What would be the cycles of a four-pole motor rated at 150 hp, 3 phase, 90% efficient, and 1800 rpm?

To determine the cycles—or more accurately, the frequency—of a four-pole motor rated at 1800 RPM, we refer to the synchronous speed of an electric motor. The synchronous speed of a motor can be calculated using the formula:

[ \text{Synchronous Speed (RPM)} = \frac{120 \times \text{Frequency (Hz)}}{\text{Number of Poles}} ]

In this case, we have a four-pole motor running at 1800 RPM. To find the operating frequency, we can rearrange the formula to solve for frequency:

[ \text{Frequency (Hz)} = \frac{\text{Synchronous Speed (RPM)} \times \text{Number of Poles}}{120} ]

Plugging in the values:

[ \text{Frequency (Hz)} = \frac{1800 \times 4}{120} = \frac{7200}{120} = 60 \text{ Hz} ]

This shows that the motor operates with a frequency of 60 cycles per second (or Hz), which corresponds directly to the standard frequency used in most electrical power systems in the United States and is typical for induction motors.

Therefore, the correct answer is indeed 60