Rotor

Rotor Points : Rotor, Armature, Commutator, Armature Winding , Bearing, Shaft Rotor consists of mainly armature core whose outer periphery is slotted to accommodate the armature winding. The armature core is a stack of cylindrical steel lamination of about 0.4 mm to 0.6 mm thick to decrease the eddy current losses. Layer of varnish insulates these laminations from one another.
Rotor consists of:
(1) Armature
(2) Commutator
(3) Armature Winding
(4) Bearing
(5) Shaft 1. Armature It is a rotating part of a dc machine and is built up in a cylindrical or drum shape. The purpose of armature is to rotate the conductors in the uniform magnetic field. It consists of coils of insulated wires wound around an iron and so arranged that electric currents are induced in these wires when the armature is rotated in a magnetic field. In addition, its most important function is to provide a path of very low reluctance to the magnetic flux. The armature core is made from high permeability silicon - steel stampings, each stamping, being separated from its neighbouring one by thin paper or thin coating of varnish as insulation.

2. Commutator Commutator is a group of wedge shaped Copper segment of 0.5 mm to 1.00 mm thick, these segments are insulted from each other by Mica sheet. Current is conducted to the armature coils by Carbon brushes that are held against the cylindrical surface of the Commutator by the force of spring. For a d.c. motor Commutator acts like a mechanical inverter to invert direct applied voltage to the alternating voltage in the armature winding. It acts like converter to convert a.c. generated emf in armature winding to d.c. in case of d.c. generator.

3. Armature Winding The armature winding is wound around the armature core. There are two types of armature winding:
(a) Wave connected armature winding.
(b) Lap connected armature winding.
These two types of connections are different in the manner in which ends of armature winding connected to commutator. The function of armature winding is to induce an emf due to cutting of flux.

4. Bearings With small machines, ball bearings may be used at both ends. For larger machines, roller bearings are used at the driving end, and ball bearings may be used at the non-driving end, i.e. at the commutator end. Thrust bearings are used where excessive end thrust is anticipated. Sleeve bearings, with ring lubrication are used for motors at the side cover, when very silent running is required. For large machines pedestal bearings are generally used.

5. Shaft The shaft is made of mild steel with a maximum breaking strength. The shaft is used to transfer mechanical power from or to the machine. The rotating parts such as armature core, commutator, cooling fan etc. are keyed to the shaft.