JPH03252567A - Partial discharge measuring instrument - Google Patents

Abstract

PURPOSE:To prevent the instrument from damaging and eliminate external noises by inserting the ground-side lead wires of a body to be tested and a coupling capacitor into the primary winding through hole of a current transformer in reverse directions and grounding them, and providing the partial discharge measuring instrument on the secondary side. CONSTITUTION:A partial discharging signal which is generated in the body 3 to be tested after reaching the ground from the ground-side lead wire through the current transformer 5 is sent through the ground-side lead wire of the coupling capacitor 4 and then returns to the supply body 3 through the current transformer 5 and capacitor 4. Both the ground-side lead wires of the body 3 to be tested and the capacitor 4 are wound in the current transformer 5 in mutually reverse directions, so the partial discharging signal operates to emphasize the signal of the current transformer 5 and a noise from outside a measurement system is canceled by the current transformer and never appears at the output of the current transformer 5. Both the ground-side lead wires of the body 3 to be tested and capacitor 3 are grounded respectively to prevent a surge from flowing to the measuring instrument even in case of the dielectric breakdown of the body 2 to be tested, thereby preventing the equipment from damaging and eliminating influence upon a human body.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to a partial discharge measuring device used in partial discharge testing of high voltage electrical equipment.

(Prior technology) High-voltage electrical equipment uses various methods to detect or predict defects in the insulating materials used, manufacturing defects, or abnormalities during use, and to consider countermeasures before they become serious. High voltage tests are carried out. Among these, partial discharge testing is carried out today as a non-invasive test because it can detect abnormalities in insulation without causing damage to equipment.

To measure partial discharge, for example, the High Voltage Test Handbook of the Institute of Electrical Engineers of Japan, p.401. The test circuit is constructed using the following four basic circuit elements as described in p.420 (1982).

(a) High-voltage power supply that applies voltage to the specimen (b) Detection impedance that converts the discharge pulse current to pulse voltage (C) Shunt impedance that forms a closed circuit where the pulse current effectively flows through the detection impedance (d) Device for measuring the output of detection impedance Specifically, as shown in FIGS. 3 to 5, a high voltage power supply 1, a blocking impedance 2, a specimen 3, a coupling capacitor 4 and a measuring device 6 are used There are three basic measurement circuits:

Figure 3 shows a circuit that connects the detection impedance 2 between the ground terminal of the coupling capacitor 4 and the earth, and
can be directly grounded. Therefore, even if the specimen 3 were to undergo dielectric breakdown, the measuring device would not be directly damaged. FIG. 4 shows a circuit in which the detection impedance 22 is connected between the ground side terminal of the specimen 3 and the earth E, and it is necessary to insulate the ground side of the specimen 3 from the earth. FIG. 5 shows a circuit in which a detection impedance 23 is connected between the ground side terminals of the specimen 3 and the coupling capacitor 4 (or another specimen), respectively, and the ground to maintain balance.

As is clear from FIGS. 3, 4, and 5, all of these methods have a detection impedance 21.22.23 for detecting partial discharge. .23 is directly connected to the sample or the ground side circuit of the coupling capacitor 4.

(Problem to be Solved by the Invention) By the way, if the capacitance of the sample 3 is larger than the size of the partial discharge to be detected, if you try to measure the partial discharge using these measurement circuits, the following will occur. It is known that there are drawbacks such as:

First, the circuits shown in FIGS. 3 and 4 cannot reduce the influence of noise flowing in from the high voltage side of the power supply 1 or the specimen 3. This effect is particularly large when high voltage parts are exposed to the atmosphere. Furthermore, in Fig. 4, when a voltage other than DC is used for the power source 1, the charging current due to the capacitance of the specimen 3 is large, the partial discharge signal is relatively decreased, and the S/N ratio is decreased. happens. For this reason, there was a problem that measurement sensitivity decreased. In addition, in the circuit shown in Fig. 5, although these problems can be solved by the balance detection circuit, since the specimen 3 cannot be directly grounded, there is a risk that the measuring device 6 may be damaged in the unlikely event of dielectric breakdown. . Therefore, the measurement system including the detection impedance 23 required protection measures in case the specimen 3 was short-circuited.

In addition, in both of these circuits, the detection impedance 21
．． 22 and 23 are connected to the measuring device 6 via a measuring cable 7, and the measuring system is electrically connected to the main circuit. For this reason, a closed loop for noise is formed through the power supply of the measuring instrument 6, which prevents the intrusion of external noise and ultimately increases the S/N.
There was a risk that this would lead to a decrease in the ratio, and countermeasures were needed to deal with this as well. In addition, the original waveform of a partial discharge is distorted by the resonance phenomenon due to parasitic vibration inherent in the measurement circuit and the electrical characteristics of the detection impedance because the current pulse rises quickly due to the partial discharge, making it impossible to measure the original waveform. There were drawbacks.

The object of the present invention is to take advantage of the advantages of a balance detection circuit, and to
The purpose is to prevent damage to the measuring device even in the unlikely event of dielectric breakdown of the specimen (and to prevent external noise from occurring in a closed loop via the power supply. The present invention provides a partial discharge measuring device which attempts to accurately grasp the nature of partial discharge by obtaining a waveform as close as possible to the original waveform of partial discharge.

[Structure of the Invention] (Means for Solving the Problems) The partial discharge measuring device of the present invention comprises a part to be balanced using a specimen and a coupling capacitor or another specimen connected in parallel to the specimen. The discharge measuring device is equipped with a current transformer having a through hole through which the primary winding can pass, and the test object and the ground side lead wire of the coupling capacitor are inserted into the through hole of the current transformer in opposite directions. The current transformer is characterized in that it is penetrated through the current transformer and then grounded, and a measuring device that detects partial discharge is connected to the secondary side of the current transformer.

(Function) According to the partial discharge measuring device of the present invention, the grounding side lead wire through which the partial discharge current pulse flows is passed through the current transformer in opposite directions to each other. can be canceled and external noise can be removed.

Further, since the current transformer is separated from the main circuit to which high voltage is applied, it is possible to remove noise that enters through the measurement line and the power supply line. That is,
The S/N ratio can be improved and measurement sensitivity can be improved.

(Example) The present invention will be described below with reference to the example shown in FIGS. 1 and 2. In FIG. 1, 1 is a high voltage power supply that applies voltage to the specimen 3, 2 is an impedance that prevents partial discharge pulses from flowing into the power supply 1 side, 3 is the specimen,
4 is a coupling capacitor or another test object, 5 is a current transformer, 6
indicates a measuring device.

According to the partial discharge measuring device of the present invention configured in this manner, the partial discharge signal generated in the specimen 3 reaches the ground from the grounding lead wire via the current transformer 5, and then is transmitted to the coupling capacitor 4. The grounding side lead wire returns to the specimen 3 via the current transformer 5 and the coupling capacitor 4. In this case, since the grounding lead wire of the specimen 3 and the grounding lead wire of the coupling capacitor 4 are wound in opposite directions relative to the current transformer 5, the partial discharge signal is passed through the current transformer 5 as an in-phase component. acts to emphasize the signal. On the other hand, noise components from sources other than the power supply 1 or the measurement system enter the specimen 3 and the coupling capacitor 4 as common-mode components. However, since these signals cancel each other out in the current transformer 5,
It does not appear in the output of current transformer 5.

Furthermore, since the grounding lead wire of the DUT and the coupling capacitor (or another DUT) connected in parallel with it are directly grounded to the earth, there is no possibility of dielectric breakdown of the DUT. This prevents surges from entering the measuring equipment, and there is no risk of damage to the equipment.

It is also safe for the human body.

Note that, if necessary, by inserting a resistor for suppressing parasitic vibration between the ground side lead wire and the earth, the current pulse waveform of partial discharge can be measured more accurately.

As described above, according to the present invention, only the partial discharge signal generated in the specimen can be detected and external noise can be removed. Therefore, the S/N ratio can be improved and the measurement sensitivity can be increased.

Furthermore, since the grounding leads of the specimen and the coupling capacitor are directly connected to the ground, the measurement system can be protected from abnormal voltage even in the unlikely event of dielectric breakdown.

Furthermore, according to the present invention, as is clear from the circuit configuration, the measurement system is separated from the main circuit consisting of the specimen to which high voltage is applied or the coupling capacitor by the current transformer, so the measurement line and the power supply It is possible to eliminate noise that enters through the line. That is, the S/N ratio can be improved and measurement sensitivity can be expected to be improved. Furthermore, the output of the current transformer allows the original waveform of partial discharge to be directly measured, and distortion of the waveform due to detection impedance can be prevented. Therefore, the polarity of the partial discharge, the magnitude of the charge, and the generation phase of the partial discharge can be accurately measured.

Next, FIG. 2 shows another embodiment of the present invention. In this embodiment, resistors 10 and 11 are inserted between each ground side lead wire and the earth, and the resistance value inserted between the ground side terminal and the earth is 500 ohms or less. According to this method, it is possible to suppress parasitic vibration in a circuit through which current pulses due to partial discharge flow, and S/N
ratio can be improved. In this case, distortion of the original waveform of partial discharge can be reduced by setting the resistance value to 500 ohms or less.

Moreover, by winding the low-voltage side lead wire around the current transformer 5 multiple times using the characteristics of the current transformer, only the partial discharge signal can be emphasized and detected.

Furthermore, similar effects can be expected when the partial discharge measuring device according to the present invention is applied to the grounding wire of a gas-insulated switchgear. For example, when the present invention is applied to two grounding wires, there may be a partial discharge source within the section between the two grounding wires, such as the presence of metallic foreign matter or the occurrence of partial discharge due to minute protrusions on the electrode surface. , or if there is a poor connection of equipment, an abnormality in the insulation of a spacer, etc., this can be effectively detected.

Note that although the characteristics of the current transformer have not been described here, it goes without saying that one having sufficient response characteristics to the current pulse signal of the partial discharge to be measured is used depending on the purpose. It goes without saying that the capacitance of the coupling capacitor should be equal to or close to the capacitance of the specimen.

[Effects of the Invention] As described above, according to the present invention, by directly grounding the ground side lead wire of the main circuit to which high voltage is applied to the earth, equipment damage caused by abnormal voltage due to dielectric breakdown can be prevented. It is possible to provide a highly sensitive partial discharge measuring device that prevents problems such as damage and unsafe conditions, and that does not reduce the S/N ratio due to external noise or the charging current of the specimen.

[Brief explanation of drawings]

FIG. 1 is a circuit configuration diagram showing one embodiment of the partial discharge measuring device of the present invention, FIG. 2 is a circuit diagram showing another embodiment of the present invention, and FIGS. 3 to 5 are conventional partial discharge measuring devices. FIG. 2 is a circuit configuration diagram showing a measuring device. DESCRIPTION OF SYMBOLS 1... High voltage power supply, 2... Blocking impedance, 3... Test object, 4... Coupling capacitor or another test object, 5... Current transformer, 10, 11... resistance.

Claims (1)

[Claims] (1) In a partial discharge measuring device that uses a specimen and a coupling capacitor connected in parallel with it or another specimen to achieve balance, current transformation has a through hole that allows the primary winding to pass through. The test object and the grounding side lead wire of the coupling capacitor are passed through the through hole of the current transformer in opposite directions, and then grounded, and the output is connected to the secondary side of the current transformer. A partial discharge measuring device characterized in that a measuring device for detecting partial discharge is connected to the device.