Diagnosis of degradation effects of on-load tap changer in power transformers

By performing diagnostics on on-load tap changers by means of dynamic resistance measurements a condition diagnosis of high-speed resistor-type tap changers can result in pre-failure detection of contact degradation. It provides the measurement parameters that are most suitable for detecting these defects, such as the presence of a contact film, contact wear and pitting. The resistance curves of OLTCs are interpreted, to determine the occurring degradation mechanisms, which can be used to support strategic decisions about the maintenance or overhaul of the tap changer.