The number of poles that the two machines should have in order to convert a 50-hz power to 60-hz is a 10 pole synchronous motor must be coupled to a 12-pole synchronous generator.
n = 120 f / P
n = Speed of synchronous machine
f = Frequency
P = Number of poles
For motor,
f = 50 Hz
n = 120 * 50 / Pm
For generator,
f = 60 Hz
n = 120 * 60 / Pg
To accomplish the frequency conversion, the speed of the motor and generator must be equal. So,
120 * 50 / Pm = 120 * 60 / Pg
Pg / Pm = 6 / 5
Pg / Pm = 12 / 10
Therefore, to accomplish the frequency conversion, a 10 pole synchronous motor must be coupled to a 12 pole synchronous generator.
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