Assuming the alternator shown in figure "A" of the illustration is equipped with a diode plate as configured in figure "D", what is the purpose of the diode plate? Illustration EL-0037

Correct Answer: Option C — It rectifies exciter armature AC to DC for rotating main field excitation and eliminates the need for brushes.

Rotating diode plates on brushless marine alternators rectify alternating current from the exciter armature into direct current. This DC output supplies the main rotor field winding directly, eliminating the need for high-maintenance slip rings, carbon brushes, and external excitation wiring per IEEE 45 standards.