Internal Corona Spaces in Cables Manometric Detection of Internal Corona and Autographic Mapping of Corona Spaces

This paper describes two methods of studying corona spaces in cables between insulation and conductor. The manometric method makes it possible to determine the internal corona level unambiguously. Effects of outside electrical disturbances are excluded. There appears to be no upper voltage limit to the applicability of this test. It is performed by observing on a sensitive manometer the pressure decrease inside the cable that results from absorption of oxygen activated by corona discharge. These studies have been carried out principally with polyethylene, but also with rubber, polyvinyl chloride, silicone, Teflon, and glass. In the autographic method silver is deposited on all copper surfaces accessible to the silver cyanide solution. This clearly maps the projection of the corona spaces on the conductor. The method is extremely simple and the results are direct and conclusive.