In the insulation diagnosis of high-voltage electrical equipment, partial discharge detection is one of the most technically advanced and reflective test items of the internal insulation state. It measures not the breakdown of the entire insulation, but the tiny discharge that occurs in a local area inside the insulation - this discharge has a charge of only a few to several hundred picograms at a time, which cannot be detected by the naked eye or ordinary instruments. However, long-term sustained partial discharge will slowly erode the insulation like a file, ultimately leading to insulation breakdown failure.

What is partial discharge

Partial discharge (PD) refers to the discharge that occurs in a localized area inside or on the surface of an insulation of electrical equipment. This discharge does not penetrate the entire insulation and does not immediately cause breakdown, but each discharge erodes the insulation material. The most typical example is the discharge in the bubbles inside the insulator - tiny bubbles mixed in during the winding process first break down under high electric fields, and the discharge energy carbonizes the material on the inner wall of the bubbles, gradually expanding and eventually forming a discharge channel.

Why must it be tested before leaving the factory

Insulation defects in high-voltage equipment such as transformers, cables, transformers, and bushings often exist during the manufacturing stage and cannot be detected by the naked eye. According to national standards such as GB 1094.3, the partial discharge capacity of 220kV and above transformers must be ≤ 10pC when they leave the factory, which requires the sensitivity of the detection instrument to reach the picoku level. The maximum sensitivity of HZJF-9041D can reach 0.02pC, with a measurement range covering 0.1pC to 10000nC, fully meeting the full range of requirements from research and development to factory inspection. It is a universal testing tool for power departments, manufacturers, and research institutes.