Soft Start Analysis of Induction Motor Using Current Phase Angle

Compared to other electric motors, induction motors can ensure convenience of maintenance, robustness and fast speed start-up characteristics, and are widely used in places where rotational force is required. Despite these various advantages, the voltage drop caused by high current during starting is the biggest problem. The voltage drop can make the operation of the motor itself as well as other load devices difficult. In order to solve this problem, induction motors apply various starting methods according to the motor capacity instead of direct starting. Soft starting method, which controls the voltage by fixing or adjusting the firing angle of the thyristor, is also widely used as a starting method for induction motors. Induction motor is a device with a large change in current or power until it reaches the rated speed after starting. These large changes in current and power are also related to changes in power factor. Induction motors have different power factors depending on the number of poles, rotor shape, and capacity. Since the change in power factor is an important factor for grasping the starting characteristics of the induction motor, it can be converted into a phase angle. As a method of obtaining the phase angle, there are cases where the active power and the reactive power are used, and the three-phase current applied to the stator is obtained through coordinate transformation. In this study, a method to reduce the starting current using the latter was proposed.