I am installing a 35 kw generator to backup a 70 amp 3 phase sub panel. My question is if the building has a delta high leg service, will this effect the generator?

ASSume voltage is 120/240 center tapped delta.

What are the loads on the sub panel? All single phase, all 3 phase, or mixed? If mixed, can the generator supply them, or are you going to use a transformer? Remember the issues with SDS and grounding through transfer switches.

With the 3-3 phase refridgerator units and single phase 240v water pump each leg was drawing around 31 amps apiece. Thera are other small loads.

Can you get a generator that will supply 120/240 3 phase 4 wire?
Don

the guardian type. They make 3 phase generators

jersy,
They are all 3 phase wye connected units. That is not the same as a 3 phase delta system with a high leg. I have never seen a generator that could be connected 3 phase delta with a high leg. I have only seen that configeration on transformers.
Don

When I repaired generators many years ago, the small gennys on reefer trucks were 3 phase 240 delta. I don't know if they where available in anything larger than 5 or 10 KW.

If the Guardian you are talking about has a 12 lead alternator, you could rewire it for 120/240 delta with a high leg. I would check with the factory about the maximum unbalanced load.

Larry

Larry,
I didn't look at all of the wiring diagrams, but on the ones that I did look at, the center of the wye was an internal connection.
Don

Just talked to guardian . There 3 phase units not compatible with a delta system. I have a meat packing plant that needs emergency back-up . Power always goes out they dont want there meat to go bad. Is ther an other way to go?

one more question , Why would it matter if the back-up generator Was a wye ? The equipment would work 3 phase, delta or wye connected

There are 2 issues with swapping a wye for a delta. One is that delta is 240 between legs and wye is 208. The second issue is the high leg.

You could go with a 480 3 phase generator feeding a 480/240 wye delta transformer. Power up the genny off of the gas main if available, propane and tank, or diesel and tank.

I don't know if you can get a delta high leg in a single unit. If you can't, feed the 120 V loads from a single phase 240/120 transformer.

Larry

edit because I still don't have UBB down.

[This message has been edited by LarryC (edited 10-05-2006).]

the generators are gas. I assume all the equipment will work fine off the 208 voltage. so if there is a transfer switch and there are no 240 1 pole loads what would it be the problem with backing up a 3phase delta panel with a 3phase wye generator

I don't think that might be a valid assumption.