Phase Rotation
Phase Rotation
(OP)
Hello Everyone
Is that true that Phase Rotation in UK is Negative Sequesnce ? If so why !!!
Thanks
Lenz
Is that true that Phase Rotation in UK is Negative Sequesnce ? If so why !!!
Thanks
Lenz
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RE: Phase Rotation
RE: Phase Rotation
As cranky108 noted, several US utilities have adopted an ACB phase sequence.
If equipment is installed in the US, phase sequence is mandated by various sections of the NEC; e.g. 408.3(E).
RE: Phase Rotation
RE: Phase Rotation
Our power system is ACB, and I experience modest difficulties communicating my rotation needs with motor repair shops (you'd think it'd be simple), but nothing that can't be overcome. As a result of a few historical mis-steps, we spend a little more effort... in some cases where bump check for rotation after installation is not acceptable, we do our own on-site rotation checks of large motors.
Also, for an ACB power system, I personally would call ACB positive sequence and ABC negative sequence. Because for example our negative sequence relays will sense the component of current flowing as ABC. As long as you know what you're doing, I guess it doesn't matter what you call it.
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(2B)+(2B)' ?
RE: Phase Rotation
RE: Phase Rotation
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RE: Phase Rotation
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If we learn from our mistakes I'm getting a great education!
RE: Phase Rotation
And even some relay manufactures have been confused.
That's the biggest drawback.
The rotation issue started as a nameing issue. The left wire is A, and the Right wire is C.
Now you should ask how many utilities are 30 degrees different from there phase A and the neiboring utilities phase A.
RE: Phase Rotation
RE: Phase Rotation
Regards
Marmite
RE: Phase Rotation
RE: Phase Rotation
In both scenarios the definition is widershins :)
RE: Phase Rotation
Is that rotation of the phasors, the spin direction of the phase rotation meter dial, the motor, turbine or generator rotation? From which end? (A major turbine supplier looks at the turbine and the generator from the coupling. The turbine rotates CW and the generator rotates CCW on the same shaft.)
The best description is "The voltages on terminals U1, U2, U3 will reach their positive maximum in the following sequence: U1, U2, U3." If my U1 connects to your phase C, and U2 to B it is ACB sequence.
Then we confuse ourselves by saying Phase A is on the left. Is that looking out from the substation to the line or looking into the substation? On double ended subs, either A needs to be on the right at one end or a phase swap occurs in the middle.
Bottom line, it's just names and we call the same thing different names with different reference points. When interconnecting make sure you communicate with your counterparts. Draw a vector diagram with a rotation arrow. On substations, sketch a phasing diagram. It is a real pain to swap the buswork.
RE: Phase Rotation
The problem is that most people want it short and simple. Motor runs backwards. That is a simple statement.
Why does it run backwards? Because someone wired it the wrong way! Or Because someone defined phase sequence the wrong way! Or Because my definition is right and yours isn't! It starts getting complicated already.
And then we haven't even started talking vectors and vector rotation and the fact that all rotating systems have negative (CCW) vector rotation defined as positive - simply because angles grow positive when rotating "backwards" in cartesian and polar diagrams. And so on.
Many of the posts in this thread start somewhere between motor shaft and definition of poistive angle in a polar diagram. That does not make the the issue any clearer. Personally, I think it is a non-issue.
I used to make sure the phase sequence was always "right" when commissioning new industries or new parts of an existing industry. Then I made sure that the phase sequence definitions and rotation definitions were understood by everyone involved.
After that, we walked through all motors and marked their intended rotation with permanent ink. Then we corrected all drawings and wiring diagrams/tables.
A very common remark was "It doesn't matter - more than half will still run wrong direction" They didn't. We saved lots of time and I got a reputation to be good at commissioning factories. Which I thought was good.
Also, reconnecting a heavy gauge cable ruined the good work made by the electrician and avoiding that results in a more reliable plant in the long run.
Gunnar Englund
www.gke.org
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