Oil flow surge test for 110kV power transformer during external short circuit faults

Abstract

Large oil-immersed power transformers always have the gas relay equipped between the main tank and conservator. However, due to the inherent defects, the gas relay malfunction caused by external faults happens occasionally all over the world, which jeopardizes the safe operation of bulk power systems. In order to explore the oil flow characteristics inside the pipe during external short circuit faults, we built the transient oil flow measurement system on the 40 MVA/110 kV power transformer, and carried out 34 external short circuit fault test campaigns. The test results confirmed that the deformation and vibration of transformer windings caused by the short circuit current would lead to the oil flow surge through the pipe. The surge appears with a long time delay up to hundreds of milliseconds due to the liquid inertia. The test also shows that both the fault severity and location would affect the oil flow surge.