ESTIMATION OF RESIDUAL FLUX FOR THE CONTROLLED SWITCHING OF TRANSFORMER

My paper basically explores the practical considerations of core flux transients and the applications of circuit breakers to control transformer inrush transients. The magnetizing inrush current which occurs at the time of energization of a transformer is due to temporary overfluxing in the transformer core. Transformer inrush currents are high magnitude, harmonic-rich currents generated when transformer cores are driven into saturation during energization. These currents have undesirable effects, including potential damage or loss-of-life to the transformer, protective relay misoperation, and reduced power quality on the system. Controlled transformer switching can potentially eliminate these transients if residual core and core flux transients are taken into account in the closing algorithm. Its magnitude mainly depends on switching parameters such as the resistance of the primary winding, the point-on-voltage wave (switching angle), and the remanent flux density of the transformer at the instant of energization. This report describes the development of a system for measuring the inrush current. The system is also capable of presetting various combinations of switching parameters for the energization of a transformer.