The question is based on information obtained from the Wildi Textbook, Chapter 16

An A.C. alternator is unique as the rotor is comprised of two types of windings.

The rotor features a set of squirrel cage windings that are positioned in the laminated steel core, close to the outer surface of the rotor. Just below those rotor bars, there are traditional field coils.

In order to avoid confusion with other motor types, the squirrel cage winding has a proper name which is the                   winding. This is to help differentiate the alternator from the squirrel cage motor.

Note: Fill in the blank by typing a one word answer in the field provided below, do not use numbers or special characters.