240v open delta to 230v wye transformer grounding/bonding

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SSDriver

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I have a job that is 240v open Delta with B phase grounded and I need to install a drive isolation transformer that has a wye secondary. I was curious about potentially having a grounding/bonding issue. The B phase is grounded on my primary and normally I would be bonding XO on the secondary side. I wasn't sure if I was going to have an issue due to having 2 sides of the transformer bonded. The secondary is going to a fused disconnect, then to another room to a double throw safety switch that will chose one of two drives that it will supply power to.Screenshot_20201116-084910_Drive.jpg
 
SSDriver said:
I have a job that is 240v open Delta with B phase grounded and I need to install a drive isolation transformer that has a wye secondary. I was curious about potentially having a grounding/bonding issue. The B phase is grounded on my primary and normally I would be bonding XO on the secondary side. I wasn't sure if I was going to have an issue due to having 2 sides of the transformer bonded. The secondary is going to a fused disconnect, then to another room to a double throw safety switch that will chose one of two drives that it will supply power to.View attachment 2554309
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Supply the xformer with a 2 pole breaker along with grounded B phase. You don't bond anything on the primary. On the secondary go to a 3 pole breaker or fusible switch. Bond secondary like any SDS and install a GES.
 
SSDriver said:
I have a job that is 240v open Delta with B phase grounded . . .
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This is a non sequitur. An open Delta is (almost) always a high-leg added to a typical 120/240v 1ph to supply a smaller 3ph load.

A grounded Delta would have one phase solidly grounded, as with any grounded neutral, but would supply only 3ph loads.
 
B phase is solidly grounded 0 volts from B to ground.. 240v from A -B, B-C, A-C. All loads are 3 phase only, customer told me POCO says it is open delta. I do not have access to the transformer(s) feeding the building as they are behind locked gates. They have a separate service for single phase loads. I just wanted to make sure Im not going to have an issue with the primary side having a solid ground on the B phase, and then grounding the XO on the secondary side. The existing motor is currently fed with a 3 Pole breaker. I was planning to use that to supply power to the new transformer, and then I was going to have a fused disconnect on the load side of the transformer. Thank you all of the input so far
 
SSDriver said:
I just wanted to make sure Im not going to have an issue with the primary side having a solid ground on the B phase, and then grounding the XO on the secondary side.
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No, there's no issue. That's exactly why you are using a D-to-Y transformer: for primary-to-secondary isolation.

One conductor of a separately-derived system can (and usually must) be grounded; in your case, the neutral.

Added: To me, a corner-grounded, open-Delta supply is weird, but there's no electrical reason why it can't be.
 
Thank you, I have done a bunch of transformers but this is the first one with a grounded primary phase conductor and wanted to make sure I'm wasn't missing something dumb. I have never worked on a system with a corner grounded open delta before.
 
SSDriver said:
I just wanted to make sure Im not going to have an issue with the primary side having a solid ground on the B phase, and then grounding the XO on the secondary side.
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I agree with LarryFine: what the transformer cares about is the supply line-line voltage, not the line-ground voltage (as long as the line-ground voltage is not so high as to over-stress the insulation system. As long as the primary gets 240V line-line, it doesn't matter if that is corner ground delta, high leg delta, or 240/138V wye.

SSDriver said:
The existing motor is currently fed with a 3 Pole breaker. I was planning to use that to supply power to the new transformer, and then I was going to have a fused disconnect on the load side of the transformer. Thank you all of the input so far
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Sounds reasonable. If you were to put fuses on the primary side, then you would need a 'blank' in the B phase, because you are not supposed to interrupt a grounded conductor with a fuse. But you are fine with a 3 pole _breaker_ since that interrupts all phases simultaneously.

-Jon
 
On a side note how would you identify the wires different for delta and wye even though they are both 230v? I'm not a huge fan of tags. Primary delta currently is BLACK-WHITE-BLUE. would the secondary wye have to be something other than BLACK-RED-BLUE-WHITE? What would be the least confusing way to do it if needed.
 
SSDriver said:
On a side note how would you identify the wires different for delta and wye even though they are both 230v? I'm not a huge fan of tags. Primary delta currently is BLACK-WHITE-BLUE. would the secondary wye have to be something other than BLACK-RED-BLUE-WHITE? What would be the least confusing way to do it if needed.
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That must have been the way you were taught..
Personally, I wouldn’t use white for anything other than a neutral (grounded conductor)
Orange for nothing other than a high leg. (208 or 416 high legs)
 
Hv&Lv said:
That must have been the way you were taught..
Personally, I wouldn’t use white for anything other than a neutral (grounded conductor)
Orange for nothing other than a high leg. (208 or 416 high legs)
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The white on the delta was for the B phase on the open delta system with the grounded B phase. Not a high leg. Sorry for the confusion. I wasn't sure if the colors had to be completely different on the primary vs secondary due to one side being delta vs wye.
 
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