Determine phase rotation from one line diagram

[elemke]

We are having a discussion about determining phase rotation of a generator from a one line diagram. The drawing in question has a rotation arrow moving in the counterclock wise direction. It also has phase indications of T1 @ 12'oclock, T2 @ 4 o'clock and T3 @ 8 o'clock. The opinion here is ABC rotation.

 

[unclebob]

I agree with your opinion, phasing is ABC.

 

[stevenal]

The observer is stationary while the phasors rotate in the direction of the arrow. You've described T1 T2 T3 rotation. Does diagram indicate how phases are connected? Convention would be to connect ABC to 123, but I would not assume so.

 

[elemke]

To stevenal

The drawing does not indicate what is connected to T1 T2 or T3. But the way I interpet it, if C phase is connected to T1 and B phase to T2 and A phase to T3 then the phasing would be CBA or ABC if connected 123.

 

[stevenal]

Agreed.

 

[jtkirb]

I see this on drawings all the time. It would reduce the confusion if people would put the arrow in the intended direction (CCW or CW) and use the correct phases as well.

That way there is no mistakes.

JTK

 

[rcw retired EE]

The detail you describe is on most drawings.

I like GE's statement - "The voltages reach a positive maximum in the order T1, T2, T3." No confusion on CCW or CW, viewed from turbine end or collector end. But I have had generator drawings showing "ABC, T1, T2, T3 rotation" where the gas turbine spun the rotor in the opposite direction from "standard" so the electrical drawing (and my buswork) was wrong.

Another drawing detail that is useful is a view looking at the generator terminals saying something like "Viewing the bus leads as they exit the terminal enclosure, the phase sequence is T1, T2, T3, right, center, left."

 

[mikey70]

The term "rotation" is somwhat of a misnomer. Without seeing your drawing, you may be looking at a phasor diagram which is always shown on the nameplate of modern transformers and generators. As Mr. Wilson pointed out, to be meaningful, the direction of rotation of the rotor of the generator has to be referenced to one end or the other. On the other hand, phasor diagrams are always shown with the phasors rotating counterclockwise. Don't try to make these two concepts into one, the phasor diagram will not tell you which direction the rotor turns, only the resulting electrical phasors when it turns in the direction intended by the manufacturer.

The labeling T1 T2 T3 will not tell you where ABC is located it only tells you the sequence in which the phases appear, there are only two. 123 or 132. The three phase generator can be sychronized with T1 connected to A B or C as long as the remaining two phases follow the proper sequence. The reason that all your drawings show phase A connected to particular terminal is because the synchronizing pot is permanently wired to a given phase and it always synchronizes to that phase.