Question

How is the selection of number of poles made in AC and DC machines?

(a) any number of poles can be used for both AC and DC machines

(b) fixed number of poles in both AC and DC machines

(c) fixed number of poles in DC machines and any number of poles in AC machines

(d) fixed number of poles in AC machines and any number of poles in DC machines

This question was posed to me in a national level competition.

Enquiry is from Selection of Number of Poles in portion Thermal Design Aspects of Electrical Machines & D.C of Design of Electrical Machines

Answer 1

The correct option is (d) fixed number of poles in AC machines and any number of poles in DC machines

Explanation: When it comes to DC machines, any number of poles can be made use of, but it should be within a range. Whereas in AC machines the number of poles is fixed by supply frequency and speed.