Explained: Working and use of brushless alternators

Brushless Alternator are used because there is less wear and tear on the Alternator as there are very few moving parts.
In Brushless Alternators slip rings and Brushes are eliminated and excitation is provided, not by conventional direct current exciton but by a small alternator. 
As it composed of two alternator connect end to end on a single shaft. Large Main Alternator has stationary armature and rotating magnetic field winding. Smaller AC Excitor has a field winding on the stator and armature winding on the rotor. 
AC output from the exciter armature is given to the 3 phase diode bridge circuit mounted on the extended shaft of the main alternator to produce steady DC voltage.

This DC voltage is directly to the field coil of the main alternator which is located on the rotor with arrangement carbon brushes and slip rings are eliminated. The absence of brushes, brush gears and carbon dust improve reliability and considerably reduce generator maintenance. The Power Loss is also reduced Rectification of AC Excitor voltage is achieved by 6 shafts mounted silicon diodes. The suppression resistor connected across the main generator field protect the diodes against voltage surge arising from a sudden change in excitation current.

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