Electrical Engineering ⇒ Topic : Rotor and its types

Rotor The revolving field structure is usually called the rotor. There are two types of rotors

Salient pole type rotor

Smooth cylindrical type rotor

1. Salient pole type rotor This type of rotor is used for slow-speed machines which have large diameters and small axial lengths.

• The poles are made of thick steel laminations riveted together and attached to a rotor by a devetail joint. The over hang of the pole gives mechanical support to the field coil.
• In most of the alternators where the oscillation or the limiting effect is very high the damper winding in the pole faces is provided. The copper bars short circuited at both ends are placed in the specially provided holes.
• The pole face is so shaped that the radial air gap length increases from the pole centre to pole tips. This makes the flux distribution over the armature uniform to generate sinusoidal wave form of e.m.f.

2. Smooth cylindrical type rotor

• This type of rotor is used for alternators which are coupled to steam turbines which run at very high speeds. To reduce the peripheral speed of the alternator the diameter of the rotor is reduced and avial length is increased. The no. of poles of the rotor are two or four.
• Those rotors are made from solid forging of alloy steel. The outer periphery of rotor has slots in which the field winding is placed.
• Cylindrical rotor machines have always horizontal configuration