480Y To 208Y, Derived From Generator.

Seven-Delta-FortyOne

Goin’ Down In Flames........
Location
Northern California
Occupation
EC and GC
I apologize in advance for the basic question, but I haven’t done a transformer for quite a while.

3 phase generator with a 480Y/277 output.

I need 208Y/120.

Because the neutral is derived from the generator, I need a Y-Y transformer, don’t I?

Delta/Y won’t work?
 

Seven-Delta-FortyOne

Goin’ Down In Flames........
Location
Northern California
Occupation
EC and GC
Its been so long I can’t remember but I thought that the delta primary will not have an xO lug, but I have a neutral from the genset.

I guess I just lose the neutral conductor between the generator and the transformer?
 

Seven-Delta-FortyOne

Goin’ Down In Flames........
Location
Northern California
Occupation
EC and GC
Have you checked to see if the genset can simply be reconnected for 208Y output and just change the breaker?
It a switchable type.

120/240 single phase, or 480/277 3phase.

And it has a 240/139 3 phase, which I haven’t worked with at all.

Not sure where 140v is commonly used at.

Edit: you mean internally. No I haven’t.
 

hillbilly1

Senior Member
Location
Atlanta,Ga
Occupation
Field coordinator/ technical support
I have a Generac that I’m doing the same thing too. Unfortunately Generac takes the cheap route out, and is not able to be configured for a different voltage. Delta-wye will work fine. Just wished they didn’t have a six switch rule service. Have to rebuild everything!
 

synchro

Senior Member
Location
Chicago, IL
Occupation
EE
It a switchable type.
And it has a 240/139 3 phase, which I haven’t worked with at all.
If you can't configure the generator internally for 208Y/120, then you could switch the generator to 240Y/139 and then use a 3-phase autotransformer such as one at the link below to get 208/120:

That would likely be cheaper and smaller than a delta-wye from 480 to 208Y/120.
 

don_resqcapt19

Moderator
Staff member
Location
Illinois
Occupation
retired electrician
Its been so long I can’t remember but I thought that the delta primary will not have an xO lug, but I have a neutral from the genset.

I guess I just lose the neutral conductor between the generator and the transformer?
Exactly, you just don't use the neutral from the generator to supply the primary side of the transformer. You run the3 ungrounded conductors and an EGC between the generator and the transformer.
 

infinity

Moderator
Staff member
Location
New Jersey
Occupation
Journeyman Electrician
Its been so long I can’t remember but I thought that the delta primary will not have an xO lug, but I have a neutral from the genset.

I guess I just lose the neutral conductor between the generator and the transformer?
Correct. A Delta/Wye stepdown transformer will only have three terminations on the primary 480 volt side so there would be no place to connect the primary neutral if you did pull one.
 

Seven-Delta-FortyOne

Goin’ Down In Flames........
Location
Northern California
Occupation
EC and GC
I appreciate all the help from everyone. 👍

This Forum is great. I don’t post much, but I read all the time.

So it turns out the 240/139 setting is a low voltage 3 phase. i called the importer for these units and talked to tech support.

He said to set it at that position, and turn the potentiometer down until you get 208.

I was skeptical that the voltage adjustment knob would give me that kind of range, as I’ve only ever seen about 5 volts +/-, but he assured me that that is how the new units are made. 👍

seems like kind of a goofy setup. Not sure why it wasn’t just labeled 208Y/120, but it seems to work.

But I learned something about transformers. 👍🤣
 

winnie

Senior Member
Location
Springfield, MA, USA
Occupation
Electric motor research
So it turns out the 240/139 setting is a low voltage 3 phase. i called the importer for these units and talked to tech support.

He said to set it at that position, and turn the potentiometer down until you get 208.

seems like kind of a goofy setup. Not sure why it wasn’t just labeled 208Y/120, but it seems to work.
This is pretty common. The alternator is 12 lead, made with 6 separate coils, two per phase. The voltage regulator can adjust to provide 120 to 140V per coil. Then depending upon the coil arrangement and voltage regulator settings you can get any common utilization system. 120/240 single phase, 240/120 high leg, 208/120 wye, 416/240 wye, and 480/277 wye

The switching system probably doesn't give you all the options that manually wiring from the alternator would.

Jon
 

mbrooke

Batteries Not Included
Location
United States
Occupation
Electricity
It a switchable type.

120/240 single phase, or 480/277 3phase.

And it has a 240/139 3 phase, which I haven’t worked with at all.

Not sure where 140v is commonly used at.

Edit: you mean internally. No I haven’t.

140 volts isn't used, in that system everything is simply connected phase to phase much the way it is with 240 volts ungrounded delta.
 
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