Leading power factor during crane operation?
Leading power factor during crane operation?
(OP)
Do container crane drives create leading kvars during operation? The data below is from a data logger on 4160V transformer serving a container crane. During idle periods, there was about -10.5 kvars measured per phase. During most of the operation the power factor goes to highly lagging as expected. However, during few of the period, the meter recorded large amounts leading kvars. Is this realistic? or is the meter being tricked? I don't have any details on meter, other than is a temporary meter at the 13.8/4.16kV transformer.
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DATE_______TIME__ PF__ AMPS KILOVARS 07-Feb-14 16:08:00 -0.60 5.3 -10.1 07-Feb-14 16:08:30 0.54 56.5 113.7 07-Feb-14 16:09:00 0.71 30.8 52.0 07-Feb-14 16:09:30 -0.35 50.4 -113.2 07-Feb-14 16:10:00 -0.33 29.6 -67.1 07-Feb-14 16:10:30 0.48 30.2 63.6 07-Feb-14 16:11:00 -0.49 7.7 -16.2 07-Feb-14 16:11:30 -0.56 5.2 -10.4 07-Feb-14 16:12:00 -0.55 5.3 -10.6 07-Feb-14 16:12:30 -0.58 5.2 -10.2 07-Feb-14 16:13:00 -0.61 5.3 -10.1





RE: Leading power factor during crane operation?
Keith Cress
kcress - http://www.flaminsystems.com
RE: Leading power factor during crane operation?
Going back to generator theory, If the voltage of a grid tied generator is raised above the grid voltage the voltage may not rise but the set will export VARs. I would expect that as the back EMF of a regenerating motor rises above the grid voltage, the motor, acting as an induction generator, will export VARs.
bacon4life, does the VARs out coincide with lowering heavy loads?
Bill
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"Why not the best?"
Jimmy Carter
RE: Leading power factor during crane operation?
www.KilroyWasHere<dot>com
RE: Leading power factor during crane operation?
www.KilroyWasHere<dot>com
RE: Leading power factor during crane operation?
RE: Leading power factor during crane operation?
It's a little bit of a head scratcher.
One thing that comes to mind. Sometimes the steady state induction motor model tricks us when we try to apply it to transient conditions such as acceleration, deceleration, plug reversing.
Would be interesting to try to look at currents and voltages during these transients in a transient model (a.k.a. state space model, examples in Krause's book) to try to see if anything resembling var reversal can be obtained.
I don't foresee having time to do that in the near future. I think some others on the forum have programs including ATP etc. Maybe they can try if they are interested.
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(2B)+(2B)' ?
RE: Leading power factor during crane operation?
obviously would help to know more about system (mike's questions)
And if more measurements are possibly like current and voltage waveforms or more details about operations going on during these periods, that would of course help everyone.
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(2B)+(2B)' ?
RE: Leading power factor during crane operation?
It is probably the routine used by the meter.
If the meter is using the basic formula, PF = W/VA then when the motor regenerates, the sign of W will change. The meter may assume and show positive power in every case to simplify connection.
Rather than showing the KW as negative the meter may be showing the PF and KVAR as negative.
The electronic KWHr meters our little utility used converted exported power to imported power and then summed both exported and imported power under imported power. This defeated the old dodge of removing and reinstalling the meter upside down for part of every month to reduce the power charges.
These were residential meters and I never had the occasion to investigate PF and KVARHrs.
The National utility on the mainland used a similar default setting on industrial meters.
Anecdote: A wealthy businessman installed a wind turbine at one of his locations. He didn't bother with permissions or approvals, just had it connected and turned on.
At the end of the month he found that he had been billed for all the power that he had used and for all the power that he had imported., due to the default meter setting.
Bill
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"Why not the best?"
Jimmy Carter
RE: Leading power factor during crane operation?
CR
RE: Leading power factor during crane operation?
I will say it is possible what is being measured is the true power factor. But, I won't make random guesses as to why it is possible or go beyond saying it can be possible. Post details on the motor and the drive operating the motor if you want to confirm this does happen and you want to know why it happens.
RE: Leading power factor during crane operation?
I found out that the meter was a Varcorder, which uses electric field sensor rather than a PT to calculate the power factor. It then uses the programmed nominal voltage to calculate kvars. Since it just uses the angle between current and voltage, I don't think it recorded that the real power flow changed direction during regeneration. Rather, it seems to have recorded real power flowing out and reactive power flowing to the crane as negative power factor.
RE: Leading power factor during crane operation?
If you on a crane have asynchronous motors with frequency inverters with an additional option called regenerative mode without a resistor which would be spent on energy in generator mode, it must be returned to the grid .The question is what percentage of used energy should be returned.
Good luck