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Partial discharge detection method

time:2020/11/12   source:华天电力  reading:630 time

Partial discharge detection methods include the following:

1. Ground wave detection

Electromagnetic waves are generated when partial discharge occurs in the insulating layer of the high-voltage switchgear, and the metal shell of the switchgear will shield a large part of this electromagnetic wave, but a small part will pass through the seam of the metal shell or the gas-insulated switch lining The pad propagates out, and a ground electric wave is transmitted to the ground through the outer surface of the metal casing of the device. The range of the earth wave is usually from a few millivolts to a few volts, and the rise time is a few nanoseconds. The probe can be set on the outer surface of the switch cabinet in the working state to detect partial discharge activities.

Partial Discharge Detector.png

2. Ultrasonic testing

In fact, ultrasonic detection is a kind of mechanical vibration wave. From the perspective of energy, the process of partial discharge is the process of instantaneous energy explosion. Electric energy is released in the form of sound energy, light energy, heat energy and electromagnetic energy, and electrical breakdown Occurs in the air gap, the discharge can be completed in an instant. At this time, the electrical energy will be converted into heat energy in an instant. The gas in the center of the discharge will expand under the action of the heat energy, and spread outward through sound waves. The gas in the propagation area is heated to form a In the isothermal zone, the temperature exceeds the ambient temperature; when the gas starts to shrink after cooling, subsequent waves will be generated. The frequency and intensity of the subsequent waves are relatively low, including various frequency components, and have a wide frequency band. The ultrasonic frequency is greater than 20kHz . Because the area of partial discharge is relatively small, the partial discharge sound source is a point sound source.

3. Ultra-high frequency detection method

In the process of time change, the electromagnetic vibration generated by the partial discharge will generate electromagnetic waves. In the solid gas and gas medium, the partial discharge pulse will generate very rich electromagnetic wave ultra-high frequency components, up to GHz. In the actual application process, the detection of partial discharge signals can be carried out by using two probes. The time sequence of the detection of the signal by the probe is used as the basis for judgment. If the distance of the discharge source is close, it will be detected first; the position of the probe is constantly changing. Judge the approximate location of the discharge source step by step. Or through multiple probes, the time difference equation set of the probe to detect the partial discharge signal can be calculated to find the three-dimensional space coordinates of the discharge source, and finally the discharge source can be determined. This method has relatively high sensitivity and strong anti-interference ability, and there are usually seams or small glass windows on the switch cabinet, so it is not necessary to consider the requirement that this method is difficult to detect under completely sealed conditions.

4. Comprehensive detection technology

In fact, no matter which detection method has certain limitations, it cannot objectively, comprehensively and truly reflect the operating status of electrical equipment switch cabinets, and there may be misjudgments. Due to the different release forms of discharge energy, the practicability and sensitivity of various detection methods are also different, so in the process of partial discharge detection of the switchgear, the above detection methods should be comprehensively applied, mainly ground wave detection, ultrasonic detection And UHF detection is supplemented.

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