can someone please explain two phase power?
I understand single phase and three phase systems, but i dont see where two phase fits in.

If you can think of single phase power as being similar to a single cylinder engine, with intermittent delivery of power to the load, and three phase power resembling a three cylinder engine, well, two phase power would be equivalent to, you guessed it, a two cylinder engine.

The two phase generator has two separate windings physically spaced so that the voltages are generated 90 degrees out of phase.

As a matter of interest, the generators at the first Niagara Falls power station, built in 1895, were two phase, 25 Hz, 2200 volts.

Ed

[This message has been edited by electric-ed (edited 09-16-2002).]

You may generate 2 phase from any regular three phase system, if you use capacitors for changing the phase vectors acordingly. In fact, you may start with only 2 phases and neutral ( star connection ) out of the three phases. It's been along time since I calculated the phasors ( vectors ) for the capacitors. Maybe the easiest way is to do it graphically on milimetric paper. Another way to generate the 2 phases is wiring a small 3 phase transformer, delta-star insulated windings, in such a way that you obtain a phase angle right between the angle of two regular phases. Call that the zero degrees phase. Put two other windings in series, to make another phase, so that the new "phase" will be 90 degrees apart from the zero phase. Connect one wire from each phase to the other to obtain the common "neutral", and see if you can change Xformer taps or use a Variac to get both voltages equal, and preaferible equal to required motor voltage.

[This message has been edited by Sean WB (edited 09-16-2002).]

PS they have "phased" out 2 phase systems , you may run across this sometimes, I would avoid it if possible

Wow, Sean, for a pre-Journeyman, you kick my Master butt...

I like your image, Ed. Permit me to twist it just a little.

Think of the early aircraft engines with a single propeller. Right behind the propeller is the. . .what did they call'em, radial cylinders of all the pistons that power the prop. The crankshaft that the prop is mounted to has only one saddle in it, and all the connecting rods of all the pistons connect to that one spot.

Single phase 120 V would have one piston.

Single phase 3 wire 120/240 V would have two pistons opposite each other, 180 degrees apart.

Three phase, either 120/208 V four wire or 240 V three wire would have three pistons equally spaced from each other, 120 degrees apart.

Two phase would have four pistons, at right angles to each other, 90 degrees apart.

Al

Sweet motor!

What's the HP? The weight? RPM?

I didn't know Rotec was making modern radials!

Gorgeous!

Harley Davidson Evo x 3.5!

*drooling*

its not imprtant to know everything, it is important to know where to get the information!!!
Hey ,consider me a journeyman, this saturday at 12 noon!!!!
sparky66 are you the one who took the master 2 months after getting journeyman?? How the heck did you do that??
confident from passing journeyman?? was it the SBCCI?

Nope, not me... I had a good 12 months between, maybe a little more...

Did I typo in a thread somewhere?

WV requires one year, and I did come close to that minimum.

Go get 'em on Saturday, Sean!

Sean,that was me.Yes it was SBCCI.There is not alot of difference in the two tests (on the open book part) and it just seemed easier to continue prepping for the Masters exam.I already had Houston and Conroe journeyman card

I'm with Sparky66wv,sounds like you won't have any problem passing Saturday

GOOD LUCK!!!

[This message has been edited by txsparky (edited 09-17-2002).]

[This message has been edited by txsparky (edited 09-17-2002).]

'66

I believe that's the Rotec 2800: Total swept volume of 2800cc (172ci). 110HP @ 3700 RPM geared. Total engine diameter is 810mm (31.9"). Dry Weight is 108kg (220 lbs) complete with bolt on engine accessories.

Al

Modern stepper motors that are used for robotics and motion control applications operate from an electonically produced version of two phase power.

Ed

For giggles see 99NEC Table 430-149. {Is it in the 2002 edition?}

Footnote: Sometimes the term “two phase” is incorrectly used to describe 1) 120/240V 3-wire service {which is still single phase} or, 2) two ungrounded conductors and a neutral are tapped from a 4-wire wye system {which is correctly termed ‘network service.’}

Two-phase may be mentioned in the fine print of some electric utility’s service agreements, but it is always qualified as “not for new work,” and sometimes with verbiage to the effect of, “If we own special equipment to provide you, the customer, with two-phase service, and it breaks, you have to, at that time, now accept three-phase service from us,” effectively mandating an upgrade of your old stuff at your expense.

I understand that the Sierra Nevada mountains in the early past century had sawmills with 2-phase motors. Also, two-phase power was described as once popular in the "Philadelphia District."

Yep,

2002 NEC Table 430.149 Full-Load Current, Two-Phase Alternating-Current Motors (4-Wire).

Gentlemen:
For what it's worth, I faintly remember going to the Philadelphia area, a long time ago, with one of the "old timers".
I think it was some type of hotel, and it had two phase power. Can't remember all of the details; something about "2 hots, 2 neutrals, & 1 grd" maybe?????
Had to be in mid 70's???

John

Thanks for the repies. I was not planning on doing any work with it...I was just curious...I was reading somthing about philadelphia and saw two-phase mentioned.

I have also heard of other poly-phase systems...such as six-phase??? maybe this is used for large equipment? I have never heard of this being used.

Mike,
With regard to you last comments about Six-Phase wiring, I come from New Zealand and we quite regularly hook up motors, in a configuration we call 'Star-Delta', this uses a 3-phase motor (400V), the motor starts in Star, and runs in Delta, this requires that there are two 3-phase wires
running to the motor, hence the 6 phases.
Just as a note, polyphase in my language,
means any circuit that has more than one
un-earthed(live)conductor.
Normally poly-phase over here means 3-phase
400V, wether or not that it has a Neutral conductor.

The star-delta motor configuration is also commonly used on larger motor starters in England.

The only problem with that definition is that is falls down when we come to a single-phase 3-wire service, such as the normal 120/240V American residential system.

Trainwire,

Woof.

. . .ah. . .32 Ø ?

now the six phase makes sence...i didnt think about it that way...six-phase - double star, six-phase - doule delta, six phase - star-delta...

Bjarney,

For even more giggles, see table 430-150

I never seen a 115 volt 3 phase motor??!!

BTW,

I believe 2 phase can be configured as 3, 4, or 5 wire.

[This message has been edited by Redsy (edited 09-19-2002).]

Just for fun, here are some links for 2 Phase related Schematics, which are located in the ECN Technical Reference Area:

2 phase transformer schematics

2 phase motor schematics

These, plus other items can be found in the

Menu for Technical Reference Section

Scott S.E.T.

P.S. edits due to mistakes with UBB code [a.k.a. mistakes in spelling with HTML stuff results in worthless links!]

Scott

[This message has been edited by Scott35 (edited 09-19-2002).]

The wye-delta (star-delta) motor starter is not a six-phase system. It simply connects the motor windings in wye for starting and reconects them in delta after a predetermined time interval, normally a few seconds.

The sketch below is the power circuit only, it does not include the control circuit.



Ed

Redsy — Apparently a past use was by the US Navy on shipboard systems. Once came across a pile of surplus, quite nice-looking $5 {Bell & Gossett} compressors, all with one-third horsepower, 115V 3ø motors. I’ll bet there were a lot of suckers for those.




[This message has been edited by Bjarney (edited 09-19-2002).]