A more accurate numerical method to calculate pressure rise due to internal electrical faults in oil-filled power transformer tanks

摘要

Methodologies in the current state of knowledge to optimize tank geometries for rupture mitigation when internal faults of given arc energy take place, particularly those which use the formula of Hydro Quebec's specification, are sustained on physical conditions valid for early experiments with empty tanks. Such conditions do not happen inside power transformer tanks during normal operation. A numerical method has been devised to calculate pressure rise caused by internal fault gases in tanks of oil-filled power transformers. Fundamental assumption is that compressed volume of hot gases generated from decomposition of oil equals the expansion of transformer tank that withstands inner static pressure. Dynamic load factor that incorporates dynamic effects is used to estimate maximum value of pressure, which then is applied as surface load in finite element model to calculate stress field in tank walls and validate that maximum stress is below rupture strength of steel. Design margin pressure easily follows.