Question

4. In a remote location, it is necessary to supply 300kw of 60 Hz power. The only power source available operates at 50Hz. It is decided to generate the power by means of a motor-generator set consisting of a synchronous motor driving a synchronous generator, both machines are coupled with mechanical link at the same rotational speed. How many poles should each of the two machines have in order to convert 50Hz power to 60Hz power?

Answer 1

Power Source Available is of 50 H2. from 50 Hz power supply, motor is being given voltage - supply from the output shaft of the motor, generator is connected. Hence motor acts as a prime mover for the generator. Both are synchronous machines, hence the rotor - rotates at synchronous speed. - Let the number of poles in motor= Pm frequency of supply to motor = 5042. Let the number of poles in generator = Pq. Desired output frequency = 60812 Synchronous speed is given by - Ns = 120f uy nis Since, speed of both machinco are some i 120 fm - 120 60 im = 120x50 = 120x60 & rg Pm Pg 6 1. Pm

Hence the ratio of number of poles in a generator to the number of poles in a motor should be to Since the number of poles are always in even numbers. Hence Pg = 6x2 = 12 oo - Po 5x2 Hence number of poles in generator = 12 Number of poles in motor = 10