8. A] With neat sketches, explain the construction of two types of synchronous generators.
Answer:
There are two types of generators:
i) Salient pole of generator
ii) Non Salient pole generators
CONSTRUCTION:
- The two basic parts in of an alternator are: (i) Stator, (ii) Rotor.
- Stator is the stationary part and Rotor is the revolving part.
- The Stator Construction of both alternator is same as explained below.
Stator:
The stator of the synchronous generator is cylindrical in shape made up of silicon steel laminations. It consists of a stator frame and stator core. The stator frame is used for holding the armature stampings and windings in position. Ventilation is maintained with the help of holes cast in the frame itself, which assist in cooling the alternator.
The armature core is supported by the stator frame and is built up of laminations of steel alloys or magnetic iron. The core is laminated to minimize the loss. The laminations are insulated from each other. The stator is made up of a number of slots on its inner periphery, as shown in the below figure. The slots are used for holding the armature winding.
Rotor:
Rotor construction is different in both types of generators.
There are two types of rotor: i)salient pole type and ii)smooth cylindrical type.
i) Salient pole or Projected pole type generators
The poles are made of thick steel laminations bolted together to a shaft. The poles are also laminated to minimize the eddy current losses. The salient pole type of rotors is characterized by their large diameters and relatively short axial lengths. All the poles are projected outside; since they are projected outside the mechanical strength is less. It is generally used for low and medium-speed operations, mainly employed in engine-driven generators.
ii) Smooth Cylindrical or Non salient type generators
The rotor consists of a smooth solid steel cylinder, having a number of slots along its outer periphery to accommodate the field coils. They do not have projected poles, instead the slotted portion acts as pole. As shown in the figure below. Here, the rotor has 4 poles. The pole areas are surrounded by field windings placed in slots.
It has a very long axial length but small diameters. The construction of the rotor gives better balance and quieter operation.
This type of rotor is generally used for very high-speed operation and hence called turbo generators, which are employed in generators driven by a steam turbine.
