JP2593669B2 - Method for locating defective electrical insulation - Google Patents

Description

Description: FIELD OF THE INVENTION The present invention relates to a method for searching for a defective insulation portion of an electric circuit or an electric device connected to the electric circuit.

(Prior Art) There is a method proposed by the same applicant (Japanese Patent Application Laid-Open No. 56-63270) as a method for detecting insulation failure of an electric circuit in a live state.

 This method will be described with reference to FIG.

In the figure, 1 and 2 are frequencies ₁ and 2 which are equal to each other.
An AC power source with a _2, the signal through the ground wire 5 of the power receiving transformer is applied to the path 4, the insulation resistance R ₁ present in the electric path 4, R _2, ...... R _N and ground stray capacitance c _1, c _2, for detecting a current which returns to the ground line via a ...... c _N by the current transformer 3 which was allowed through the ground line.

For example, output voltages of AC power supplies 1 and 2 are respectively Vsinω ₁ t and Vsinω
Assuming that ₂ t (here, ω ₁ = 2π ₁ , ω ₂ = 2πf ₂ ), the output of the current transformer 3 is amplified by the amplifier AMP and applied to the filter F ₁ for detecting the component of the frequency _1. i is Becomes

On the other hand, the output of the filter F2 that detects the frequency ₂ component
i ₂ Becomes The output of each filter F1, F2 is squared detection circuit SQ1, SQ2
To the output of the square detection circuit SQ1 Is And the output of one SQ2 Is Becomes

Further, the output of the square detection circuit SQ1 is used as one input of a subtractor SUB, and the output of SQ2 is similarly input to a coefficient circuit c (ω ₁
/ omega ₂₎ ^twice or _(1/2) output of the subtracter by applying to the other input terminal of the subtracter SUB after ² times If the output of the subtracter is applied to a circuit ROOT that takes the square root, the output ROOT of the ROOT becomes Therefore, it is possible to collectively measure the insulation resistance value of the electric circuit.

However, the insulation resistance measurement by this method has a drawback that it is not possible to detect at which point on the electrical circuit insulation failure has occurred even if an abnormal value is indicated.

(Object of the Invention) The present invention has been made in view of the above, and has been made in consideration of the above-described problems. An object of the present invention is to provide a method for detecting a defective portion.

(Summary of the Invention) In order to achieve the above object, the present invention applies an AC power supply that generates mutually different frequencies ₁ and ₂ to an electric circuit, and first and second current transformers are applied to two points of the electric circuit to be searched. To detect the current component of frequency _{1 and} the current component of frequency ₂ included in the difference between the output currents of the first and second alternators.
And square value of the amplitude of the _first component, the frequency ₂ of the square value of the amplitude of the component _(1/2) obtains the difference between ^twice the value,
The difference area is a method of detecting an insulation resistance between two points on the electric circuit by detecting a square root of the difference, thereby detecting a defective insulation of the electric circuit.

(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.

2, the same symbols as those in FIG. 2 have the same meanings.

In this figure, the output of the split type current transformer coupled to point A on the circuit is input to an amplifier AMP2, and the output of AMP2 is a phase adjuster PH.
Subtraction circuit SUB1, SUB via 1, PH2 and amplitude adjuster AD1, AD2
2, and the output of the AMP1 is input to the other inputs of the SUB1 and SUB2.

The output of the SUB1 is input to a square detection circuit SQ1 via a filter F1 for detecting a frequency ₁ component.
Is input to a square detection circuit SQ2 via a filter F2 for detecting a frequency ₂ component. Further, the SQ2 output is changed to (ω
₁ / omega ₂₎ to the other input terminal receives an input to one input terminal of the subtraction circuit SUB3 through ^twice the coefficient circuit for inputting said SQ1 output. By inputting the obtained value to the square root circuit ROOT, OUT1 is obtained as its output.

Thus the circuit configured Vsinomega ₁ the output voltage of the alternating current 1 and 2 At a _{t, Vsinω 2 t (ω 1} = 2π 1, ω 2 =
2πf ₂ ), the output of the amplifier AMP2 contains the current i of frequency ₁ corresponding to the above equation (1), while the output of the amplifier AMP1 contains the current i of frequency ₁
^′ ₁ ▼, ie Is included. Therefore, if the outputs of the amplifiers AMP1 and AMP2 are applied to the respective input terminals of the subtractor SUB1 and the outputs are applied to the filter F1, the output of the filter F1 is calculated according to the equations (1) and (7). Becomes This is because the phase amplitude characteristics of current transformers 6 and 7 are frequency ₁
When the characteristics are different at the frequency _1, the phase adjuster PH1 connected to the output terminal of the amplifier AMP2 and the amplitude adjuster connected to the next stage of the PH1 are obtained.
What is necessary is just to correct by AD1.

The correction may be performed by coupling the current transformers 6 and 7 to the same location on the electric circuit so that the output of the filter F1 at this time becomes zero.

Furthermore it said output of said amplifier AMP2 as an output related to the frequency ₂ (2) of the frequency f ₂ to the output of one the amplifiers AMP1 to include current i ₂ of the frequency ₂ shown in formula currents ▲ i _^'2 ▼, That is Is included. Therefore, the outputs of the AMP1 and AMP2 are subtracted by the SU
By inputting each to B2 and applying the obtained output to the filter F2,
The output of the filter F2 is obtained from the above equations (2) and (9). Is obtained. Since the filter F2 output phase amplitude characteristic of the case of the filter F1 as well as the current transformer 6 and 7 can not be obtained to be equal at a frequency f _2, the phase amplitude characteristic is phase adjuster PH2 and amplitude adjuster Correct with AD2.

When the output of the filter F1 is applied to the square detection circuit SQ1,
Its output Is When the output of the filter F2 is applied to the square detection circuit SQ2, the output Is Becomes Enter the square-law detection circuit SQ2 output to the coefficient circuit, by multiplying (ω ₁ / ω _{²⁾ 2} And input the value to one input terminal of the subtractor SUB3, and to the other input terminal to the square detection circuit SQ2.

Thus, the output of the subtractor SUB3 is Becomes That is, as is apparent from the equation (13), the subtractor SU
B3 output is inversely proportional to the square of the insulation resistance R ₁ of the path AB interval, thereby it is possible to know in insulation resistance in a predetermined section of the path.

Further, if the output of the subtracter SUB3 is applied to the square root circuit ROOT, the output is obtained from the equation (13). Since the can know the insulation resistance R _1.

In the above embodiment, the case of the section AB on the electric circuit is shown. However, if the current transformer 6 is moved to the point B and the current transformer 7 is moved to the point c, the insulation resistance in the section BC can be measured. Clearly what you can do. Furthermore, the amplitude and phase characteristics of current transformers 6 and 7
It is clear that if the currents are equal in ₁ and ₂ , the outputs of the current transformers may be connected in series so as to have opposite phases, amplified and then directly input to the filters F1 and F2.

(Effects of the Invention) The present invention makes it possible to measure the insulation resistance of an arbitrary section on an electric circuit without being affected before and after the section by the above-described method, so that the present invention is very effective in detecting a defective insulation.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an embodiment of an apparatus used in carrying out the present invention, and FIG. 2 is a block diagram showing a conventional method. 1,2 ... AC power supply, 3,6,7 ... Current transformer, 4 ... Electric circuit, 5 ... Ground line, AMP, AMP1, AMP2 ... Amplifier, PH1, PH2 ... Phase adjuster, AD1, AD2: Amplitude adjuster, SQ1, SQ2: Square detector circuit, c
…… Coefficient circuit, SUB, SUB1, SUB2, SUB3 …… Subtractor, ROOT…
... square root circuit.

Claims (1)

(57) [Claims] An AC signal having frequencies f1 and f2 (f2> f1) different from each other is applied to an electric circuit, and first and second current transformers are coupled at arbitrary two points on the electric circuit. A current component of the frequency f1 and a frequency f2 included in the difference between the first and second current transformer output currents are detected, and the square value of the amplitude of the current component of the frequency f1 and the amplitude of the current component of the frequency f2 are detected. To the squared value of (f1 / f
2) ² times the value as an electrical insulation failure portion exploration method characterized by measured the insulation resistance between two points of the conductive path by obtaining a difference.