Difference between cylindrical Rotor and Salient pole type rotor | Electrical Machines - Electrical Engineering (EE) PDF Download

A synchronous generator, also called alternator, is a most widely used electric generator that produces alternating current supply. It is the main component of every power generating station.
Based on the rotor construction, the synchronous generators are of two types namely −

• Cylindrical Rotor Synchronous Generator
• Salient Pole Rotor Synchronous Generator

However, both types of generators are similar in stator construction. The stator of both types of generators consist of a three-phase winding distributed over its inner periphery.

In this article, we will explain the key differences between cylindrical rotor and salient pole rotor synchronous generators along with their basic description.

What is a Cylindrical Rotor Synchronous Generator?

When the rotor of a synchronous generator has non-salient pole or smooth cylindrical construction, the generator is called cylindrical rotor synchronous generator or cylindrical rotor alternator.

In the cylindrical rotor alternator, the rotor has a smooth cylinder made of solid forged steel and has a number of slots on its outer periphery. The rotor winding is placed in these slots. The cylindrical rotor has smooth surface because there is no poles projected on it. Hence, it maintains a uniform air-gap between the stator and rotor in the alternator.

The cylindrical rotor synchronous generators are usually driven by steam turbines and mostly used in very high speed applications such as turbo alternators.

What is a Salient Pole Rotor Synchronous Generator?

When the synchronous generator uses a projected pole type rotor, it is known as salient pole rotor synchronous generator or salient pole alternator.

In a salient pole alternator, the rotor poles are made of steel laminations and are fixed to the rotor hub. This type of rotor has rotor poles that are physically separated. Each pole carries a concentrated excitation winding. The salient pole rotor is usually used in alternators having 4 poles or more.
The salient pole alternators are mainly used in the applications where the speed of the prime mover is less because at high speeds the centrifugal forces will be large and may damage the poles of the rotor.

Difference between Cylindrical Rotor and Salient-Pole Rotor Synchronous Generator

The following table highlights all the significant differences between a cylindrical rotor alternator and a salient-pole alternator −

Conclusion

We have highlighted all the major differences between salient pole rotors and cylindrical rotor synchronous generators in the above table. Depending on their suitability, both types of alternators are widely used in various types of power plants to produce electricity.