JP2593668B2 - Insulation fault detection method for electric circuit - 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 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 frequency ₁ , the output i becomes Becomes

While the output i ₂ of the filter F2 for detecting the component of the frequency ₂
Is 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 electric circuit an insulation failure has occurred even if it shows an abnormal value.

(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 ( ₂ > ₁ ) to an electric circuit, and also applies an AC power source to any two points on the electric circuit. First
And the second current transformer, and the square value of the amplitude of the leakage current component of frequency ₁ obtained at the output of each of the first and second current transformers And the square of the amplitude of the leakage current component at frequency ₂ And detect Is a method of measuring the insulation resistance between two points on the electric circuit by performing the above calculation.

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

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

In the same figure, the same meaning as in FIG.
The difference from the figure is that two systems of a leakage current component detection system including a current transformer are provided, and the outputs of the two systems are input to a subtractor SUB3 to detect the output.

In this figure, an electric circuit 4 is passed through a split-type current transformer 6 on an electric circuit A, the output of which is input to an amplifier AMP2, and the output of AMP2 is a filter F3 for detecting _one frequency component and a frequency.
It is applied to a filter F4 that detects _two components. Thus, a current represented by the above equation (1) is obtained at the output of the filter F3. When this current is applied to the square detection circuit SQ3, the output is represented by the above equation (3). Is equivalent to While the output i ₂ of the filter F4 becomes the current represented by the equation (2), applying this to the square-law detection circuit SQ4, the output is represented by the equation (4) Is obtained.

The square-law detection circuit outputs at the coefficient circuit c ₂ of _{SQ4 (ω 1 / ω 2)} 2 = (1/2) 2 multiplied by its output to one input terminal of the subtractor SUB2, the other input terminal Is the square detection circuit
By inputting the output of SQ3, an output corresponding to the equation (5) is obtained as the output of the subtraction circuit SUB2. If the output is further input to the square root circuit ROOT2, the output of the ROOT2 becomes the above (6).
The total insulation resistance from the point A corresponding to the equation to the end of the circuit is measured.

On the other hand, the output of the current transformer 7 through which the electric circuit penetrates at point B on the electric circuit is input to the amplifier AMP1, and the output of the AMP1 is input to the filter F1 for detecting the frequency ₁ component and the filter F2 for detecting the frequency ₂ component. .

The output ▲ i ^′ ₁ ▼ of the filter F1 is On the other hand, the output ▲ i ^′ ₂ ▼ of the filter F2 is Becomes The output of the filters F1 and F2 is squared detection circuit SQ
1, if input to SQ2, output as SQ1 And the output of the SQ2 Get.

Further first input terminal of the square-law detection output of the circuit SQ2 ▲ i '2 2 ▼ at the coefficient circuits c 1 (omega 1 / omega 2) 2 or (1/2) is doubled, subtraction circuit SUB1 its output And the other input terminal receives the output of the square detection circuit SQ1 so that the output of the subtractor SUB1 is And applying the SUB1 output to the square root circuit ROOT1 produces the output Becomes This is the total insulation resistance from point B to the end of the circuit. If this value and the output of the square root circuit ROOT2 are input to the subtractor SUB3, the output SUB3 OUT1 becomes (6), (1)
2) From equation Thus, the insulation resistance of the section AB on the electric circuit can be measured.

In the above embodiment, the section AB on the electric circuit has been described and shown. However, the present invention is not limited to this. If the current transformer 6 is moved to the point B and the current transformer 7 is moved to the point C and measured, the section BC of the section BC is measured. It is clear that the insulation resistance can be measured.

(Effect of the Invention) Since the present invention operates by the method as described above, the insulation resistance (including that of the electronic device connected to the electric circuit) in an arbitrary section on the electric circuit is determined before and after the section. Since the measurement can be performed without being affected, it is extremely effective in searching for a defective insulation.

[Brief description of the drawings]

FIG. 1 is a view showing an embodiment of an apparatus used in carrying out the present invention, and FIG. 2 is a view showing a conventional measuring method. 1,2 …… AC power supply, 3,6,7 …… Current transformer, AMP, AMP1, AMP2 ……
_{Amplifier, F 1, F 2, F} 3, F 4 ...... filter, SQ1, SQ2, SQ3, SQ4 ......
Square-law detection circuit, SUB, SUB1, SUB2, SUB3 ...... subtractor, c _1, c
₂ ...... Coefficient circuit, ROOT1, ROOT2 ... 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. The square value of the amplitude of the leakage current component of the frequency f1 obtained at each of the outputs of the first and second current transformers And the square of the amplitude of the leakage current component at frequency f2 And detect A method for detecting an insulation failure portion of an electric circuit, wherein an insulation resistance between two points on the electric circuit is measured by performing the above calculation.