Checking phase sequence in synchronization operation

We know that the phase sequence is one of many conditions of the synchronization operation, and made in the beginning of construction. But if for any reason we need to check the phase sequence for two different sources of power. How to do that?

Sequence, or what we call positive sequence is a relative rotation for phases that we call as A-B-C, so positive sequence has this rotation. By convention this rotation in counter-clockwise.

If you are in a substation that is fed from 2 sources, making sure the sequence are the same is of primary importance.

You can not tell at the local substation what is the designated phase-A conductor from the two sources unless you visually confirm what is the phase-A conductor and trace it all the way back to the from source to destination, or as an alternative, ring it out.

Many utility require that all phase-A, Phase-B and Phase-C are matched in all subs.

The above is not required if all you want to do is to ensure phase sequence are the same so that 2 sources can be synchronized successfully.

example:

A-B-C can be synchronized to A-B-C
A-B-C can be synchronized to B-C-A
A-B-C can be synchronized to C-A-B

So what we have above is positive sequence can be synchronized to positive sequence, the rotation needs to be the same.
You need a phase angle meter a reference 3-phase VT or CVT set. This voltage reference set, must be able to be energized from the two sources separately. Connect channel one of the meter to Van and channel two to Vbn. For delta connected VT, connect channel 1 to Vab and channel 2 to Vbc.
Apply power to the VT set and measure the phase angle and record. Now deenergize, isolate the first source and energized with the other source.

Same angle = same sequence
Different angle = u have a problem!