drawout switchgear main tie main

[drktmplr12]

main tie and main in the middle with distribution on sides

or

main on each end, tie in the middle, distribution inbetween

this is new construction.

my way of thinking is that a MTM in middle makes more sense. not sure if you can expand a main bus both directions either, although I don't see why not so long as you spec it that way... Looking for other perspectives.

 

[jim dungar]

My preference, for maintenance and short circuit reduction, is to use a Main-Tie-Tie-Main.

In normal MTM one side of the Tie device or compartment is always energized, making maintenance an 'energized task'. With a MTTM a Tie there is only one short circuit current available when both Ties are opened.

 

[David Castor]

Putting mains and tie in adjacent sections increases the risk of a catastrophic failure taking out both sides. If the two buses are physically separate, then this is less of a concern. Two tie breakers with a physical separation is a better configuration, but a tough sell due to the expense of the second tie.

 

[paulengr]

Putting mains and tie in adjacent sections increases the risk of a catastrophic failure taking out both sides. If the two buses are physically separate, then this is less of a concern. Two tie breakers with a physical separation is a better configuration, but a tough sell due to the expense of the second tie.

The second tie need not be a full breaker. It’s just for maintenance. It can be a disconnect or even just cables or bus bars.

 

[drktmplr12]

I should clarify, it is a single lineup of draw-out switchgear that serves at service entrance for two 2000 kva transformers.

Very good point about a single failure impacting adjacent sections, I would have thought that the equipment is compartmentalized in such a way to minimize propagation, but this is not arc flash rated gear I am considering.

 

[GoldDigger]

The second tie need not be a full breaker. It’s just for maintenance. It can be a disconnect or even just cables or bus bars.

If you want to be able to work deenergized in all circumstances, where D is disconnect switch and C is cable to bus connection you would need either M-T-D-M or M-C-T-C-M, yes?

 

[paulengr]

If you want to be able to work deenergized in all circumstances, where D is disconnect switch and C is cable to bus connection you would need either M-T-D-M or M-C-T-C-M, yes?

Actually if you have MTTM you have to shut down one M to work on a tie cell. MTDM and MTCM work exactly the same except it’s not a full breaker.