Partial discharge is mainly discharged under the action of high voltage through high-voltage electrical engineering equipment such as transformers and transformers. The discharge occurs inside the insulation. For example, partial discharge only exists in the insulating part, and the insulation does not immediately pass through to form an overall breakdown or flashover, that is, the so-called partial discharge. The amount of partial discharge is very weak and can only be detected by a sensitive partial discharge tester.

The internal insulation of the transformer is under the action of the working voltage for a long time in operation, especially with the increase of the voltage level, the electric field strength of the insulation is very high.

Partial discharges are prone to occur in places with weak insulation. The reason for partial discharge is that the electric field at a certain point is too concentrated, or the electric field strength at a certain point is too large. If there are air 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 severe electric field distortion at the interface.

Traces of partial discharge usually leave only a small spot on the insulating layer of solid material, or through dendritic burn marks. Although the partial discharge time is short and the energy is small, it is very harmful. Its long-term existence will cause great damage to the insulating material. First, the insulating material adjacent to the partial discharge is directly bombarded by the discharge particles, resulting in partial insulation damage. The second is the chemical action of the heat generated by the discharge, ozone, nitrogen oxides and other reactive gases.

Local insulation is corroded and aged, conductivity increases, and eventually thermal breakdown occurs. During the operation of the transformer, the internal insulation is aged and damaged, most of which are caused by partial discharge startup. The research of transformer partial discharge detection technology and method generally includes:

(1) Electrical measurement. The characteristic waveform of the discharge or the degree of radio interference is detected by a partial discharge detector (also known as a partial discharge tester).

(2) The ultrasonic measurement method detects the sound wave. When the sound wave is converted into an electrical signal, discharge occurs. Using the time difference to analyze the transmitted sound signal of the electrical signal, the time from the detection point to the discharge point can be obtained.

(3) Chemical measurement method. Detect the content of various soluble gases in oil and the development law of increase and decrease. This test method can discover the composition, proportional relationship and change of the number of enterprises in the oil, thereby improving the judgment of whether there is partial discharge (or partial overheating)