JP2002323533A - Partial discharge testing method for electric power equipment - Google Patents

Abstract

PROBLEM TO BE SOLVED: To facilitate discrimination between a noise and a partial discharge signal and identification of a cause in a partial discharge test for a direct current electric power equipment. SOLUTION: When a direct current voltage is applied to an electric power equipment 10 to be tested, a partial discharge signal generated from the electric power equipment is detected by having an alternating voltage overlapped. Overlapping of the alternating voltage is applied by inserting an alternating power source 50 in series between a low-voltage side terminal 22 of a direct current power source 20 to generate the direct current voltage and an earth point, or between a low-voltage side conductor of the electric power equipment to be tested and the earth point. A detection signal when only the direct current voltage is applied to the electric power equipment to be tasted is compared with the detection signal when the alternating voltage is made to overlap to discriminate the partial discharge signal from the noise signal.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a partial discharge test method for testing and diagnosing power equipment.

[0002]

2. Description of the Related Art Partial discharge (hereinafter, referred to as PD (Partial Discharge)) is a technique for evaluating the electrical soundness of power devices such as power cables.
Is widely used. For example, in a power cable, PD occurs due to slight insulation failure of an insulator between a conductor that is a high-voltage part and a sheath that is on the ground potential side. In some cases, a pulse current of an extremely weak charge flows. Since a defective portion can be found by detecting the PD before dielectric breakdown, PD measurement is performed at the time of shipping the power cable or as a test after laying the track. The partial discharge measuring device for these measurements is based on a method of detecting a weak current flowing through the ground wire of the sheath, or by attaching a signal detection unit such as a foil electrode to the sheath insulated connection box (IJ) that connects the power cable. Many methods and measuring instruments have been put into practical use, such as a method of detecting current pulses, a method of detecting electromagnetic waves radiated into space with an antenna, and a method of detecting weak mechanical vibrations due to electric discharge as a signal with an acoustic sensor. Have been.

A PD signal is generated due to a projection on a conductor surface, a foreign substance, a void, a void, or the like in an insulator, and its characteristics vary depending on the type of the insulator, the foreign substance, the void, and the like. It is known. The nature of the PD signal is primarily related to the phase of the alternating voltage being imposed. That is, there are waveforms that are generated near the peak position corresponding to the vibration waveform of the AC voltage, waveforms that are concentrated in the first and third quadrants, and waveforms that are generated near the zero cross. Due to these properties, it is possible to specify the cause of the PD occurrence based on the frequency of occurrence and the pattern of the occurrence phase, and to discriminate the noise signal that occurs independently of the potential application phase.

[0004]

[0006] The partial discharge test is also used for a test of a power device using a direct current, and a PD measurement is performed in a state where a direct current voltage is applied. However, the frequency of PD generation in DC voltage application is much lower than that in AC voltage application, and there is no phase characteristic as described above. Was.

[0005]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and makes it easier and more reliable to perform a partial discharge test of a DC power device such as a DC power cable by the following means.

In a partial discharge test method by detecting a signal generated from a power device under test while a DC voltage is applied to the power device, an AC voltage is superimposed on the DC voltage to be applied. . The occurrence frequency of the partial discharge pulse signal is increased as compared with the case where only the DC voltage is applied, and the detection becomes easier.

Here, the superimposed AC voltage is a voltage of 20% or less of the applied DC voltage, more preferably 10% or less, and further preferably 5% or less. Therefore, a small AC power supply can be used, and the test is easy.

The superposition of the AC voltage can be performed by inserting an AC power supply in series between the low voltage side terminal of the DC power supply for generating the DC voltage and the ground point.

It is also possible to insert an AC power supply in series between the low voltage side conductor of the power device under test and the ground point.

In a test with such a configuration, a partial discharge signal and a noise signal are compared by comparing a detection signal obtained when only a DC voltage is applied to the power device under test with a detection signal obtained when an AC voltage is superimposed. Can be easily determined.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 schematically shows a configuration of a test apparatus used to carry out the present invention. A method for testing a partial discharge of the power device under test will be described with reference to FIG.

In FIG. 1, reference numeral 10 schematically shows a cross-sectional structure of a power device as a device under test, which includes a high-voltage conductor 11 and a low-voltage conductor 13 to which a high voltage is applied and an insulator 12 for insulating them. Be composed. The power devices under test include power cables and their accessories, terminal devices, and power devices such as switches and transformers. The basic configuration of any device can be represented in this way. The low-voltage side conductor is usually grounded by the grounding wire 14, and is a portion generally called a metal sheath or a shielding layer in the case of a power cable.

The partial discharge test is performed by applying a DC voltage generated by the DC power supply 20 as a test voltage to the high-voltage side conductor 11 through the lead wire 21. As a signal detection method when a PD occurs, many methods and sensors have been put to practical use, and are not limited in the present invention.
Here, as a very general method, a PD signal, which is a high-frequency signal, is extracted from the high-voltage side by coupling with a capacitor 30, and a detection impedance 4 is inserted in series.
A method for measuring the voltage V generated at 0 has been described.

Here, one configuration embodying the present invention is that the AC power supply 50 is inserted on the low voltage side of the DC power supply 20. The AC power supply 50 is configured to receive a supply of AC power from the outside and impress power by a transformer, for example.
It is inserted in series between the low voltage side terminal 22 of the DC power supply and the ground point. FIG. 2 illustrates a voltage applied to the power device under test by inserting an AC power supply. 2A shows the output voltage of the DC power supply, FIG. 2B shows the output voltage of the AC power supply, and FIG. 2C shows the voltage applied to the power device under test. Is added.

[0015] With this configuration, when the power device under test has a cause of PD generation, the frequency of PD generation is higher than in the case of applying only DC voltage, and depending on the cause, the PD is superimposed. It will show generation characteristics related to the phase of the AC voltage. Therefore, it is easier to detect the occurrence of PD than in the case of only the DC voltage.

The DC voltage, which is a test voltage, ranges from several kV to several hundred kV or more depending on the withstand voltage value of the power device under test. The higher the superimposed AC voltage, the greater the effect on PD generation. Therefore, it is preferable that the AC voltage be as large as possible within the range permitted for the withstand voltage performance of the equipment to be used and the power device under test. However, if a too large voltage is applied, the purpose of the DC test is deviated, and the power supply equipment is required to be as small as possible. From these viewpoints, the AC voltage is 20% or less, preferably 1%, of the DC voltage to be charged.
It is desirable to have a low pressure of several hundred V to several kV or less, which is 0% or less, and even such a voltage has an effect of changing the PD generation. For example, by superimposing an AC of 2 kV during a DC voltage test of 40 kV in a DC power cable, an increase in the frequency of occurrence of PD is recognized,
Further, the effect is obtained even with the AC superposition of about 200 V.

Further, in the above configuration, by turning on and off the AC power supply, the detection signal in the case of only the DC voltage application and the detection signal in the case of superimposing the AC voltage are compared to determine whether the signal is a noise signal or a PD signal. Discrimination becomes easy. That is, noise generated by devices other than the device under test, radio waves such as broadcast waves and radio waves are not affected by the difference in power application, but the PD signal changes in accordance with the application voltage. When the voltage is superimposed, it is possible to determine whether or not the signal is a PD signal by observing the occurrence frequency and magnitude of the detection signal and the relationship with the AC phase.

FIG. 3 shows another configuration for carrying out the present invention, which is different from the configuration shown in FIG. 1 only in that an AC voltage applying device 50 is inserted on the low voltage side of the power device under test. ing. In FIG. 3, the low voltage side conductor 13 of the power device under test is shown.
An AC power supply 50 is inserted between the power supply and the ground point, and a DC voltage is applied to the high voltage side of the power device under test by the DC power supply.

According to this configuration, a voltage obtained by superimposing an AC voltage on a DC voltage is applied to the insulator of the device under test as in FIG. 2, and the same effect as in FIG. 1 can be obtained.

The configuration shown in FIG. 1 or the configuration shown in FIG. 3 can be arbitrarily selected depending on the scale and arrangement of the test object, the configuration of the test equipment, and the like. For example, if the power device under test is spatially spread and multi-point grounded,
The configuration shown in FIG. 3 is easier when the DC power supply is large and it is difficult to insert the AC power supply into the ground side.

[0021]

As described above, according to the partial discharge test method of the present invention, it is possible to easily and more reliably measure the partial discharge test of a DC power device by applying a DC voltage, thereby improving the reliability of the device. Help.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of a test apparatus that performs a partial discharge test method of the present invention.

FIG. 2 is a diagram illustrating a voltage applied to a power device under test.

FIG. 3 is a diagram showing a configuration of a test apparatus for performing the partial discharge test method of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Power device under test 11 High voltage side conductor 12 Insulator 13 Low voltage side conductor 14 Ground wire 20 DC power supply 21 Lead wire 22 Low voltage side terminal 30 Capacitor 40 Detection impedance 50 AC power supply

Claims (5)

[Claims] In a partial discharge test method in which a DC voltage is applied to a power device under test and a signal generated from the power device is detected, an AC voltage is superimposed on the DC voltage to be applied. A partial discharge test method for electric power equipment, characterized in that: 2. The method according to claim 1, wherein the superimposed AC voltage is a voltage equal to or less than 20% of an applied DC voltage. 3. The superimposition of an AC voltage is performed by inserting an AC power supply in series between a low voltage side terminal of a DC power supply for generating a DC voltage and a ground point.
Or the partial discharge test method for power equipment according to 2. 4. The method according to claim 1, wherein the AC voltage is superimposed by inserting an AC power supply in series between the low voltage side conductor of the power device under test and the ground. Partial discharge test method for power equipment. 5. A partial discharge signal and a noise signal are distinguished by comparing a detection signal when only a DC voltage is applied to a power device under test with a detection signal when an AC voltage is superimposed. Partial discharge test method for power equipment.