Re: 50 hz VS 60 hz and a 120 HZ question
- From: Don Foreman <dforeman@xxxxxxxxxxxxxxxxxxxx>
- Date: Tue, 30 Oct 2007 23:44:45 -0600
On Tue, 30 Oct 2007 09:01:36 -0500, Randy <rbraun333@xxxxxxxxx> wrote:
This group seems to have alot of electrical knowledge, sooo.....
The US is 60 HZ and Europe is 50 HZ, a 60HZ motor is more efficient,
so, what would happen if the US or the world for that matter would
switch to 120 HZ or maybe even as high as 400HZ (which is common in
aircraft). Motors and transformers would be much more efficient,
power savings could be enormous, both in transmission and use.
I realize this would have to be a 50 to 100 year task. Laws would
need to be passed and electronic devices would need to be sold that
would work on both frequencies. (many switching power supplies such as
in computers do not care what freq. power is input.)
I've read a bunch of articles about the newer inverter type welding
power sources that use 400 HZ and use small transformers and use much
less input power for the same output power.
I'm guessing it would take a panel of "experts" a few years to work
out the costs VS savings for this one. I've heard of some really
stupid things being studied by our government, maybe someone should
look into this.
I bought some old machinery from the Bethlehem Steel plant that was 25
cycle, WOW, talk about inefficient!! I had a 5hp motor that was built
on a 15 hp frame size.
Ideas, thoughts??
Biggest problem I think would be the generating end of things.
Thank You,
Randy
Remove 333 from email address to reply.
Higher frequency motors can be smaller for given power because they
run at higher speeds. A 4-pole 400 Hz induction motor would run at
about 11,500 RPM. System efficiency would probably be less because
speed reduction by gears etc would usually be required, but system
weight is what counts in aircraft.
As Bob Swinney points out, effiency is a matter of design, traded off
against other parameters like size, weight, cost, etc. In one sense,
lower frequency motors, though larger and more costly for given power,
could be more system-efficient where their lower speeds might reduce
or eliminate need for speed reduction kit which also has losses. Gear
trains are often considerably less efficient than ordinary AC
induction motors.
Power transmission over significant distance is generally more
efficient at lower frequency, with DC being most efficient. Further,
DC distribution would have the same advantage as 3-phase in that it
can deliver power continuously while single-phase AC delivers power
intermittently and thus requires energy storage in most useful
devices. In an ordinary motor this energy storage is in kinetic
energy and in the magnetic field. In electronic gear it's in
capacitors.
Developments in power electronics have made huge advances in the past
decade, and this will continue in terms of lower cost, higher
effiency and higher power levels. Power elex makes line frequency
about irrelevant because the power can be modified to suit the load --
as is already done in VFD's and brushless DC motors.
Power elex makes the notion of a "DC transformer" possible. The
actual xfmr is AC, usually at frequencies considerably higher than 400
Hz, but the functional block is DC in and DC out.
Inverter-type welders don't draw less power, but they do have much
better power factor than copper-iron machines so they draw less line
current, and thus result in lower losses in the distribution system.
.
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