at the required period T. Also, the low frequency oscillator O8
When applying a part of the output of C to the synchronous detector MULT1, it is applied via the automatic phase shift control circuit PC by replacing it with the shift Tt1''6PS, and at the same time, the output of the synchronous detector ML!
The output D1 of LT1 is passed through a bandpass filter BPl that passes only the frequency 1/T.
Input to one input terminal of T2.

Further, a part of the input of the synchronous detector MULTI, that is, the output of the filter FIL is inputted to a second synchronous detector MULT3, and the output of the synchronous detector MULT3 is passed through a second band-pass filter BPx that passes the 1/T frequency. The above multiplication is calculated by the calculator MUL'
In addition to the other input of L"2, this section is connected to the calculator MULT.
The automatic phase shift control circuit P uses the DC component signal obtained by passing the output of 2 through the low-pass filter LF1t.
90, and a part of the automatic phase shift control circuit PC.
° The second synchronous detector M U via the phase shifter PSS
The connection configuration is such that it is connected to the other input of L T 3.

The operation of the device having the insulation resistance of the electrical circuit constructed in this way, in particular the phase adjustment method, will be described in detail below.

In the figure, when the switch SW connected in parallel with the grounding line LE is turned on, the grounding line Lx has ωlcVω.
An additional current of 5alt will flow, and at this time, the leakage current Io of the applied low frequency component flowing through the grounding wire will be (7). Therefore, zero-phase current transformer ZCT, amplifier AMP
Considering the phase shift generated in the filter FILO system, the output 2 of the filter FIL becomes (ω11+θ) (8) from the relationship of equation (2), and the synchronous detector MULTI at this time The output Dl becomes sin (0-θ1) ·−·−(91) from the relationship of equation (4).

Now, since the term C that is passed through the switch SW with a period T (T here) repeats presence and absence with a period T, the synchronous detector MULT
A component of frequency 1/T will be generated in the output Dt of I (as can be seen from equation (9), when θ=01, straw 2
Since the term becomes zero, the component of frequency 1/T will not occur).

By the way, the output of the synchronous detector MULT 1 has a frequency of 1/T.
The output A of the filter BPI is expressed by the following equation.

. . . However, here, k is a constant, and ψ is a phase determined from the phi/′/t characteristic.

On the other hand, the output branched from the output of the @filter FIL is @
The synchronization signal in the core part is input to the synchronous detector 2 to 1TJLTa, and the synchronous signal in the core part is the signal a 5in (ωtt+01) for the first synchronous detector MULT1, which is input to the 90° phase shifter P.
Because it was obtained by passing the SS, a. ■S(ω1
t-IJ1). Therefore, the second synchronous detector Mtl
The output of LT3, that is, the reactive component D2 is Dz=Izxaoco
s(ωst+e)1)−・−・−・−011, this equation means to remove the components with angular frequency of 01 or higher, similar to the above equation (3), and as a result, the above equation is expressed as cos(θ-θl) . If it is applied to a filter BP2 that extracts only the frequency l/T component, the output B of the filter BP2 can be expressed as . Here, the relationship is the same as the ψ (to) expression. Bandpass filter B obtained in this way
If the output Bi2 equation of P2 and the output AC[l1 equation of the bandpass filter BPI are applied to the input terminals of the multiplication circuit MULT2, the output D of the multiplication circuit M[JLT2
3 becomes D3=AXB・5in(θ−θl). Therefore, the DC component D4F obtained by applying the output of the multiplication circuit MULT2 to the low-pass filter LF
It can be expressed as i.

Therefore, the synchronization reference signal a is inputted to the two synchronization detectors MOLT1 and MUL'['3 by the automatic phase control circuit PC. sin (ω1t+θ1), 3oco
If the phase 01 of s(ω1t+θ1) is adjusted so that the low-pass filter LF output D4 becomes zero, that is, θ=θl, the first synchronous detector MtJLTl expressed by the equation (4) can be obtained. The second term in D of output 01) T2 becomes zero, and an accurate detection signal can be obtained.

Lake, the automatic phase adjustment circuit required here is the first in the PC.
The closed loop in the figure, that is, the first synchronous detection aiMULT 1.
First band pass filter DPI, multiplication unit MULT
2 and low-pass filter LF and 90' phase shifter pss
, a synchronous detector MULT3 of BO2, a second bandpass filter BP2 . @Any device that automatically adjusts the phase of the output signal of the low frequency oscillator O8C supplied to the two synchronous detectors so that the DC component D4 obtained via the multiplier MIJLT2 and the low-pass filter LF becomes zero may be used. , this automatic phase adjustment circuit can be easily realized using existing technology, so its explanation will be omitted.

Furthermore, in the above explanation, the capacitor C was simply turned on and off with a period T, but the value of the capacitor C was changed continuously with a period T (
For example, the above phase control method can be applied to a sinusoidal change (K), and in this case, a variable capacitance element may be used instead of the capacitor C.

Also, if the above phase adjustment is performed for a certain period of time and θ−σl=0, θ! It may be configured such that the above-mentioned phase adjustment is performed intermittently, such that the phase adjustment is fixed and the phase adjustment is performed randomly after a certain period of time.

Further, in the above description, a case has been described in which the capacitor C is inserted between a grounded electric line and the earth, but the present invention is not limited to this, and may be inserted between an ungrounded electric line and the earth, for example. However, in this case, since commercial power is applied to the capacitor C, the current flowing through the capacitor C and switch SW becomes significantly large, so it is necessary to use a capacitor that can withstand this.

Also, in reality, the above-mentioned AC/DC inserted between the electrical circuit and the ground
A small amount of resistance may be inserted in series due to the influence of connecting wires, etc., but in this case, the current flowing through the capacitor CK will not change the phase accurately by 900 degrees with respect to the applied low frequency voltage, resulting in a slight error. However, this error is generally so small that it does not interfere with measurement.

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

In this embodiment, instead of the transformer OT used to apply a low frequency signal to the ground wire Lz, an OT' having a secondary winding is used, and the secondary winding is equipped with a capacitor C and a switch S.
A series circuit with W is connected so that a part thereof passes through the inside of the zero-phase current transformer ZCT.

According to this example, unlike the embodiment shown in FIG. 1, there is no need to directly connect the grounding line LEK capacitor C and the switch SW, so that the installation work can be simplified.

Note that the operation is exactly the same as that described in the explanation of 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 connected to the primary side of a transformer OT for applying a low frequency to the ground line Lg. It is well connected. At this time, when the voltage on the negative side is higher than the voltage on the secondary side, if the capacitance of the capacitor C is made smaller by that ratio, the operation can be the same as that shown in FIG. 1 and its explanation.

Please check the voltage applied to the capacitor/suC (F in formula 71).
iv, but there are only nine steps to implement the present invention.

There is no problem in operation even if other voltages are used without being restricted by this.

(9) The synchronization signals inputted from the automatic phase control circuit PC to the two synchronous detectors MOLT1 and MtJLT3 should be adjusted so that their phases are precisely 90° shifted from each other, and the output of the low-pass filter is zero. The period of phase synchronization can be shortened by adjusting the phase using a harpoon and then compensating for the phase shift caused by temperature change, aging, etc. using the automatic phase control method described above.

In the above explanation, a capacitor element was used to flow a current with a phase difference of 90 degrees from the low frequency voltage for mll regulation.
It is not necessarily limited to this, and other circuits 114 (
For example, it is obvious that a circuit combining an inductance and a capacitor may also be used. Furthermore, in order to generate a current with a phase difference of 90° from the applied low-frequency voltage, the oscillator O8C generates a voltage with a phase shift of 90°, and this is passed through a resistor etc. to a zero-phase current transformer with a period T. good.

Furthermore, in the above explanation, when performing phase adjustment, the phase of the signal applied to the second input of the synchronous detector is adjusted, 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, in which a low frequency excavator O8 is used as means for applying a low frequency signal with a phase shift of 90 degrees to the leakage current detection system that returns to the ground line.
Directly derive a 90° phase-shifted signal from C, insert it into the switch SW, and insert it into the zero-phase current transformer ZCT K! In addition to applying voltage to the signal line passed through, the automatic phase control circuit P
C is inserted into the input terminal of the first synchronous detector to 1ULT1.

With this configuration, as well as those shown in FIGS. 1, 2, and 3, if the automatic phase control circuit PC is controlled so that the low-pass feed LF ratio output becomes zero, the electric circuit can be insulated accurately. Resistance can be measured.

Further, in the above description, the low frequency signal voltage was explained as a sine wave, but it is not limited to this, and it may be a rectangular wave, for example, and its fundamental wave component or harmonic component may be used.

Further, in the above explanation, the case where the 90' phase shift signal applied to the leakage signal derivation system is intermittent at the period T, but various methods can be considered for this intermittent timing.

The first method is to constantly repeat this intermittent cycle, and the DC component of the locus filter LP is monitored at normal pressure, and the automatic phase control circuit is operated so that this becomes zero or minimum.The second method is to A method of doing this intermittently at predetermined intervals, or a method of repeating the above-mentioned phase adjustment operation by repeating the above-mentioned phase adjustment operation intermittently at random intervals including the frequency component 1/T can be considered. It is obvious that it may be used.

In addition, in the above embodiment, the case of a single-phase two-wire system was shown, but
The present invention can be carried out in the same manner even in the case of a single-phase three-wire electric circuit or a three-phase three-wire electric circuit in which one end of the low voltage side is grounded.

(Effects of the Invention) As explained above, the present invention is configured to automatically adjust phase characteristic fluctuations of the insulation resistance measuring circuit, so it is possible to realize an insulation resistance measuring device that is extremely stable and accurate at all times. It is very effective.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of the present invention, FIG.
3 and 4 are partial block diagrams showing other embodiments of the present invention, and FIG. 5 is a block diagram showing a conventional method for measuring insulation resistance. T......Trans, 1,2...
...Electric circuit. Lx・・・・・・Ground wire, E・・・・・・
...Grounding point. ZCT・・・・・・Zero phase current transformer, AMP
・・・・・・・・・Amplifier, FIL・・・・・・
····filter. MULT l, and MULT 3...
Synchronous detector. MULT3・・・・・・Multiplier, PC・
−・・・・・・Automatic phase control circuit, BPl,
BPz・・・・・・Filter, DET・
...... Rectifier circuit.

Claims (1)

[Claims] 1. Applying a low frequency signal voltage having a frequency f_1 different from the commercial frequency to the electric line via a grounding wire of a transformer, etc., and extracting the effective component of the low frequency signal that returns to the grounding wire. In the method of measuring the insulation resistance between the electric circuit and the ground, the leakage current of the low frequency signal that is returned to the ground wire is a signal whose phase is shifted by 90 degrees from the low frequency signal applied to the electric circuit. The voltage is applied to the detection circuit continuously at a period T, or at predetermined intervals, or intermittently at random intervals containing the frequency component 1/T, and the component of the frequency 1/T included in the effective component and the effective Find the product of the reference signal used to extract the component and the frequency component of frequency 1/T included in the reactive component extracted from the leakage current of the feedback low frequency signal based on the 90° phase-shifted signal. The phase of the insulation resistance measuring device, characterized in that the phase of the reference signal used for extracting the effective component and the reactive component is adjusted manually or automatically so that the direct current component in the product output becomes zero. Preparation method. 2. The means for applying the 90° phase-shifted signal to a circuit that detects a leakage current component of a low frequency signal that returns to the ground line inserts a variable reactance between the electric line and the ground, and the variable reactance The phase of the insulation resistance measuring device according to claim 1, characterized in that the value of is changed continuously with a period T, or intermittently at predetermined intervals, or at random intervals including a frequency component 1/T. Adjustment method. 3. A circuit consisting of a fixed reactance and a switching means is inserted in place of the variable reactance, and the switching means is opened and closed continuously with a period T, or intermittently at predetermined intervals or at random intervals. A phase adjustment method for an insulation resistance measuring device according to claim 2, characterized in that: 4. If the means for detecting the leakage current component of the low frequency signal that returns to the grounding wire is carried out through a zero-phase current transformer coupled to the grounding wire, the zero-phase current transformer is penetrated. 4. A phase adjustment method for an insulation resistance measuring device according to claim 1, wherein a circuit comprising said variable reactance element or fixed reactance and switching means is inserted into the signal line. 5. The means for zeroing out the direct current component in the product output adjusts the phase of the leakage current component of the low frequency signal that is returned to the ground line instead of adjusting the phase of the reference signal for extracting the effective component and the reactive component. 5. A phase adjustment method in an insulation resistance measuring device according to any one of claims 1 to 4, wherein