6000A circuit breaker at 480V LVPCB 2

[living2learn]

Has anybody ever used one this size at 480V. I am wanting to use a 6000A circuit breaker as my cross tie between (2) 2500kVA transformers on each side and was told they don't make them that big.

 

[rbulsara]

It's unusual, but available. Can't comment on your design needs or choices.

Rafiq Bulsara

http://www.srengineersct.com

 

[Zogzog]

Yes they do, I have a few of them in stock, ABB, GE, and some old Westinghouse ones.

However, you may wan't to rethink your idea. That is a lot of fault current you are proposing.

 

[cherry2000]

2.5MVA Xmer with LV secondary is like skimming the limits..both operating current and short ckt current will be difficult to address.

 

[living2learn]

That's exactly where I am at right now with the client. Is it a decent idea to lower the transformer kva (1500) and utlize fans and pumps to increase the kVA. Because the fault current will be base upon the self cooled level of the transformers.

 

[Zogzog]

Guess I am a little confused here, if the application is a tie breaker why do you need 6000A? The tie should be the same size as the mains are. Add key interlocks and you won't have to worry about fault currents either.

Maybe I am just thinking wrong, perhaps a sketch would help.

 

[davidbeach]

My rule of thumb has been that for anything over 4000A you're looking at the wrong voltage.

 

[VTer]

3000A on Mains and tie is sufficient. Where are u getting 6000A?

"Throughout space there is energy. Is this energy static or kinetic! If static our hopes are in vain; if kinetic — and this we know it is, for certain — then it is a mere question of time when men will succeed in attaching their machinery to the very wheelwork of nature". – Nikola Tesla

 

[living2learn]

So they can sync with eachother. 2500/480*1.732 = 3000A's x2 = 6000A's

 

[living2learn]

Medium voltage is not an option. Even though it is the correct answer.

 

[ScottyUK]

You're building a maintenance department's nightmare.

FWIW, at a previous employer we had a number of boards fed from 2.5MVA transformers with 4000A incomers at 415V. We struggled to get a board with adequate fault bracing to allow paralleled operation, and the arc energy was approaching 200 Cal/cm² when on a single feed (slow protection to coordinate with some big stuff downstream). At that energy level the question is whether the clean-up guys will need a vacuum cleaner or just a dustpan & brush to collect you, not whether you'll be alive or not.

Have you any option to split into two boards with smaller transformers?


----------------------------------

If we learn from our mistakes I'm getting a great education!

 

[Zogzog]

Why x2?

 

[living2learn]

x2 because if they ever want to kill one side but not the xfmr's. They don't ever want to be on just one utility circuit. How the building is now. Arc flash and fault current are another issue that I am trying to deal with as well. This is my 3rd VERY large client that is getting rid of all the medium voltage no matter what it takes/costs.

 

[davidbeach]

But the tie will never have to carry the load of two transformers, always only one. There is no need for the tie to be larger than the mains.

 

[TurbineGen]

From the diagram it looks like you are referring to the 6000A breaker that is serviced by two 2500 kVA transformers on either side? So you have 5000 KVA worth of transformer on either side of the tie. May I ask how you are dealing with the 152kA worth of short circuit current?

------------------------------------------------------------------------
If it is broken, fix it. If it isn't broken, I'll soon fix that.

 

[davidbeach]

Oops, I hadn't looked at the one-line, thought M-T-M and wrote away. The one-line is a disaster waiting to happen.

Why not a ring bus with two of the breakers open and the rest closed, something like:

      |               |               |               |
      |               |               |               |
<-[x]---[x]-------[x]---[o]-------[x]---[x]-------[x]---[o]------>
            |   |           |   |           |   |           |   |
            |   |           |   |           |   |           |   |
           [ ] [ ]         [ ] [ ]         [ ] [ ]         [ ] [ ]

That version adds in a few extra, but purchasable, breakers. A 12 breaker ring would save a breaker or two. Have an interlock scheme that never allows more than two transformers on any bus segment at once and you're good to go. Except you're still at the wrong voltage level.

 

[Zogzog]

That one line sure clears a lot up, I was also thinking M-T-M like DB was.

 

[alehman]

This is way too much for one board. You really should consider splitting the load some how.

Are the utility circuits synchronized? Is the utility aware that you want to parallel their circuits on the secondaries? Most would not allow that.

Alan
“The engineer's first problem in any design situation is to discover what the problem really is.” Unk.

 

[living2learn]

I was going to deal with the 152kA of fault current by installing a 200kAIC board. I was also looking at the cutler hammer current limiting fuseless circuit breakers. The utility is aware that we are sync'n their circuits and are ok with it.

Also to deal with the arc flash problem - I was going to install a maintenance switch and make it so nobody unauthorized would be allowed in the room and tie the door contacts and motion sensor into that.

At the end of the day I just want to deliver a safe system to my client. They already had everything worked out for me before I got there, so just trying to chizzle it back one thing at a time.

David - I really like your setup and I pitched that on day 1, but they said they want all 4 transformers supplying load at the same time. But I am going to fight the good fight.

 

[alehman]

Have you found an ATS that can handle the fault current, or are you planning to add fuse protection?

The Cutler-Hammer breakers may not coordinate above 100kA, if that's a concern.


Alan
“The engineer's first problem in any design situation is to discover what the problem really is.” Unk.