Breakdown Characteristics of Transformer Oil under Vibration and Electric Field

The Converter transformer is the core device in HVDC power system. Partial discharges may occur, or even breakdown of oil-paper insulation when bubbles accumulate into bridges. The generation of bubbles and their behavioral characteristics are closely related to vibration. Transient vibration inevitably exists in the oil-paper insulation of the converter transformer. More microbubbles are formed in the oil due to vibration. In this study, a piezoelectric transducer was used to simulate the transient vibration in transformer oil. The relationship between AC/DC breakdown electric field strength and vibration intensity were acquired. An increase in vibration intensity can significantly reduce the insulating properties of transformer oil. The AC breakdown field strength of transformer oil is more sensitive to the change of vibration power. Vibration changes the existing form of bubbles in the oil gap, resulting in a change in breakdown electric field strength. At the same time, the gas content also limits the generation of bubbles under vibration. The results presented here may provide theoretical support for the threat assessment of converter transformers.