It is important to understand the surface breakdown characteristics and the surface discharge behavior of ethylene propylene rubber（EPR） insulation material. For this purpose

three different electrode structures

namely

plane to plane electrode

rod to ring electrode

and needle to plane electrode

have been chosen to simulate different electric field distribution. During the experiment

surface breakdown voltage and breakdown tracking under three different electrode structures

by which AC voltage and negative polarity DC voltage are applied

respectively

are measured and analyzed. Then

the discharge patterns of surface discharge under different AC voltage levels are measured

and inception and development processes of surface discharge are also analyzed. The experimental results show that the increase of surface discharge voltage magnitude becomes higher when the electric field distribution is more uniform. Under plane to plane electrode

the inception discharge voltage depends on the gap distance of two electrodes. Moreover

under rod to ring electrode and needle to plane electrode

the inception discharge voltage magnitude is closely related to the inception voltage magnitudeof corona

ranging from 1.9 k V to 2.4 k V. The discharge type and discharge pattern are also different under different electric field distribution and discharge stages. The magnitude of discharge pules is small at the beginning of the surface discharge

about 1.2 V. When the flashover occurs

the discharge distribution is more scattered

and the magnitude of discharge pulses rises to about 43 V. From the above mentioned

the severity degree of surface discharge development can be discriminated.