Criteria for estimation of end of life of power and station transformers in service

Power and station transformers are among the more expensive and critical elements of a power system. In principle, ensuring the reliability of power transformers is a two-step process, involving the detection of an impending failure in its formative stage so as to preclude catastrophic failures and if, for any reason, an outage occurs, evolving an appropriate replacement strategy of the failed units in a minimum possible time. In diagnostic testing, physical parameters used as indices of impending failure shall be sensitive to the amount of ageing and shall possesses a reasonably high degree of correlation with dielectric strength and mechanical strength. Concerted research work is being carried out to try and identify such properties of insulation as are sensitive to the amount of degradation. The authors of this paper aim to suggest techniques for acquisition and analysis of ageing data in order to propose a condition-monitoring schedule.