Partial discharge is mainly through transformers, transformers and other high-voltage electrical engineering equipment under the action of high voltage. Discharge occurs inside the insulation. For example, the partial discharge only exists in the insulation position, and the insulation does not immediately pass through the formation of the entire breakdown or flashover, which is the so-called partial discharge. The amount of partial discharge is very weak, and it is felt by human intuition. If the eyes and ears cannot detect it, only a sensitive partial discharge tester can detect it.
The internal insulation of the transformer is under the action of the working voltage for a long time during operation, especially with the increase of the voltage level, the electric field strength value of the insulation is very high. Partial discharge is easy to occur in weak insulation. The reason for the partial discharge is that the electric field is too concentrated at a certain point, or the electric field intensity at a certain point is too strong. If there are bubbles in the solid medium, the impurities have not been removed; the oil contains water, gas, and suspended particles. The combination of different media also has severe electric field distortion at the interface. The traces of partial discharges often leave only a small spot on the solid material insulation, or through a dendritic burn mark.
Although the partial discharge time is short and the energy is small, it is very harmful. Its long-term existence will have a greater destructive effect on insulating materials. One is to cause the insulating material adjacent to the partial discharge to be directly bombarded by the discharge particles to cause damage to the local insulation. The second is the chemical action of heat, ozone, nitrogen oxide and other reactive gases generated by the discharge. The local insulation is subject to corrosion and aging, and the conductivity increases, which eventually leads to thermal breakdown. During the operation of the transformer, the internal insulation is aging and damaged, most of which come from partial discharge initiation.
The research on the detection technology method of transformer partial discharge generally includes:
(1) Electrical measurement. Use a partial discharge detector (also called a partial discharge tester) to detect the characteristic waveform of the discharge or the degree of radio interference.
(2) Ultrasonic measurement method. The sound wave is detected and the sound wave is converted into an electric signal to generate discharge, and the transmitted sound signal can be obtained from the detection point to the discharge point by analyzing the electric signal by using the time difference.
(3) Chemical measurement method. Detect the content of various soluble gases in the oil and the law of change and development of the increase and decrease. This test method can find changes in the composition, proportions, and the number of companies in the oil. This improves the determination of whether there is partial discharge (or local overheating).