Here, too. About a half-dozen years ago phasing of a radial transmission feed into two distribution substations became a problem when it was decided to build a secondary tie line between the two stations. One was first energized in 1981; the other in 1985.
‘ACB’ was the serving utility’s standard; while the customer had extensively documented ‘ABC’ for its transmission feeds, medium- and low-voltage lines and buses. This somehow had been overlooked during construction of the ‘ACB-phased’ station.
During the design stage of the tie, phasing was discussed and dismissed as unimportant, for it was inconceivable that they could be different, and besides, any difference could be easily fixed by flopping cables at the MV level. {We realized before tie-line completion that flopping cables would be a lot of work; the ‘ACB-phased’ station had bus duct on the transformer secondary and multiple 750MCMs per phase in the ‘ABC’ yard.} After a number of line patrols and lots of phasor sketches, we found that for the two ANSI-standard delta-wye power transformers, no flopping or rolling of low-side connections could fix a high-side phase reversal. In the end, it became necessary to build a model using six 100VA machine-tool transformers to demonstrate the misconception of configuring the two 20MVA transformers.
Before tie-line heat up, the serving utility had to come on site, take an outage and swap two 4/0 ACSR spans into the ‘ACB’ station. Of course, it then became necessary to flop phases at cable terminations on that station's eight MV feeder breakers. It was a costly lesson. Phasing across the open tie breaker was triple-checked before closing the first time.