Why is the Rating of a Power Plant Capacity Expressed in MW instead of MVA?
For the following reasons, a power plant capacity rating may be expressed in megawatts (MW) instead of megavolt-amperes (MVA).
In a generating station, the prime mover (turbine) generates only and only active power in Watts. A generator then converts the mechanical power into electrical energy i.e. Volt x Amps x Power factor which is further transmit and distribute in a typical power system scheme. That’s why we express the rating of a a power plant capacity in MW instead of MVA. It means no matter how large your generator is, but it depends on the capacity of the engine (prime mover / turbine) i.e. a 50 MW turbine connected to a 90MVA alternator (which generates both active and reactive power) in a power plant will generate only 50MW at full load.
In short, a power plant rating is specified in terms of prime mover / turbine (turbine rating may be seen by nameplate rating which is in MW or Horsepower (HP) not in MVA) and not by the alternator set coupled to it.
Another thing is that, electric power companies charge their consumer for kVA (electricity bill) while they generate kW (or MW) at the power station (power plant).They penalize their consumer for low power factor because they are not responsible for low power factor and kVA but you. Moreover, in a power plant, power factor is 1 therefore MW is equal to MVA …… (MW = MVA x P.F).
Another interesting and funny answer by one of our Facebook page fan…“Power House means house of the Power, and we know that the unit of power is Watt. That’s why we rated a power plant capacity in MW and not in MVA”.
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