Bus Phase Sequencing in MV Switchgear

[rockman7892]

Is there a particular requirement or standard for the sequencing of bus phases in MV Switchgear to be A, B, C, top-to-bottom / left-to-right?

We have an issue where we are installing busduct from a transformer located across from switchgear that has phasing A, B, C left to right on bushings so if we being that directly across to switchgear the phasing in switchgear would be C, B, A, left to right. We are trying to decide if it is necessary to have bus transpose in order to make switchgear phasing A, B, C left to right.

This is single ended gear so that only thing I can see that this would affect would be internal labeling of CT', PT's, etc.. and use in troubleshooting or perhaps a specific standard that requires the A,B,C left to right orientation?

 

[dpc]

No standard I'm aware of. Some utilities try to standardize, but there are generally exceptions. North-South/East-West etc, until it doesn't work. I wouldn't transpose to maintain consistency, but would clearly mark the phasing.

 

[jraef]

The only standard I am aware of for bus bar phase orientation is UL-845 for LV Motor Control Centers.

8.2.9.4 The phase arrangement of 3-phase horizontal common power and vertical bus bars shall be A, B,
C from front to back, top to bottom, or left to right, as viewed from the front of a motor control center.

BECAUSE of that, I've had this issue come up on UL-347 MV gear where an inspector red-tagged me because the said the bus orientation was incorrect (Top horizontal bus, A in the back, C in the front) he said it was in UL-347. I challenged him on his assessment, I won because it is not. It's not called out in ANSI C37 either.


" We are all here on earth to help others; what on earth the others are here for I don't know." -- W. H. Auden

 

[davidbeach]

What ever your gear is, it should either be all the same - identically - or any exceptions should be clearly - to the point of being obnoxious - labeled, signed, etc., to indicate the differences. My experience is that field personnel know what "should" be and will correct any abnormal installations to match "correct" installations. Therein lies ugly and unnecessary outages.

 

[Marmite]

I've worked in Companies where there are all kinds of legacy system phasing standards. In the UK system phasing uses the colours Red, Yellow and Blue, and by convention you would expect them to correlate with ABC physical terminals, but that isn't necessarily so. It's important that the switchgear secondary cabling is ferruled as standard, so CT's on pole A are ferruled for pole A, which might not necessarily correlate with system phase A or red in my case. You would get into all kinds of mess if you relabelled all the secondary cabling just because you happened to have connected system phase B onto physical phase A bushing.

Regards
Marmite

 

[rockman7892]

I did come across a reference in IEEE C37.121-2012 Guide for Switchgear-Unit Substation Requirements.

Section 9.1 (Phase and polarity arrangement) states the following:

As viewed from the main switching-device side of the operating mechanism, the phase arrangement on
buses and primary connections of all sections should be 1, 2, 3 counting from front to back, top to bottom,
or left to right.

However, the following exception should be noted. For other arrangements of unit substations, the
transformer bushing phasing may be other than 1, 2, 3 counting from front to back, top to bottom, or left to right.
With these arrangements, a phase transposition shall be made at the connection to the outgoing and
incoming sections so that 1, 2, 3 phasing is maintained in these sections.

Panel devices should be mounted with 1, 2, 3 phasing counting from left to right and top to bottom, as
viewed from the front of the panel.

Based on this it appears that it is recommended to include a phase transform when the transformer bushings are opposite orientation of switchgear?

 

[dpc]

It's a Guide - and a good recommendation. Perhaps my experience is atypical, but inconsistent phase orientation was extremely common in the facilities I dealt with. Mirror-image generating units created untold messes in phasing. I would never make any assumptions about phase orientation. That doesn't mean it isn't a desirable goal. If you've got the budget and space to roll the phases, then go for it. But I wouldn't spend much money (including engineering time) trying to force it. I've seen screwed up phase transitions shipped from the factory, not to mention the creative ways it can be screwed up in the field. But I'm a glass half empty guy, so there's that.