Brushless alternators
March 10th, 2010Brushless alternators
Construction
A brushless alternator is composed of two alternators built end-to-end on one shaft. Smaller brushless alternators may look like one unit but the two parts are readily identifiable on the large versions. The larger of the two sections is the main alternator and the smaller one is the exciter. The exciter has stationary field coils and a rotating armature (power coils). The ac generator uses the opposite configuration with a rotating field and stationary armature. A bridge rectifier, called the rotating rectifier assembly, is mounted on a plate attached to the rotor. Neither brushes nor slip rings are used, which reduces the number of wearing parts.
AC alternator
The ac alternator has a rotating field as described above and a stationary armature (power generation windings).
Control system
Varying the amount of current through the stationary exciter field coils varies the 3-phase output from the exciter. This output is rectified by a rotating rectifier assembly, mounted on the rotor, and the resultant DC supplies the rotating field of the main alternator and brusheless alternator output. The result of all this is that a small DC exciter current indirectly controls the output of the main alternator.
Automatic voltage regulator (AVR)
An automatic voltage control device controls the field current to keep output voltage constant.
Varying the amount of current through the stationary exciter field coils varies the 3-phase output from the exciter. This output is rectified by a rotating rectifier assembly, mounted on the rotor, and the resultant DC supplies the rotating field of the main alternator and brusheless alternator output. The result of all this is that a small DC exciter current indirectly controls the output of the main alternator.
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