The soft starter also uses the voltage reduction technique. It uses the semiconductor switches like TRIAC to control the voltage as well as the starting current supplied to the induction motor.
A phase-controlled TRIAC is used to provide variable voltage. The voltage is varied by varying the conduction angle or firing angle of the TRIAC. The conduction angle is kept at minimum to provide reduced voltage. The voltage is increased gradually by increasing the conduction angle. At maximum conduction angle, the full line voltage is applied to the induction motor & it runs at rated speed.
It provides a gradual & smooth increase in the starting voltage, current as well as the torque. Thus there is no mechanical jerk & provide a smooth operation that increases the life span of the machine.
Advantages of Soft Starter
- It provides better control over starting current & voltage
- It offers smooth acceleration, thus no jerks.
- It reduces the power surges in the system.
- Extends the life span of the system
- Provide better efficiency & lack the need for maintenance
- Its size is small
Disadvantages of Soft Starter
- It is relatively expensive
- There is energy dissipation in the form of heat
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