Re: MD-80 Electrical

Date:         18 Apr 98 00:49:22 
From:         k_ish <kenish@ix.netcom.com>
Organization: Netcom
References:   1
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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?

The power to the outlets in your house is single-phase.  There is a "hot" and
a "neutral", plus a safety ground.  The AC voltage looks like a 60Hz sine
wave.

Most industrial power systems use 3-phase power.  There are either three
"hots" and a "neutral", or just three "hots" and no neutral.  If you look at
the overhead wires in a residential area, there are usually two wires (hot +
neutral), and in many industrial areas four wires (3xhot + neutral).  The
three "hots" are all the same voltage and frequency, but are phase-shifted 120
degrees apart.

To answer your question, 3-phase power delivers more energy to the load per
unit of time.  It also reduces the current per phase for a given load (e.g. a
single-phase, 5HP motor will require lots more current per phase than a
three-phase 5HP motor).  This allows smaller, lighter wiring.

Lastly, aircraft power systems are 400Hz, not 50-60Hz like in your house.
This allows transformers, motors, etc. to be smaller and lighter for the same
amount of power.

Hope this isn't too much detail.

Ken Ishiguro