Convert 120/240 split phase service to 3 phase 208/120 service 120KVA

[winnie]

At full three phase load the alternator would be oversized for the engine.

At full single phase load the alternator is better matched to the engine

 

[Todd0x1]

So a full load on the alternator (at its rating) would stall the supplied engine?

The intent being cheaper than the same alternator with an engine capable of driving it?

Not quite. The genset is rated 70kw (on the ones I have). The alternator is oversized to allow it to produce nameplate KW in single phase mode.

 

[Saturn_Europa]

Not quite. The genset is rated 70kw (on the ones I have). The alternator is oversized to allow it to produce nameplate KW in single phase mode.

Tod, what are the hours on those machines? Have you seen more wear and tare from running them double delta single phase as compared to a well balanced 3 phase machine?

We tend to put 10,000 - 12,000 hours on our generators before we scrap them.

 

[Todd0x1]

Tod, what are the hours on those machines? Have you seen more wear and tare from running them double delta single phase as compared to a well balanced 3 phase machine?

We tend to put 10,000 - 12,000 hours on our generators before we scrap them.

These have low hours, in the hundreds. Single phase in these is zig/zag not double delta. I don't have any data about increased wear from running single phase. Theyre mostly used in 3ph mode.

 

[synchro]

I don't have any information about lifetimes when running generators on single-phase.
But here is a discussion of the effects of using single-phase in application notes from Cummins:

https://www.stamford-avk.com/sites/stamfordavk/files/AGN017_E.pdf

https://www.stamford-avk.com/sites/stamfordavk/files/AGN154_D.pdf

 

[Hv&Lv]

We wired old military gennys several different ways depending on the wiring configuration.
12 wire got a double delta or zig zag.
Mostly a parallel zig zag, but it was preference only.

The 10 wire units got the connection I posted earlier, which was (I believe) called a Collins connection by the old man that drew it and taught me about it. It’s not a popular configuration from what I understand, but it works great.
only used it because there wasn’t a #11 and a #12 on a 10 wire gen set.

either way, we de-rated the generators 50% of nameplate on single phase.

 

[winnie]

Thinking a bit outside of the box:

Your power company will provide single phase service. You also want to use a generator.

Your preference (stated from the beginning) is to wire the structure for 3 phase, use the 3 phase generator directly and have some way to convert the POCO supplied single phase to 3 phase.

But you are willing to consider wiring the structure for single phase, and running the generator single phase.

This tells me that you don't have any 3 phase loads, you just want the whole building as a 3 phase load to match your generator.

How about wiring the building single phase, but as three separate 120/240V 200A 'systems'. All three of these are supplied from the POCO 120/240V split phase, but when transferred to generator power they are on separate phases.

-Jon

 

[Hv&Lv]

Thinking a bit outside of the box:

Your power company will provide single phase service. You also want to use a generator.

Your preference (stated from the beginning) is to wire the structure for 3 phase, use the 3 phase generator directly and have some way to convert the POCO supplied single phase to 3 phase.

But you are willing to consider wiring the structure for single phase, and running the generator single phase.

This tells me that you don't have any 3 phase loads, you just want the whole building as a 3 phase load to match your generator.

How about wiring the building single phase, but as three separate 120/240V 200A 'systems'. All three of these are supplied from the POCO 120/240V split phase, but when transferred to generator power they are on separate phases.

-Jon

?
I’m lost here or not thinking right..
How you going to get 120/240 three phase from the generator

 

[wwhitney]

How you going to get 120/240 three phase from the generator

You'd wire the alternator to give you (3) 120/240 single phase systems, pairwise 120 degree apart. So the "hexaphase" version of 208Y/120V. Assuming the alternator could do that (I'm not knowledgeable about what the 12 wire alternator means).

Cheers, Wayne

PS As an aside, it occurs to me that a balanced 3 phase load has a constant power draw, while a single phase load does not. So with a single phase generator, is the rotational inertia of the spinning shaft used to smooth the power demand on the engine? Do alternators have flywheels for this purpose?

 

[Todd0x1]

You'd wire the alternator to give you (3) 120/240 single phase systems, pairwise 120 degree apart. So the "hexaphase" version of 208Y/120V. Assuming the alternator could do that (I'm not knowledgeable about what the 12 wire alternator means).

Cheers, Wayne

PS As an aside, it occurs to me that a balanced 3 phase load has a constant power draw, while a single phase load does not. So with a single phase generator, is the rotational inertia of the spinning shaft used to smooth the power demand on the engine? Do alternators have flywheels for this purpose?

The engine has a flywheel and the alternator has quite a bit of rotating mass.

 

[gene6]

I get the feeling someone did talk to the right people at the local POCO. I have been that someone, they told me no that 3 phase is "not available". That goes up the chain of command on my side and comes back down the chain on their side, "oh sure were putting in a new vault and pad-mount what size did you want again?" In Hati you need to look into battery storage, the grid is not on 24 hr a day and generators are expensive to run. Also you need to secure that fuel tank. Like really secure it.

 

[Hv&Lv]

You'd wire the alternator to give you (3) 120/240 single phase systems, pairwise 120 degree apart. So the "hexaphase" version of 208Y/120V. Assuming the alternator could do that (I'm not knowledgeable about what the 12 wire alternator means).

Cheers, Wayne

PS As an aside, it occurs to me that a balanced 3 phase load has a constant power draw, while a single phase load does not. So with a single phase generator, is the rotational inertia of the spinning shaft used to smooth the power demand on the engine? Do alternators have flywheels for this purpose?

Ok, could you draw that for a 10 wire, then a 12 wire?

for a 12 wire tie T4&T7, T6&T9, T5&T8 to ground?
leave the others open to loads?
looks like your opening yourself up to some extreme imbalance

 

[tortuga]

We would like the facility to be 3 phase. Is there a way to convert the the 120/240 split phase into 3 phase.

I'd be curious to see a summary load calc of what 208V 3 phase load the hospital has proposed. You mentioned earlier you had lots of 230V equipment from overseas. Might be better off with a 240V delta generator.

 

[ggunn]

?
I’m lost here or not thinking right..
How you going to get 120/240 three phase from the generator

120/240V three phase does not exist. 120V phase to neutral three phase is only 208V phase to phase. It's that pesky SQRT(3).

 

[winnie]

120/240V three phase does not exist. 120V phase to neutral three phase is only 208V phase to phase. It's that pesky SQRT(3).

With 6 hots, displaced by 60 degrees, you have the option of 120V, 208V or 240V L-L, depending upon which hots you select.

-Jon

 

[tortuga]

With 6 hots, displaced by 60 degrees, you have the option of 120V, 208V or 240V L-L, depending upon which hots you select.

-Jon

Yes exactly. And if I am not mistaken you can get 240/120 delta hi-leg off it. 240 three phase for your 230V EU equipment and 120 / 240 single phase.

 

[winnie]

Ok, could you draw that for a 10 wire, then a 12 wire?

for a 12 wire tie T4&T7, T6&T9, T5&T8 to ground?
leave the others open to loads?
looks like your opening yourself up to some extreme imbalance

Can you link a normal 10 wire diagram?

I think you have it right for the 12 wire.

I can't see the imbalance being _worse_ than double delta for single phase.

-Jon

 

[synchro]

With a 12-lead generator there are 6 separate windings, each of them with two terminals or "wires." There is a pair of windings for each of the 3 phases that are 120 degrees apart, and each of these pairs of windings could be configured for 120/240V single-phase (aka split-phase). I believe this was what winnie (Jon) and Wayne were referring to.

PS As an aside, it occurs to me that a balanced 3 phase load has a constant power draw, while a single phase load does not. So with a single phase generator, is the rotational inertia of the spinning shaft used to smooth the power demand on the engine? Do alternators have flywheels for this purpose?

The references from Cummins I put in post #5 mention some additional vibration associated with this pulsating torque. Also, this causes some variation in the speed of the rotor during each rotation, and this causes additional current and heating in the damper cage windings. This imposes an additional limit on the amount of kVA a generator is allowed to provide in a single-phase configuration.

... How about wiring the building single phase, but as three separate 120/240V 200A 'systems'. All three of these are supplied from the POCO 120/240V split phase, but when transferred to generator power they are on separate phases.

-Jon

In an earlier thread from the OP, the post below by hillbilly1 mentioned a similar idea but with the three panels at 120/208V:

https://forums.mikeholt.com/threads/120-240-volt-service-208-120-back-up-genset.2565481/post-2724932

With a delta-delta there will always be some current imbalance causing torque variations. With three independent 120/240V split-phase outputs, the best case balance can be excellent. However, the worst case imbalance could be poorer than in the delta-delta (for example, with loading on only one of the 3 phases.

I see that winnie has posted an explanation already, some some of this will be redundant.

 

[Hv&Lv]

120/240V three phase does not exist. 120V phase to neutral three phase is only 208V phase to phase. It's that pesky SQRT(3).

Yeah, I know that.
it wasn’t my suggestion. I was trying to figure out how it was going to be done.
I’m wondering now about the wiring configuration I mentioned earlier..

 

[Hv&Lv]

Can you link a normal 10 wire diagram?

I think you have it right for the 12 wire.

I can't see the imbalance being _worse_ than double delta for single phase.

-Jon

Here’s a 12 wire and a 10 wire.
I don’t think that would be possible with a 10 wire.
you've got me wondering now about the 12 wire…