Design Insulator (electricity)

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high voltage ceramic bushing during manufacture, before glazing.


the electrical breakdown of insulator due excessive voltage can occur in 1 of 2 ways:



a puncture arc breakdown , conduction of material of insulator, causing electric arc through interior of insulator. heat resulting arc damages insulator irreparably. puncture voltage voltage across insulator (when installed in normal manner) causes puncture arc.
a flashover arc breakdown , conduction of air around or along surface of insulator, causing arc along outside of insulator. insulators designed withstand flashover without damage. flashover voltage voltage causes flash-over arc.

most high voltage insulators designed lower flashover voltage puncture voltage, flash on before puncture, avoid damage.


dirt, pollution, salt, , particularly water on surface of high voltage insulator can create conductive path across it, causing leakage currents , flashovers. flashover voltage can reduced more 50% when insulator wet. high voltage insulators outdoor use shaped maximise length of leakage path along surface 1 end other, called creepage length, minimise these leakage currents. accomplish surface moulded series of corrugations or concentric disc shapes. these include 1 or more sheds; downward facing cup-shaped surfaces act umbrellas ensure part of surface leakage path under cup stays dry in wet weather. minimum creepage distances 20–25 mm/kv, must increased in high pollution or airborne sea-salt areas.



suspension insulator string (the vertical string of discs) on 275 kv suspension pylon.



suspended glass disc insulator unit used in suspension insulator strings high voltage transmission lines








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