Study and diagnosis of the power transformer bushing insulation system

Bushings are a critical component in electricity transportation. They are used in substation buildings, transformers, locomotives, and switchgear. Bushings cause more than 15% of transformer failures. The main purpose of a bushing is to transfer load currents in and out of metal (grounded) enclosures at system voltages. The insulation system breaks down, causes bushing failure results in catastrophic event such as tank rupture, violent explosion of the bushing and fire. Clearly, the risk and likelihood of collateral and personnel damage is a major concern in such an eventuality. This research is undertaken to study and diagnosis of the power transformer bushing insulation system and in-field measurement of power-factor and capacitance using the Doble M4100 insulation analyzer. The case studies on the different transformers showed how the trend of moisture and dielectric properties changes with the variation of power factor and capacitance of insulation system.