Analysis of vibration evolution and propagation characteristics due to mechanical degradation in transformer iron cores

Abstract

This study investigates vibration changes due to transformer core deterioration by monitoring core vibration, compression force and shell wall vibrations simultaneously. The transformer core operates in a compound environment of mechanical vibration and thermal ageing for extended periods, and the correlation mechanism between core structural deterioration and shell vibration changes remains unclear. This study first derives and analyses the propagation mechanism of core vibration in oil. The experiments simulate the internal deterioration of a 10 kV transformer using pressure sensors to monitor the compression force on the core and windings and vibration sensors on the internal upper yoke and the enclosure to capture full vibration measurements. Analysis of the vibration data during the experiment, using two quantitative indicators—vibrational entropy and fundamental frequency weight—reveals that measurement point #2 (on the outer case wall corresponding to the internal upper yoke) shows a value approximately 1.2 times that of the internal upper yoke. However, measurement point #5 (located away from the upper yoke near the windings) demonstrates a value about 2.3 times that of the internal upper yoke. The results indicate that measurement point #2 has high vibration consistency with the internal upper yoke, whereas it exhibits significant variability compared to measurement point #5. To validate these findings, researchers collected 24-h vibration data from 105 in-service 220 kV transformers and the results aligned with those from the experimental platform. This study quantitatively addresses the changes in case vibration characteristics caused by core degradation and proposes a novel method for detecting the mechanical state of transformer cores through vibration analysis.