Backfeed a 480Y to 240delta transformer... Awkward scenario.

[SPJPROD]

That is what I figured, I just couldn't find much information on it...

I was just looking through 250 and it seems you could ground B phase and be legal so it's just like a corner ground only the inside of the transformer would know the difference.

 

[SPJPROD]

Thank you for all of the input. I know that no one likes to respond to the new guys.

 

[jumper]

Thank you for all of the input. I know that no one likes to respond to the new guys.

We like new guys just fine here.

I am still a bit leery on this idea of corner grounding a wye output/secondary though, but lotsa stuff I do not know.

 

[Jraef]

You only need to ground the 480V corner if you DON'T provide ground monitoring. One or the other.

 

[winnie]

That is a weird transformer.

Normally you have a delta primary and wye secondary, and then people try to figure out grounding when the transformer is reversed.

But this beastie is normally a wye primary delta secondary.

I'd suggest actually looking inside the enclosure...there might actually be an 'H0' terminal in there. If it exists, I'd contact the manufacturer again, and ask if you can use the H0 terminal for grounding when the transformer is backfed.

Also, this is a 'high efficiency' transformer. I'd be concerned about very high inrush current tripping the supply breaker on startup; you expect increased inrush current when you backfeed a transformer (relative to a similar technology transformer designed from the start with your required primary voltage); this might be worse with a 'high efficiency' transformer. (Or maybe not...I'm extrapolating from 'high efficiency' motors.)

-Jon

 

[GoldDigger]

We like new guys just fine here.

I am still a bit leery on this idea of corner grounding a wye output/secondary though, but lotsa stuff I do not know.

If the output were 208Y/120 the provision about mandatory grounding of the neutral if it allowed less than 150V from each hot to ground would probably apply, even if the neutral was not used. But for 480 there does not seem to be a code restrictions against corner (end) grounding.
If the neutral were used, then the phase and system identification would be far from standard.

Sent from my XT1585 using Tapatalk

 

[jumper]

If the output were 208Y/120 the provision about mandatory grounding of the neutral if it allowed less than 150V from each hot to ground would probably apply, even if the neutral was not used. But for 480 there does not seem to be a code restrictions against corner (end) grounding.
If the neutral were used, then the phase and system identification would be far from standard.

Sent from my XT1585 using Tapatalk

Okay, still weird for me.

 

[SPJPROD]

I have heard this can be an issue with these high efficiency transformers. That is the reason that manufacturers prefer not backfeeding transformers.




That is a weird transformer.

Normally you have a delta primary and wye secondary, and then people try to figure out grounding when the transformer is reversed.

But this beastie is normally a wye primary delta secondary.

I'd suggest actually looking inside the enclosure...there might actually be an 'H0' terminal in there. If it exists, I'd contact the manufacturer again, and ask if you can use the H0 terminal for grounding when the transformer is backfed.

Also, this is a 'high efficiency' transformer. I'd be concerned about very high inrush current tripping the supply breaker on startup; you expect increased inrush current when you backfeed a transformer (relative to a similar technology transformer designed from the start with your required primary voltage); this might be worse with a 'high efficiency' transformer. (Or maybe not...I'm extrapolating from 'high efficiency' motors.)

-Jon