On-line Monitoring of Power Transformers:

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-the Issues, the Technology, and its Role in Strategic Risk Mitigation-

Trevor LORD and Graham Hodge (LORD Consulting)

October 2007

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1. Abstract

Transformers are vital components in our aging power network infrastructure. They often give little outward warning of
impending failure. The failure frequency in older transformers requires a different approach to monitoring, in particular
the need to sample more frequently if not continuously. Strategies that worked for the fi rst half of the asset’s life are not
necessarily appropriate for the second half. The increasing availability of on-line monitoring systems can assist detecting
potentially damaging faults in transformers early enough to take appropriate offsetting action. This paper overviews typical
failure mechanisms in large power transformers and their associated auxiliary components and reviews some of the on-line
monitoring systems now available.