Most Induction Motors are started directly on line, but when very large motors are started that way, they cause a disturbance of voltage in the supply lines due to large starting current surges.
To limit the starting current surge, large induction motors are started at reduced voltage and then have full supply voltage reconnected when they run up to near rotated speed.
This is the reduced voltage starting method. Voltage reduction during star-delta starting is achieved by physically re-configuring the motor windings as illustrated in the figure below. When starting the motor windings are connected in star configuration and this reduces the voltage across each winding . This also reduces the torque by a factor of three.
Star-delta Starter Consists
- three Main, star and delta contactors (For Open State Starter) or four (Close Transient Starter).
- A Time relay (pull-in delayed)
- A Three-pole thermal over current release
- Three fuse elements or automatic cut-outs for the main circuit
- A Fuse element or automatic cut-out for the control circuit
A special thanks Waqar Akbar (B.tech Electrical) and Danyal Arshad (B.tech Electrical) for submitting this project to our website. Hope this will help other students.