# A hydraulic turbine turning at 100 r/min is coupled to a synchronous generator. If the induced voltage has a frequency of 50 Hz, then how many poles d

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A hydraulic turbine turning at 100 r/min is coupled to a synchronous generator. If the induced voltage has a frequency of 50 Hz, then how many poles does the rotor have?
1. 60
2. 80
3. 50
4. 70

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Correct Answer - Option 1 : 60

Concept:

Speed of synchronous generator in rpm is given by

${N_s} = \frac{{120f}}{P}\;$

Where,

f = supply frequency in Hz

P = Number of poles

Calculation:

Given-

Ns = 100 r/min = 100 rpm,

f = 50 Hz

When hydraulic turbine is connected to synchronous generator, then both are running at same speed

∴ $100 = \frac{{120 \times 50}}{P}$

P = 60