Aging assessment of transformer solid insulation: A review

Abstract

Power transformer is one of the key equipment in electrical transmission and distribution network. Most of power transformers, cellulose made solid and petroleum extracted liquid as chief insulation. In transformers, liquid insulation plays a vital role in providing insulation as well as cooling. There are mainly few mechanisms that exposed to the insulation degradation because of the aging, high temperature and chemical reactions such as the hydrolysis, oxidation and pyrolysis. The condition of oil has to be checked on the basis of repeatedly and retrieved when it necessary, to avoid the quick failure of transformer. Failures of transformer can have controlled to strong effect on security, reliability of power supply and cost. Because of higher operating temperature earlier degradation of paper/oil insulation system of transformer leads to variation in some insulation characteristics, therefore remaining life time of power transformer is degraded. Conventional time-based maintenance and subsequent replacement is not possible for transformer safety. Online monitoring and condition based maintenance are necessary. Various electrical and chemical diagnostic techniques are existing for monitoring of insulation condition of power transformers. This paper presents a study of generally used solid insulation diagnostics techniques along with their analysis its schemes.