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Electrical Systems On New Airplanes

Wed Oct 15, 2014 1:36 am

So the 787 has an electrical system far more advanced than the rest of the Boeing types. I am very curious to learn more about the wild frequency voltage and how it works. I heard the system is 270 volts or something until the voltage is converted to DC when it gets to the motor/actuator?

Will Embraer, Airbus, Bombardier or any other manufacturer adopt this system architecture?

Can anyone elaborate? Thanks in advance.

[Edited 2014-10-14 18:47:45]
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RE: Electrical Systems On New Airplanes

Wed Oct 15, 2014 2:47 am

The Dash 8 already uses this- the A/C generators are run off the propeller reduction gearbox. The hydraulic pumps, boost pumps, TRU and prop heaters are all non- frequency sensitive.
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RE: Electrical Systems On New Airplanes

Wed Oct 15, 2014 5:31 am

Quoting slimshady (Thread starter):
I heard the system is 270 volts or something until the voltage is converted to DC when it gets to the motor/actuator?

The generator output is 235 Volts/AC. Most of the large hydraulic motors are 270Volts/DC, Flight Deck displays 28Volts/DC and the cabin is 115Volts/AC. The galleys are normally 235Volts/AC.
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RE: Electrical Systems On New Airplanes

Sun Oct 19, 2014 11:21 am

The basis of the wild-frequency electrical system on the 787 is that the generators vary speed proportionally with engine speed, this dispenses with the need for a constant speed drive typically used on older electrical generators.

The wild frequency output from a variable-speed generator can then be smoothed to a constant frequency with an AC-AC converter, or rectified to DC output depending on the end user electrical consumer.

I think the benefit of the variable frequency gen on the 787 is that it then doubles up as a starter motor for the engines, a function which a CSD-governed generator cannot perform.

Also, an old thread on the topic-
A/C Wild Electrical Power (by TOGA Sep 4 2003 in Tech Ops)

Some AC hydraulic pumps are wild frequency - the MD-80 has them, probably some others - where the pump is a constant pressure, variable displacement in-line type, it doesn't necessarily matter what speed the motor turns at within a given range, and so the motorpump speed is governed by the wild frequency, which itself varies with engine speed, ultimately varying the pump flow capacity proportionally with engine thrust, which is quite clever I think  

But I digress - yes, other manufacturers probably are looking at wild-frequency AC power systems, the more-electric trend of aircraft systems development is making the old pneumatic-starter systems on jet engines redundant, reduces weight and has efficiency benefits.

Wild frequency AC is not new though, have a look at this article from 1958;
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