# Wye generator to Corner Grounded Delta



## telsa (May 22, 2015)

I'm assuming that the generator in question is a hefty truck mounted 480 or 208 -- voltage selectable -- unit. 

In which case the new source of juice is electrically isolated// magnetically isolated. 

If you get the rotation right, you should be good to go.


----------



## CoolWill (Jan 5, 2019)

stiffneck said:


> A building needs to be taken off it's primary feed, so we can service it's 4.1KV breaker at nearby sub. The secondary in this building is a 480V Corner Grounded Delta or Grounded "B" Phase Delta, whatever it is called. *Question*, when connecting a Wye generator to the Corner Grounded Delta, will it work without any abnormalities. I've been given two different answers for the same set-up. Trust is hard to come by in St. Louis these days and my experience with these systems is repair or replace, not experiment. Connection difference will be that the "Common" or "Neutral" cables, Grey in color is not to be used. Only the 3-phase cables and "Grounding" or Green cables. A total of 4, not 5 spans to be connected.


I can envision three ways this can work.

1) Disconnect the bonding jumper that grounds the grounded phase and check each phase to ground to ensure that there are no downstream grounds on the grounded phase. Connect the generator to the phases only when the bonding jumper is removed.

2) Isolate the generator from the earth and DON'T connect any ground from the generator to the building. This is a bad idea because now the generator frame will be hot with respect to the local earth due to the bonding jumper that grounds the grounded phase.

3) Install a 1:1 isolation transformer between the generator and the building. This is probably the safest bet.


----------



## stiffneck (Nov 8, 2015)

telsa said:


> I'm assuming that the generator in question is a hefty truck mounted 480 or 208 -- voltage selectable -- unit.
> 
> In which case the new source of juice is electrically isolated// magnetically isolated.
> 
> If you get the rotation right, you should be good to go.


Yes and Yes with the Grounding cable connected, Not the Ground or Neutral cable and the bond between Grounding and Grounded on the Generator itself removed..


----------



## brian john (Mar 11, 2007)

I would reconnect the generator to match the building or.

Make sure the XO in the generator is not grounded.

I am sure there will be a phase shift between the two sources

OR WHAT HE SAID



> I can envision three ways this can work.
> 
> 1) Disconnect the bonding jumper that grounds the grounded phase and check each phase to ground to ensure that there are no downstream grounds on the grounded phase. Connect the generator to the phases only when the bonding jumper is removed.
> 
> ...


----------



## stiffneck (Nov 8, 2015)

stiffneck said:


> telsa said:
> 
> 
> > I'm assuming that the generator in question is a hefty truck mounted 480 or 208 -- voltage selectable -- unit.
> ...


Correction; misspoke, NOT connecting Green “Grounding” cable from building to generator.


----------



## varmit (Apr 19, 2009)

I am thinking that the best plan would be to:

1. Check the phase rotation at the service.

2. Temporarily remove the existing GEC from the corner grounded system. Test for any ground faults- intentional or accidental.

3. Bond the generator XO to the building grounding system.

4. Check generator phase rotation.

5. Connect a few , small, 3 phase equipment loads to test proper operation.

6. On with the show.


----------



## micromind (Aug 11, 2007)

varmit said:


> I am thinking that the best plan would be to:
> 
> 1. Check the phase rotation at the service.
> 
> ...


I would do it this way too. Sort of convert the building system to 277/480 Y while the gen is supplying the service. 

Point #2 is the most important, there should be only one ground bond but there's only one way to find out.


----------



## 460 Delta (May 9, 2018)

varmit said:


> I am thinking that the best plan would be to:
> 
> 1. Check the phase rotation at the service.
> 
> ...


A couple years ago I changed out a service on a plant from a floating 480 Delta to a 480 Star doing doing what you said here minus the 2nd step as it was already done. I was able to measure about 280 to ground on all phases so it was good to go and heated it up. The hardest part was forcing the POCO to swap the phase rotation to me to ABC rather than CBA.


----------



## CoolWill (Jan 5, 2019)

I'm not seeing how removing the GEC connection is changing anything. The main bonding jumper is what you should be looking for.


----------



## varmit (Apr 19, 2009)

CoolWill said:


> I'm not seeing how removing the GEC connection is changing anything. The main bonding jumper is what you should be looking for.


Please read the second sentence of item 2.


----------



## CoolWill (Jan 5, 2019)

varmit said:


> Please read the second sentence of item 2.


Right. There will always be a ground "fault" even with the GEC removed because the main bonding jumper is still there.


----------



## stiffneck (Nov 8, 2015)

Curious, have any of you connected a "Corner Grounded Delta" configured generator before? Portable or permanent fixed location types.
Have any of you reconfigured a WYE Gen. to a "Corner Grounded Delta", without to much fuss? Note, I have never seen a "Corner Grounded Delta" set up Generator.
Which term do you use; "Corner Grounded Delta" or "Grounded B Phase" ? Which is proper or more common?


----------



## CoolWill (Jan 5, 2019)

stiffneck said:


> Curious, have any of you connected a "Corner Grounded Delta" configured generator before? Portable or permanent fixed location types.
> Have any of you reconfigured a WYE Gen. to a "Corner Grounded Delta", without to much fuss? Note, I have never seen a "Corner Grounded Delta" set up Generator.
> Which term do you use; "Corner Grounded Delta" or "Grounded B Phase" ? Which is proper or more common?


Corner grounded is just a way to picture it. Grounding the B phase is just a word-of-mouth industry standard.

The proper term I think would be a 3-phase, 3-wire grounded delta.


----------



## 460 Delta (May 9, 2018)

stiffneck said:


> Curious, have any of you connected a "Corner Grounded Delta" configured generator before? Portable or permanent fixed location types.
> Have any of you reconfigured a WYE Gen. to a "Corner Grounded Delta", without to much fuss? Note, I have never seen a "Corner Grounded Delta" set up Generator.
> Which term do you use; "Corner Grounded Delta" or "Grounded B Phase" ? Which is proper or more common?


In my opinion Grounded B is more specific than Corner Ground, as it could possibly be an A or C or B if you just say Corner Ground.


----------

