where can i get a working sketch of brushless alternator used in modern aircraft?

Question

the voltage generation at starting and then voltage regulation after starting : can some one explain clearly

Answer 1

Here's a link that attempts to explain how it works: http://avstop.com/AC/apgeneral/BRUSHLESS.html

Basically, a small permanent magnet generator mounted on the end of the alternator provides initial excitation. It's output is fed to the voltage regulator where it is rectified and fed to the exciter coils in the stator assembly, located between the PMG and the main stator windings. This induces an AC voltage in the pilot exciter armature located in the rotor. This AC voltage is rectified by a full-wave rectifier bridge located in the rotor assembly and fed to the main rotor windings where it excites a voltage in the main stator windings. Output is regulated by regulating the current to the exciter coils.

It's possible to dispense with the PMG if a source of DC power is available to provide initial excitation and this is being used in automotive applications where the battery provides this excitation. Aviation applications normally are self-excited to assure output even when no initial DC excitation source is available.

Answer 2

I don't know of any schematics on the web, but they are similar to wind turbine brushless alternators.

The brushless alternator is the same as a regular alternator except the rotor (field) gets its current from a small generator (exiter) mounted on the rotor. This is why there are no brushes.

First, when the rotor spins, the exiter generates current from the residual magnetic field from its field magnets (the same way a dc gen exites itself). This sends current to the field (which is on the rotor) of the alternator so it generates a magnetic field and makes the stator produce power.

To regulate the voltage, the field of the exiter is regulated. The stronger the exiter field, the stronger the exiter current, the stronger the alt field current (since they are connected) and the more power is produced.

The stator is a three phase Y winding and remains separate to produce three phase current at 400Hz. So there are four contacts A phase, B phase, C phase, and Ground. The speed of the alternator is kept constant by a Constant Speed Drive (CSD) or an Integrated Drive (IDG), but that's another story.

Answer 3

Aircraft Systems for Pilots by Dr. Dale DeRemer.

That was my textbook when I was in school and I just used it to study up for an airline interview. Has good pictures and I know for a fact theres a sketch of one of those in there.

The book should be available at sportys.com or Amazon.com for about $35. Its an invaluable resource for anyone interested in becoming a commercial pilot