Partial discharge is mainly the discharge of the internal insulation of transformers, transformers and other high-voltage electrical equipment under the action of high voltage. This discharge only exists in a local part of the insulation and will not immediately form the entire insulation breakdown or breakdown. Flashover is called partial discharge. The amount of partial discharge is very weak. It is not noticeable by human intuition, such as seeing and hearing. Only highly sensitive partial discharge measuring instruments can detect it.

The internal insulation of the transformer is under the effect of working voltage for a long time during operation, especially with the increase of the voltage level, the electric field strength of the insulation is very high, and it is easy to produce partial discharge at the weak insulation. The reason for the partial discharge is: electric field It is too concentrated at a certain point, or the electric field intensity at a certain point is too strong, such as solid media with bubbles, impurities not removed, oil in water, gas, and suspended particles. In different media combinations, there is serious electric field distortion at the interface , The traces of partial discharge often leave only a small spot on the solid insulation, or a dendritic burn mark, while in the oil, some decomposed small bubbles appear.

Although the partial discharge time is short and the energy is small, it is very harmful. Its long-term existence will cause greater damage to the insulating material. First, the insulating material adjacent to the partial discharge is directly bombarded by the discharge particles. Cause local insulation damage. The second is the chemical action of heat, ozone, nitrogen oxide and other active gases generated by the discharge, which causes the local insulation to be corroded and aged, and the conductivity increases, which eventually leads to thermal breakdown, and the aging of the internal insulation of the transformer in operation. And damage, mostly starts from partial discharge.

The detection methods of transformer partial discharge generally include:

1. Electrical measurement method, using oscilloscope or radio interference meter to find the characteristic waveform of discharge or the degree of radio interference.

2. Ultrasonic measurement method detects the sound waves appearing in the discharge, converts the sound waves into electric signals, and records them on a tape for analysis. Using the difference in the transmission time of the electric signal and the sound signal, the distance from the detection point to the discharge point can be obtained.

3. The chemical measurement method detects the content of various dissolved gases in the oil and the law of increase or decrease. This method can find changes in the composition, proportion and quantity of the oil, so as to determine whether there is partial discharge (or local overheating).

In addition, in recent years, an on-line partial discharge detector has been developed to automatically detect partial discharge during transformer operation.

In order to prevent the occurrence of partial discharge, the manufacturing unit should carry out reasonable structural design of the transformer, careful construction, improve the purity of the material, and strictly deal with the quality of each link. The operation unit should strengthen the maintenance and monitoring of the transformer to effectively prevent the partial discharge of the transformer happened.