- Power Rating Definition: The power rating of an alternator is defined as the maximum power it can safely and efficiently deliver under specific conditions.
- Losses and Heating: Copper losses (I2R) depend on armature current, and core losses depend on voltage, both contributing to the alternator’s heating.
- Independence from Power Factor: Alternator ratings are in VA, KVA, or MVA because these losses are not influenced by the power factor.
- Output Calculation: The electrical output is the product of power factor and VA, expressed in KW.
- Additional Ratings: Alternators also have ratings for voltage, current, frequency, speed, phases, poles, field ampere, excitation voltage, and maximum temperature rise.
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.The table below shown a standard rating plate of alternator Make …………… Kilo Watt Rating 5000 Power Factor 0.85 lag KVA Rating 5,88,000 Stator Volt 21,000 Stator Ampere 16,200 Rotor Volt 340 Rotor Ampere 4040 R.P.M 3000 Hz 50 Phase 3 Armature Connection Double Star Coolant Water & Hydrogen (Forced) Gas Pressure 3.5 bar Insulation Type + F Type …………… Specification IS5422 & IEC34 Product Serial Number …………… Manufacturing Year ……………
