Dry type transformer generator power

[xguard]

Someone proposed having a dry type ventilated transformer in between generator and transfer switch. The transformer would only be energized when the generator is running. Digging through instruction manuals for the transformers it looks like it's better to have them energized all the time to keep moisture out? Thoughts? Anyone have experience with having them energized intermittently?

 

[TwoBlocked]

You would want the same voltage coming from each feeder to the x-fer switch. Will putting the transformer between the generator and transfer switch do that?

 

[xguard]

You would want the same voltage coming from each feeder to the x-fer switch. Will putting the transformer between the generator and transfer switch do that?

Correct. 480 volt generator with a 208 volt service.

 

[TwoBlocked]

Gotta ask, why not a 208 generator?

 

[zbang]

Most modern generators are readily switched between 208/120 (and 240/139) and 480/277, or at least I've never seen one that wasn't switchable.

 

[drcampbell]

If I were specifying in Louisiana, and the transformer wasn't going to be in a humidity-controlled environment, I would be reluctant to specify anything less than epoxy-encapsulated.

Keeping it energized when not in use will waste a lot of energy and money, and emit a lot of waste heat, in perpetuity.

But I have to repeat (and emphasize) TwoBlocked's question: Why not install/configure the right generator in the first place? Is there some compelling reason for installing a transformer at all?

 

[winnie]

To emphasize the point about the generator: remember that the stator coils of a generator are essentially transformer secondary coils already. There is rarely a good reason to connect a small generator to a transformer for building backup applications.

Most larger backup generators have alternators which can be connected in a high or low voltage configuration. The generator voltage regulator then tweaks this to the correct output. You should be able to easily set the same generator up for 480/277 wye or 208/120 wye.

 

[xguard]

Most modern generators are readily switched between 208/120 (and 240/139) and 480/277, or at least I've never seen one that wasn't switchable.

I'll dig into that deeper. I asked and they said it couldn't be, the owner. I'll ask the dealer.

 

[xguard]

To emphasize the point about the generator: remember that the stator coils of a generator are essentially transformer secondary coils already. There is rarely a good reason to connect a small generator to a transformer for building backup applications.

Most larger backup generators have alternators which can be connected in a high or low voltage configuration. The generator voltage regulator then tweaks this to the correct output. You should be able to easily set the same generator up for 480/277 wye or 208/120 wye.

It's an 800 kw generator. Where the generator will be installed will require a run of conductors of about 150 feet.

I asked about the voltage of the generator being changed and was told it couldn't be. I'll bring that up again. After I saw the layout though I thought maybe 480 would be better given the distance.

 

[xguard]

You would want the same voltage coming from each feeder to the x-fer switch. Will putting the transformer between the generator and transfer switch do that?

Gotta ask, why not a 208 generator?

They already had it at another building.

 

[xguard]

They already had it at another building.

Meaning they already own this generator.

 

[zbang]

I asked about the voltage of the generator being changed and was told it couldn't be.

Might mean they've never checked, might also mean that where they use it now is 480 and they think this change takes too long (at that size, I'll assume it's not portable since that wasn't mentioned).

Go over and take a look inside the cabinet, also get the make/model specifics and look it up online (in this case, don't take their word for it).

 

[xguard]

Might mean they've never checked, might also mean that where they use it now is 480 and they think this change takes too long (at that size, I'll assume it's not portable since that wasn't mentioned).

Go over and take a look inside the cabinet, also get the make/model specifics and look it up online (in this case, don't take their word for it).

I contacted Cummins. They recommended not swapping it to 208 due to the size and number of conductors we'd need.

 

[PaulMmn]

You spoke of keeping the transformer 'warm' to avoid difficulties with moisture damage. What about the generator? Any source of waste heat that could keep them both toasty? Exhaust from the A/C?? (have to watch the moisture with that one...)