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 transmitted and distributed in a typical power system scheme. That’s why we express the rating of 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 50MW turbine connected to a 90MVA alternator 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.