SYNCHRONOUS MACHINE WINDINGS
The three types of windings used in synchronous machines are distributed, solenoid, and damper windings.
Distributed Windings. This type of winding is made of bundles of wire or insulated wire. It is inserted in slots around the rotor or stator air gap surface. In large machines, this winding is made of rectangular copper or aluminum bars. These bars are made from many elemental units (known as coils) insulated from each other with a cloth of nylon or Mylar. They are also coated with an insulated varnish and baked or thermally cured to form a rigid unit. The bars are inserted into slots similar to the ones shown in Fig. 11.4c. These bars are known as preformed coils.
In smaller-rated machines, these conductors are made of insulated wire known as magnet wire. The bundles of wire are inserted into slots in the core. They are coated with insulating varnish and baked or thermally cured for rigidity and high insulation resistance. These coils are known as random-wound, or mesh, coils.
Distributed windings are used as armature windings and as field windings in cylindrical machines.
Solenoid Windings. This type of winding is made of a multilayer of conductors separated by insulating strips. Hard electrical insulation separates the pole from this winding. This type of winding is used in salient-pole and dc machine fields, electromagnets, and power relays.
Damper Windings. The damper windings are installed at the outer surface of the rotor in a similar arrangement to the squirrel-cage bars in an induction machine.