JP2764582B2 - Simple insulation resistance measurement method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial application field) The present invention relates to a method for measuring insulation resistance of an electric circuit or the like in a live state, and particularly to an influence on a ground resistance which cannot be ignored when a stray capacitance to the ground is large. The present invention relates to a simple insulation resistance measurement method that compensates and enables simultaneous measurement of stray capacitance to ground and ground resistance.

(Prior Art) Conventionally, a method of measuring insulation resistance of an electric circuit as shown in FIG. 4 has been generally used for early detection of electric leakage or the like.

In other words, the ground line L _E of the power receiving transformer T having a load Z, or to penetrate the applied transformer OT connected to an oscillator OSC which oscillates a low-frequency signal for measurements made different frequencies ₁ and the commercial power source frequency, or equal cutting the ground line connecting the oscillators also in series thereto paths L ₁ and L ₂ in the low-frequency voltage V for measurement
Was applied to detect the leakage current which returns to the ground line via an insulation resistor Ro and ground stray capacitance Co exists between path and the earth by transducers ZCT that allowed through the ground line L _E,
After amplifying this with the amplifier AMP, select only the frequency ₁ component from which the commercial frequency component has been removed by the film FIL, add this component to the rectifier DET, and measure the insulation resistance of the circuit using the DC voltage obtained. This can be represented by the equivalent circuit shown in FIG.

Ro In the figure of the measured circuit insulation resistance, Co is also a ground stray capacitance, the output signal of the measuring low frequency oscillator OSC which flows in the induced to the measured circuit to the ground line L _E is the R
It shows a case where the signal returns to the ground line again via o and Co. Note that r is a ground resistance at the ground point E.

Conventionally, based on such an equivalent circuit, a leakage current value has been obtained from the following calculation to measure the insulation resistance.

That is, the frequency ₁ via a ground point E, E 'In figure
The current flowing to the oscillator OSC and I _1, which is referred to as _{I 1 = (A + jB)} ...... (1). still, It is.

Generally at ^{_{Ro»r, (ω 1 Cor) 2}} «1 ...... (4) become as the since it is possible to choose ω ₁ (2) equation In addition, since the above equation (3) can be expressed as Bω ₁ Co (6), | I ₁ | obtained by actually measuring the feedback current value I ₁ when the ground stray capacitance Co is small and the frequency ₁ is low. Wanted the insulation resistance Ro.

However, according to the conventional insulation resistance measuring method as described above, when the stray capacitance Co to the ground is large, and when the frequency _{1 of the} low-frequency signal is high, the component related to Co is large, as is clear from the equations (5) and (6). In addition to the fact that an accurate value of the insulation resistance Ro cannot be obtained, there is a disadvantage that if the value is further increased, the influence of the ground resistance r cannot be ignored and the measurement itself becomes impossible.

(Object of the Invention) The present invention has been made to eliminate such a defect in the conventional method for measuring the insulation resistance of an electric circuit, and is intended for a case where the capacitance between the electric circuit and the ground becomes large. It is another object of the present invention to provide an insulation resistance measuring method which enables accurate measurement of insulation resistance.

(Summary of the Invention) In order to achieve this object, an insulation resistance measuring method according to the present invention is used for measuring a ground wire or an electric circuit of a transformer at frequencies f ₁ and f ₂ (f ₁ > f ₂ ) different from the commercial frequency. As a means for applying the low-frequency signal to the electric circuit to be measured by penetrating the core of the transformer to which the low-frequency signal has been simultaneously applied, and detecting a leakage current of the low-frequency signal component that returns to the ground line. Penetrating the ground wire or the electric circuit through the current transformer, and synchronously detecting the leakage current with the low frequency signal supplied through a phase shifter to compensate for a phase shift generated after the current transformer. To obtain an effective component of the leakage current (a component having the same phase as the applied voltage), and apply a current to the current transformer and the transformer core so that the currents acting on the current transformer and the transformer core are in opposite phases to each other. New penetrating loop connection Provide a connection line, insert a variable capacitor into this,
The frequency f ₁ and f ₂ or f _1, the frequency magnitude of one of the leakage current component of f ₂ is obtained in the state that adjusting the variable capacitor so as not to exceed a predetermined value f ₁ and f ₂ Of the effective component in the leakage current component and the frequency f ₁
And take means to calculate the in insulation resistance in the circuit under measurement from f ₂ Metropolitan.

(Examples) Hereinafter, the present invention will be described in detail based on illustrated examples.

FIG. 1 is a block diagram showing an embodiment of an apparatus used in carrying out the present invention.

4, the same components as those in FIG. 4 are denoted by the same symbols, and their description is omitted.

Terminating the variable capacitor CV provided a new connection lines Lp penetrating them as opposite phase from that of the ground line to the annexed been current transformer ZCT and applied transformer OT to the ground line L _E as shown in FIG.

The output terminal of the current transformer ZCT is connected to an amplifier AMP, and the output terminal is connected to filters FIL ₁ and FIL ₂ .

The output end of the filter FIL ₁ is connected to one input of the rectifier DET and synchronous detector MULT _1, the output end of the filter FIL ₂ is connected to one input of synchronous detector MULT _2.

The synchronous detector MULT _1, the other input terminal of the MULT ₂ phase shifter P
S ₁ and PS ₂ are respectively connected,該移phase shifter PS _1, PS ₂ is connected to the oscillator OSC _1, OSC ₂ was connected to an application transformer OT.

Further, the output terminal of the MULT ₂ is connected to the coefficient circuit C ₁ , the C ₁ output terminal is connected to one input terminal of the subtractor SUB, and the output of the MULT ₁ is connected to the other input terminal of the subtracter SUB. The ends connect. The rectifier DET is connected to the meter M.

Oscillator in the insulation resistance measuring device thus configured
When low frequency signals ( ₁ and ₂ ) different from the commercial frequency are applied to the transformer OT from OSC ₁ and OSC ₂ , the insulation resistance of the circuit
Ro and component of the frequency ₁ of the measuring low-frequency signal to be fed back to the ground line L _E via stray capacitance Co is an amplifier AMP, a frequency
It is extracted via a filter FIL ₁ that selects _one component.
At this time, if there is no loop connection line Lp, the filter FIL ₁
The output signal Ig ₁ is obtained from the above equations (1), (5) and (6). Is represented by

Meanwhile the current flowing through the variable capacitor Cv connected to the case of providing the loop connection line Lp new rata as described above acts in mutually canceling directions for a phase opposite to Ig _1, the variable capacitor Cv If the value is C and the output of filter FIL ₁ is Ig ₁ ′, Becomes Therefore, the output M of the rectifier DET connected to the output of the filter FIL ₁ is When the variable capacitor Cv is adjusted so that the rectifier output M becomes equal to or less than a predetermined value, the dynamic range of the filter FIL ₁ output ig ′ ₁ can be sufficiently reduced.

When the output of the filter FIL _{1 at} this time is input to the synchronous detector MULT ₁ and the output of the oscillator OSC ₁ is input as the other input of the MULT ₁ via the phase shifter PS ₁ , the output of the MULT ₁ becomes (8) ) expression leakage current in active component are obtained, which active component X ₁ is Is represented by Note that the phase shifter PS ₁ is a current transformer ZCT → AMP AMP →
This is for compensating the phase shift of the filter FIL system.

Then similarly detected and the output of performing the synchronous detector MULT ₂ synchronous detection also the leakage current of the frequency ₂ Is obtained.

Therefore, from equations (10) and (11), Is introduced.

Of this formula Is known to the output X ₂ of the synchronous detector MULT ₂ ( ₁ /
₂ ) ² , that is, (ω ₁ / ω ₂ ) ² is weighted by a coefficient circuit C ₁
In adding, insulation resistance value of the measured circuit is obtained is a difference between the output X ₁ of this and synchronous detector MULT ₁ to the cited adder SUB output OUT ₁ by taking in subtracter SUB.

The condition under which the rectifier DET output M becomes equal to or less than the predetermined value by changing the capacitor Cv as is apparent from the above equation (9) is different at the frequencies ₁ and ₂ , but when both frequencies are not extremely different, the frequency is not changed. Cv may be adjusted for only _one leakage current component.

FIG. 2 is a view showing another embodiment of the apparatus used in carrying out the present invention. The difference from FIG. 1 is that the application and detection of the measurement signal are not performed by the ground line and the electric lines L ₁ and L ₂ Input from the output of the phase shifter PS ₁ to one input terminal of the synchronous detector MULT ₃ via the phase shifter PS, and a filter F to the other input terminals.
This is the point that the IL ₁ output is applied, and the absolute value circuit ABS and the meter M ₁ are attached to the MULT ₃ output terminal.

The insulation resistance measuring device thus configured performs the same operation as the above-described device, and adds the output of the phase shifter PS ₁ to the 90 ° phase shifter PS, and outputs the filter FIL ₁ output and the 90 ° phase shifter PS output. By inputting to the synchronous detector MULT ₃ , an invalid component in the above equation (8) is obtained at the output of the MULT ₃ , and the invalid component X ₃ is X ₃ = ω ₁ (Co−C) V (13) ) And when applied to the absolute value circuit ABS at the next stage, the output M ₁ becomes ω ₁ | Co−C | V. Therefore the ABS output M ₁ and adjusting the variable capacitor Cv is less than a predetermined value, i.e., to suppress as a Cv ≒ C performs an operation in such described method in the first view to the effects of reactive component in the leakage current You can measure the correct insulation resistance.

In the above description, the connection line Lp is simply passed through the injection transformer OT and the rectifier ZCT so that the electric wiring is in the opposite phase. If the ZCT is simply passed through so that the phases are reversed, the value C of the capacitor Cv may be equivalently prepared with a value of C / N. Similarly, only the current transformer ZCT side may be wound N times, and the same result can be obtained by winding both of them and setting the winding number ratio to N.

In the embodiments of the present invention, the case of a single-phase two-wire circuit has been exemplified for the sake of simplicity. However, the present invention is not necessarily limited to this. For example, a single-phase three-wire system or a three-phase three-wire circuit It will not be necessary to explain that it is equally effective in the case of an electrical circuit.

Further, as described above, the variable capacitor Cv is set to the measurement frequency ₁
And the output M at either ₂ or ₁ , ₂ was adjusted so as to be less than the predetermined value M or M ₁ .
If this is done automatically by providing an automatic adjustment loop circuit, not only can the measurement be simplified, but if it is performed intermittently, it is possible to constantly monitor the insulation state of the electric circuit, and to deal with failures. Can be faster.

In the above explanation, the current flowing through the variable capacitor Cv was used to suppress the leakage current component shifted by 90 ° from the applied voltage, but the voltage obtained by winding the core of the transformer OT was applied to the 90 ° phase shifter. The current obtained when this output voltage is terminated with a resistor or the like is passed through the connection line, and this is flowed in the reverse phase as the primary current of the current transformer ZCT, so that the output voltage of the phase shifter is variable. Alternatively, even if the terminated resistance value is made variable, the same canceling current can be generated.

(Effects of the Invention) Since the present invention measures the insulation resistance of an electric circuit or the like using the apparatus configured as described above, the present invention is applicable to a case where the capacitance between the electric circuit and the ground becomes large. Also, the insulation resistance can be measured accurately.

[Brief description of the drawings]

1 is a diagram showing an embodiment of the present invention, FIG. 2 is a diagram showing another embodiment of the present invention, FIG. 3 is a diagram showing an equivalent circuit of an insulation resistance measuring system of an electric circuit, and FIG. FIG. T …… Transformer, L ₁ , L ₂ …… Electrical circuit, L _E …… Grounding wire, OSC, OSC ₁ , O
SC ₂ …… Oscillator, AMP …… Amplifier, FIL, FIL ₁ , FIL ₂ …… Filter, ZCT …… Current transformer, OT …… Measurement signal applying transformer, Lp
…… Connection loop, Cv …… Variable capacitor.

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁶ , DB name) G01R 27/18

Claims (2)

(57) [Claims] A transformer is provided by passing a ground wire or an electric circuit of a transformer through a core of a transformer to which low frequency signals for measurement having frequencies f ₁ and f ₂ (f ₁ > f ₂ ) different from commercial frequencies are simultaneously applied. The low-frequency signal is applied to a measurement circuit, and a current transformer serving as a means for detecting a leakage current of the low-frequency signal component that returns to the ground line is caused to penetrate the ground line or the current path. A synchronous detection of the leakage current with the low-frequency signal supplied through a phase shifter to compensate for a phase shift that occurs after the transformer obtains an effective component of the leakage current, and the current transformer and Providing a new loop connection line penetrating the current transformer and the transformer core so that the currents acting on the transformer core are in opposite phases to each other,
A variable capacitor is inserted and connected to this, and the frequency f ₁ and
f ₂ or f _1, f of one of the leakage current component of the ₂ magnitude of the leakage current component in the frequency f ₁ and f ₂ obtained in a state of adjusting the variable capacitor so as not to exceed a predetermined value active component size and the simple insulation resistance measuring method characterized in that the frequency f ₁ and f ₂ Metropolitan was to calculate the in insulation resistance in the circuit under measurement of. _2. The variable capacitor according to claim 1, wherein the variable capacitor is adjusted so that the effective component in the leakage current component of one of the frequencies f ₁ and f ₂ or f ₁ or f ₂ is equal to or less than a predetermined value. 2. The simple insulation resistance measuring method according to claim 1, wherein: