Help Phase Angle vs Rotation

Thread Starter


Joined Nov 21, 2008
Incoming utility power is ABC and rotation is clockwise. Viewing an SEL 311L that shows Phase Angle as follows;
A= +120
B= 0
C= -120

If the utility were to flop A and B phases the rotation would reverse but would the Phase Angle now show;
A= 0
B= +120
C= -120

I guess the question is would the phase angle for "A" phase always be +120 no matter where it is located in a three phase system?

Any help would be appreciated.



Joined Nov 21, 2006
The relay uses whatever voltage that is connected to the A phase input as the reference. If the poco swapped A and B phases, the relay would continue to use whatever is connected to the A phase input as the reference. In this case, because the present system is sequenced ABC, the relay would see the phase sequence reversed and would show in metering relatively large amounts of negative sequence components. If your system is normal now, execute a meter command and note the magnitude of negative sequence quantities. If you were to reverse the A and B phase potential connections on the back of the relay, you should note after executing another meter command that the relay reports normal load currents as negative sequence currents.
PLEASE note that this procedure requires significant preparation and qualified persons to execute such a test. If you are not INTIMATELY familiar with this equipment and the necessary procedures to accomplish this test safely,
seek qualified assistance.

OR, at least be prepared to explain where you were when the lights went out.....
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