High Power Contactor Size

littleblackdo

I am designing a transfer switch to switch main power to Generator when main power is lost. Main power is 3 phase, 480VAC and rated at 300amps. Is a contactor a good choice for this? I cannot seem to find one rated this high of power.

dlgoff

I'm curious. Why design and not just purchase a Automatic Transfer Switch?



Anyway, just do a google search on "3 phase 300 amp contactors". There's a bunch.

Bobbywhy

There are also "static switches" that easily handle 300 A at 480VAC. They use SCRs and are commonly used in large UPS installations.

For instance, http://www.redoups.com/F24156/static...251000amp.html

Cheers,
Bobbywhy

Windadct

Are you looking for a True Transfer Switch - these are typically interlocked (electrically or mechanically) so both sources are not connected at the some time ( I prefer mechanical because electricians LOVE manually pushing contactors closed - so think of manually pushing the Gen Contactors closed when the line contactor is being used - ugly)
So there are mechanical "kits" for some of the larger 3 phase contractors so that both units are not in the same device -

I just googled Surplus ATS and they pop right up

Typically Static Switches ( Thyrisotr / SCR ) are not needed (or are cost justified) due to start up time of Generators - but in critical loads this is sometimes done - can also help with the transfer back to the line(utility)

littleblackdo

I have to "conceptually" design this for a work project and was looking for ideas prior to meeting on it.

Main voltage is 480VAC, 3 phase Wye with 300A maximum. The Emergency/Alternate Source is 480VAC, 3 phase wye Generator. I was thinking of connecting the Main Source to 3 phase, 4 pole contactor. When power is lost, contactor closes time delay relay which will close another contactor after time limit expires to send start signal to Generator. Does the Contactor need to be rated at 277V or 480? Am I even on the right track with my ideas?

dlgoff

What if the generator doesn't start?

littleblackdo

I am working on transfer switch. I should not have said "send start signal to Generator". I guess it will close contacts in start circuit.

Bobbywhy

Why try to formulate a "conceptual design" in a vacuum? The protection of "critical loads" with an UPS and diesel generator is a mature technology and has developed over many decades. Hundreds of equipment suppliers and thousands of consultants can easliy answer all your questions.

Cheers,
Bobbywhy

berkeman

Thread closed temporarily for Moderation...

berkeman

So, littleblackdo, I'm uncomfortable with your lack of professional EE knowledge and the powers involved in your "project". If you have been given this as a work assignment, you should have the professional EE qualifications to answer these questions on your own. Posting high power high voltage questions in a web forum is not a good thing, and is against the PF rules for a reason. This thread is closed.