JPH083508B2 - Insulation resistance measuring device phase compensation method - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method of compensating for a temperature change or an aged change of a circuit constant 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. 3, for example.

This is to insert a transformer OT in which a measuring low-frequency signal oscillator OSC having a frequency of _1, which is different from the commercial power frequency, is connected to the second-type grounding line L _E of the power receiving transformer T having a load of Z, or Apply the low frequency voltage for measurement to the electric lines 1 and 2 by inserting the oscillator OSC in series with the ground line L _E or by penetrating the electric lines 1 and 2 into the toroidal core transformer to which the oscillator is connected. , Leakage of the low-frequency signal for measurement 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 by the current transformer ZCT that penetrates the ground line L _E. The current is detected, this is amplified by the amplifier AMP, and the frequency is set by the filter FIL.
Only _one component is selected, which can be
The insulation resistance of the circuit is measured by detecting the effective component (OUT ₁ ) in the leakage current component (that is, the component in phase with the applied low frequency voltage) by synchronously detecting with the multiplier MULT using the output signal of It was composed.

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

If the measurement signal voltage applied to the ground line L _{E is} , for example, a sinusoidal wave and is V _sin ω ₁ t (ω ₁ = 2π ₁ ), the frequency ₁ of the frequency ₁ returned to the ground line L _E via the ground point E is The leakage current I is 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, the leakage current returning to the ground wire is detected by the current transformer ZCT and the frequency contained in this is detected.
_In the conventional method in which the leakage current component of ₁ is selectively output by the filter FIL, the phase of the leakage current of frequency ₁ is usually shifted in the system of current transformer → amplifier → filter, so these synchronous detection outputs are inversely proportional to R _O. It is necessary to compensate for this phase shift in order to obtain this value. 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, in the state where there is no stray capacitance C _O to the ground (C _O = 0),
It has been 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 phase characteristics of the current transformer ZCT, the filter FIL, the phase shifter PS, etc. fluctuate due to temperature changes or changes in the characteristics of the parts used over time. However, there is a drawback that correct measurement results cannot be provided. In order to deal with these problems, the influence of the phase error was conventionally minimized by adopting an extremely high-quality current transformer or filter with less characteristic fluctuation, but it is still difficult to completely eliminate the influence. Met.

(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 applies, in principle, a measurement low-frequency signal voltage different from the commercial power supply frequency to an electric line via a grounding wire to cause insulation resistance and floating between the line and ground. The leakage component of the low-frequency signal for measurement that returns to the ground line via a capacitance is extracted through a current transformer coupled to the ground line, and the insulation resistance of the electric path is measured by synchronously detecting this signal. In the device, a new conductor is made to penetrate the current transformer, and a low-frequency voltage for measurement is applied to the conductor while the low-frequency voltage for measurement is not applied to the circuit.
The phase of the low frequency signal voltage for reference measurement applied to the synchronous detector so that the output of the synchronous detector obtained at this time is energized by applying a signal with a 90 ° phase shift automatically or manually. Configure to adjust.

In this state, if current supply to the conductor is stopped and normal measurement is performed, fluctuations in the phase characteristic of the measurement circuit are compensated, and the measurement result obtained at this time becomes accurate.

(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.

Leakage current component I of frequency ₁ shown in the equation (1)
There current transformer ZCT, an amplifier AMP, Tosureba filter FIL outputs I ₁ the phase shift θ generated when passing through the system filter FIL is 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 a _Osin (ω ₁ t + θ ₁ ) having a 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), the equation (6) is used.
Ω ₁ C _O R when R _O = 20 KΩ and C _O = 5 μF at ₁ = 25 Hz
_{Since O is} 15.7, 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 the above-mentioned measurement error due to the phase shift as much as possible.

FIG. 1 is a circuit diagram showing an embodiment of an insulation resistance measuring apparatus according to the present invention. For measuring the insulation resistance of the electric paths 1 and 2 with one of them grounded as in the case shown in FIG. Device.

That is, the load the two ground lines L _E to one 2 of the secondary electrical path and second transformer T having a Z is strained facilities, the grounding line L _E current transformer ZCT is also directly as it passes through Trans by binding O
Connect T respectively.

The output side of the power amplifier PAMP is further connected to the secondary side of the transformer OT via the changeover switch SW _1, and
A phase control circuit PC for generating a low-frequency signal for measurement having a frequency of ₁ is connected to the input terminal of.

The primary impedance of the transformer OT is low,
It does not interfere with the grounding function of the electric circuit. The current transformer ZCT
The secondary coil output of is input to the synchronous detector MULT via the amplifier AMP and the filter FIL for removing the commercial frequency, and its output is divided into two routes by the second switch SW ₂ , one of which is the resistor R ₂ and the capacitor C. _The phase control circuit is connected to the output terminal OUT ₂ through a holding circuit in which ₁ and ₁ are connected in an inverted L shape, and the other through a holding circuit which is similarly composed of a resistor R ₃ and a capacitor C _2.
Give feedback to your PC.

As the reference signal of the period detector MULT, the output of the phase control circuit PC is applied, and the two changeover switches SW ₁
And SW ₂ are controlled by the output of the phase control circuit PC.

Further, a signal line 3 including a capacitor C in series is connected to _one of the change-over switches SW _{1 in} a loop so that a part of the signal line 3 penetrates the current transformer ZCT and reaches the negative electrode of the power amplifier PAMP.

Hereinafter, the operation and operation of the insulation resistance measuring device configured as described above will be described in detail.

First, when the first switch SW ₁ is connected to the solid line side as shown in FIG. ₁ , the leakage current of frequency ₁ flowing in the ground line L _E is given by the equation (1) and the synchronous detector The output is given by the equation (2) as described above. On the other hand, switch SW ₁
Is connected to the side of the broken line, the primary side of the transformer OT is terminated by the resistor R ₁ , so if the output voltage of the power amplifier PAMP is e, the output of the power amplifier PAMP is connected via the capacitor C to the current transformer. The current I ₂ flowing in the conductor penetrating through is I ₂ = ω ₁ C _ecos ω ₁ t (7). Further, the output I ₃ of the filter FIL at this time is I ₃ = ω ₁ C _ecos (ω ₁ t + θ) (8) Therefore, the output D ₁ of the synchronous detector MULT is Becomes

That is, as is clear from equation (9), if ω ₁ , c, e, a _O are constant, If θ-θ ₁ > 0 then D ₁ <0, and if θ-θ ₁ <0 then D ₁ >
0 because made, measuring the action applied to the synchronous detector by determining the value or polarity of the D ₁ low-frequency signal a _Osin (ω ₁
By adjusting the phase θ ₁ of t + θ ₁ ) so that D ₁ approaches zero, θ−θ ₁ → 0 can be obtained.

FIG. 2 shows the output waveform of each part of the measuring device shown in FIG. In the figure, (a) is the switch
The output voltage of the synchronous detector MULT when SW ₁ and SW ₂ are switched at the cycle T / 2, where (a) shows the switch as a solid line and (b) shows the switch as a broken line. Also, (B) is the output OUT ₂
The output of the synchronous detector MULT appears as it is while the switches SW ₁ and SW ₂ are in the solid line, but the function of the holding circuit consisting of the resistor R ₂ and the capacitor C ₁ is shown in the period when the switches are in the broken line. As a result, the voltage immediately before switching is maintained as it is. Further, FIG. 2C shows the input voltage of the phase control circuit PC, that is, the voltage across the capacitor C ₂ , and when the switches SW ₁ and SW ₂ are broken lines, the synchronous detector MULT
The output voltage of appears as it is, but when the switch is a solid line, the value immediately before switching is retained.

As is clear from the figure, according to the circuit described above, even if the switches SW ₁ and SW ₂ are switched at the cycle T / 2, for example, the output terminal
Even if the insulation resistance value of the electric circuit is calculated from the signal appearing at OUT ₂ , no inconvenience will occur. Therefore, while calculating the insulation resistance value using this output, the voltage across the capacitor C ₂ , that is, in FIG. The voltage is used to adjust the phase of the reference signal applied to the synchronous detector MULT so that it becomes zero.

In this case, although the switches SW ₁ and SW ₂ are switched in conjunction with each other, the switching cycle need not be limited to T / 2 as in the above embodiment, and the point is that a low-frequency signal for measurement is applied to the circuit. Any means may be used as long as a low frequency signal for measurement is applied to the signal line penetrating the current transformer in the absence of the current and the voltage across the capacitor C ₂ at that time is controlled to be zero.

Furthermore, the means for energizing the low frequency signal for measurement which is 90 ° phase-shifted to the route of the current transformer ZCT, the amplifier AMP, the filter FIL and the synchronous detector MULT is not limited to the above-mentioned embodiment, and other methods may be used. You may use.

Further, since such a phase control circuit can be realized by a known technique, its detailed description is omitted. In order to avoid the transient phenomenon that occurs in the output of the synchronous detector when the switch SW ₁ is switched, the synchronous detector is used in order to use only the output of the synchronous detector when the transient phenomenon becomes steady after switching. And switch SW
_A sampling circuit may be added between the _two .

In the above embodiment, the case of the single-phase two-wire type electric circuit has been shown, but it is obvious that the electric circuit may be a single-phase three-wire type or a three-phase three-wire type electric line.

Further, with respect to the method of inserting the capacitor C and the like, many expanded developments are possible under the same principle.

(Effects of the Invention) As described above, the present invention compensates for the phase fluctuation characteristics of the measuring circuit of the insulation resistance measuring apparatus, and therefore a measuring apparatus with extremely high accuracy can be provided.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention, and FIG. 2 is a diagram showing waveforms of respective portions showing an embodiment of the present invention. (A) is an output waveform of a synchronous detector, (b) is Output waveform of output terminal OUT ₂ , (C) shows voltage across capacitor C ₂ ,
FIG. 3 is a block diagram showing a conventional insulation resistance measuring device. T …… transformer, 1,2 …… electric line, L _E …… ground wire, E …… ground point, ZCT …… current transformer, AMP …… amplifier, FIL …… filter, MUL
T …… Synchronous detector, OSC …… Oscillator, OT …… Applying transformer, P
S …… Phase shifter, SW ₁ , SW ₂ …… Switch, PC …… Phase control circuit, PAMP …… Power amplifier.

Claims (1)

[Claims] 1. An output of a current transformer coupled to the ground line while intermittently connecting and disconnecting a measuring low-frequency signal voltage of frequency ₁ different from the commercial frequency to the circuit through the ground line of the transformer. In a device for measuring the insulation resistance of an electric circuit by synchronously detecting the leakage current of the frequency ₁ contained therein by the low frequency signal voltage, a conductor penetrating the current transformer is connected to the low frequency signal voltage 90 ° A low frequency signal voltage applied to the synchronous detector so that the synchronous detection output approaches zero when a current having a phase-shifted predetermined value is applied while the low frequency voltage is not applied to the ground line. A phase compensation method for an insulation resistance measuring device, characterized in that a phase characteristic variation of a measuring circuit is compensated by automatically adjusting the phase.