How Alternators Are Rated

Rating definition

The power rating of an alternator is defined as the maximum power it can safely and effectively deliver under certain conditions.

Loss and heating

The copper loss (I2R) depends on the armature current and the iron core loss depends on the voltage, both of which cause the alternator to heat up.

Not affected by power factor

Alternators are rated VA, KVA, or MVA because these losses are not affected by the power factor.

Output calculation

The power output is the product of the power factor and VA, expressed in KW.

Additional rating

Alternators also have ratings for voltage, current, frequency, speed, phase, pole, excitation amperage, excitation voltage, and maximum temperature rise.