Why alternator are called synchronous generator? Because it rotates at a constant (i.e.synchronous speed) no matter whats the load on alternator.For instance if its a 2 pole machine it will rotate at 3000 rpm to produce a f … requency of 50 Hz in India.When a synchronous motor has current applied to the windings on its rotor and the stator is energized with … say a 50hz line supply (with little or no physical load) then the exact amount of excitation provided by the rotor can determine whether the stator displays inductive or capacitive properties.