Transformer insulation life assessment

This paper presents novel techniques for life assessment of the insulation of the generator stepup units in power plants. Load and ambient temperatures are two important factors that influence the life of insulation in transformers. Hourly load and ambient temperatures obtained through condition monitoring are used to assess the operating profile of the equipment. Modeling techniques for estimating load factors and the ambient temperatures using the operating history are discussed in this paper. The estimated load factors and ambient temperatures are input to the IEEE life consumption models to assess the consumed life of insulation. A full simulation approach and a renewal process approach have been presented to evaluate the time to failure of the insulation. Estimation of some relevant reliability parameters such as B_X life, time-to-reach design life, and probability of failure at a given time are also presented. The methods discussed are useful for estimating residual life of insulation to support the repair and maintenance policies of transformers.