JPH1010184A - Abnormal insulation detector - Google Patents

Abstract

PROBLEM TO BE SOLVED: To perform measurement accurately while reducing the size by providing a noise canceling circuit comprising a subtractor and a correction voltage setter at the output stage of leakage current signal, setting a correction voltage such that the leakage current signal goes zero under a state where the input to a measuring signal system is zero and performing a subtractive correction at the time of measuring the leakage current signal. SOLUTION: When a measuring signal system is superposed with power supply noise or induction noise and the DC output from a synchronous detection circuit 12 contains a measurement error, the DC voltage of a power supply/induction noise is set, as a correction voltage, in the correction voltage setter 15 in a noise cancel circuit. A subtractor 14 performs corrective subtraction of the correction voltage at the time of measuring a leakage current signal and produces a leakage current signal from which the power supply/induction noise is removed. Consequently, voltage setting of the setter 15 is regulated manually such that the output from the subtractor 14 goes zero when the leakage current signal is inputted. According to the arrangement, induction noise can be removed even when respective circuit elements are arranged compactly on 1 printed board in order to reduce the size and an accurate measurement can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a probe for detecting a location where insulation is abnormal, such as when an insulation alarm is issued from an insulation monitoring device due to leakage of a distribution line, and more particularly to a leak current signal. The present invention relates to an insulation anomaly detector that detects from measurement of Igr.

[0002]

2. Description of the Related Art In electrical equipment, grounding work is performed to protect humans and animals and equipment from damage due to electric shock. The grounding work may be performed, for example, by connecting the neutral point or one terminal of the transformer low voltage side to the high voltage or extra high voltage distribution line.
Grounded by seed grounding work.

The distribution line insulation monitoring device applies an AC voltage having a frequency different from the commercial frequency between the distribution line and the ground line of the second-class grounding work, and the applied voltage causes the distribution line to pass through the ground line. The insulation state is monitored by determining the insulation resistance from the flowing leakage current.

[0004] The insulation abnormality detector detects an alarm source generated when the insulation monitoring device detects an insulation abnormality, or when an insulation abnormality occurs during maintenance inspection of the insulation state.
Used to search for insulation abnormalities.

FIG. 2 shows a circuit configuration of a conventional insulation fault detector for detecting a faulty insulation location of a distribution line in which a conventional insulation monitoring device is installed. The insulation monitoring device 1 applies an AC voltage between the grounding phase 4 of the low-voltage side distribution line of the transformer 3 and the grounding line (E2) from the injection transformer 2 and the grounding resistance R and the stray capacitance C from the distribution line. Insulation monitoring is performed by detecting the feedback current.

The probe 5 shows only the measurement signal system and the reference signal system without the power supply, the microprocessor and the display, and converts the AC voltage injected from the insulation monitoring device 1 into the ground phase 4 into the ground phase 4 and the third phase. An AC voltage signal between the grounding point (FG) where the seed installation work is performed is taken out by the AC amplifier 6, and this signal is passed through a low-pass filter 7 to remove high-frequency components to be taken out as a reference signal for synchronous detection. .

The leakage current flowing from the secondary side of the injection transformer 2 to the distribution line is transformed by the clamp type current transformer 8 and converted and amplified into a voltage signal by the current-voltage converter 9.
The high-frequency component is removed by the low-pass filter 10, the impedance is reduced by the buffer amplifier 11, and the signal is extracted as a synchronous detection measurement signal.

[0008] The reference signal and the measurement signal are supplied to a synchronous detection circuit 12.
And synchronous detection is performed by multiplication to extract a leakage current signal Igr. The CR filter 13 is a DC leakage current signal Ig obtained by removing high-frequency components from the synchronous detection signal.
Get r.

The leakage current signal Igr is supplied to a grounding point (F
The change is caused by changing the position of G), and this change is displayed on a display provided in the search device to search for an abnormal insulation location.
Further, the signal Igr at the ground position changed variously can be stored in the memory, and the exploration analysis can be performed from this data using a personal computer or the like.

[0010]

It is desired that the probe 5 be miniaturized for easy carrying to a location to be searched, and necessary circuit elements 6 and 6 to make it a handy type.
It has a compact design in which 7, 9 to 13 are mounted on one printed board, and uses a dry battery as a power supply.

In order to reduce the size of the apparatus, it is difficult to completely separate the circuit elements from each other, and a reference signal having a level much larger than the measurement signal is guided to the measurement signal system through a circuit pattern or the air. As a result, inductive noise may be superimposed on the leakage current signal Igr, resulting in a large measurement error.

The probe 5 uses a dry cell as a power source to supply a voltage required for each circuit element from a switching regulator.
Since a digital circuit such as a microprocessor is mounted for supplying current and for measurement and display control, power supply noise and high frequency noise from the microprocessor etc. are generated inside the device. Noise may enter the measurement circuit and increase the measurement error.

In order to reduce power supply noise, the power supply should be a stabilized analog power supply, the output impedance of the power supply should be low, and the power supply pattern should be separated from the measurement system. Separating the power supply to the power supply to the like causes an increase in the size of the apparatus and an increase in cost.

An object of the present invention is to provide an insulation abnormality detector capable of measuring a leakage current signal Igr by removing various noises while reducing the size of the device configuration.

[0015]

SUMMARY OF THE INVENTION According to the present invention, even if noise is superimposed on the leakage current signal Igr due to the downsizing of the device, the noise can be canceled. A reference signal system for detecting, as a reference signal, an AC voltage different from the commercial power frequency applied to one end, and a leakage current signal Igr which is detected by detecting a leakage current of the distribution line and converted into a direct current by synchronous detection with the reference signal is obtained. A measurement signal system, and an insulation fault detector for detecting an insulation fault in the distribution line from the leakage current signal Igr, provided at an output stage of the leak current signal Igr, and having an input of the measurement signal system of zero. In this state, a correction voltage at which the leakage current signal Igr becomes zero is set in a state, and a noise canceling circuit that performs subtraction correction with the correction voltage when measuring the leakage current signal Igr is provided. .

[0016]

FIG. 1 is a circuit diagram showing an embodiment of the present invention. 2 differs from FIG. 2 in that a noise canceling circuit is provided in the output stage of the CR filter 13.

This noise canceling circuit includes a subtractor 14
And a variable voltage setting device 15. The subtractor 14
For example, it is configured as a subtraction circuit using an operational amplifier, and the output of the CR filter 13 is used as a signal to be subtracted.
5 is used as a subtraction correction signal, and the subtraction result is output as a leakage current signal Igr.

The correction voltage setting unit 15 is composed of a potentiometer or the like, and adjusts the divided voltage of the constant-voltage DC voltage to obtain a DC correction voltage output for noise cancellation.

In this embodiment, when a power supply noise or an induction noise is superimposed on a measurement signal system and a measurement error is included in a DC output of the synchronous detection circuit 12, a noise cancel circuit is provided. The DC voltage of the power supply / induction noise is set as a correction voltage in the correction voltage setting unit 15 of the above, and the correction voltage is subtracted and corrected by the subtractor 14 when measuring the leakage current signal Igr, thereby removing the power supply / induction noise. Obtain a current signal Igr.

The voltage setting of the correction voltage setting unit 15 for this purpose is manually adjusted so that the output of the subtractor 14 (the leakage current signal Igr) when the leakage current signal input is zero becomes zero. For example, the output of the subtractor 14 is adjusted to be zero with the input of the current-voltage converter 9 grounded.

Therefore, according to this embodiment, in order to reduce the size of the device, each circuit element is arranged in close contact with one printed circuit board, and the reference signal is guided to the measurement signal system through the circuit pattern or the air. Even when the induced noise is superimposed on the leakage current signal Igr, the induced noise is removed by the noise canceling circuit, and accurate measurement can be performed.

Further, a switching regulator is provided as a power source of the probe to reduce the size of the device, and a microprocessor is provided for measurement and display control. I
Even when the signal is superimposed on gr, the power supply noise and high-frequency noise can be removed by the noise canceling circuit, and accurate measurement can be performed.

Further, as a circuit configuration, a relatively small and low-cost noise canceling circuit may be added.

In the embodiment, the configurations of the measurement signal system and the reference signal system are appropriately changed in design. In addition, the configuration of the noise canceling circuit is such that the subtractor 14 and the correction voltage setting unit 15 are constituted by one potentiometer,
The design can be changed as appropriate such as a configuration for adjusting the reference voltage of the filter 13.

[0025]

As described above, according to the present invention, since the noise cancel circuit is provided at the output stage of the leakage current signal Igr, the reference signal system and the measurement signal system are arranged close to each other in order to reduce the size of the device. Leakage current signal with various types of noise removed even when various noises are superimposed on the measurement signal due to the configuration in which the induction noise is superimposed on the measurement signal system and the configuration in which the power supply noise and high frequency noise are superimposed on the measurement signal system Ig
r output can be obtained, and there is an effect that an accurate measurement of an abnormal insulation location can be performed by accurate measurement while miniaturizing the apparatus.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing an embodiment of the present invention.

FIG. 2 is a conventional circuit configuration diagram.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Insulation alarm device 2 ... Injection transformer 3 ... Transformer 5 ... Insulation abnormality detector 6 ... AC amplifier 7, 10 ... Low-pass filter 8 ... Clamp type current transformer 9 ... Current-voltage converter 11 ... Buffer amplifier 12 ... Synchronous Detection circuit 14 ... Subtractor 15 ... Correction voltage setting device

Claims (1)

[Claims] 1. A reference signal system for detecting, as a reference signal, an AC voltage different from a commercial power frequency applied to one end of a distribution line, and a direct current through synchronous detection with the reference signal by detecting a leakage current of the distribution line. A measurement signal system for obtaining a converted leakage current signal Igr, and an insulation abnormality detector for detecting an insulation abnormality of a distribution line from the leakage current signal Igr, provided at an output stage of the leakage current signal Igr, A noise canceling circuit is provided which sets a correction voltage at which the leakage current signal Igr becomes zero when the input of the measurement signal system is zero, and performs a subtraction correction with the correction voltage when measuring the leakage current signal Igr. Insulation anomaly detector.