Rotors at La Grande-3 generating station
Rotors de La Gande-3

At La Grande-3, the rotors have 32 pairs of electromagnets. To supply a 60-Hz alternating current, they must therefore rotate at a speed of 112.5 revolutions per minute (RPM).

Here is the formula that was used by the engineers:

32 pairs of electromagnets x 112.5 RPM
= 3,600 RPM or 60 revolutions per second (60 Hz).