480V corner ground issues?

[chris kennedy]

Morning all

I am currently installing 3 new customer supplied transformers, 480 delta to 240 delta. These are reverse wired, 240V primary to 480V secondary.
H2 is grounded. These transformers each supply an individual control cabinet.

Other than the obvious higher voltage to ground, what are the drawbacks of these systems?

To head off some questions;

Nothing is connected to X6
H1 brown, H2 grey and H3 yellow
All 3 loads are 3Ø 3 wire industrial laundry control cabinets built in 1996

Thanks

 

[jim dungar]

Are there VFDs or other electronics? Filter capacitors are often connected L-G and so don't often play well with non-wye systems.

 

[chris kennedy]

Good question. There is a new conveyor system not yet on site being connected to one of the cabinets. Good chance of VFD there.

 

[Jraef]

If there is a VFD, can you change to a transformer with a Wye on the 480V side? Or is it too late?

 

[Besoeker3]

Are there VFDs or other electronics? Filter capacitors are often connected L-G and so don't often play well with non-wye systems.

Do you mean L-G rather than line to neutral?
I don't recall using LN but that would just our usual practice.

 

[chris kennedy]

If there is a VFD, can you change to a transformer with a Wye on the 480V side? Or is it too late?

Never too late but customer won't be very happy. He bought the transformers.

 

[chris kennedy]

Do you mean L-G rather than line to neutral?
I don't recall using LN but that would just our usual practice.

Voltages on this system read;

L1-L2 480V
L2-L3 480V
L1-L3 480V
L1-GND 480V
L2-GND 0V
L3-GND 480V

 

[Besoeker3]

Voltages on this system read;

L1-L2 480V
L2-L3 480V
L1-L3 480V
L1-GND 480V
L2-GND 0V
L3-GND 480V

OK. Just not normally for us. No problem.

 

[hillbilly1]

I’ve done that before, but all motor loads were standard contactored loads, but as Jreaf said, if it’s freq drives, I would be concerned. It might be cheaper for the customer to pay the restocking fee, and get a transformer you know will work versus replacing drives.

 

[Jraef]

I’ve done that before, but all motor loads were standard contactored loads, but as Jreaf said, if it’s freq drives, I would be concerned. It might be cheaper for the customer to pay the restocking fee, and get a transformer you know will work versus replacing drives.

Or if there is just one or two small drives, put a Drive Isolation Transformer ahead of them. 480 primary, 480/277 secondary, with X0 grounded.

 

[zbang]

Maybe I've missed something, but if this is a new system why are you feeding it delta at all? (Because that's what the customer bought?)

 

[Besoeker3]

Maybe I've missed something, but if this is a new system why are you feeding it delta at all? (Because that's what the customer bought?)

I think it's a fair point.

 

[paulengr]

Mist VFDs have a jumper or are simply set up for delta. If not then only solidly grounded wye will work.

 

[ActionDave]

Maybe I've missed something, but if this is a new system why are you feeding it delta at all? (Because that's what the customer bought?)

Because that's the job he was given to do.

 

[ptonsparky]

Because that's the job he was given to do.

I can see adding another 480/277 system here and there throughout the plant to compensate for that need. It will be fun to see in a few years with new maintenance coming and going.