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Why not 400 Hz AC?

E

Eric R Snow

Jan 1, 1970
0
Reading the post about square wave AC I see that higher frequency AC
makes for noisy motors and transformers. Is this the only reason not
to use higher frequency power? It's obvious that smaller motors and
etc. could save tons of money so it seems that there must be a good
reason why everybody isn't switching to higher frequency devices.
Speaking of higher frquency, would it be economical to use inverters
to raise the frequency at the user's location so that smaller motors
could be used? I use VFDs on my machine tools but they still drive
physically large 60 Hz rated motors. I have them mounted in enclosures
so I don't hear the VFDs singing and the motors don't seem that noisy.
It is a machine shop though.
Thanks,
ERS
 
H

Homer J Simpson

Jan 1, 1970
0
Reading the post about square wave AC I see that higher frequency AC
makes for noisy motors and transformers. Is this the only reason not
to use higher frequency power?

The losses are higher. 16? Hz power was used for some European rail systems.

The use of lower frequencies also provided the advantage of lower impedance
losses, which are proportional to frequency. It was this argument that
resulted in the use of 25 Hz in the initial generation installations at
Niagara Falls, in anticipation of long-distance transmission to Toronto.

http://en.wikipedia.org/wiki/Alternating_current
 
M

Michael A. Terrell

Jan 1, 1970
0
Eric said:
Reading the post about square wave AC I see that higher frequency AC
makes for noisy motors and transformers. Is this the only reason not
to use higher frequency power? It's obvious that smaller motors and
etc. could save tons of money so it seems that there must be a good
reason why everybody isn't switching to higher frequency devices.
Speaking of higher frquency, would it be economical to use inverters
to raise the frequency at the user's location so that smaller motors
could be used? I use VFDs on my machine tools but they still drive
physically large 60 Hz rated motors. I have them mounted in enclosures
so I don't hear the VFDs singing and the motors don't seem that noisy.
It is a machine shop though.
Thanks,
ERS


For the same reason 25 Hz was used in mines. Motor speed. Lets see
you use a VFD on a 400 HZ motor and get any usable torque out of it at
60 HZ or below.


--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida
 
K

Ken

Jan 1, 1970
0
The losses are higher. 16? Hz power was used for some European rail systems.

Yes, exactly one third of 50Hz we use in scandinavia
for our rail systems (16000 Volts).

The use of lower frequencies also provided the advantage of lower impedance
losses, which are proportional to frequency. It was this argument that
resulted in the use of 25 Hz in the initial generation installations at
Niagara Falls, in anticipation of long-distance transmission to Toronto.

http://en.wikipedia.org/wiki/Alternating_current

For long lines low frequency is better. DC is best.
 
H

Homer J Simpson

Jan 1, 1970
0
Yes, exactly one third of 50Hz we use in scandinavia
for our rail systems (16000 Volts).

For long lines low frequency is better. DC is best.

Essential for undersea transmission.
 
J

John

Jan 1, 1970
0
Reading the post about square wave AC I see that higher frequency AC
makes for noisy motors and transformers. Is this the only reason not
to use higher frequency power? It's obvious that smaller motors and
etc. could save tons of money so it seems that there must be a good
reason why everybody isn't switching to higher frequency devices.
Speaking of higher frquency, would it be economical to use inverters
to raise the frequency at the user's location so that smaller motors
could be used? I use VFDs on my machine tools but they still drive
physically large 60 Hz rated motors. I have them mounted in enclosures
so I don't hear the VFDs singing and the motors don't seem that noisy.
It is a machine shop though.
Thanks,
ERS

The optimum frequency depends on the application. Most WWII aircraft
used a 400Hz power system for the weight savings it gave -
higher frequency = less iron in generators and power transformers =
less tare weight = more payload

John
 
J

John Larkin

Jan 1, 1970
0
The optimum frequency depends on the application. Most WWII aircraft
used a 400Hz power system for the weight savings it gave -
higher frequency = less iron in generators and power transformers =
less tare weight = more payload

John

Aircraft power systems still run at, or about, 400 Hz.

John
 
J

John Larkin

Jan 1, 1970
0
Reading the post about square wave AC I see that higher frequency AC
makes for noisy motors and transformers. Is this the only reason not
to use higher frequency power? It's obvious that smaller motors and
etc. could save tons of money so it seems that there must be a good
reason why everybody isn't switching to higher frequency devices.
Speaking of higher frquency, would it be economical to use inverters
to raise the frequency at the user's location so that smaller motors
could be used? I use VFDs on my machine tools but they still drive
physically large 60 Hz rated motors. I have them mounted in enclosures
so I don't hear the VFDs singing and the motors don't seem that noisy.
It is a machine shop though.
Thanks,
ERS


At 400 Hz, the speed of a single-pole induction motor would be close
to 24,000 RPM, which wouldn't be very practical for industrial apps. I
guess the optimum frequency for generation, distribution, and use must
be close to 55 Hz, since the US picked 60 and Europe went with 50.

As noted by others, there were 25 Hz systems, used for big pumping
stations among others, and 400 Hz for aircraft.

400 Hz is terrible; it leaks into everything and is very audible.

We have a VFD drive for a blower on the roof. It's an unfiltered IGBT
chopper, and radiates immense amounts of emi. We had to hang all sorts
of toroidal inductors on its outputs to tone it down. The blower on
the roof still sings audibly.

John
 
P

Paul E. Schoen

Jan 1, 1970
0
John Larkin said:
At 400 Hz, the speed of a single-pole induction motor would be close
to 24,000 RPM, which wouldn't be very practical for industrial apps. I
guess the optimum frequency for generation, distribution, and use must
be close to 55 Hz, since the US picked 60 and Europe went with 50.

I wound a motor that was originally 4 pole single phase (1720 RPM at 60
Hz), as a three phase 12 pole motor, which I ran at about 1720 RPM at 180
Hz. I couldn't make more poles because there were only 36 stator slots. I
found some three phase 400 Hz induction motors online that were 4 pole and
ran at 12,000 RPM, which is OK for small motors. I think a 1 HP motor was
about the size of a one pound can of beans, and not a whole lot heavier.

It seems that the industry is just resisting what I see as obvious, that
you can wind a standard motor for a lower voltage at 60 Hz, and use V/F
drive easily up to 150 Hz or 180 Hz before eddy currents and other losses
prevail. Better steel and thinner laminations, although more costly, might
push that to 360 Hz or even maybe 600 Hz. If you can design the rotor and
stator properly, with something like 72 slots, you could make a 24 pole
motor that would run nicely at 1800 RPM at 360 Hz. If the losses don't make
it impractical, you could have a 40 HP automotive motor about the size and
weight of a lawnmower engine.

Certainly you could save a lot of weight and volume by using DC to transmit
power. A 480 VAC motor drive runs on a "link" of about 720 VDC, which is
just 480 VAC rectified. A drive about the size of a shoebox can produce 3
phase power of about 5 HP, or 3.75 kW, and you could easily carry two or
three of them in one hand. An equivalent 50 or 60 Hz transformer would be a
tough weight for Aarnold to clean and jerk.

Eventually I would not be surprised to find DC used to power appliances
directly, with internal 3 phase modules (such as IRAMS from International
Rectifier) to supply drive power for the motors. Lamps and heaters don't
care if it's AC or DC, and high end electronics like computers use
switching supplies which convert incoming AC to DC anyway.

The problem with DC is that it is harder to switch, and possibly more
deadly than AC, although 60 Hz is "just perfect" for causing heart
fibrillation.

Paul
 
H

Homer J Simpson

Jan 1, 1970
0
At 400 Hz, the speed of a single-pole induction motor would be close
to 24,000 RPM, which wouldn't be very practical for industrial apps. I
guess the optimum frequency for generation, distribution, and use must
be close to 55 Hz, since the US picked 60 and Europe went with 50.

http://en.wikipedia.org/wiki/Utility_frequency

"Though many theories exist, and quite a few entertaining urban legends,
there is little certitude in the details of the history of 60 Hz vs. 50 Hz.
What is known is that Westinghouse in the US decided on 60 Hz and AEG in
Germany decided on 50 Hz, eventually leading to the world being mostly
divided into two frequency camps. Frequencies much below 50 Hz gave
noticeable flicker of arc or incandescent lighting. Westinghouse decided on
60 Hz before 1892 and AEG decided on 50 Hz by 1899. Tesla is believed to
have had a key influence in the choice of 60 Hz by Westinghouse. Use of 60
Hz allowed induction motors to operate at the same speeds as standardized
steam engines common in the late 19th century.

However, the first generators at the Niagara Falls project, built by
Westinghouse, were 25 Hz because the turbine speed had already been selected
before alternating current power transmission had been definitively
selected.

Westinghouse would have selected a low frequency of 30 Hz to drive motor
loads, but the turbines for the project had already been specified at a
speed which was incompatible with a generator designed for 30 Hz. Because
the Niagara project was so influential on electric power systems design, 25
Hz prevailed as the North American standard for low-frequency AC. A
Westinghouse study concluded that 40 Hz would have been a good compromise
between lighting, motor, and transmission needs. Although frequencies near
40 Hz found some commercial use, this frequency never overcame the
"installed base" of 25 Hz, 50 Hz and 60 Hz equipment."

60 Hz is cheaper to use - smaller transformers. 50 Hz is more efficient.

25 Hz makes lamps flicker - fluorescents are bad - you need two tubes phased
apart.
 
C

Charlie Siegrist

Jan 1, 1970
0
Aircraft power systems still run at, or about, 400 Hz.

As do ocean-going vessels. Same benefit from the weight savings, I
suppose.
 
H

Homer J Simpson

Jan 1, 1970
0
As do ocean-going vessels. Same benefit from the weight savings, I
suppose.

News to me. In my day they all ran on DC. Now they run on AC and I believe
many can run 50 or 60 Hz so they can use dockside power in most of the
world.
 
C

Charlie Siegrist

Jan 1, 1970
0
News to me. In my day they all ran on DC. Now they run on AC and I believe
many can run 50 or 60 Hz so they can use dockside power in most of the
world.

Well, I was speaking via hearsay. I have been told that the US Navy uses
400Hz power. Maybe it's because they like to use the same equipment as the
zoomies. Maybe it's because they have a lot of aircraft and like their
stuff to be compatible. Maybe I'm up in the night.
 
J

John Larkin

Jan 1, 1970
0
As do ocean-going vessels. Same benefit from the weight savings, I
suppose.

All the commercial ship I've seen were all 60 Hz. Who needs to save
weight on a ship?

John
 
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