FAILURE MECHANICS OF ALUMINIUM WOUND DISTRIBUTION TRANSFORMERS DUE TO MECHANICAL STRESSES

Abstract

The reliability of Power Distribution System depends upon the reliability of Distribution Transformers. It is essential that a transformer gives a reliable and efficient performance during normal service. Failure of Distribution Transformers causing concern to the Electricity utilities and other users. Damage to the distribution transformers causing loss in the country affecting agricultural, industrial production etc. For these reasons, the concern towards the causes of failure of Distribution transformers is increasing. In this thesis work, the mechanical stresses developed due to the short circuit current responsible for the early failure of Distribution Transformers (DTs) are calculated; the data has been collected from UP and Punjab Electricity Boards. Special attention has been given to the inrush conditions in Distribution Transformers. Inrush currents are mainly encountered due to repeated switching operations which are more in India. An algorithm has been presented to estimate the probability of dangerous switch in and loss of life of DTs due to inrush current for different remanent flux values, with the help of transformer design parameters. Experiments has been performed for tensile testing, chemical composition analysis of the aluminium conductor used in the windings of the DTs. Tensile strength, chemical composition has been analyzed using the experimental results. Creep Phenomenon may be one of causes of the early failure of the Distribution Transformers, has been experimentally performed for different temperatures and stresses combinations. The effect of increasing temperature and stress on the creep of aluminium has been examined. The creep rate without flow of current and with flow of current has been compared with the help of the experimental results obtained. The increase in creep rate with the increase in the magnitude of the pulse current has been discussed.