The impact of oil decay on gassing and reliability of aging power transformers

The cause of incipient electrical failures that generate gas evolvements in high voltage power transformers is currently diagnosed by interpreting the results of dissolved gas analysis (DGA). According to the existing condition-based maintenance procedures for liquid insulation, there is no relationship between the gassing tendency of oil and its degree of aging. Incipient electrical failures are considered to be solely responsible for the dissolved gas content of oil. Over the past years progress has been made in the testing procedures for insulating oils which has provided evidence that in certain cases the reclamation of aged oils reduces the level of gases generated by this complex blend of hydrocarbons. Thus, by selectively removing decay products from oils in service, the interpretation of DGA can be significantly improved and the cost effectiveness of reclamation technology economically justified. This paper intends to present evidence that besides incipient electrical failures, the purity of liquid insulation also plays a role in gas evolvement under electric and thermal stress.