Question

Which of the following methods could be used to start a Three-phase cage-type induction motor?

I. Direct-on-line starting

II. Auto-transformer starting

III. Star-delta starting

Choose the correct answer from the options given below.

1. Only I and II
2. Only II and III
3. I, II and III
4. Only I and III

Answer 1

Correct Answer - Option 3 : I, II and III

Methods used to start a three-phase cage-type induction motor

DOL starter:

• The direct on line (DOL) starter method of an induction motor is simple and economical.
• In this method, the starter is connected directly to supply voltage.
• In this method, small motors up to 5 hp rating are started to avoid the supply voltage fluctuation.

 

Star-delta starter:

• The star-delta starter method of starting three-phase induction motors is very common and widely used among all the methods.
• In this method, at stating motor in star connection and runs at delta connected stator windings.

 

Auto-transformer starter:

• The Autotransformer is used in both the type of the connections, i.e., either star connected or delta connected.
• The autotransformer is used to limit the starting current of the induction motor.
• This method is used for the high rating of squirrel cage induction motors. So, this method is most suitable for a 20 hp squirrel cage induction motor.
• The auto-transformer starter is expensive compare to the “direct on line” (DOL) starter