Loose Neutral

That and some shades.

steelersman

hahahaha! That's funny as hell.

mattsilkwood

no it wont, it will generate two phase power.

drsparky

Two phase works just fine, nothing shakes apart.

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"Pay attention son, this is for your own good." - Foghorn Leghorn

InPhase277

A two phase generator has four poles, each at 90 degrees.

I was joking about a two pole generator at 90 degrees. It would be horribly imbalanced, and would shake violently. It was a joke, haha, just kidding, a funny.

drsparky

I get it now, I am not very bright.

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"Pay attention son, this is for your own good." - Foghorn Leghorn

76nemo

This is the longest standing debate in electrical theory. As Marc stated, I use the term split phase, but look over your head at your nearest can, it's one leg of the system. Query "Battle of the phases" on Holt's site and see how far this goes, many have different opinions.

Larry Fine

More specifically, it's the center tap of the secondary that 'creates' it. But, just like two batteries in series inside a flashlight, the two halves of the secondary are definitely 'in phase.'

They have to be in phase in order for their voltage to add. If they were genuinely out of phase, their voltages would buck and the line-to-line voltage would be zero.

The only reason we see what we call opposing polarities, and what merely resembles a 180 degree phase shift, is because we're using the center tap as the point of reference.

Hoping that cross-forum linking is permitted, read this.

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steelersman

Hey Larry. How many coils are there on the primary side of a typical POCO x-former? I'm thinking for most residential applications it's not 3 coils or 3 phase, but just only 2?

InPhase277

I'm not Larry (but I'm much better looking), but there is only one coil in the primary of a single phase transformer, and one on the secondary. That's why there is only one, or some times two, insulators sticking out of the top.

wwilson174

In any AC circuit the average voltage is actually zero!

steelersman

Ok. I didn't know if some x-formers might have a 3 phase primary with only a single phase secondary. So is there only 1 coil on the primary side? I understand the secondary just fine, it's the primary I'm just wondering about.

steelersman

If it's a single coil, then what do they supply it with? Like is each end of the coil supplied with 2 of the POCO's 3 phase conductors? Or do they just feed one side with a hot conductor and the other end is grounded perhaps?

InPhase277

Yeah, if it is fed with two of the three phase conductors, the transformer will have two insulators on top. If it is fed with a single phase and neutral, it will have one insulator, and the can itself is the neutral terminal. So just one coil.

While three-phase transformers exist, I have never seen one on top of a pole. It is always just 3 single phase transformers,

Larry Fine

If you mean a single can, like you see hanging on a pole, just one, and it's usually what we call single-ended; one primary conductor is tied to the primary neutral conductor.

If there are three cans on the pole, it's three 1-ph tansformers, connected wye, just as we would connect a 208Y/120 feeder or load with a neutral connection.

Now, a pad-mounted transformer can be a 1-ph unit, or it can contain three 1-ph units, like the 3-ph transformers (three 1-ph units) we use, just a lot bigger.

They don't use dual-primary transformers like we sometimes do, but most of their residential units have dual secondaries, which can be re-connected with jumpers.

If connected in parallel, we get 120v between the left (usually) and center bushings, and is used in 208Y/120v systems, with all three units connected the same way.

If they connect the secondaries in series, we get 120/240v using all three bushings, with the center bushing again bonded. That's what we get in our homes.

However, if they connect three of those series-connected secondaries in Delta, we get 240v 3-ph. We can either bond one phase (corner-ground) or bond one neutral.

That would give us a high-leg Delta, with the B phase having the higher voltage to neutral. Note: the A-N-C 3-wire 120/240 section is exactly the same as the 1-ph supply.

If you remove one of the Delta's transformers (not the one with the bonded neutral), you have an open Delta. It behaves just like the Delta. but with a bit less efficiency.

The open Delta began as a modification to existing 1-ph services, for new 3-ph motors. The omitted third transformer eliminated the need for a third primary wire.


Sorry I don't have time to go into a detailed explanation.

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Larry Fine

Yeah. Sure, you are. Uh-huh.






To a Tasmanian Devil, maybe!

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Larry Fine

Nope. There'd be no reason to have the other two primaries there. Only electronics could let us make use of three phases for one.

There's no magic in higher voltages. Their transformers work just like ours do. There's just more turns of wire in theirs.

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Larry Fine

Sometimes, they use line-to-line connections (Delta) and sometimes they use line-to-neutral (Wye). Most modern installations that I see have Wye primaries.

The Delta primaries I usually see are in older industrial neighborhoods, where there's a pair of poles with a platform between them that three cans sit on, side by side (by side ).

The primaries are strung between the poles on cross-arms, jumpers reach up to the wires, and the secondaries are likewise jumpered to wires below the cans.

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CFL

I hear this excuse alot and I'm sick of it. I never went to school to learn electricity and somehow I learn more about it each day I'm alive. I hear this crap at work and I guess people expect me to believe they are still smarter than me, they've just forgot more than I've ever learned. Just admit you don't have the answer. Sorry, just one of my pet peeves.

Larry Fine

Compact, there must be some things you learned (or were at least exposed to) in some school that you've forgotten from lack of need or use.

I agree that field-learned knowledge is valuable, but not everyone here is in the position to use engineering and math in their everyday work.

Sure, he could have said "I don't know" or merely not have posted, but even posting shreds of information and then getting corrected is a method of learning.

And that's why we're al here, right?

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