How does reduced-voltage starting mitigate the high starting current of induction motors?
1 Answer
Reduced-voltage starting is a method used to mitigate the high starting current of induction motors. When an induction motor starts, it initially draws a high amount of current, which can be several times its rated or full-load current. This high starting current can cause voltage drops in the power supply system, and it may lead to voltage sags and other operational issues for other connected equipment.
There are several techniques for reduced-voltage starting, and I'll explain a couple of common methods:
Star-Delta Starting: This method involves connecting the motor in a star (wye) configuration during the starting phase and then switching it to a delta configuration once it reaches a certain speed. In the star configuration, the line voltage across each motor winding is reduced to 1/√3 times the line voltage in the delta configuration. As a result, the starting current is reduced to approximately 1/3 of its value during the star connection. Once the motor reaches a predetermined speed, the switching from star to delta occurs, and the motor operates at its normal voltage and current levels.
Autotransformer Starting: In this method, an autotransformer is used to step down the supply voltage during motor starting. The motor is initially connected to a tapped winding on the autotransformer, which reduces the applied voltage to the motor. The starting current is limited due to the reduced voltage, and once the motor reaches a sufficient speed, it is switched to the full voltage.
Both of these methods, and other reduced-voltage starting techniques, help reduce the starting current drawn by the induction motor, thus mitigating the negative effects of high inrush current on the power system and minimizing mechanical stresses on the motor itself. Reduced-voltage starting is commonly used in applications where starting an induction motor at full voltage could cause voltage fluctuations, damage to the motor, or disturbances to other connected equipment.
There are several techniques for reduced-voltage starting, and I'll explain a couple of common methods:
Star-Delta Starting: This method involves connecting the motor in a star (wye) configuration during the starting phase and then switching it to a delta configuration once it reaches a certain speed. In the star configuration, the line voltage across each motor winding is reduced to 1/√3 times the line voltage in the delta configuration. As a result, the starting current is reduced to approximately 1/3 of its value during the star connection. Once the motor reaches a predetermined speed, the switching from star to delta occurs, and the motor operates at its normal voltage and current levels.
Autotransformer Starting: In this method, an autotransformer is used to step down the supply voltage during motor starting. The motor is initially connected to a tapped winding on the autotransformer, which reduces the applied voltage to the motor. The starting current is limited due to the reduced voltage, and once the motor reaches a sufficient speed, it is switched to the full voltage.
Both of these methods, and other reduced-voltage starting techniques, help reduce the starting current drawn by the induction motor, thus mitigating the negative effects of high inrush current on the power system and minimizing mechanical stresses on the motor itself. Reduced-voltage starting is commonly used in applications where starting an induction motor at full voltage could cause voltage fluctuations, damage to the motor, or disturbances to other connected equipment.