Variable Frequency Generators
Thread Starter
Joined: Apr 2009
Posts: 645
Likes: 16
From: Canada
Variable Frequency Generators
The manuals for the aircraft I fly state that the AC generator does not output at a constant frequency. The range is around 200-800Hz. This has left me a bit confused. Firstly, can electrical users in the aircraft accept such variable frequencies? We have power outlets that clearly mention that they're on a fixed frequency of 60Hz. What's going on? The manuals don't mention when or how this variable frequency power from the AC generators are converted to a fixed frequency. I believe that all the users of electricity must need a fixed frequency.
Secondly, what's the benefit of a VFG vs an IDG or alternator/generator with a separate CSD
THANKS
Secondly, what's the benefit of a VFG vs an IDG or alternator/generator with a separate CSD
THANKS
Joined: Sep 2011
Posts: 352
Likes: 148
From: FL390
To answer your questions...
Yes, in three ways. Firstly, they could accept frequency-wild AC with no caveats. The amount of power delivered per second is the same regardless of frequency. Such items are usually purely resistive (so wing anti-ice, window heating, electrical heaters etc). Secondly, they could actually run on 28v DC, where a switching-type power supply rectifies the AC to DC. These typically don't care about the frequency of AC power supplied. Finally, you can rectify into DC and then invert back into AC for heavy duty motor loads (a synchronous motor on frequency wild AC is a bit useless). The 787 does this for the air compressors / CACs / engine starting / etc etc.
See point three above - they'll be rectified and inverted.
Weight saving. You can also use a VFG as a starter motor in some instances.
1. can electrical users in the aircraft accept such variable frequencies?
We have power outlets that clearly mention that they're on a fixed frequency of 60Hz
Secondly, what's the benefit of a VFG vs an IDG or alternator/generator with a separate CSD
