Generation and prevention of partial discharge in transformer

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, partial discharge only exists at the position of the insulation, and the insulation does not immediately pass through the formation of the whole breakdown or flashover, that is, the so-called partial discharge. The amount of partial discharge is very weak, which can be felt by human intuition. If the eyes and ears cannot be detected, only a sensitive partial discharge tester can detect it. The internal insulation of transformer is under the action of working voltage for a long time in operation, especially with the improvement of voltage level, the electric field strength of insulation is very high. Partial discharge is easy to occur at weak insulation. The reason for 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 large. If there are bubbles in the solid medium, the impurities are not removed; The oil contains water, gas and suspended particles. The combination of different media also has serious electric field distortion at the interface. The trace of partial discharge often leaves only a small spot on the insulation of solid materials, or through dendritic burn marks. Although the partial discharge time is short and the energy is very small, it is very harmful. Its long-term existence will cause great damage to insulating materials. First, the insulating materials adjacent to partial discharge are directly bombarded by discharge particles, resulting in damage to partial insulation. The second is the chemical action of heat, ozone, nitrogen oxide and other active gases produced by discharge. The local insulation is corroded and aged, the conductivity increases, and finally leads to thermal breakdown. During the operation of transformer, the internal insulation is aged and damaged, most of which comes from partial discharge startup. The research on the detection technology and methods of transformer partial discharge generally includes: (1) electrical measurement. The characteristic waveform or radio interference degree of discharge is detected by partial discharge detector (also known as partial discharge tester). (2) The ultrasonic measurement method detects the sound wave and the discharge occurs when the sound wave is converted into an electrical signal, which can be obtained from the detection point to the discharge point by analyzing the transmitted acoustic signal of the electrical signal by using the time difference. (3) Chemical measurement method. Detect the content of various soluble gases in the oil and the change and development law of increase and decrease. This test method can find the composition, proportion relationship and changes in the number of enterprises in the oil, so as to improve the judgment of whether there is partial discharge (or partial overheating).