Double Ended Station

[adavey]

I'm trying to find some good resources on "double ended substations" and "tie-breakers" and can't seem to find anything on the internet. Can anyone lead me in the right direction ?????????

 

[charlie b]

I have included them in several design projects. But I do not know of an Internet resource for information. It might help, however, if you can give us an idea of what type of information you are seeking.

 

[adavey]

I'm looking at a single line. It appears 2-2000A 480V (3 phase) switchboards are fed from seperate MV transformers, but are connected via the bus bar with a "tie-switch". Is this done for redundancy purposes in case one of the POCO transformers fails ???????????

 

[charlie b]

Yes, redundancy is the principle reason for a "Main-Tie-Main" design. But it also provides an opportunity to conduct maintenance on one transformer, without loss of power to the building.

 

[adavey]

Thanks Charlie.

 

[dinkelja]

I'd add that ties could be regularly operated in either the normally open or normally closed configurations, merely a question of choice. From a survey aspect however, with a lot of the the double ended system arrangements, the tie breaker is normally open, with a fast auto close in the event of a fault free loss of any one of the transformers. For some in-depth reading check out the IEEE Gold Book (Recommended Practice for the Design of Reliable Industrial and Commercial Power Systems)

 

[mayanees]

.. another M-T-M note...

.. another M-T-M note...

Another note about double-ended Main-Tie-Main substations is that they are typically only loaded to half of the xfmr rating so that if one xfmr fails the other can carry the load.
.. obvious point, but one worth mentioning.
JM

 

[kingpb]

This most certainly could be a double ended secondary unit substation arrangement, however it could also be a spot network. Two entirely different animals.

 

[zog]

And....they are typically key interlocked to ensure proper operation. The usual configuration is to have both mains closed with the tie open. There are 2 keys and 3 breakers, you need a key to close a breaker. Upon a loss of 1 main (Transformer or primary ffeder failure) you would open the main on the affected side, remove its key, put that key in the tie and close the tie. Nowq both busses are being fed from 1 transformer.

 

[mayanees]

... and one more "and"...

... and one more "and"...

...In cases of critical power delivery, like in data centers, the tie-breaker is often Normally-closed, so that if one of the transformers fails, or if a main breaker trips, there will be no power interruption since all of the load will be supplied through the other transformer.
But, this parallel operation results in twice the amount of fault current on the secondary bus, so systems designed to operate with the Tie-breaker closed must have twice the fault current rating for the distribution gear as compared to a system where the breakers are interlocked such that the secondaries can never be paralleled..
JM

 

[robomatic]

I just ran into the interesting case of asking why there are 'two' tie breakers next to each other. Should have been able to think it through but eventually read that this is done so as to be able to isolate and perform maintenance on the tie breakers themselves.

Short lesson here is that you spend a lot of money but you get reliability and longevity and back-up out of the deal, which is often priceless and allows your maintenance folks to sleep easier at night.