Further studies of anomalous phenomena in dielectric-loss measurements-transformer bushings model

The results of AC dielectric loss measurements on bushings mounted in certain three-phase transformers, if not performed in accordance with the prescribed procedure, can deviate significantly from the correct values. An investigation of the incorrect procedure has shown that the capacitive coupling between adjacent windings and the lower portion of the bushings influenced the results such that dielectric losses were elevated to several times their normal values. Experience has shown that bushing test results on all three phases form a pattern in cases where this phenomena is evident. Results of investigative field measurements showing this phenomena are presented, and an explanation of its origin is given