Study of single phase transformer inrush current

Abstract

When a transformer is initially connected to a source of AC voltage, there may be a substantial surge of current through the primary winding called inrush current. This analogous to the inrush current exhibited by an electric motor that is started up by sudden connection to power source, although transformer inrush is caused by a different phenomenon. Inrush currents associated with motor starting and transformer energizing can cause interaction problems with other loads in a facility or on the power system, particularly sags that trip loads. Protection devices can misinterpret these events as fault currents, if the devices are not properly coordinated. Coupled with the tendency of other constant power devices to increase current to make up for the reduced voltage, the inrush current may cause protection devices to trip. The selection of overcurrent protection devices such as fuses and circuit breakers is made more complicated when high inrush currents must be tolerated. The overcurrent protection must react quickly to overload or short circuit but must not interrupt the circuit when the inrush current flows. This project presents an analysis report on inrush current based on hardware and software studies. The purpose of project is to understand the concept and effect of inrush current to electrical machines especially on single phase transformer and also to give a brief explanation about the effect of inrush current towards power quality.