Rating of Alternator

The power rating of an alternator is defined as the maximum power it can deliver safely and efficiently under specific conditions. As the load increases, the losses in the alternator also increase, causing the machine to heat up. The conductor and insulator have limits on how much overheating they can withstand. Manufacturers set the power rating to ensure that, even at maximum load, the temperature rise stays within safe limits.

Copper losses (I²R losses) vary with armature current, while core losses vary with voltage. The heating of the alternator depends on the combined effect of these losses. Since the power factor does not affect these losses, alternator ratings are usually given in VA, KVA, or MVA.
Since alternator losses do not depend on the electrical power factor, the power factor is not considered when calculating the power rating. While losses are based on the KVA or MVA rating, the actual output varies with the power factor.

The electrical output of an alternator is the product of its power factor and VA, expressed in KW.
Sometimes alternators are rated by their power in KW instead of VA. In such cases, the power factor must also be specified.
In addition to KVA rating, an alternator has also voltage, electric current, frequency, speed, number of phases, number of poles, field ampere, excitation voltage, maximum temperature rise limit ratings, etc.