Risk of casing surface cracks and dirtAddtime：2015/3/27 

casing surface dirt will enable the flashover voltage (i.e. flashover lowest voltage) is reduced, if dirty wet surface, flashover voltage is lower. At this time, the line if there is a certain value of the overvoltage invade, that is caused by flashover. Flashover has the following hazards:  (1) caused by grid grounding fault protection action caused, tripping of the circuit breaker; < / P >  < Br (2) on the surface of the casing damage, become the future may produce a factor of insulation breakdown.  casing surface dirt to absorb moisture, improve the conductivity, the leakage current increases, the insulating casing heat, there may make the casing inside cracks and finally lead to the breakdown. The crack of

casing can decrease the electric strength of the resistance.. Because the crack filled with air, the air dielectric coefficient is small, the porcelain casing parts of porcelain dielectric coefficient is big, and the distribution of electric field strength, electric field strength of low dielectric constant, dielectric coefficient of the electric field intensity is small, cracks in the electric field intensity high to a certain value, the air is free, caused by partial discharge, causing further damage to the insulation until the complete breakdown of the. When the crack enters the water freeze, it may also split the casing..