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#64415 - 04/07/06 11:14 AM Phase Rotation
Bill39 Offline
Member
Registered: 11/28/01
Posts: 75
Loc: Indianapolis, IN, USA
With respect to 3-phase systems in the USA, is clockwise rotation in Baltimore also clockwise rotation in Oregon?

In other words, are all of the power grids "phased" the same?

Probably a dumb question, but whatever.
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#64416 - 04/07/06 12:57 PM Re: Phase Rotation
Rewired Offline
Member
Registered: 01/01/06
Posts: 558
Loc: Hamilton, Ontario, Canada
From what I understand you want to know: Phase A in one location is Phase A in another.. same for Phase B and Phase C?
If so the answer is yes ( as far as I know), that is if its all part of the same power system (grid)and most likely it is.. Phase "A" will not just change and be Phase "C" somewhere else along the line.. If that were the case it would cause mass confusion should the utilities try to so some switching of their lines..
Mind you if you are talking two entirely different power systems or supplies, they could be both rotating the same way but out of sync, or at worst rotating in opposite directions.. The only time that would come into play is if you are trying to paralell another generator onto the grid or into a local power system..
A.D
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#64417 - 04/07/06 02:15 PM Re: Phase Rotation
ianh Offline
Member
Registered: 06/16/04
Posts: 54
Loc: Douglas, Isle of Man, UK
Depends on the vector of the transformers used by the PoCo.

Phase rotation on the HV side is likely to be the same all over the country where systems will be paralleled, but the LV phasing could differ between sites and regions.
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#64418 - 04/07/06 05:52 PM Re: Phase Rotation
renosteinke Offline
Cat Servant
Member
Registered: 01/22/05
Posts: 5316
Loc: Blue Collar Country
It's not that silly of a question!

Until the mid-'70's, the USA was divided into two sections, which could NOT exchange power. All PoCo gennys were "synchonised" with others in their respective grids- but somewhere (in Nebraske, I believe), the "western" grid met the "eastern" one....and they were just far enough out of sync to make interconnection impossible.

Now, I do not recall the specific details, but I recall quite a fuss was made over some chap who found a way to interconnect the grids. I seem to recall him getting some fancy prize for his efforts. I believe the two grids are still out of sync, but they are able to feed each other.
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#64419 - 04/07/06 08:14 PM Re: Phase Rotation
JoeTestingEngr Offline
Member
Registered: 11/04/05
Posts: 781
Loc: Chicago, Il.
If I walk into one of our locations with a scope, I can easily determine phase rotation. That's really all you know unless you have a wild leg. Consider an aux transformer with four unmarked conductors coming out.(safely landed for my metering pleasure.) I would know after a few seconds of metering, which conductor to mark as the neutral. I can scope a phase I choose to call "A" to neutral, and positive trigger on it. If the second phase I observe has its positive peak 5+ mS (120 degrees) later, I would call it "B". If 11+ mS (240 degrees), I would call it "C". But what I think is ABC, might teally be BCA, or CAB. Its usually just the rotation that matters, unless we have bus ties. Even if the phases are landed correctly, opposite sides of a bus tie might not be in sync. If I have a Wye source that I trust the phasing on, I can meter known Phase "A" to unknown phase "A","B","C". If I guessed right, "A" should give me the lowest AC voltage.
In DC traction power, we deliberately use out of phase sources. A 2 rectifier house will feed one rectifier Delta : Delta, and the other Delta:Wye. This helps smooth out the ripple since there is only rail inductance and no, building sized, filter capacitors to smooth out the 600 VDC.
Joe

[This message has been edited by JoeTestingEngr because a smile ate my elta

[This message has been edited by JoeTestingEngr (edited 04-07-2006).]
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#64420 - 04/07/06 08:29 PM Re: Phase Rotation
gfretwell Offline


Member
Registered: 07/20/04
Posts: 9038
Loc: Estero,Fl,usa
Phase rotation was such an issue with IBM that they gave the CEs a jumper in the power tub to swap them. Before that it was always swapping them at the easiest place to get at it. The odds of the recepticle being right was pretty much 50:50. Part of the problem was whether it was clockwise at the face of the Russell Stoll plug or the receptacle.

Joe I have done it many times like you say with the scope but usually we just plugged stuff in and saw which way the fans ran.
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Greg Fretwell
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#64421 - 04/07/06 09:02 PM Re: Phase Rotation
JoeTestingEngr Offline
Member
Registered: 11/04/05
Posts: 781
Loc: Chicago, Il.
Greg,
One of my first call outs was to a substation that had its 12.6 KV Line 1 fault. When the Load Dispatcher gave me the go ahead, I stood clear and had our Power Controller close the line via SCADA. KABOOM!!! I had Power open the AC bus tie and reclose Line 1 uneventfully. I went over to one ATS and got different voltages A to A, B to B, and C to C. I jogged the air compressor, caused the ATS to transfer, and jogged the compressor again. Then I called the Load Dispatcher and told him they swapped the phase rotation. When they called an hour later, I had Power close the line with the bus tie open and did the measuements again after jogging the compressor. I wasn't willing to trust their phasing if they had already gotten the rotation wrong. With my luck, they would have switched the wrong 2 phases to correct the rotation.
Joe
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#64422 - 04/07/06 10:31 PM Re: Phase Rotation
RODALCO Offline
Member
Registered: 12/08/05
Posts: 854
Loc: Titirangi, Akld, New Zealand
That's correct what Ianh sais.
Depends upon POCO requirements.
Here in Auckland a historical error was made between the 11 kV networks from the former Auckland Electric Power Board and the Waitemata Electric Power Board.
One uses Dy11 the other Dy1 for 11 kV hence we can't tie 11 kV feeders across the borders which are 60° out of phase instead of 120° which only requires swapping phases to get it corrected.
With the 60° phase difference special interphasing transformers are needed to get it right and this method is not used, because of unnecessary costs.

It is therefore very important to check that phasing is correct when backfeeding utility networks.
_________________________
The product of rotation, excitation and flux produces electricty.
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