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#### phamousgrey

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##### Work Speaks for Itself
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lmfao, sry,. that mostly applies to the americas. the NEC ...[i havent read it], but im pretty sure it does differentiate between a ground wire and a neutral...i think.. half or more or less states dont even follow the basic tenants of the NEC code.

#### splatz

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##### Hackenschmidt
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I occasionally find a bootleg copy of the more current versions kicking around but I think that's the only PDF I have found of the older versions.

If you like this one, the Hawkins Electrical Guides are great, even older and available for free on Project Gutenberg:

http://www.gutenberg.org/ebooks/search/?query=hawkins+electrical+guide

#### splatz

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From splatz's 1916 Handbook link, and his posted screenshot, the configuration shown is, an open delta connection from 2Φ to 3Φ, with two 1:1 ratio transformers possible. It has the possibility of unequal voltage imbalance and can be detrimental in some situations, as shown in the text.

View attachment 138598
Excellent post. I am not sure I follow with the open delta conversion. When you connect two phases of a three phase system open delta, the open leg gives you what you want because the phase angle is 120 degrees. When you draw the vector diagram, the third line is the same length, indicating the voltage of the open phase is the same as the other two.

With two phase, the phase angle is 90, and when you draw the vector diagram, the open phase is not the same length. With two phases 240V 90 degrees apart, you'd get 339V on the open leg.

If that's so, what can you do with that unbalanced 3-phase?

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#### CMP

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Unbalanced Open Delta

If that's so, what can you do with that unbalanced 3-phase?
Burn up some 3Φ motors in time, or run some 1Φ loads, or convert back to 4W 2Φ

The graphic, shows the 1.41 voltage increase on the open phase, but imply's that it was used in the early period. Also notes that the center leg carries x1.41 the current as well.

And then GE goes on to say its troublesome, and there are superior methods.

Your the one that found and posted the diagram, I followed up on the link, and found it interesting, because of the open delta configuration mainly. And found it even more interesting that it was used at one time.

My main interest in the articles was information about open delta uses, and found it surprising that it was once used for 2Φ. Not many open delta systems used out there today, that I know of besides utility banks for center tapped open delta services.

This is one that SqD published in the past that I find useful, at times.

And thank's for the second reference link, I'll check it out.

#### CMP

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Well it looks like from the Hawkins Guide, the real use for 2Φ 3W was for transmission purposes, which makes sense, because it need not be balanced for that use.

#### splatz

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Well it looks like from the Hawkins Guide, the real use for 2Φ 3W was for transmission purposes, which makes sense, because it need not be balanced for that use.

View attachment 138632
So it's actually looking simpler than it looked to me at first. The three-wire two phase is just sharing a wire for transmission. The four wire there's no connection.

I was missing the 86% tap on the Scott T connected transformers, that makes perfect sense now.

#### bostonPedro

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2 Phase?

Learn something new everyday. I have never seen it here nor have I ever heard of it. Typically and very seldom when I hear 2 phase its an apprentice talking about single phase and confusing the number of wires as phases.
Interesting BUT I am glad I don't have to deal with it. :smile:

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