25 Jul
2018
25 Jul
'18
11:06 a.m.
Eric Smith via cctalk wrote:
On Wed, Jul 25, 2018 at 7:54 AM, Paul Koning via
cctalk <
cctalk at classiccmp.org> wrote:
I'm not sure about motors, but 60 Hz power transformers can't handle as
high a maximum power (or current) when used for 50 Hz. The maximum power
has to be derated. Some transformers are specified/sold with a single power
specification for both 50 and 60 Hz use, which just means that the vendor
has built the necessary derating into even the 60 Hz specification.
Some products were built using different transformers for 50 vs 60 Hz
models, and the 60 Hz models uses a transformer inadequate for 50 Hz
operation.
It has to do with the physics of flux linkages and saturation. Under
sinusoidal operation, voltage is proportional to the product of maximum
flux and frequency.? If you fix the voltage, in order to operate at 5/6
of the nominal frequency you need a flux that is? 6/5 the nominal one.?
This might not seem like much more flux, but due to the nonlinear
magnetization characteristics,? the required magnetization current will
not be 6/5 times the nominal current, but it could in fact be three
times higher or even more, and highly distorted.
Under-frequency and over-voltage can kill power transformers easily.
A transformer designed to operate at 50 Hz will therefore have much more
iron mass in its core, power and voltage being equal.? That's why in
airplanes power is distributed at 400Hz; the transformers will be much
lighter.
carlos.
On Jul
25, 2018, at 9:50 AM, GerardCJAT via cctech <
cctech at classiccmp.org>
wrote:
Why don't you simply power it through an
inverter that will output 60
Hz, eventually even "down to" 120 V , true
sine wave, of course ??? They
are not that expensive by now.
I wouldn't worry about "true sine wave". That seems more of a marketing
thing anyway, and motors don't care. Just feed them with a variable
frequency motor drive and all should be well.
And be carefull : motor designed for 60 Hz,
running "under" 50 Hz, OR
THE OPPOSITE, I do not recall !!!, display a
significant reduced life time.
I have to check which is which, but I know this
is a question of
saturated magnetic field. Better check first.
That doesn't sound right. If you run the frequency up high enough you
might get into problems with magnetic materials not designed for it. And
much lower probably gives you reduced torque. But 50 vs. 60 Hz is a
trivial difference for a motor, I can't see any reasons for that to cause
trouble. I routinely run my lathe at half frequency if not less, and it
doesn't complain.