CORRELATING POWER TRANSFORMER TANK VIBRATION CHARACTERISTICS TO WINDING LOOSENESS

The capability to predict equipment maintenance needs can reduce forced outages, avoid catastrophic failures and the consequential secondary damage. It can also allow confident deferral of routine maintenance, and improve equipment performance, availability, reliability and safety In order to capitalise on these potential benefits directed toward power transformers, several studies have been initiated by Powertech Labs Inc to investigate the possibility of determining the degree of winding looseness (loss of clamping pressure) by conducting non-intrusive vibration tests. Preliminary investigations to date have involved taking vibration signals from the sides and top of two identical 25/12 kV transformers, one of which was suspected of having loose windings. Vibration samples were also taken from three single-phase 500 kV reactors where one phase had recently had a high-voltage bushing replaced. Before and after refurbishment (including coil reclamping) vibration samples were also taken from three single-phase 500 kV transformers. The results of these preliminary tests are presented and reveal that there exist significant differences in she raw vibration signal amplitudes and frequency content, dependent on the degree of winding looseness. It is hoped that further study of these phenomena will lead to development of a useful non-intrusive diagnostic tool. Such a tool could be used to assess the mechanical integrity of transformer windings without the need to significantly interrupt operation.