We recently purchased an air compressor, which has a 220V, 3 phase, 30hp motor.

Some say we should have purchased a 480V, 3 phase, 30hp motor, as the operating costs for electricity would be less.

We understand that the installation cost would be different, and the cost of the air compressor would be different, BUT strickly speaking about operational costs for electricity, would it be cheaper to run on 480 volts or cheaper to run on 220 volts, or the same??

Especially considering they are both 3-phase, which is more efficient than single-phase, neither would cost any less to run.

You pay for watts, regardless of voltage. 30HP is a certain amount of watts, most would say 22,380 watts, so however you use those watts does not matter.

In all likeliness the cost of a 480 V motor would have been cheaper and weigh less because there is less copper in it. For a dual 208-240/480 the copper and weight will be the same.

Your motor may be dual voltage anyway, so check the nameplate.

As Stan said, 30 HP X% efficient motor is the same no matter what the voltage.

Depending on your utility billing and if peak rates are involves, you could save operating money by incorporating a soft starter.