phase rotation

[SG-1]

Actually, he probably said the phasor rotation is CCW. If he used the term "phase rotation" I'm sure he did so in the context of "sequence".

As rattus has stated, phase sequence is the proper term. The term "phase rotation" is used but it is not what we might call "proper english".

Rattus properly covered phasor rotation in his post #10

He actually said:

"Phase rotation or, preferably , phase sequence is the order in which successive phase phasors reach their positive maximum values. Phasor rotation is, by international convention , counterclockwise in direction. Practically, then, phase rotation or sequence is the order in which the phasors pass a fixed point.

All standard relay diagrams are for phase rotation a, b, c. It is not uncommon for power systems to have one or more voltage levels with a, c, b rotation; then specific diagrams must be made accordingly. The connection can be changed from one rotation to the other by completely interchanging b and c for the equipment and connections." END QUOTE.


No matter if the sequence is abc or acb the phasor diagram shows the rotation anti-clockwise. The arrow heads for phasors b & c are exchanged, to designate the difference.

 

[Smart $]

True enough, and the first questions would be: which one is A, which one is B, and which one is C. You just got to have a rotation meter in the field.

Well any good field installer (electrician, of course) will tell you determining which is A, B, or C (or U, V, W, or other such nomenclature) doesn't matter. Only thing that matters is which direction the motor will rotate. Rotation meters help but mostly if one is refeeding a motor having a known rotation per the meter's indication. For all new motor installs, the motor is the "meter". Standard practice is to bump decoupled motors.

 

[mivey]

Well any good field installer (electrician, of course) will tell you determining which is A, B, or C (or U, V, W, or other such nomenclature) doesn't matter. Only thing that matters is which direction the motor will rotate. Rotation meters help but mostly if one is refeeding a motor having a known rotation per the meter's indication. For all new motor installs, the motor is the "meter". Standard practice is to bump decoupled motors.

Who knows where "A" is? (actually, sometimes we do have to know when tying two long circuits together and we will ride it out to verify phasing notes on the maps and poles).

I heard a young electrician at another table in a restaurant one day going on and on about "once they found the A phase". I thought the older guys would never correct him and it was driving me nuts.

 

[LarryFine]

For all new motor installs, the motor is the "meter". Standard practice is to bump decoupled motors.

Agreed. I wouldn't presume any 3ph motors are correct based on wiring them to a standard.