Partial discharge refers to localized electrical breakdown within insulating materials of high-voltage equipment that does not fully bridge the insulation between two conductors

1. Internal cavities & voids
Gas-filled gaps left during insulation casting, molding or impregnation trap air; air breaks down at lower voltage than solid insulation to trigger discharge.

2. Contaminants and impurities
Foreign particles, moisture or residual metal fragments embedded inside insulation distort local electric field concentration.

3. Sharp conductor edges / surface burrs
Irregular metal protrusions create extremely high localized electric field, inducing corona-type partial discharge in surrounding air.

4. Insulation aging & mechanical damage
Thermal cycling, vibration or mechanical stress produces tiny cracks inside insulating materials and forms air gaps over long operation.

5. Poor manufacturing & assembly defects
Incomplete resin pouring, loose fitting and improper component installation leave hidden gaps between different insulating layers.

6. Excessive operating voltage & overvoltage
Surge overvoltage or sustained overrated operating voltage boosts electric field beyond the withstand limit of defective insulation sections.

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