Degradation in dielectric strength of FRP insulators and its countermeasure in a static Scherbius system speed controller of the JT-60 motor generator

Degradation in dielectric strength of FRP (fiber reinforced plastic) insulators was examined and its countermeasures were taken in a static Scherbius system speed controller of a motor generator for the JT-60 NBI and RF heating devices. Deliquescent substances such as CaCl2 and Ca(NO3)2 were detected on surfaces of the FRP insulators by X-ray photoelectron spectroscopic analysis. Hence, it is concluded that the degradation of the insulator was caused by these deliquescent substances adsorbing water at high humidity. It is estimated that these deliquescent substances were made by chemical reactions between calcium carbonate contained in FRP and acid substances contained in the cooling air introduced from outside of the MG building. The acid substances originated in slime - preventive chemicals used in the secondary cooling tower located near the MG building. Therefore, the insulators are replaced with new ones of calcium carbonate free FRP for maintaining the dielectric strength of the insulators at a good level. (author)