Patent ID: 9228992
Filing Date: 2016-01-05
CPC Classification: G01N

Claim Text:
1. An electric insulating oil inspection method for determining whether or not an inhibitor-consuming substance is present in an electric insulating oil, said inhibitor-consuming substance being such a substance that causes to decrease over time a concentration of an inhibitor which is added to said electric insulating oil to inhibit generation of copper sulfide on an insulating paper immersed in said electric insulating oil, the electric insulating oil inspection method comprising: a first step of preserving said electric insulating oil at a temperature of at least 40° C. but not higher than 60° C. and measuring the concentration of the inhibitor; and a second step of determining that the inhibitor-consuming substance is present in the electric insulating oil upon condition that a decrement of the concentration of the inhibitor relative to an initial concentration thereof becomes not less than a specified amount within a predetermined period, said inhibitor being a benzotriazole compound, and the inhibitor-consuming substance being determined to be present at said second step upon condition that a decrease ratio of the concentration of the inhibitor in the electric insulating oil after 10 days from the start of inspection is greater than 10%.