Assessment of AgedInsulating Oil of Transformer in Service for Ranking of Health Condition

Power transformers are the most critical machinery in power transmission and distribution system. Failure of a transformer causes huge loss of revenue and also affects the reliability of power supply to the consumers. With the increasing population of transformers in service and their extended operating duration, extensive care is being paid on their reliability and availability. The health status of transformer is needed to be ascertained in order to avoid any possible outage and decide a suitable maintenance schedule. Insulating oil is one of the most important components of a transformer. There is a need for continuous monitoring and assessing ageing tendency of insulating oil as an essential part for estimating remaining life of a power transformer. This paper presents the concept of Ageing Index through relative scoring of various oil parameters like Acidity, Interfacial tension, Breakdown voltage, Water content and Tan delta through a scheme that combines theses results of routine oil tests. A simplified software program is used for analyzing the results of routine oil parameter testing. This paper includes a case study on several power transformers that are in continuous service with commissioning period ranging from year 1956 to 2016.