# Questions raised by Bob's VFD experiment

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?
--
Roger Shoaf
If you are not part of the solution, you are not dissolved in the solvent.
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Any phase angle difference is always at a maximum of 90 degrees out.
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wrote:

times
the
Any phase angle difference is always at a maximum of 90 degrees out.
What stops it at 90 degrees?
--
Roger Shoaf
If you are not part of the solution, you are not dissolved in the solvent.
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wrote:

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
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Well said Mark.
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
Mark Rand wrote:

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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.
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" < snipped-for-privacy@nospamsyix.com> wrote in message
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Wild_Bill wrote:

Not necessarily. I heard about a wood shop that ran all their motors on 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.

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
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says...

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

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I read your report. You clearly had a lot of fun. Nowadays they could even fire you for "bringing a weapon to work".
i

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ignoramus23515@NOSPAM.23515.invalid says...

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

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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.
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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: < snipped-for-privacy@d-and-d.com> | Voice (all times): (703) 938-4564
(too) near Washington D.C. | http://www.d-and-d.com/dnichols/DoN.html
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wrote:

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
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DoN. Nichols wrote:

We had a much lower level of "security". :-) 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...
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Lewis Hartswick wrote:

You would be surprised how well that muzzle flash shows up on the naked eyeballs, Lew.
--

Richard Lamb
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cavelamb wrote:

Yea BUT you cant be looking the full hemisphere under a chopper all the time. :-) ...Lew...
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On Fri, 19 Feb 2010 17:18:35 -0500, the infamous DT

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
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snipped-for-privacy@diversify.invalid says...

snipped-for-privacy@wustl.edu

flywheel

wound

to

we

averaging

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

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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.
i
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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.
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