Re: MD-80 Electrical

Date:         18 Apr 98 00:49:23 
From:         ehahn@mitre.org (Edward Hahn)
Organization: The MITRE Corporation
References:   1
Followups:    1
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In article <airliners.1998.586@ohare.Chicago.COM>, stein1111@aol.com (Stein1111) wrote:
>Can someone help explane " 3 phase" when it comes to a 40KVA  115 volt and
>3 phase output generator.  What does 3 phases do for you?

It refers to the type of electrical generator connected to the aircraft
engines.  The "three phase" designation means that the generator is outputing
three separate 115VAC lines, which have waveforms which are 120 degrees out of
phase from each other.

The reason for having three-phase electrical equipment is two-fold.  1) it
allows three-phase heavy-duty motors to be driven (such as in the stabilizer
trim on a B727), and 2) redundancy: if one of the phases shorts out, a
three-phase motor will still operate.

(The way the generator produces the three phases has to do with the way the
rotor is wound - it has three completely separate sets of windings, and is
wound in such a way that the resulting windings produce voltages 120 deg out
of phase with each other.)

Incidentally, older aircraft also have three-phase 28VAC  on them.  They are
used in analog angle-position-sensors called synchros.

ed

>>>>  Ed Hahn    |    ehahn@mitre.org    |    (703) 883-5988  <<<<
The above statement is the opinion of the author.  No endorsement
or warranty by the MITRE Corporation is expressed or implied.
Really, I wouldn't kid you about a thing like this.