Adding Bus Tie between (2) MV Switchger Lineups

[rockman7892]

I am looking into a customer request to provide a bus tie (w/Tie breaker(s)) between two existing 6.9kV Siemens-Allis Switchgear lineups. To me he most straight forward solution would be to try to expand the existing main bus on each lineup adding a tie-breaker section on the end of each lineup with an overhead bus-tie in-between (lineups are about 25ft apart).

I was wondering in this case if it made sense to provide (2) tie breakers (provides better means of isolation) or just a single tie breaker on one-lineup and a direct bus connection on the other. Is a (2) tie-breaker application usually preferred vs the one?

If it makes sense to go with only a single tie-breaker on the end of one lineup I'm wondering if it makes sense to expand main bus into new termination section on 2nd lineup for connection of new tie bus or if its worth looking into weather or not one of the existing sections can be modified to accept the new bus (perhaps a PT section)?

The existing Switchgear appears to be Siemens-Allis type FC which I am not familiar with, but appears to have the main bus located towards the bottom of the Switchgear (see attached photo). Is anyone familiar with this gear and know how practical it would be to expand the main bus to the left of the main or after the last feeder breaker?

 

[mparenteau]

Not familiar w/ that gear, but I would think if you went w/ a single tie breaker, you'll need some type of transition section on the end of your 2nd lineup for the feeder bus connections.
One breaker would certainly simplify any kirk-key setup you might need.

Mike

 

[Zogzog]

Have you looked at the switchgear install guide for these? Should show you everything you need to know. Too big to

 

[rockman7892]

Thanks for the feedback.

Is there a general industry practice/philosophy on when to use one vs two tie breakers? Obviously using (1) is less costly and requires a less complex interlocking scheme as mentioned. (2) Tie breakers allows you greater flexibility for completely isolating switchgear but in a situation that I'm looking at where the tie scenario would only be used for extreme emergency situations I'm thinking I can get away with only one.

Zogzog - Thanks for sending the instruction manual. I was looking for that but was not able to find it. Do you have a good source on where to find vintage manuals such as that?

 

[Zogzog]

We have a gigantic library of those old manuals/drawings/WD's, etc...

 

[bacon4life]

Part of the evaluation should be thinking about maintenance requirements. Sometimes a direct bus connection requires both switchgear lineups to be out of service simultaneously. Other than this, the second breaker doesn't add much reliability.