mdunst@smtplink.coh.org wrote:
>Bottom line: What is the benefit of Three phase? Can you get more
>"cluck for your buck" with three phase? i.e. is it more cost effective
>to run a one hp motor on standard 220 or 3P 208??
I believe you can get more power for the same size wire from 3 phase, but I
have tried to work it out mathmatically.
Another advantage is less pulsing; single phase (and I include 220vac in as
single phase, because that's how it is used in AC motors) has 120 dips (0
volts) every second-the motor rotor is not being pulled at this time.
(because of this, many AC 110vac motors can go backwards if the starter coils
are wired backwards-the magnetic field is the same to the rotor spinning
either direction).
3 phase has distinct peaks between all 3 pairs of the three wires-as someone
else said, 120 degrees apart (or around 2 milliseconds, I think). 3 phase
has no point at which there is no voltage or current flow, and smaller/higher
frequency pulses in the rotor. because the rotor is always being pulled
forward, three phase motors can be smaller for the same power. (and I think
they are more efficient, but I don't know that for sure)
It's a lot easier to see this with graphs and drawings, but that's the idea.
(and I'm doing a really poor job of explaining this-maybe someone else can do
better (if anyone cares)
Scott M Ryan
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