120/240 three phase

[K8MHZ]

Our local fire station is requesting bids for a 45kW stand by generator. The specs call for '120/240 volt three phase'.

Wouldn't that be a 240 volt three phase delta, split (center tapped for the 120)?

If so, wouldn't that require just a 240 volt three phase generator with the 120 being created after the fact?

 

[ceb58]

Our local fire station is requesting bids for a 45kW stand by generator. The specs call for '120/240 volt three phase'.

Wouldn't that be a 240 volt three phase delta, split (center tapped for the 120)?

If so, wouldn't that require just a 240 volt three phase generator with the 120 being created after the fact?

No, they can tap the gen. for 120/240. 120v -N on each leg 240v phase to phase.

 

[K8MHZ]

No, they can tap the gen. for 120/240. 120v -N on each leg 240v phase to phase.

Wye or delta and how would it be configured?

For a wye, 120 L- N would mean 208 L - L.

For a delta, 120 from a 240 3 phase would need a center tap. If that tap is 'N', then it needs to be grounded and would only be a single phase 120 as you can't ground more than one conductor.

A sketch would be easier for my feeble mind to grasp.....

 

[infinity]

No, they can tap the gen. for 120/240. 120v -N on each leg 240v phase to phase.

I'm assuming that you mean a 3 phase, 4 wire Delta configuration. That would be 120v-N/G on two of the phases and 208v-N-G on the high leg.

 

[Fulthrotl]

Our local fire station is requesting bids for a 45kW stand by generator. The specs call for '120/240 volt three phase'.

Wouldn't that be a 240 volt three phase delta, split (center tapped for the 120)?

If so, wouldn't that require just a 240 volt three phase generator with the 120 being created after the fact?

i'd seek clarification to make sure that is really what they want....
there is no logic to why, unless it is to match the existing service,
and THAT doesn't even make any sense, cause you can feed a
120/240 3ph 4w delta service with a 120/208 3ph 4w Y generator
quite nicely....

ow. this makes my head hurt.

 

[K8MHZ]

I'm assuming that you mean a 3 phase, 4 wire Delta configuration. That would be 120v-N/G on two of the phases and 208v-N-G on the high leg.

Could you sketch that out for me?

 

[kwired]

.. cause you can feed a
120/240 3ph 4w delta service with a 120/208 3ph 4w Y generator
quite nicely....

that may depend on exactly what loads you are feeding. 240 volt resistive loads will have reduced capacity of what they have when running on utility power. 240 volt inductive loads will draw more current than they normally do if run at 208. the question is can these differences be withstood or tolerated?

 

[infinity]

Could you sketch that out for me?

How's this:

 

[Fulthrotl]

that may depend on exactly what loads you are feeding. 240 volt resistive loads will have reduced capacity of what they have when running on utility power. 240 volt inductive loads will draw more current than they normally do if run at 208. the question is can these differences be withstood or tolerated?

valid point. best to ask them before bidding.

if it was a process control situation, with ovens and such, you could very well
run into problems with setpoints that were near the maximum capability of the
oven... and while you can have running overcurrent protection
set for either voltage, you can't always have it set for BOTH voltages, unless
you are using VFD's with running overcurrent based on true power instead
of just current.

didn't think that one all the way thru.

 

[don_resqcapt19]

...

If so, wouldn't that require just a 240 volt three phase generator with the 120 being created after the fact?

A 12 lead generator with 120 volt coils can be used for almost any configeration that you want to have. With conventional numbering of the coil ends, 1&12 would be a hot, 2&10 the second hot, 3&11 the third hot, you would also connect 4 to 7, 6 to 9 and 5 to 8. The 5&8 connection would be brought out as the neutral.
You could also connect this as a double wye to give you a 208Y/120 system and I have seen it connect in a zig-zag connection to give you 120/240 single phase.

The connections I listed would be for a 240/120 wild leg system.

 

[K8MHZ]

i'd seek clarification to make sure that is really what they want....
there is no logic to why, unless it is to match the existing service,
and THAT doesn't even make any sense, cause you can feed a
120/240 3ph 4w delta service with a 120/208 3ph 4w Y generator
quite nicely....

ow. this makes my head hurt.

I did ask for clarification via e-mail.

 

[K8MHZ]

How's this:

Thanks.

That is what I would call a split phase.

The bid sheet only said '45kW 120/240 three phase'. If the station had a split phase, the bid sheet should indicate that because, as you have noted, there would be a high leg to deal with.

 

[renosteinke]

That spec needs to be clarified.

I'd go to the site and measure what's beiong supplied by the PoCo ... then suggest they spec the genny to match the existing voltage. Supplying 240 to equipment that's accustomed to 208 is not a good thing.

 

[ceb58]

A 12 lead generator with 120 volt coils can be used for almost any configeration that you want to have. With conventional numbering of the coil ends, 1&12 would be a hot, 2&10 the second hot, 3&11 the third hot, you would also connect 4 to 7, 6 to 9 and 5 to 8. The 5&8 connection would be brought out as the neutral.
You could also connect this as a double wye to give you a 208Y/120 system and I have seen it connect in a zig-zag connection to give you 120/240 single phase.

Thanks Don, I did not have connection diagram with me. This is the thing some get stuck on. A gen. configuration is more versatile than the regular transformers. I have three 3ph 25kw units on trailers for back up's. They are tapped for 120v A-N,B-N,C-N 240v A-B, A-C and B-C. This way if I do need 3ph at a site it is not a problem since any equipment we have is slash rated single phase and will not effect it going from 120/208 to 120/240

 

[tufts46argled]

i'd seek clarification to make sure that is really what they want....
there is no logic to why, unless it is to match the existing service,
and THAT doesn't even make any sense, cause you can feed a
120/240 3ph 4w delta service with a 120/208 3ph 4w Y generator
quite nicely....

ow. this makes my head hurt.[/QUOT

That depends on the generator and how it's operating system works. Not all will work with different incoming and out going voltages. Trying to fix a mistake made by others on a 100KW Generac with an H panel.The generator was installed where the utility is 120/240 delta and they installed a generator that was 120/208 Y. The H panel reads that stinger leg and thinks there is a problem, starts and transfers. The only option is to rebuild the alternator. The stator windings have to be replaced along with the ct's. Already have the parts, plan to tackle it in the next couple of weeks. Just to add the alternator is a 6 wire and the rest are wired internally in the windings of the stator.

 

[K8MHZ]

I drove by the building today and it's pretty sad. Luckily our strongest winds come from west.

If I don't hear back I'll just drop in. (I live about 5000 feet from the fire station) The Chief is a great guy. I am pretty sure I got notified because I gave him my card and told him if he needed anything to feel free to ask. The FD is the Egelston Township Fire Department. Egelston Township is named after my great-great-great (I think I got them all) uncle Adna Egelston, the first person to own land here. I really would like to make sure the paperwork and the panels have some resemblance to one and other, or at least make a noble offer look into it for them.