This is another common starting method used in industries for large motors. The windings of 3 phase induction motor are switched between star and delta connection to start the motor.
To start the induction motor, it is connected in star using a triple pole double throw relay. The phase voltage in star connection is reduced by the factor 1/√3 & it reduces the starting current as well as the starting torque by 1/3 of the normal rated value.
When the motor accelerates, a timer relay switches the star connection of the stator windings into the delta connection, allowing the full voltage across each winding. The motor runs at rated speed.
Advantages of Star Delta Starter
- Its design is simple & cheap
- It does not require maintenance
- Provide a low surge current.
- It is used for starting large induction motors.
- It is best for long acceleration time.
Disadvantages of Star Delta Starter
- It works on delta connected motor
- There are more wire connections.
- It offers low starting torque which cannot be maintained.
- There is very limited flexibility is starting characteristics.
- There is a mechanical jerk while switching from star to delta.
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