Status and trends in transformer monitoring

A manufacturer's view on transformer monitoring is presented. Based on a review of the changes occurring on the electricity market, monitoring of transformers is discussed emphasizing its commercial aspects. Definitions of the words "monitoring" and "diagnostics" are proposed, and it is stressed that the key issues related to on-line monitoring are reliability and low cost. A survey of the most important methods for on-line monitoring and off-line diagnostics is given. The area of life assessment is discussed, and in particular, the difference between end-of-life of the insulating material and of the transformer is emphasized.