Main-Tie-Main

[dicklaxt]

Thanks Jeff exactly the way I drew it from your circuit description.

Heres the scenarios as I see them

Ckt "A" with transfer selected,tie open,then Ckt "A" is feeding "A" bus and CKT "B" feeding "B" bus everything okay so far,now close the "Tie" and "A" and "B" are butting heads(thats not good) so there is probably an interlock to stop the tie from being closed,now open "B" main and Ckt "A" is feeding both bus "A" and "B",things are okay again.

Now transfer switch selects Ckt "B",Ckt "B" is feeding both bus "A" and "B" whether tie is open or closed(not the norm I would say) so again there must be an interlock to keep the tie from being closed when both mains are closed.I now see Ckt "B" feeding bus "A" thru the transfer switch and bus "B" is dead because of the interlock having main "B" open.

It appears to me that the transfer switch is only intended to be there so that bus "A" is the critical bus and can be fed from either Ckt "A" or "B" and bus "B" would be offline because of the interlock that locks out "B" main.

So assuming all that to be true then the main-tie-main interlock must have a hitch in its get a long where Ckt "A" or Ckt "B" can close in on each other before the tie opens
which is what others have said, phases being out of sync,I think..

I normally think of a transfer switch being used between normal feed and a generator feed on an Essential bus without a tie. Is this setup referenced here a norm in the industry?I guess a main-tie-main electrically operated in a control scheme is in itsself a transfer switch.
dick

 

[charlie b]

I don't have answers to a number of other questions posed.

Let me pose a couple more, then, just to further complicate the situation.

(1) Is the M-T-M set up such that on loss of power to one side, the system automatically transfers to the other side (i.e., open the "dead side" main and close the tie)?

(2) If that answer is "yes," then does the system also automatically return to the "normal" configuration (i.e., open the tie and close the main) when power is restored from the "dead side"?

If that answer is also "yes," then I am concerned over a loss of "Bus A." My thoughts are that the M-T-M will transfer the the Bus B side, and at the same time the transfer switch will switch over to the Bus B source, at which time the M-T-M will sense a return of power to the Bus A side (not being able to recognize that the power source is actually Bus B), and transfer back. That is a lot of transient activity to ask the large motors to put up with.

 

[msu-ee]

Main-Tie-Main

I hate to be blunt but it seems you are going on a lot of here say.
Sounds like you need to spend a little more time in the field to confirm your service entrance.
It looks like your two transformers should both be feed from your transfer switch. Not the way you have it drawn.

Did the damage occur during a substation transfer?

 

[msu-ee]

Move your second transformer feed to the bottom of your transfer switch and you will probably have a correct service riser.