Electric Machine Theory

Question 1

Salient Pole Rotors

Answer 1

Salient Pole Rotors have an even number of laminated projecting poles and are used in low (50 rpm) to medium (300 rpm) speed generators since the winding loss is small at these speeds. They are usually driven by hydraulic water turbines. A much greater number of poles are required to produce the required frequency of 50 or 60hz at these slower speeds since Frequency is a product of the number of poles (see synchronous speed formula below). The larger number of poles likewise requires a much larger rotor diameter to physically fit them all and the shaft is usually mounted vertically.

Question 2

Cylindrical Rotors

Answer 2

Cylindrical Rotors have 2 or 4 poles, are used in high speed applications, and are made of smooth solid forged steel cylinder. They operate much quieter, provide better balance, and have reduced winding loss. They are usually driven by high-speed steam turbines. They are smaller and more efficient than low-speed turbines. For a 60hz system, the number of poles are limited to either 2 for 3600rpm or 4 for 1800rpm. Compared to salient pole rotors, they are much longer with a small diameter.

Question 3

Short Circuit Test

Answer 3