The winding where dummy coils are used is sometimes called

Duplex winding
Triplex winding
Forced winding
None of the above

The correct answer is: A. Duplex winding

A duplex winding is a type of winding where two coils are wound on the same core, with each coil having its own set of terminals. This type of winding is often used in transformers to reduce the leakage inductance.

A triplex winding is a type of winding where three coils are wound on the same core, with each coil having its own set of terminals. This type of winding is often used in transformers to reduce the core losses.

A forced winding is a type of winding where the current is forced to flow through the winding in a particular direction. This type of winding is often used in motors to create a rotating magnetic field.

None of the above options are correct.