JP2896572B2 - Simple 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.

T In the figure transformer, L _1, L ₂ is the secondary path of the transformer T, L _E is a ground line of the transformer T, has a load Z to the secondary side path of the transformer T .

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

Frequency f ₁ to the ground line L _E In thus constituted circuit
Is applied from the injection transformer OT, and the electric circuit L ₁ ,
The leakage current is fed back to the ground line L _E via the insulation resistance R ₀ and the earth capacitance C ₀ exists between L ₂ and ground is detected by current transformer ZCT that allowed through the grounding line L _E, The output is connected to amplifier A
Selecting only the leakage current component of the frequency f ₁ by the filter FIL was amplified by MP, the component synchronous detection by the synchronous detector MULT with the measurement signal of the frequency f _1, the path by using the output The insulation resistance was being measured.

However, when 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 f ₁ is sufficiently low. It was difficult to measure the current component with the correct insulation resistance. Further, since the voltage of the measuring signal can not be too low in order to prevent the influence of path noise, typically 0.5V, the frequency f ₁ is about 20 Hz, the magnitude of the injection transformer OT is There was a drawback that the river was too large to be transported.

That is, when passing the ground line L _E injection transformer, but injected it is possible to increase the signal voltage by increasing the secondary winding number N ₂ of the transformer OT, the higher the transformer output impedance with it tends Therefore, it is not desirable to increase the output impedance of the transformer in consideration of safety at the time of a ground accident or the like.

So the secondary winding number N ₂ of the transformer OT is set to 1 turn, I had to increase the transformer core in order to increase the low and signal voltage frequency f ₁ of the measurement signal as described above.

(Object of the Invention) The present invention has been made in view of the above-mentioned problems, and it is intended to reduce the size of an injection transformer while keeping the output impedance of the transformer low, and to measure 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 frequency f ₁ to the insulation resistance measuring method the measured circuit through the transformer of applying an AC signal comprising a frequency f ₁ and f ₂ (f _1> f ₂₎ of the present invention in order to achieve this object a current detecting means and by the current detector and the like that the was allowed through the ground line or path to detect leakage current by the measurement signal fed back to the means and the transformer ground line for injecting the measurement signal of f ₂ the comprising, obtain a first modulated signal by modulating the leakage current of the frequency f ₁ with an AC signal of the frequency f ₂ included in the output obtained by said current detecting means, and an output obtained by said current detecting means said frequency leakage current of a frequency f ₂ included in the
obtain a second modulated signal by modulating an AC signal f _1, the first modulation signal and the second of said components of the frequency f ₁ -f ₂ included in the signal of the sum of the modulation signal frequency f Means for measuring the insulation resistance of the circuit from the output value obtained by synchronous detection with the voltage of the frequency f ₁ −f ₂ generated using the AC signal of ₁ and f ₂ or the output of the original oscillator of the AC signal. Take.

(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 Applying a measuring signal _{e 0 sinω 1 t + e 0} sinω 2 t between the path and the earth by adding two oscillator OSC _1, OSC ₂ of. Thus detecting a leakage current which returns to the ground line L _E in the current transformer ZCT amplifying the output by the amplifier AMP, the filter F ₂ for detecting the components of the filter F ₁ and frequency f ₂ for detecting the component of the frequency f ₁ leakage current component i ₁ of the frequency f ₁ obtained at the output of the filter F ₁ by entering the And it becomes the other hand the leakage current component i ₂ of frequency f 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 terminal an output es of the oscillator OSC ₂
inω ₂ t while the output of filter F ₂ is coupled to modulator M ₂
Of the oscillator OS
Input the output esinω ₁ t of C ₁ . Thus, the output of modulator M ₁ is i ₁ × esinω ₂ t, and the output of modulator M ₂ is i ₂ × esinω
₁ t is obtained. By applying the output of the modulator M ₁ and M ₂ each adder ADD the output S of the adder ADD becomes _{S = e (i 1 sinω 2} t + i 2 sinω 1 t) ...... (3). In the equation, i ₁ and i _{2 correspond} to the above (1) and (2)
Substituting i ₁ and i ₂ in the equation When the output of the adder ADD is applied to the low-pass filter LF at the next stage to remove the frequency f ₁ + f ₂ component, the output S ₀ of the low-pass filter LF becomes Can be obtained.

Further applies the output of the oscillator OSC ₁ to first input terminal of the modulator M _3, modulator by applying an oscillator OSC ₂ output to another input terminal
The output of the M ₃ is the ^{_{e 2 sinω 1 t · sinω 2}} t. In the same way the output of the oscillator OSC ₂ is applied to the 90 degree phase shifter PS _1, and applies the output to one input terminal of the modulator M _4, the other input terminal oscillator
If the output of OSC ₁ is applied to phase shifter PS ₂ and the output is applied, the output of modulator M ₄ will be e ² cos ω ₁ t · cos. Therefore, when the outputs of the modulators M ₃ and M ₄ are added by the adder ADD ₁ ,
ADD ₁ output S ₁ is S ₁ = e ² · cos ω ₁ t · cos ω ₂ t + e ² sin ω ₁ t · s
inω ₂ t = e ² cos (ω ₁ −ω ₂ ) t, and a voltage of frequency f ₁ −f ₂ can be generated. The output of the adder ADD _{1 and the} output of the adder ADD are used as a synchronous detector MULT.
, The output of the synchronous detector MULT becomes And if that DC component is obtained at OUT ₁ , Therefore, the insulation resistance can be measured.

By the way, when the measurement signal e _i sinω ₁ t of the frequency f ₁ is applied by the conventional method as shown in FIG. 3, the leakage current i of the frequency f _i obtained in the filter FIL output is In the second term, the leakage current (reactive component current) due to the ground capacitance C ₀ is the frequency It is understood that it is proportional to.

Therefore, as the frequency f _i increases, the reactive current increases and the accurate insulation resistance cannot be known. However, according to the present invention, as is apparent from the second term of the equation (5), the reactive current is reduced to the frequency f _1. the reactive current if the frequency f _1, f ₂ is smaller its difference with higher individually proportional to the difference between f ₂ is small.
For example, if e ₀ = e _i f _i = 20 Hz in the above equations (5) and (6), then f ₁ = 320H when the method of the present invention is used.
z, f ₂ = 280 Hz, so it is sufficient to use an extremely small transformer (about 1/10).

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 of the active component current to the reactive component current in equation (6) is ω _i C
_{Since 0} R ₀ , both ratios are equal (ω ₁ −ω ₂ ) / 2 =
ω _i , and in the method of the present invention, the difference f ₁ −f between the frequencies f ₁ and f ₂
It is also possible to select the frequency so that ₂ is sufficiently small. In this case, the second term in parentheses in equation (5) is sufficiently smaller than the effective component of the first term, so that the low-pass filter
It becomes possible insulation resistance measured by the output OUT ₂ obtained by rectifying the output S ₀ of the LF by the rectifier DET.

However, since the frequency difference f ₁ −f ₂ is small, the filter F ₁
F ₂ selection characteristics must remarkably narrow band, the measurement time of the insulation resistance becomes longer must consider.

In the above description, the phase shift that occurs when the signal passes through a filter or the like has been described. However, the phase shift of the system may be corrected by using a phase shifter as necessary. Alternatively, the filters F ₁ and F ₂ Must use a sharp narrow-band filter because the frequencies f ₁ and f ₂ are close to each other and f ₁ −f ₂ is small as described above, and the phase characteristic fluctuation in this filter is extremely small. It is desirable to use an “N-path filter” that operates in synchronization with the outputs of the oscillators OSC ₁ and OSC ₂ as a filter that satisfies this condition.

In the above description, the grounding wire is connected to the injection transformer OT and the current transformer ZCT.
Has been described by penetrating the L _E is path as shown in Figure 2 injection not limited to this transformer OT, may be configured as to whether or clamps provided to allowed to pass through the current transformer ZCT, the clamp In this case, a portable and movable insulation resistance measuring device can be constructed.

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 it includes the commercial frequency f ₀ and the leakage current components of its harmonic components, it is desirable to select a frequency that does not match the commercial frequency f ₀ and its harmonic frequency components as the measurement signals f ₁ and f ₂ .

(Effects of the Invention) Since the present invention employs the means described above, a higher frequency signal can be used as a measurement signal than before, and therefore, the insulation resistance can be measured with a small injection transformer. Since the frequency of the measuring signal is high, without increasing the increasing the transformer core or secondary winding number N _2,
The voltage of the measurement signal can be increased while keeping the output impedance low. Therefore, it is very effective in configuring a portable 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: Power 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, ADD, ADD ₁ ...... adder, L _E ...... ground line, L _1, L ₂ ...... paths, R ₀ ...... insulation resistance,
C ₀ …… Capacitance to ground, Z …… Load.

Claims (2)

(57) [Claims] A frequency f ₁ and f ₁ having a small frequency difference from each other.
By ₂ (f _1> f ₂₎ comprising alternating signal through the transformer of applying the measuring signal to be fed back to the ground line means a transformer for injecting the measurement signal of the frequency f ₁ and f ₂ in the circuit under measurement And a current detecting means penetrating through the ground wire or the electric circuit to detect a leakage current, wherein a frequency f ₁ included in an output obtained by the current detecting means is included.
Obtain a first modulated signal by modulating the leakage current in the AC signal of the frequency f ₂ of, also, the frequency f ₂ included in the output obtained by said current detecting means
Obtain a second modulated signal by modulating the leakage current in the AC signal of the frequency f ₂ of the frequency f ₁ included in the first modulation signal and the signal of the sum of the second modulated signal -f ₂ characterized in that the components measured DC component path of the insulation resistance from the output values obtained by synchronous detection at the frequency f ₁ -f ₂ voltage which is generated by using an AC signal of the frequency f ₁ and f ₂ Simple insulation resistance measurement method. 2. A mutual frequency difference is sufficiently small frequencies f ₁ and f ₂ (f _1> f ₂₎ comprising alternating signal applied to the measurement signal of the frequency f ₁ and f ₂ to the measured circuit via a transformer Means for injecting the current and a current detecting means for penetrating through the ground wire or the electric circuit to detect a leakage current due to the measurement signal returning to the ground wire of the transformer. obtain a first modulated signal by modulating the leakage current of the frequency f ₁ with an AC signal of the frequency f ₂ included in, and the frequency f ₂ included in the output obtained by said current detecting means
Obtain a second modulated signal by modulating the leakage current in the AC signal of the frequency f ₂ of the frequency f ₁ included in the first modulation signal and the signal of the sum of the second modulated signal -f ₂ be one that the components measure the insulation resistance of the electrical path from the output value extracted by using a rectifier, setting a difference between the frequencies f ₁ and f ₂ as reactive current contained in the signal of the sum is smaller A simple method for measuring insulation resistance, characterized in that: