"The Natural Philosopher" wrote in message
...
Fred wrote:
"The Natural Philosopher" wrote in message
...
Fred wrote:
"The Natural Philosopher" wrote in message
...
Fred wrote:
To get the advantages of 3 phase, each waveform has to be close to
sinusoidal.


No it doesn't.

3 phase as far as a motor is concerned, simply means it knows which
way to go round.
What on earth are you talking about? Are you seriously suggesting that
it doesn't matter what the waveform is for each of the phases, that you
can still tell me which way the motor will turn? Wow.


As long as they are 120 degrees apart, it doesn;t matter whether they
are sine, square or spikes. It will go round


If we're measuring degrees then it implies a sinusoid, though in practise
there would be harmonics of the fundamental.


wrong.

If we apply an arbitrary waveform to each phase of a 3 phase motor, I can
assure you will not be able to tell which way it will turn.



as long as teh three wavefortms are poahse related, whether sinusoid or
nnot, it will turn.

There is a lot of difference between sinusoid, repetitive non sinusoid
with a common fundamental frequency harmonically and phase locked, and
'arbitrary'.

YOU have merely set up a straw man by saying arbitrary. I never claimed
the signals applied to the poles were random and arbitrary, merely that
they don't need to be sinusoidal.


AC motors are motors designed to work on an "AC supply"

An "AC supply" is an electrical supply system supplied by an alternator

An alternator provides a sinusoidally varying voltage/current (it has to)

AC theory allows design of such alternators and motors to be effective and
takes as a given that the supply is sinusoidal

The fact that a sawtooth waveform alternates in direction does not make it
an "AC supply"

The fact that some AC motors might "go round" if supplied by a sawtooth
waveform is irrelevant

A "DC motor" is not an "AC motor"

OK?


--
Bob Mannix
(anti-spam is as easy as 1-2-3 - not)