In later years, motors improved and could be run directly from a 60 Hz power sup
ID: 1802236 • Letter: I
Question
In later years, motors improved and could be run directly from a 60 Hz power supply.As a result, 25 Hz power systems shrank and disappeared. However, there were
many perfectly good working 25 Hz motors in factories around the country that
owners were not ready to discard. To keep them running, some users created their
own 25 Hz power in the plant using motor-generator sets. A motor-generator set
consists of two machines connected on a common shaft, one acting as a motor and
the other acting as a generator. if the two machines have different numbers of poles. but exactly the same shaft speed, then the electrical frequency of the two machines will be different due to Equation (3- 34). What combination of poles on the two machines could convert 60 Hz power to 25 Hz power?
f(se)=(n(sm)P)/120 (3-34)
Explanation / Answer
as in motor generaror are connected to same shaft then both machines are working with same speed but number of poles are different with same speed means both machines are working with different frequencies we know frequency F = N*P/120 speed N = 82120F/P given motor speed = generator speed 120F1/P1 = 120F2/P2 F1/P1 = F2/P2 output frequency is 25 which is obtained from generator so F2=25 input frequency is 60 which is given to motor soF1=60 60/P1 = 25/P2 60/25 = P!/P2 P1/P2 = 12/5 multiply and divided by 2 becuase poles are even P1/P2 = 12*2/5*2 =24/10 P1= 24 poles a P2 =10 poles we get 25 hz frequency from 60 hz frequency
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