Constructional Features of Wound-Rotor Induction Motors

Question 1

How does the rotor of a wound-rotor induction motor differ from that of a squirrel-cage induction motor?

Answer 1

Contains a three-phase winding rather than a squirrel-cage design. The rotor may be either wye or delta connected, with the leads brought out so that external resistance may be placed in the rotor circuit.

Question 2

What is the purpose of the three slip rings and their corresponding brushes on the wound-rotor motor?

Answer 2

Slip rings and brushes provide an electrical connection between the moving rotor and the external rotor leads.

Question 3

How are the three rotor terminals designated on a wound-rotor motor?

Answer 3

M1, M2, and M3

Question 4

What is the purpose of the spring on the brush holders in a wound-rotor motor?

Answer 4

The spring on each brush holder applies force on the brush to keep it in contact with the slip ring.

Question 5

What is the purpose of the pigtail or shunt attached to each brush?

Answer 5

Makes the electrical connection between the brushes and the external rotor leads.

Question 6

What two additional pieces of information are normally supplied on the nameplate of a wound-rotor induction motor that you would not find on a squirrel-cage induction motor?

Answer 6

Rotor voltage and rotor current

Question 7

For what would an electrician use the two additional pieces of information supplied on a wound-rotor motor nameplate?

Answer 7

Select components for the secondary circuit that have the proper voltage and current ratings