A long shot...

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rhamblin

rhamblin

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Kaukauna, Wisconsin
This is going to be strange but, at some point in the last couple years I came across a slide show that I printed out. I was a really well done tutorial on grounding. I printed it out and borrowed it to a few people, I've changed employers and now can't find it. I'd like to find it again. I ran into a coworker that tried explaining to me that you never connect X0 and the grounding lug on a transformer, thought it would help him out.

Any way I believe the slide show was based on 2005 or earlier code, because part of it was explaining why grounding terms are so confusing, and that they changed some of the verbiage in that cycle. It's a long shot, but does anyone know what I'm talking about?
 
FWIW, your buddy gave you good advice IF the transformer in question is wye-delta or wye-wye with a third delta secondary.
Connecting input X0 to neutral or to ground can cause very large circulating currents if the source wye voltages are even slightly unbalanced.
 
GoldDigger said:
FWIW, your buddy gave you good advice IF the transformer in question is wye-delta or wye-wye with a third delta secondary.
Connecting input X0 to neutral or to ground can cause very large circulating currents if the source wye voltages are even slightly unbalanced.
Click to expand...
It’s a delta eye transformer.
 
SG-1 said:
Look under the Grounding vs Bonding section of the forum, The Big Picture Post (Sticky) by George Stolz is at the top. Read down through & you will see a link to Bob Ludecke's Grounding Presentation at Tirebiter. Follow the link & down load the presentation. It may be what you seek. I have tried to copy it here;

http://www.tirebiter.net/downloads/ludecke.html
Click to expand...

Porgy Tirebiter
He's a spy and a girl delighter!
 
GoldDigger said:
FWIW, your buddy gave you good advice IF the transformer in question is wye-delta or wye-wye with a third delta secondary.
Connecting input X0 to neutral or to ground can cause very large circulating currents if the source wye voltages are even slightly unbalanced.
Click to expand...
Can you explain a little more. Why would you want a wye-delta transformer? And what is a third delta secondary on a wye-wye transformer.
 
rhamblin said:
Wouldn't forward direction be from delta to wye and why would you connect the primary to the X terminals? Would you connect the secondary to the the H terminals?
Click to expand...

Independent of whether the transformer is step-up, step-down, or equal voltage (isolation or delta-wye conversion), it is designed based on the magnetizing current being initially supplied by one winding when it is energized. That winding is usually thought of as the primary. In general the power in input on the primary side and output on the secondary side, but that is NOT always a match to the first way of determining it.
In general any voltage adjusting taps will be on the primary side so that the transformer can accept a wider range of input voltages without getting too close to saturation, with its non-linear effects and power waste.
As to what the letter designation of the two windings is, it could either follow the rule that the H side is the high voltage or the rule that H is the primary.

The NEC now recognizes the problems of asymmetric behavior of a transformer by allowing, for example, as designed step-up transformer to be used instead as a step-down transformer (backwards) unless the manufacturer explicitly approves such operation.

As for why a wye-delta transformer in a customer environment, one reason is to adapt a wye service to a delta-wired renewable energy source (gird interactive. Or just because that was the type of transformer sitting in the yard at the time.

For utility distribution networks, the reason for using delta or wye at any particular point in the network is a lot more complicated.
A third delta winding on a wye-wye transformer is often used for harmonic mitigation.
 
LarryFine said:
I've been a Firesign Theater fan for decades! :D
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Me, too. Anyone who is has been for decades. :D

Back in the day I used to regularly get together with a few folks sitting around listening to FT records by candlelight for hours. Anyone who kept trying to start a conversation while the record was on was not asked back. You have violated Robot's Rules of Order and will be asked to leave the Future immediately! :D
 
So thanks for the link to the slide show. But just to make sure, on a Delta-Wye transformer, 480 primary 120/208 secondary, 75KVA Xfmr, you do need to bond the neutral XO to the ground lug, right?
 
ActionDave said:
Yes, you must bond the XO. You can do it either in the transformer case or in the first disconnect. 250.30
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So this brings up another question. I know you can bond in the first disconnect which usually is like a 12-24 thread green screw. Why is this tiny screw ok, to use instead of a much larger neutral wire?
 
rhamblin said:
So this brings up another question. I know you can bond in the first disconnect which usually is like a 12-24 thread green screw. Why is this tiny screw ok, to use instead of a much larger neutral wire?
Click to expand...

Remember when you asked your parents a question and they said "Because" and that's all they said, it's kinda like that.
 
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