ECN Forum Forums General Topics of the Trade General Discussion Area 240 volt 3 phase

Yo Watt,
Howz it hangin' dude? In all seriousness, after the purple left the leg, it started getting better, been working about a month (part time at first) and it seems to be getting better, but I'll always have to wear the heavy duty (30-40mm) compression hose.

Frankly, I think it was that special medicine you prescribed, but I still don't understand the worm at the bottom of the bottle of medicine, but I gotsta admit, sho' took the pain away.

I realize I got the voltage from sparkys thread, geeez it's awful to get old.

Industrial guru? Nah, probably not, but I've worked at Bethlehem Steel in Baltimore, RJ Reynolds in Richmond, every press around Wash. DC, coal mines in SW VA, so every cockeyed, wierd, oddball transformer has been mine to hook up. Add to that a stint in the Metro tunnels of DC when they were building them - Delta 3 phase UNGROUNDED for the continuous miners, oh and when we started the actual construction instead of changing the transformers, we had to connect a zig-zag to create a neutral, I've probably seen some very odd combos. Then throw 17 years of teaching transformers to apprentices and the subject becomes clear as mud.

Good to hear from you again Watt, how'd you make out from your little debacle?

George,
What does the 4th wire connect to in a 4 wire corner ground system? I've never heard of that one.
Don

If it's a 240V corner-grounded delta, my guess would be that the 4th wire is a center tap on one of the winding connected to ground to provide 120V for light loads.

Am I anywhere near the mark???

Paul,
How can you ground both a corner and the center of one winding. Looks like that would produce smoke, not power.
Don

This may be way off the mark, but corner-grounded 3ø4W∆ doesn't sound right. If one coil center tap is not grounded, then one 120V winding is properly grounded, but the other 120V winding is 120V to ground on one side, and the other is 240V to ground. That could make for a deadly screwshell in a 120V lampholder. That seems to go against a lot of electrical custom in the US, particularly when the mid-coil ground would provide two grounded 120V connections.

There might be some old systems found that way, but to do it intentionally doesn't seem likely. There would be no point or advantage to such an arrangement, and it would take a more complex metering arrangement to measure power flow.


[This message has been edited by Bjarney (edited 06-08-2002).]

Sorry -- I didn't mean to ground the center tap. It was late & I didn't phrase my message very clearly.

Here's what I meant:
Take a 240V delta with, let's say, phase B grounded. Now take a center-tap from either the A-B winding or the B-C winding and bring this hot line to a separate 120V busbar.

Now you have a 240V corner-grounded delta for 3-ph (or 240V 1-ph) loads, but it's possible to get 120V from the "tap" wire to phase B (ground). I would imagine such a strange set-up being used only where a very small 120V load was to be powered, perhaps a couple of lights in a pumping-house full of 3-ph 240V motors or something like that.

Just a guess, mind you.

P.S. I can't think how this would have any advantage over your more conventional 3-ph 4-w delta, but it would be a way to get a small amount of 120V power if one phase of the delta had to be grounded for some obscure reason.



[This message has been edited by pauluk (edited 06-09-2002).]

A center tapped transformer with a 240 3Ø corner Grounded would not be per 250-20(b)(1)

as one of the legs of the center tap would be 240V to ground, thus exceeding the 150V to ground.

I wasn't thinking of having two 120V circuits run from opposite ends of the center-tapped winding.

Just a single 120V busbar for very light loads fed from the center-tap. This would only be 120V to ground.

If the 120V terminal to ground (the center tap) is available, and it would be to be able to use the 120V tap, then someone will certainly use the remaining 120V coil ( center tap to the matching ungrounded leg of the center tapped transformer. Just because the terminals are available.

Codes are for overall safety, I hope.

[This message has been edited by Gwz (edited 06-11-2002).]