Energy is one of the basic data for economic and social development. Sufficient electrical energy, high quality, continuous, low-cost and environmentally compatible manner should be available to consumers. Power system reliability depends on the reliability of the equipments in the system. For this reason, transformers of the power system are the most important equipments. In power transformer, failure rate is quite high compared to that in some parts of the world; and as such, the necessity to work in the best operation case of transformer and preventing transformer failures have obviously emerged. This study proposes the failure of insulating oil in power transformers. However, the electrical and thermal effects of cellulosic materials subjected to degradation have been analyzed in details and these gases emission show different type of failures. Also, these failures are seen in the production rate point to the magnitude of the failures. Analysis of failures using Fuzzy logic computer program have been tried in order to achieve the optimum method of evaluating the causes that play a role in the formation of probable transformer failures.

Key words: Power transformers, gases, fault analysis, Fuzzy expert system.