State working principle of alternator. State the meaning self and separate excitation.
Working principle of alternator: When a conductor is moved in magnetic field or a magnetic field moved with respect to conductor, according to Faraday’s law of electromagnetic induction, the conductor cuts the magnetic field and an electromotive force is induced in the conductor.
Self-excitation: When the A.C. current from alternator itself is rectified and used for its excitation, then the excitation is said to be self-excitation.
Separate excitation: When D.C. excitation required for field winding of alternator is provided by using a separate source like battery or shaft-mounted exciter, then the excitation is said to be separate excitation.