Emergency/Stand By generator feeding two voltage

[ros]

Hi Everybody,

I have a situation, where we have to feed two connection 480/277V and 120/208V by a 480/277v standby generator. I want to know


1. How should I connect my 120/208V side to generator
2. Can I use step down Xmer in this case
3. If I use 480 to 208 Xmer what will be position of my ATS, before or after Xmer
4. Are there generators in the market which can output multiple voltage at the same time
5. Can you please refer to single line below and advise me changes
Thank you so much for Advise.

 

[Ingenieur]

...

what happens if only one util feed is lost?

 

[topgone]

Hi Everybody,

I have a situation, where we have to feed two connection 480/277V and 120/208V by a 480/277v standby generator. I want to know


1. How should I connect my 120/208V side to generator
2. Can I use step down Xmer in this case
3. If I use 480 to 208 Xmer what will be position of my ATS, before or after Xmer
4. Are there generators in the market which can output multiple voltage at the same time
5. Can you please refer to single line below and advise me changes
Thank you so much for Advise.
View attachment 19190

On Q1:
1. Generator CB is closed.
2. 480/208 transformer is closed.
3. ATS 2 is swtiched to 208V side of the transformer!
Crystal!

 

[Sahib]

...

what happens if only one util feed is lost?

Operation of generator would be required unless step up/step down transformers are inserted on the two utility sides (To question no.5 also:happyyes.

 

[steve66]

...

what happens if only one util feed is lost?

The ATS's usually have normally closed dry contacts to start the generator. For multiple ATS's, the contacts are wired in series.

If only one utility is lost, the generator will still start, but only one ATS will transfer to the generator.

Its a pretty common setup, so maybe I'm not understanding your question?

 

[drktmplr12]

Residential/Commercial/Industrial?

I am guessing you are intending for the 208/480 to power the 480V panel when 480V utility is lost..What size will the 208/480 xfmr need to be? My guess would be the higher of the demands between the two panels. The conductors and breakers will need to be rated to carry the entire load both ways..This could have an unintended side effect of arc flash issues depending on the available fault current.

Are these services on the same power line/utility substation? If so, the likelihood of losing one and not the other is extremely low..nonetheless you might consider having two 480V services with main-tie-main and use a step down to develop 208/120, if that is an option. Then use a 480V generator, widely available.

Be careful with specialty rated generators because if its hard to find a new one, I'm thinking its going to be hard to find a replacement as well.

 

[ron]

Hopefully the only neutral downstream you need is for ATS#2.

That way, you can bond N-G at the 480V service disc and at the gen and not bring them to the ATS's. Of course you will bond the N-G at the 208V service disc.

That way you can sue 3 pole ATSs.

If you start running neutrals from the gen and 480V service disc, then you will need 4 pole ATSs to separate stuff because it will be a circulating ground current party. Especially a mess if you have GF protection.

 

[steve66]

I never like leaving the 480V/208V step down transformer unpowered 99% of the time except the 1% when the generator is running.

Not sure its any real issue, but it just doesn't seem like the most ideal solution. Although I think the only other options are changing the service to 480V, and having the step down on the load side of the ATS.

Or changing the generator to 208V and eliminating the xformer altogether.

 

[Sahib]

Are these services on the same power line/utility substation? If so, the likelihood of losing one and not the other is extremely low..nonetheless you might consider having two 480V services with main-tie-main and use a step down to develop 208/120, if that is an option. Then use a 480V generator, widely available.

My thought is to minimize running of the generator. In case one utility is lost, supply could be made available through other utility without running the generator. Of course that plan involves additional transformers and ATS and distinct utility sources.

 

[kwired]

I never like leaving the 480V/208V step down transformer unpowered 99% of the time except the 1% when the generator is running.

Not sure its any real issue, but it just doesn't seem like the most ideal solution. Although I think the only other options are changing the service to 480V, and having the step down on the load side of the ATS.

Or changing the generator to 208V and eliminating the xformer altogether.

I am presuming there is 480/277 volt loads on the premises also, for some reason they are subscribing to two service voltages and probably receive two separate bills from power supplier.

If one is going to have a generator that can supply entire load as well as have the "standby transformer" for 208 volts, why not just make that a permanent source for the 208 and supply everything via the 480 volt service?

You could have situation where you lose one service but not the other - but that will likely be for local reasons. Any widespread area outage will probably mean both services are off line.