A 60 Hz synchronous generator will run at the greatest possible speed if it is wired for how many poles?

The speed of a synchronous generator is fundamentally linked to the frequency of the electrical output and the number of poles in the machine. The synchronous speed (in RPM) can be calculated using the formula:

[ \text{Synchronous Speed} (N_s) = \frac{120 \times f}{P} ]

where ( f ) is the frequency in Hz and ( P ) is the number of poles.

For a generator operating at 60 Hz:

When the generator is wired with just 2 poles, the calculation becomes:

[ N_s = \frac{120 \times 60}{2} = 3600 , \text{RPM} ]

This indicates that the synchronous generator will run at 3600 RPM, which is indeed the greatest possible speed for a generator at this frequency.

As the number of poles increases, the synchronous speed decreases. For example, if you were to wire the generator for 4 poles, the synchronous speed would reduce to 1800 RPM, and with 6 poles, it further lowers to 1200 RPM, and so on. Therefore, fewer poles allow for a higher synchronous speed, making 2 poles the choice that results in the greatest operational speed at 60