Questions raised by Bob's VFD experiment
Roger Shoaf
the design speed by increasing the frequency to 360 Hz.
In school they talk about an induction motor causing the voltage to lead the
current, but in the situation where the frequency is increased, does the
phenomenon ever cause the voltage to come back into phase with the current
albeit one cycle out?
If so does the motor then run more efficiently at that frequency?
--
Roger Shoaf
If you are not part of the solution, you are not dissolved in the solvent.
Cross-Slide
Any phase angle difference is always at a maximum of 90 degrees out.
Roger Shoaf
"Cross-Slide" <3t...@centurytel.net> wrote in message
news:f5cd8c85-a54b-4aae...@o30g2000yqb.googlegroups.com...
On Feb 19, 10:51 am, "Roger Shoaf" <sh...@nospamsyix.com> wrote:
> After reading Bob Engalhardt's post about running his motor at about 6
times
> the design speed by increasing the frequency to 360 Hz.
>
> In school they talk about an induction motor causing the voltage to lead
the
> current, but in the situation where the frequency is increased, does the
> phenomenon ever cause the voltage to come back into phase with the current
> albeit one cycle out?
>
> If so does the motor then run more efficiently at that frequency?
>
>
Any phase angle difference is always at a maximum of 90 degrees out.
What stops it at 90 degrees?
Wild_Bill
around or over 4x the rated RPM.
I suppose that the HP ouput is much lower at higher speeds.
Although the motor continues to run at many times the rated speed, I suspect
that it would fail (smoke, not explode) at or before 4x maybe if a
reasonable load (of 1/2 to 1 HP) was being driven.
I'm not suggesting that Bob connect the motor to a load since the original
experiment is dangerous enough.
Being able to see the results of such experiments performed in appropriate
protective enclosures would be ineresting (or at an isolated location like
where Mythbusters did the water heater experiments).
Very high speed video cameras would most likely make some enjoyable videos.
There must be some occupations where rotating mechanisms to the point of
destruction was a fairly common event, but I suspect that much of that type
of analysis is done with computers now, not actually scattering parts.
--
WB
.........
"Roger Shoaf" <sh...@nospamsyix.com> wrote in message
news:12665982...@news01.syix.com...
Ignoramus23515
I will set out to acquire a free or almost free 3600 RPM motor for a
similar experiment.
I actually have such a motor (3 HP), but it is too nice to ruin.
i
Bob Engelhardt
relevant to your question.
DoN wondered whether it would even start with an initial freq of 360, so
I reduced to "accel" time to 1/10 sec (with output freq of 360 Hz).
When I pushed "start" the speed snapped up, but not to 10700 (2400 IIRC)
& there was a different sound from the motor windings.
As I turned down the speed pot at some point the motor started speeding
up & then down as I continued. I may not have the behavior exactly
right, but it was quite peculiar. This strangeness was present as I
increased the accel time until I got to 6 sec. Then it was fine.
So I expect that I'm going to be learning something new about motors,
Bob
Joe AutoDrill
Almost free "inverter capable" motor I can't help with, but if you want to
work with a brand new one and make a nice video:
Automationdirect.com
MTR-P33-3BD36 - $70 + shipping
Free shipping if you order more than $300 worth of stuff from them.
--
Regards,
Joe Agro, Jr.
(800) 871-5022
01.908.542.0244
Automatic / Pneumatic Drills: http://www.AutoDrill.com
Multiple Spindle Drills: http://www.Multi-Drill.com
Production Tapping: http://Production-Tapping-Equipment.com/
Flagship Site: http://www.Drill-N-Tap.com
VIDEOS: http://www.youtube.com/user/AutoDrill
V8013-R
Ignoramus23515
>> Very inspiring and commendable.
>>
>> I will set out to acquire a free or almost free 3600 RPM motor for a
>> similar experiment.
>>
>> I actually have such a motor (3 HP), but it is too nice to ruin.
>
> Almost free "inverter capable" motor I can't help with, but if you want to
> work with a brand new one and make a nice video:
>
> Automationdirect.com
> MTR-P33-3BD36 - $70 + shipping
This would be mean spirited, destroying a brand new motor.
I will look for a free used one in bad shape.
i
Joe AutoDrill
Not if it were posted on a business web site or YouTubbe to generate
business leads to your company... Or educate young minds (regardless of the
age of the body...) <grin>
> I will look for a free used one in bad shape.
I'll still look for the results and video. :)
Bob Engelhardt
> Very inspiring and commendable.
>
> I will set out to acquire a free or almost free 3600 RPM motor for a
> similar experiment.
Oh, yeah! A 3600 rpm motor on 360 Hz -> 21,000 rpm. That would be too
cool.
>
> I actually have such a motor (3 HP), but it is too nice to ruin.
>
And then there's that much more mass to wreak havoc if things go bad <G>.
Bob
Jon Elson
> After reading Bob Engalhardt's post about running his motor at about 6 times
> the design speed by increasing the frequency to 360 Hz.
>
> In school they talk about an induction motor causing the voltage to lead the
> current, but in the situation where the frequency is increased, does the
> phenomenon ever cause the voltage to come back into phase with the current
> albeit one cycle out?
>
phase shift where current leads voltage. it IS possible, in an inductor
with a large number of turns of very fine wire where the interwinding
capacitance will overtake inductance, but you are usually talking about
RF not 400 Hz where that happens. With an ideal inductor, a full 360
degree phase lag is impossible. With a real inductor with winding
capacitance, too, then the phase lag will go to 90 degrees, stay there
until this crossover frequency (at which point the capacitive reactance
approaches the inductive reactance) is reached, and then will head back
to zero degrees. When the cap. and inductive reactances are equal, the
phase angle will be zero - this is parallel resonance, and so the
winding current would be maximum, but the impedance of the winding would
be ZERO, ie. short circuit! This would be hard on your power supply.
it would also be at low RF frequencies, I would expect. WAY faster than
you could spin the motor.
> If so does the motor then run more efficiently at that frequency?
>
No, the motor efficiency would drop to zero, as all the current would be
feeding the winding capacitance, and never be available to do work.
Jon
Jon Elson
> I wonder if the motor's HP output starts to drop significantly at
> somewhere around or over 4x the rated RPM.
> I suppose that the HP ouput is much lower at higher speeds.
>
> Although the motor continues to run at many times the rated speed, I
> suspect that it would fail (smoke, not explode) at or before 4x maybe if
> a reasonable load (of 1/2 to 1 HP) was being driven.
800 Hz power. They were using conventional 50 Hz iron but rewound for
higher poles, I believe. So, they were not running plain 2-pole and
4-pole motors at 800 Hz, but they were still running them QUITE fast,
perhaps 12,000 RPM for an 8-pole motor. You definitely can get more HP
out of them by running the RPM up, pretty much on a linear scale, except
for windage losses and hysteresis losses. You can compensate for the
hysteresis loss by reducing stator excitation just a little bit,
sacrificing just a little bit of torque. You have to be careful
balancing eddy losses against frequency, though. For a proper ground-up
design of a high-frequency motor, the stator laminations should be made
thinner. At 400 Hz, you'd want to go to .001" laminations or so, and
then the varnish would be thicker than the iron, and really sabotage the
whole effort. If you can't change the laminations, then the stator iron
is going to get hot for sure, and I don't know how you combat that.
but, whoever rewound the motors for that wood shop figured all this out
and apparently made it work.
>
>
> There must be some occupations where rotating mechanisms to the point of
> destruction was a fairly common event, but I suspect that much of that
> type of analysis is done with computers now, not actually scattering parts.
>
The guys who build the smaller turbine engines have to do this
routinely. They generally use spin test pits, rotating the device on a
vertical shaft down in the pit. One popular scheme for making Titanium
turbine rotors is to machine them undersize, then run them up to 2X
normal operating RPM which stretches the metal in the direction of
stress. Somehow they figure out when the stretching has completed and
slow it down for balancing.
Anyway, testing to failure on new designs is certainly used less than
before, but testing high-speed rotating machinery for material defects
is a practice that still has to be done. You sure don't want to put
untested rotors in a $1 million++ engine and have it fly apart.
Jon
Ignoramus23515
Yep. Ideally I want to find a 3450 RPM 1 HP motor in 56 frame, ugly
and rusted with a busted keyway.
i
Jon Elson
never build up an adequate rotor field, and will "stagnate" at a low
speed. The rotor will also get REAL hot after a while.
Jon
Mark Rand
wrote:
>
>What stops it at 90 degrees?
With a pure resistor, the current is in phase with the voltage.
With a pure inductor, the current is 90 degrees behind the voltage.
With a pure capacitance, the current is 90 degrees ahead of the voltage.
With a mixture, you get somewhere in between.
If it helps visualize it ,mechanically, think of:-
Voltage=force (Still alternating :)
Current=speed
resistance=friction
inductance=inertia
capacitance=elasticity
it gives a feel for the effects
regards
Mark Rand
RTFM
DT
says...
>The guys who build the smaller turbine engines have to do this
>routinely. They generally use spin test pits, rotating the device on a
>vertical shaft down in the pit. One popular scheme for making Titanium
>turbine rotors is to machine them undersize, then run them up to 2X
>normal operating RPM which stretches the metal in the direction of
>stress. Somehow they figure out when the stretching has completed and
>slow it down for balancing.
We had several spin pits at NASA's Glenn Research Center for advanced flywheel
testing. The highest rpm flywheels were made with titanium rotors, then wound
with carbon fiber. The fiber was wound so tight it would compresss the hub to
within a high percentage of its failure at the highest stress points. Then we
spun until the forces cancelled out the compression, and the hub was averaging
neutral stress. Then went higher until the tension forces were too high.
I helped design a containment system using 12x121x12 cubetainers filled with
water to aborb an explosion so we could test above ground. Here is a pdf
describing the system. On page 7 is a photo of my test setup when I used my
Garand to fire blunted 30-06 bullets into the water boxes, great fun!
http://gltrs.grc.nasa.gov/reports/2002/TM-2002-211722.pdf
--
Dennis
Ignoramus23515
even fire you for "bringing a weapon to work".
i
pent...@yahoo.com
wrote:
At normal supply frequencies an induction motor looks like a
lossy inductance to the supply so the supply current phase angle
lags the supply voltage. The loss component is the combined
effect of mechanical and electrical losses plus the power
delivered to the load.
With small, not very efficient, motors the phase lag can be
large but can never reach 90 deg because this would correspond to
a pure inductance. A pure inductance has zero loss component so
it cannot draw power from the supply!
The inductive component of a motor load is the combined
effect of the shunt magnetising inductance and the series leakage
inductance . In conjunction with the internal winding stray
capacitance this results in parallel resonance (very high
impedance) at a fairly high frequency and series resonance (very
low impedance) at a much higher frequency. With typical motors
both these frequencies are vastly higher than any likely supply
frequency and can be ignored.
Small 3 phase motors will cheerfully run at many times their
design speed. Apart from obvious mechanical limitations the main
limiting factors are leakage inductance and overheating.
If the frequency is raised, but at the original nominal
voltage, a perfect motor would deliver the same HP independent
of speed. With a real motor the leakage inductance at the
increased frequency reduces the effective supply voltage so the
deliverable HP will decrease. The reduction is very dependent
on detail motor design.
If the flux density is maintained constant by increasing
the supply voltage at the same rate as the supply frequency the
iron losses increase rapidly. In addition, if advantage is taken
of the increased available HP, copper losses will increase.
Overheating then limits the available HP.
Jim
DT
ignoram...@NOSPAM.23515.invalid says...
>I read your report. You clearly had a lot of fun. Nowadays they could
>even fire you for "bringing a weapon to work".
They could have even then, it wasn't that long ago. But that testing was done
at my local range.
We used to have a gun club at NASA, in fact the range is still there. We used
to bring in weapons all the time, you just needed to have your name on a list.
Management succeeded in shutting down the range by saying to was a hazard to
the day care center. At some point they removed all the shooting related
trophies from the glass case in the employee center.
--
Dennis
sparky
> In article <6N2dnRb9adENjeLWnZ2dnUVZ_sGdn...@giganews.com>,
> ignoramus23...@NOSPAM.23515.invalid says...
Back before the days of electronic speed controls ( a very long time
ago ) I worked at a furniture factory where they used a motor/
generator set to produce 400 hz 3 phase power to operate the motors
on the wood shapers. These motors operated at 10,800 rpm.
Martin H. Eastburn
Voltage leads Current in Inductive circuit.
Current leads voltage in capacitive circuit.
Martin
Martin H. Eastburn
Beyond 90 degrees - consider 4 quadrants - resistance is to the right.
Inductance goes up and capacitance goes down. Rational values of the
combination or Z the AC impedance - is between -90 zero and +90 degrees.
beyond +90 and before 270 (or -90) is imaginary values.
Remember the root of -1 ? or "i"
Martin
whit3rd
> After reading Bob Engalhardt's post about running his motor at about 6 times
> the design speed by increasing the frequency to 360 Hz.
> ...does the motor then run more efficiently at that frequency?
The higher frequency causes the stator metal to heat more than in
'normal use'. The amount of such heating, and its effect on
the achievable torque, will vary from motor to motor.
At high frequency, there's a 'skin effect' in the stator
magnetization that will cause torque to drop, and a
stray inductance that will cause current to decrease,
in addition to the stator heating from magnetic hysteresis.
If there's a thermal overload for the motor, the worst that
will happen is it will open (if the motor has a resettable
thermal overload, that isn't a big problem).
All medium/large motors have a thermal protector of some sort.
Bob Engelhardt
<snip>
> If the frequency is raised, but at the original nominal
> voltage, a perfect motor would deliver the same HP independent
So raised frequency means raised speed, with same HP means reduced
torque. Then torque is inversely related to frequency. Right?
> If the flux density is maintained constant by increasing
> the supply voltage at the same rate as the supply frequency ...
Or, flux density is inversely proportional to frequency? Then what
happens at DC?
Thanks - good stuff.
Bob
pent...@yahoo.com
<bobeng...@comcast.net> wrote:
>pent...@yahoo.com wrote:
><snip>
>> If the frequency is raised, but at the original nominal
>> voltage, a perfect motor would deliver the same HP independent
>> of speed. ...
>
>So raised frequency means raised speed, with same HP means reduced
>torque. Then torque is inversely related to frequency. Right?
******* correct
>
>> If the flux density is maintained constant by increasing
>> the supply voltage at the same rate as the supply frequency ...
>
>Or, flux density is inversely proportional to frequency? Then what
>happens at DC?
*******Flux density tries (unsucessfully) to reach infinity. The
iron is saturated and the current determined by the winding
resistance.
Larry Jaques
<dthomp...@wowway.com> scrawled the following:
This is _highly_ irregular, Dennis. Why weren't you out wasting
taxpayer dollars like all the other govvies? (Many kudos, BTW.)
P.S: Did you use NHRA-approved flak jackets on those things?
--
"Just think of the tragedy of teaching children not to doubt."
-- Clarence Darrow
DT
lja...@diversify.invalid says...
That's not a bad idea, but I think the energy levels are too high to use them
alone. Most of our flywheels were in the 50,000 to 60,000 rpm range so the
peripheral speeds were in the 2500 to 3000 fps range. For the above ground
test rig, we used two or three layers of water filled boxes, then backed that
up with a bomb blanket that was custom built. Basically it strapped together
to form a cube about 6 feet on each side. Anything that made it through the
water would be traveling pretty slow by then and the blanket could handle it.
Compared to building a hardened concrete room or another underground spin pit,
we saved about 90% of the cost.
Commercial water barriers are used to suppress explosions and are quite
effective. A car with 8" thick water bags hanging on its sides will survive a
bomb blast alongside that would completey demolish an unprotected car. And
anti-bomb squads have disposable containment systems that are one cardboard
box inside another, with 8-10" of water bags in between.
There are even transportable magazine systems that are formed of 1 meter wide
hollow plastic columns that are arc shaped in cross section. They overlap to
provide a solid 1 meter wall of water. You build rooms made of them, they will
contain 1000 lb aircraft bombs.
--
Dennis
DoN. Nichols
> I read your report. You clearly had a lot of fun. Nowadays they could
> even fire you for "bringing a weapon to work".
Well ... while I never brought a weapon to work, I brought
something considered as bad -- a camera.
The trick is getting the proper paperwork *before* you bring it
in, and then make sure that the guards see the paperwork and the item
covered by the paperwork. Do that, and you are fine. Short circuit it
and you are in trouble.
No -- I couldn't bring in film. That was supplied, and
processed on post, so the images did not leave.
I have fired firearms there, but they belonged to the lab
(testing night vision sights of various styles under the actual
vibration from a M16A2 and such.)
Enjoy,
DoN.
--
Email: <dnic...@d-and-d.com> | Voice (all times): (703) 938-4564
(too) near Washington D.C. | http://www.d-and-d.com/dnichols/DoN.html
--- Black Holes are where God is dividing by zero ---
Pete Keillor
wrote:
>On 2010-02-19, Ignoramus23515 <ignoram...@NOSPAM.23515.invalid> wrote:
>> I read your report. You clearly had a lot of fun. Nowadays they could
>> even fire you for "bringing a weapon to work".
>
> Well ... while I never brought a weapon to work, I brought
>something considered as bad -- a camera.
>
> The trick is getting the proper paperwork *before* you bring it
>in, and then make sure that the guards see the paperwork and the item
>covered by the paperwork. Do that, and you are fine. Short circuit it
>and you are in trouble.
>
> No -- I couldn't bring in film. That was supplied, and
>processed on post, so the images did not leave.
>
> I have fired firearms there, but they belonged to the lab
>(testing night vision sights of various styles under the actual
>vibration from a M16A2 and such.)
>
> Enjoy,
> DoN.
I once took a weapon out of work and brought back, a Rem 700 in
.30-06. With five rounds of armor piercing obtained for me by the
head of security from the county sheriff. I was testing some vehicle
armor I had made. A security captain travelled with me while I
conducted the test.
Pete Keillor
Robert Swinney
happens at DC?"
If I may speak for Jim Pentagrid, DC is a special case not applicable to induction motors.
Bob Swinney
"Bob Engelhardt" <bobeng...@comcast.net> wrote in message news:hlnr7...@news4.newsguy.com...
pent...@yahoo.com wrote:
<snip>
> If the frequency is raised, but at the original nominal
> voltage, a perfect motor would deliver the same HP independent
> of speed. ...
So raised frequency means raised speed, with same HP means reduced
torque. Then torque is inversely related to frequency. Right?
> If the flux density is maintained constant by increasing
> the supply voltage at the same rate as the supply frequency ...
Lewis Hartswick
> On 2010-02-19, Ignoramus23515 <ignoram...@NOSPAM.23515.invalid> wrote:
>> I read your report. You clearly had a lot of fun. Nowadays they could
>> even fire you for "bringing a weapon to work".
>
> Well ... while I never brought a weapon to work, I brought
> something considered as bad -- a camera.
>
> The trick is getting the proper paperwork *before* you bring it
> in, and then make sure that the guards see the paperwork and the item
> covered by the paperwork. Do that, and you are fine. Short circuit it
> and you are in trouble.
>
> No -- I couldn't bring in film. That was supplied, and
> processed on post, so the images did not leave.
>
> I have fired firearms there, but they belonged to the lab
> (testing night vision sights of various styles under the actual
> vibration from a M16A2 and such.)
>
> Enjoy,
> DoN.
>
When were developing a muzzle flash detector for a helicopter
(to tell if it were being fired at from the ground) I just used
an old M1 while the other helper operated the breadboard.
We just went out back and fired toward the woods. :-) Those
were the "good old days", I guess about 1968 or so.
Incidentally it worked pretty well. :-)
...lew...
cavelamb
You would be surprised how well that muzzle flash shows up
on the naked eyeballs, Lew.
--
Richard Lamb
http://www.home.earthlink.net/~cavelamb/
Lewis Hartswick
chopper all the time. :-)
...Lew...