Determination of optimized soft starter firing angle to mitigate high inrush current during motor starting using PSCAD

Abstract

Starting of an induction motor is a process that creates many challenging problems for the motor and operations of the power system. The induction motor can be damaged, characteristic can be changed and performance of the motor can be worsen. An induction motor draws a high starting current and develops a high torque during the start-up. Inrush current often causes problem such as voltage dips and sags that occur in electrical power system associated with motor. The different motors starters available in Malaysia market are being discussed and analyzed. It includes both conventional electromechanical starters and power electronic drives. A comparison between the starters found that soft starter is the most convincing because the configuration just involves some power conductor device that control the current flow from power source to the motor. The switch is in the form of thyristor and being connected back-to-back. The current output can be controlled by varying the firing angle. This changing of firing angle is managed by a firing angle control circuit. PSCAD/EMTDC software is used for model implementation and in carrying out extensive simulation studies. Firstly, the power source was directly connected to the induction motor and the circuit is simulated to analyze the inrush current. The analysis of the starter is repeated by using star delta starter and soft starter. For soft starter, the thyristor acts as a gate to control the voltage applied to the motor. The firing angle was varied until the high current was mitigated. This research was finally concluded that soft starter circuit is designed to be used to mitigate inrush current.