Why Is American 220v Not Considered 2 Phase?

Ok, so how does all this work for the electric meter? If the hot legs are not evenly loaded, can the meter tell and account for the difference?
 
There is a technical description on Wikipedia:

https://en.wikipedia.org/wiki/Electricity_meter

I have wondered about this myself - The answer must lie in the number and mechanical orientation of the coils so unbalanced loads spin the disc at a speed half the difference between the 2 loads. The 240 volt component (balanced load) needs adds full rotation speed and the unbalance adds half the speed. Then again, an electronic meter would just have one coil for each 'leg' and perform the necessary calculation in software.
 
They only care about kilowatts
 
I've worked for 2 power companies, both in distribution & transmission for 26 years. If read start to finish, you guys have it all figured out. I'll attempt an additional explanation of the USA 120/240V residential power transformer. Current does have a flow direction & that direction is back to ground. Since the center tap of the 120/240V transformer is connected to ground, the flow or direction of the phase angle for each leg is in opposite directions or 180 degrees out from each other. But what about the 240V use of the same transformer? It doesn't use the ground or neutral. True the 240V circuit completes itself. The transformer on the pole has the neutral connection on the primary side. Let any part of that 240V system have chance & it's going to ground to get back to the source.

Quick story similar to the O'scope your power feed joke. A field tech thought that since his Fluke 87 says O.L. for overload above 600V he could measure the primary of a station power pot, 7200 phase to ground. Not sure how he lived to tell the tale. The meter leads melted immediately. The meter died permanently. The field tech suffered permanent hearing damage.
 
Not sure how I stumbled onto this ancient thread. Certainly a lot of interesting explanations here.

Let me just say this: do you ever wonder why three phases and 120 degrees comes about? It is because, surprisingly enough, if you sum the phases, it adds to a constant number, anywhere during a full cycle. That is why 3 phase is said to be “smoother” than single phase, which drops to zero so many times per second. Does that matter for a lathe or mill? That I do not have any direct comparison for, just know that all the motors I have seem pretty smooth.
 
  • Wow
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My first (and only) experience with "2 phase" was in Seattle at the Ball Glass plant. They (the site electricians & electrical engineers) call it square phase.

The glass furnaces are initially fired with natural gas and then switched to electric. Incoming is 26.4 KV transformed down to 135/265. The furnaces are very square and the opposing poles are placed in the corners via three for each side of the corner three inch stainless round bars. Each bar is clamped to six 750MCM conductors and they get fed in as they are consumed.

The power is run around the outside of the furnace in a paralleled open bus, two 1x12 alum bars.

None of this is insulated.

Consumption is a bit over 10,000 amps. Runs 24/7 for hopefully ten years or so. Impressive.

The EMF floating around these things is impressive too. One day a man came in and set down a just fixed porta band. We were working under the furnace and there is a lot of steel superstructure. When he put the saw down, the ground prong happened to contact a piece of steel. The cord was wrapped in a small circle, with three turns, held with twisty ties. Didn't take long and it was smoking. After we noticed it, we Amprobe clamped it - it was drawing +40 amps.


Cat
 
If some of the content has already been covered, please forgive. That is an awful lot of reading for a Sunday, even if it is an electrifying subject.

Out in the boonies in Wisconsin, our electric service is single phase. Two wires can only supply a single phase. The nearest three phase lines are about five miles away. They are only routed where there is enough demand to justify running the additional wire.

Three phase generation from a a single phase can only be done in one of three ways: A static phase convereter using reactance (capacitance and/or inductance) to electrically shift the phase, a rotary phase converter where secondary windings on a motor are physically positioned 120º and 240º from the primary winding, and using a VFD to create three new phases 120º apart. I suppose using single phase to drive a motor driving a three phase generator would be a fourth.

An excellent reason for 120/240 is efficiency. On the standard 120-0-120 feed, the most tcurrent the neutral will ever carry is the larger curren of the two legs as the neutral current is the difference between the currents in each leg because they are 180º out of phase. It is the reason that we can use a 12-3 cable instead of a 12-12-8, If two equivalent lines that were in phase, an additional wire would be required.

The same is true for three phase. The current through a wire will be the vector sum of the currents in the two connected circuits. Because of the 120º phase shift, it will be less than the current in either circuit.

Add to that, that three phase is better for converting to d.c. With full wave rectification, there are six peaks per cycle instead of two. The peaks are 2.7 msec. apart rather than 8.3msec. for single phase full wave rectification which means better voltage regulation and lower cost filtering. Modern automotive alternators are three phase generators using full wave rectification.
 
"Modern automotive alternators are three phase generators using full wave rectification. "

I had no idea!
R
 
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