Why do we use kVA instead of kW to rate alternators and transformers?
because when representing ability of the system or component, we always use the maximum value. in case of AC, that would be the kVA.Why do we use kVA instead of kW to rate alternators and transformers?
To some degree, it is an indirect way of specifying amperage capacity. The heat and stresses in a transformer are primarily functions of the current in the windings, independent of the voltage. If you have a low power factor, you can have a large current but be delivering a lower real power -- but the windings see the current and don't really care about the phase relationships. Since the RMS voltage across the transformer is essentially fixed, the kVA is proportional to the RMS current. Having said that, there are other losses that really only depend on the voltage, largely independent of the current. So kVA is a way of taking both into account in a reasonable way.Why do we use kVA instead of kW to rate alternators and transformers?