Dielectric Behavior of the Coolant for a Gas Insulated HVDC Thyristor Valve

The objective of this paper is to report on studies made on a fullscale model of the coolant system for a gas insulated, fluorocarbon liquid cooled HVDC thyristor valve. Confidence in the selection of the coolant system and its associated dielectric containment structure stemmed from the parametric study of the coolant, and the more than adequate dielectric strength of the coolant even when it was in the cavitated state. An explanation is proposed on the apparent anomoly of the exceptional dielectric strength of the system, even when bubble nucleation is induced by the injection of a dielectrically weak (nitrogen) gas into the flowing coolant.