एक सिंक्रोनस जनरेटर (अल्टरनेटर) में, प्राइम मूवर की गति सीधे किसे नियंत्रित करती है?

Which of the following factors primarily affects the efficiency of a synchronous generator, in addition to the core and copper losses?

Select the option that is true regarding the following Assertion (A) and Reason (R): Assertion (A): In a synchronous generator phasor diagram under a specific unity power factor condition, the armature current (Ia) is in phase with the excitation voltage (Ef), and the excitation voltage leads the terminal voltage (Vt). Reason (R): When a synchronous generator operates in generating mode delivering power, the excitation voltage always leads the terminal voltage by the load angle.