Relationship between the paper covering thickness of the electrode and the development of the surface flashover at impulse voltages

The surface flashover (SF) is one of the main causes of the breakdown in high voltage devices insulated with composite materials such as oil/cellulose system. It is highly probable that the SF can be initiated in the oil near the highly stressed electrode then propagates along the oil solid interface to the ground. In this paper the development of the streamer in oil to a creep discharge or surface flashover is qualitatively analyzed, as well as its relationship to the thickness of the paper covering the high voltage electrode. A sphere plane electrode configuration and impulse voltage were used for the investigation. The experimental result has shown a tendency of a thicker paper covering of the high voltage electrode to lower the partial discharge level thus decreasing the probability for the discharge to develop as a surface flashover. The puncturing of the paper seems to be the main cause of the breakdown. This is explained by the facility of the streamer to extract the discharge from the metal source in the punctured region of the electrode.