During the production of generator stator bars, there may be air gaps or impurities between insulation layers or between insulation layers and strands due to technological reasons. Under the combined action of electricity, heat and mechanical force, KCB6743A will directly or indirectly lead to insulation deterioration, resulting in a new air gap between insulation layers. Because of the different dielectric coefficients of air gap and solid insulation, the electric field distribution of this sandwich medium composed of air gap (impurity) and insulation is uneven. Under the action of electric field, when the working voltage reaches the initial discharge voltage of air gap, partial discharge occurs. The initial voltage of partial discharge is closely related to the dielectric constant and air gap thickness of insulating materials.

The partial discharge of gas in air gap belongs to streamer high-voltage glow discharge, and a large number of high-energy charged particles (electrons and ions) hit the main insulation at high speed, thus destroying the molecular structure of insulation. In the air gap where partial discharge occurs in the main insulation, the local temperature can reach 1000℃, which deteriorates the insulation of adhesive and stranded wire, leads to loose stranded wire and short circuit between strands, leads to local overheating and hot cracking of the main insulation, and finally damages the main insulation. The further development of partial discharge is to produce dendritic discharge in insulation, which further deteriorates the main insulation and eventually forms discharge channels and destroys insulation.