Transformers is one of the key equipment of the power system. Power rating of the transformers varies from KVA to several hundreds of MVA. The transformer is expensive equipment of the power system. Failures of transformer usually lead to substantial profit loss to the utility, potential environmental damage, explosion and fire hazards and expensive repairing or replacement costs, thus, it is desirable that the maximum service life of transformer is required. Condition monitoring of transformer can help to increase the life of the transformer and reduce the maintenance cost. Online monitoring is the record of significant data of a transformer and analysis of data and including the history of the transformer. In this paper percent the different techniques adopted for condition monitoring of transformer.

power system, transformers, preventing transformer failure