PURPOSE: To add a specific quantity of polyoxyethylene alkyl phenyl ether to an electric insulating oil consisting essentially of a mineral oil, thereby to improve the charge preventing characteristic of the composition without lowering the electrical characteristic thereof.
CONSTITUTION: As a charge preventing agent 1 to 1000 ppm of polyoxyethylene alkyl phevyl either is added to an electric insulating oil composed essentially of a mineral oil. Polyoxyethylene alkyl phenyl ether is represented by the formula shown in right hand, where R is a saturated or unsaturated alkyl group having 7 to 11 carbon atoms in a molecule and n and m are integers, respectively, in the range of from 2 to 15, in average, as total sum, and, for instance, suitable are polyoxyethylene nonyl phenyl ether added with 5 to 10 moles of ethylene oside per mole, and the like. To the insulating oil, alkyl benzene in a quantity of 5 to 50 % by weight with respect to the full part of the oil may be added. This insulating oil can be circulated at high speeds and can carry out excellent cooling of electric apparatuses.
TANII TAKESHI
IWATA NORIYUKI
ISHIOKA YASUAKI
