By hvhipot 
If containing gas in the liquid and solid electrolyte composition, as a result of the gas breakdown strength relative to the solid and liquid medium, the breakdown of the electric field is low, so this part within the medium gas breakdown, easy to result in gas or liquid discharge, appeared in the insulation of internal partial discharge occurs, call partial discharge, Although this partial discharge does not lead to the whole insulation layer through, but partial discharge will also bring great harm, partial discharge will cause the deterioration of the dielectric accelerated, and eventually lead to the breakdown of the whole medium.
Generally, the mechanism of dielectric damage caused by partial discharge can be expressed in the following three aspects:
1, the effect of electricity, charged particles by the action of the electric field will be high-speed movement directly to impact the medium, so that some substances in the medium fracture and decomposition;
2, the effect of heat, charged particles under the action of the electric field on the medium molecule impact and thermal effect, making the temperature of the medium rise, part of the medium thermal decomposition;
3, chemical action, due to the decomposition of the medium and produce some new substances, these substances contain some of the molecules of the candle nature, which is a very dangerous substance.
Under the condition of general operating voltage, partial discharge can only occur in some insulation layer peeling, impurities, cracks or pores at the interface.
If there are some micropores in the insulation or there are pores in the insulation between the semiconductor layers, the partial discharge will lead to the rapid decline of the insulation performance, thus accelerating the aging process, and eventually lead to insulation failure.