Dynamics of leakage current in LDPE under different types of high field application

For high voltage dc cable insulation, LDPE is considered as a prospective material. With increasing voltage levels of power transmission, the need for understanding high filed phenomena is also increasing. In general a strong interrelation among leakage current, space charge, breakdown and ageing of insulation is believed to exist. The leakage or conduction current in LDPE is very important due to the fact that it is linked to charge accumulation in it. It is of very interesting to observe current dynamics in LDPE at high fields due to the fact that charge packets emerge from electrodes and move into the insulation - a phenomena known as packet charge formation. In the present paper authors report long-term current measurements on thin LDPE samples under different types of electric field application. The measurements are performed using a guarded three-terminal electrode system. The difference in current profiles between short duration voltage application and long duration application has been examined. A significant difference has been observed in the leakage current profiles for different voltage time durations and different history of voltage application which may indicate different type of charge formation.