JP2750705B2 - Insulation resistance measurement method - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for measuring insulation resistance of an electric circuit or the like in a live state.

(Prior Art) Conventionally, in order to detect a leakage current or the like at an early stage, a method of measuring insulation resistance of an electric circuit as shown in FIG. 3 has been generally used.

In the figure, T is a transformer, and L ₁ and L ₂ are ₂ of the transformer T.
Next side path, L _E is a ground line of the transformer T, the secondary side path of the transformer T with the load Z.

The injection into the ground line L _E transformer OT, current transformer ZCT is provided, said injection oscillator OSC oscillating a different frequency ₁ from the commercial frequency ₀ the transformer OT is, the amplifier AMP in the current transformer ZCT, The filter FIL and the synchronous detector MULT are connected in series, and the other end of the synchronous detector MULT is connected to the oscillator OSC.

Frequency to the ground line L _E In the thus constituted circuit
₁ is applied from the injection transformer OT
Insulation resistance R ₀ and ground capacitance C existing between L ₁ , L ₂ and ground
Grounding line leakage current which returns to the ground line L _E through ₀ L
_The output is detected by the current transformer ZCT penetrating _E , the output is amplified by the amplifier AMP, then only the leakage current component of frequency ₁ is selected by the filter FIL, and this component is synchronized using the measurement signal of frequency _1. Synchronous detection was performed by the detector MULT, and the output was used to measure the insulation resistance of the circuit.

However, if the ground capacitance C ₀ is large, the current component due to the ground capacitance in the leakage current at the frequency f ₁ becomes extremely large unless the frequency ₁ is set sufficiently low. It was difficult to measure the current component by the insulation resistance. In addition, the voltage of the measurement signal cannot be too low to avoid the influence of circuit noise, and is generally 0.5 V and the frequency ₁ is about 20 Hz. However, there was a drawback that it became so large that it was difficult.

Further, when passing the ground line L _E injection transformer, a secondary winding N ₂ is the transformer core Higher low signal voltage frequency ₁ of the measurement signal as described above for the one-turn injection transformer OT I had to make it bigger.

Also, 2 it is possible to increase the signal voltage by increasing the winding number N _2, it accompanied not tend to transformer output impedance is high transformer and consider the safety of such time ground fault It was not desirable to increase the output impedance of.

(Object of the Invention) The present invention has been made in view of the above-mentioned problems, and has a compact injection transformer, keeps the output impedance of the transformer low, and measures the insulation resistance without being affected by capacitance. It is an object of the present invention to provide an insulation resistance measuring method which enables the above.

SUMMARY OF THE INVENTION insulation resistance measuring method of the present invention to achieve this object, the frequency f ₁ and f ₂ (f _1> f ₂₎ comprising alternating signal frequency f in the circuit under measurement through the applied transformer means for injecting a ₁ and the measurement signal f _2, transformer of the ground line or the line current detection by current transformer or the like allowed through the to detect leakage current by the measurement signal fed back to the ground line and means, from the measurement signal of the frequency f ₂ the leakage current of a frequency f ₁ included in the output obtained by said current detecting means
By modulating at 90 ° phase-shifted voltage to obtain a first modulated signal, also the leakage current of the frequency f ₂ included in the output obtained by said current detecting means from the measurement signal of the frequency f ₁
A second modulation signal is obtained by modulating with a voltage shifted by 90 degrees, and a component of a frequency f ₁ -f ₂ included in a signal of a difference between the first modulation signal and the second modulation signal is rectified. or the frequency f ₁ and the frequency f ₁ generated using the AC signal f ₂
Take means to measure the insulation resistance of the electrical path from the output value obtained by synchronous detection at a voltage of -f _2.

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

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

3, the same components as those in FIG. 3 are denoted by the same symbols.

Have different frequencies to the primary winding N ₁ of the injection transformer OT By adding the _two oscillators OSC ₁ and OSC ₂ , a measurement signal of e ₀ sin ω ₁ t + e ₀ sin ω ₂ t is applied between the electric circuit and the ground. Thus current transformer ZC leakage current which returns to the ground line L _E
Detected in T amplifies the output by the amplifier AMP, the leakage filters F ₁ and the frequency ₁ obtained at the output of the filter F ₁ if the input to the filter F ₂ for detecting the component of the frequency ₂ for detecting the component of the frequency ₁ The current component i ₁ is Next, whereas the leakage current component i ₂ frequency ₂ obtained at the output of the filter F ₂ is The output of the filter F ₁ from the input to one input terminal of the modulator M _1, the other input line output e of the oscillator OSC ₂
The sin omega ₂ t enter the e cos ω ₂ t obtained by applying the 90-degree phase shifter PS _2.

The output of the filter F ₂ is input to one input terminal of the modulator M ₂ , and the output OSC ₁ output e sin ω is input to the other input terminal.
Ecos ω ₁ t obtained by applying ₁ t to the 90-degree phase shifter PS ₁ is input.

Thus, the output of modulator M ₁ is i ₁ × e cos ω ₂ t
The output of M ₁ is i ₂ × e cos ω ₁ t.

Next, if the outputs of the modulators M ₁ and M ₂ are applied to the subtractor SUB ₁ , the output S of the subtractor SUB ₁ becomes Next (3) of i _1, i ₂ on the (1), (2) of i _1, i ₂
Substituting It can be expressed as. When the output of the subtractor SUB ₁ is applied to the low-pass filter LF of the next stage to remove the frequency ₁ + ₂ component, the output S _{0 of the} low-pass filter LF becomes Becomes

Further, the output of the oscillator OSC _{1 and the} output of the phase shifter PS ₂ obtained by shifting the output of the oscillator OSC ₂ by 90 degrees are applied to the modulator M ₃ , respectively, so that the output of the modulator M ₃ is e ² sin ω ₁ t · cos omega ₂ give t, whereas the oscillator OSC ₂ output and the oscillator OSC ₁ outputs the modulator M ₄ output by applying the phase shifter PS ₁ output by 90 degrees phase shift to each modulator M ₄ is e ² sin ω ₂ t · cos ω ₁ t can be obtained. Thus, the cited adder SUB ₂ outputs S ₁ by applying the modulator M ₃ and M ₄ outputs to subtracter SUB ₂ is ^{_{S 1 = e 2 sin ω 1}} t · cos ω 2 t-e 2 sin ω ₂ t · cos ω ₁ t = e ² sin (ω ₁ −ω ₂ ) t (6) That the cited adder SUB ₂ output synchronous detectors by applying a said with the cited adder output S ₁ becomes the voltage of f ₁ -f ₂ low-pass filter LF output S ₁ to the next synchronous detector MULT ₁ MULT ₁ output
From OUT _1, a DC component of the product of S ₀ and S ₁ is obtained. That is, And the output OUT ₁ is a DC component in the equation (7). Therefore, the insulation resistance can be measured.

Incidentally frequency ₁ at the 3 such conventional method shown in FIG.
The leakage current i of the measuring signal e _i sin omega _i when applying t frequency i obtained at the filter FIL output Therefore, the leakage current (reactive component current) due to the ground capacitance C _{0 in} the second term is the frequency It is understood that it is proportional to. Thus although the reactive current with frequency _i is increased and it is difficult to accurately measure the insulation resistance increases, according to the present invention (5) reactive current as is apparent from the second term frequency ₁ , ₂ is proportional to the difference, and the reactive current is small if the difference is small even if the frequencies ₁ and ₂ are individually high.

For example, e _o = e _{i i} = 2 in the above equations (5) and (6)
If the frequency is set to 0 Hz, ₁ is obtained when the method of the present invention is used.
= 320 Hz, ₂ = 280 Hz, so it is sufficient to use an extremely small transformer (about one tenth).

That is, the ratio of the current flowing through the resistance indicated by the first term in the parentheses of the equation (5) to the current flowing through the ground capacitance indicated by the second term is (ω ₁ −ω ₂ ). C ₀ R _0/2 , while the ratio between the active component current and the reactive component current in equation (6) is ω
_{Since i} C ₀ R ₀ , both ratios are equal (ω ₁ −ω ₂ ) /
2 = the omega _i, the difference between the frequency ₁ and ₂ in the method of the present invention ₁ - ₂ selecting a frequency so that sufficiently small is also possible, the second parentheses in this case (5)
Since the term becomes sufficiently smaller than the effective component of the first term, an output OUT _{2 obtained} by rectifying the output S ₀ of the low-pass filter LF by the rectifier DET.
Can be used to measure insulation resistance.

However, the frequency difference ₁ - for ₂ small filter F ₁
And it is necessary to significantly narrow-band selective properties of F _2, the measurement time of the insulation resistance becomes longer must consider.

In the above description, the phase shift generated when the signal passes through the filter or the like has been ignored. However, if necessary, the phase shift of the system may be corrected by using a phase shifter, and the filters F ₁ , F _{1 2} frequency ₁ as described above, ₂ is not accompanied therewith proximate ₁ - ₂ is not necessary to use a sharp narrowband filter for small, very small it is desirably in the phase characteristic variations in the filter, As a filter that satisfies this condition, it is preferable to use an “N-path filter” that operates in synchronization with the outputs of the oscillators OSC ₁ and OSC ₂ .

In the above description, the grounding wire is connected to the injection transformer OT and current transformer ZCT.
It described by penetrating the L _E but not limited to this, the second
As shown in the figure, the electric circuit may be provided so as to penetrate the injection transformer OT and the current transformer ZCT, or may be configured to be clamped. Can be configured.

Although the present invention has been described using a single-phase two-wire circuit, the present invention can be applied to any one-side grounded circuit such as a single-phase three-wire or three-phase three-wire circuit. Since the leakage current components of the commercial frequency ₀ and its harmonic components are also included therein, it is desirable to select the measurement signals ₁ and ₂ from frequencies that do not coincide with the commercial frequency ₀ and its harmonic frequency components.

(Effects of the Invention) Since the present invention employs the above-described means, it is possible to use a signal having a higher frequency than the conventional one as a signal for measurement. Therefore, the insulation resistance can be measured with a small injection transformer. This is very effective in configuring a measuring instrument.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram showing a configuration of an apparatus used in carrying out the present invention, FIG. 2 is a view showing a modified embodiment of the present invention,
FIG. 3 is a diagram showing a conventional measuring method. T ...... receiving transformer, ZCT ...... current transformer, OT ...... injection transformer, AMP ...... _{amplifier, FIL, F 1, F 2} , LF ...... filter, MULT, MULT ₁
… Synchronous detector, M _{1 to} M ₄ … Modulator, PS ₁ , PS ₂ … 90-degree phase shifter, OSC ₁ , OSC ₂ …… Oscillator, SUB ₁ , SUB ₂ …… Subtractor, L _E ...... ground line, L _1, L ₂ ...... path R ₀ ...... insulation resistance, C ₀ ...... capacitance to ground, Z ...... load, DET ...... rectifier.

Claims (1)

(57) [Claims] 1. A frequency f ₁ and f ₂ frequency (f _1> f ₂₎ to the AC signal to be measured path through the applied transformer comprising f ₁ and f ₂
Means for injecting the measurement signal of the above, and current detection means for penetrating through the ground line or the electric circuit to detect a leakage current due to the measurement signal returning to the ground line of the transformer, the current detection means Frequency f ₁ included in the output obtained by
Obtain a first modulated signal by modulating the leakage current at a voltage which is 90 ° phase-shifted from the measurement signal of the frequency f ₂ of, also, the frequency f ₂ included in the output obtained by said current detecting means
The second modulation signal is obtained by modulating the leakage current of the above with a voltage shifted by 90 degrees from the measurement signal of the frequency f ₁ , and a signal having a difference between the first modulation signal and the second modulation signal is obtained. Rectify the contained frequency f ₁ −f ₂ component or
A method for measuring insulation resistance of an electric circuit, comprising: measuring an insulation resistance of an electric circuit from an output value obtained by synchronous detection with a voltage of a frequency f ₁ −f ₂ generated using alternating current signals of f ₁ and f ₂ .