Electrical tree inception characteristics of XLPE insulation under power-frequency voltage and superimposed impulse voltage

This paper deals with treeing inception voltage characteristics of XLPE cable insulation subjected to impulse voltage superimposed on power-frequency voltage. The tree initiation tests were performed on specimens removed from a section of 220 kV transmission cable. The impulse inception strength of an electrical tree was found to be dependent on the pre-applied power-frequency stress and the relative polarity of the superimposed impulse voltage. Besides, it also shows an obviously accumulative effect and tree inception delay. These phenomena are discussed in connection with the space charge effect