On-load tap changer diagnosis with dynamic resistance measurements

A modern tendency is to perform condition-based rather than time-based maintenance on power transformers. This requires the use of diagnostic measurements to know the condition of the tap changer and to determine when and what kind of maintenance is necessary. In addition, diagnostic measurements on OLTCs can be used for the pre-failure detection of defects not seen during maintenance and to assess the condition of parts that are not easily accessible. A number of diagnostic tests can be performed and utilities combine different tests to determine its need for maintenance. Several utilities apply dynamic resistance measurement (DRM) to OLTCs during regular maintenance. Results showed that DRM is sensitive to major degradation mechanisms in on-load tap changers.