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Switchgear partial discharge detection method

time:2020/7/1   source:华天电力  reading:300 time

For switchgear, its partial discharge detection methods include the following:

1. Ground wave detection generates electromagnetic waves when partial discharge occurs in the insulating layer of the high-voltage switchgear, and the metal shell of the switchgear will shield this electromagnetic wave for a large part, but a small part will still pass through the joint of the metal shell Or the gas-insulated switch gasket propagates out, and a ground wave will also be generated to be transmitted to the ground through the outer surface of the metal shell of the device. The range of ground waves is usually a few millivolts up 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 the partial discharge activity.

2. Ultrasonic testing Ultrasonic testing is actually a type of mechanical vibration wave. From the perspective of energy, the process of partial discharge is the process of instantaneous energy burst, and the electrical energy is released in the form of sound energy, light energy, heat energy and electromagnetic energy. The electrical breakdown occurs in the air gap, and 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 discharge center will expand due to the heat energy, and spread outward through the sound wave. The gas in the propagation area is After heating, an isothermal zone is formed, and its temperature exceeds the ambient temperature; when these gases begin 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. Ultrasound The frequency is greater than 20kHz. Because the area of partial discharge is relatively small, the PD source is a point source.

3. During the time change of the UHF detection method, the electromagnetic vibration generated by the partial discharge will generate electromagnetic waves. In solid gas and gas media, the partial discharge pulses will generate very rich electromagnetic wave UHF components, up to a few GHz . In the actual application process, the detection of the partial discharge signal can be carried out by using two probes. The time sequence of the signal detected by the probe is used as the basis for judgment. The distance of the power supply is closer, it will be detected first; the position of the probe continuously changes, you can Judge the approximate location of the power supply gradually. Or through multiple probes, the time difference equations of the partial discharge signals detected by the probes can be used to find the three-dimensional space coordinates of the discharge source, and finally determine the discharge source. The sensitivity of this method is relatively high, and it has strong anti-interference ability, and there are usually joints or small glass windows on the switchgear. It is not necessary to consider the requirement of this method that it is difficult to detect under completely sealed conditions.

4. The comprehensive detection technology actually has certain limitations regardless of which detection method, it cannot objectively, comprehensively and truly reflect the operation state of the switchgear, and there may be a possibility of misjudgment. Due to the different discharge types of energy discharge types and the differences in the practicality and sensitivity of various detection methods, in the process of partial discharge detection of switchgear, the above detection methods should be comprehensively applied, mainly ground wave detection, ultrasonic detection And ultra-high frequency detection as a supplement.

5. Partial discharge analysis technology Specifically, the commonly used partial discharge analysis technology includes the following: First, the lateral analysis method, that is, to make a horizontal comparison of the test results of the switchgear in the same switch room, if one of the switchgears The test result is greater than the field background value and other switch cabinet test results, you can determine that the device may be defective; Second, the trend analysis method, analyze the test results of the same switch cabinet at different times, make a longitudinal comparison of the switch cabinet Operating trends. Detect the switchgear in the switch room according to a specific cycle, retain the test results of each time, and then analyze the trend of partial discharge state of the device based on the test results; third, threshold comparison, that is, to provide a judgment threshold, compare it with The test results of the switchgear are compared, and the analysis results determine the running state of the switchgear. The judgment can be made based on the following: when the background value and test value of the switch room are below 20dB, the switchgear is normal, and the inspection will be conducted again next month; the background value of the switch room is below 20dB, and the test value of some switch cabinets is 20 ~30dB, pay more attention to the switchgear, shorten the detection period, and observe the change trend of the detection amplitude; if the background value of the switch room is below 20dB, and the test value of some switchgears is greater than 30dB, the switchgear has a partial discharge phenomenon , Positioning technology should be used to locate the discharge point. <BR> In short, partial discharge shows a certain complexity. Generally, partial discharge is prone to occur in the location where the breakdown field strength is relatively low inside the insulation, and the electric field distribution inside the insulating medium and the electrical properties of the insulation are all responsible for partial discharge. Conditions play a decisive role. In the actual detection process, it is necessary to select a reasonable and applicable detection method and analysis method to eliminate the fault in a timely manner and ensure that the switchgear is in a good operating state.

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