Partial discharge is mainly discharged by high-voltage electrical engineering equipment such as transformers and transformers under high voltage. Discharge occurs inside the insulation. For example, partial discharge only exists in the insulation part, and the insulation does not immediately pass through the formation of overall breakdown or flashover, which is called partial discharge. The local discharge is very weak and can be felt by human intuition. If eyes and ears cannot be detected, only sensitive partial discharge testers can detect them.
The internal insulation of a transformer is under the action of operating voltage for a long time during operation, especially as the voltage level increases, the electric field strength of the insulation is very high. Parts with weak insulation are prone to partial discharge. The reason for partial discharge is that the electric field at a certain point is too concentrated, 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; Oil contains water, gas, and suspended particles. The combination of different media also has severe electric field distortion at the interface. The trace of partial discharge usually leaves only a small spot on the insulating layer of solid material, or through a dendritic burning trace. Although partial discharge time is short and energy is small, it is very harmful. Its long-term existence can cause great damage to insulating materials. Firstly, the insulating material adjacent to the partial discharge is directly bombarded by the discharge particles, resulting in local insulation damage. The second is the chemical action of active gases such as heat generated by discharge, ozone, and nitrogen oxides. Local insulation is corroded and aged, resulting in an increase in electrical conductivity, which ultimately leads to thermal breakdown. During the operation of transformers, the internal insulation is deteriorated and damaged, mostly due to partial discharge startup. The research on partial discharge detection techniques and methods for transformers generally includes:
(1) Electrical measurements. The characteristic waveform or radio interference level of the discharge is detected by a partial discharge detector (also known as a partial discharge tester).
(2) The ultrasonic measurement method detects sound waves. When the sound waves are converted into electrical signals, an electrical discharge occurs. The time difference is used to analyze the transmitted acoustic signals of the electrical signals, and 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 the oil and their change and development rules. This test method can detect the composition, proportional relationship, and changes in the number of enterprises in oil products, thereby improving the judgment of whether there is partial discharge (or partial overheating)