Is the ugly's book wrong?

[jes25]

OK, First of all I was under the impression there is no such thing as "two-phase", but below we have a excerpt from the uglys reference manual. It has calcs for single and three phase that sound right but look at this.


To Find Horsepower

Two-Phase

HP= Volts X Amperes X Efficiency X Power Factor X 2 / 746

The X 2 at the end is throwing me off.

It show the same formula with multplier of 1.73 at the end for 3 phase.

 

[bbaumer]

There is such a thing as 5-wire two phase. Never seen it, only references to it. Don't know the application for it either.

Here's a link to a discussion on this on this forum:

http://forums.mikeholt.com/archive/index.php/t-53674.html

 

[chris kennedy]

I'll see your 2? and raise you 4.

647.5 Three-Phase Systems.
Where 3-phase power is supplied, a separately derived 6-phase ?wye? system with 60 volts to ground installed under this article shall be configured as three separately derived 120-volt single-phase systems having a combined total of no more than six disconnects.

 

[rattus]

OK, First of all I was under the impression there is no such thing as "two-phase", but below we have a excerpt from the uglys reference manual. It has calcs for single and three phase that sound right but look at this.


To Find Horsepower

Two-Phase

HP= Volts X Amperes X Efficiency X Power Factor X 2 / 746

The X 2 at the end is throwing me off.

It show the same formula with multiplier of 1.73 at the end for 3 phase.

In any balanced polyphase circuit,

Preal = Vphase x Iphase x PF X N

where "N" is the number of phases, in this case "2",
Vphase is the secondary voltage, and
Iphase is the secondary current.

The constant "746" converts watts to horsepower.

Or, if one uses line voltages and currents, as is more common,

Preal = Vline x Iline x PF x sqrt(N) for 2 and 3 phase systems.

 

[electricalperson]

OK, First of all I was under the impression there is no such thing as "two-phase", but below we have a excerpt from the uglys reference manual. It has calcs for single and three phase that sound right but look at this.


To Find Horsepower

Two-Phase

HP= Volts X Amperes X Efficiency X Power Factor X 2 / 746

The X 2 at the end is throwing me off.

It show the same formula with multplier of 1.73 at the end for 3 phase.

two phase is pretty much extinct. its a very old system that isnt around anymore. maybe there is still 2 phase services in old factories. i never seen it before i only read about it in books

 

[bphgravity]

I thought the multiplier of 1.414 was used for two-phase circuits?

 

[frenchelectrican]

I do see very few true 2? around here but that is sorta like hen's teeth now. AFAIK there is one industail building in my area still using that oddball format but otherwise some case they converted from 3? supply to run 2? supply by running scottT transformer setup.

However someone mention X2.,, Yes that is correct for 2? 4 or 5 wire setup but for 2? 3 wire set up go by 1.73 IIRC due common phase conductor.

Merci,Marc

 

[electricalperson]

while were talking about the uglys book, they have the formula for finding the wire size using voltage drop, it gives a table for steel conduit that you use for that formula, how do you do it for cable or nonmetallic conduit? i havnt done these calculations since trade school :grin:

 

[rattus]

I thought the multiplier of 1.414 was used for two-phase circuits?

Read the last line of post #4.

 

[quogueelectric]

Did someone say TWO PHASE??

 

[jes25]

If anyone has a drawing of this two phase system and the voltages that you would read line to line and line to ground, that would be helpful. The uglys book says a 2-phase 230 Volt system in it's example. I take it that would be line to ground? and 460 across both phases?

Rattus,

Could you explain the "secondary" and "line" voltages/currents a little more? If I put my amprobe on one leg of a 3 phase motor do I have a line current reading or secondary current reading?

If I read 480v across two lines is that line voltage? and 277V to ground/neutral is that secondary voltage?

 

[Jraef]

I have heard that there are still a few true 2-phase systems still in use around the country, the only ones I have seen mentioned in the past 2 years were in some of the oldest industrial buildings in Philadelphia in old furniture making machinery. But you can't buy any new 2-phase equipment, i.e. motors, so I would not waste a lot of brain power thinking about it unless you are one of the handful of people in the US who need to understand it in order to maintain it.

If you want to satisfy your curiosity, do a search on a "Scott-tee transformer" (also spelled Scot-tee, or Scott-t or Scot-t). It is a special design used to convert 2-phase to 3-phase or vice-versa. By looking at the diagrams you can see the different connections for 2-phase systems. Some are 4 wire, some are 5 wire; all are rare.
I'm of the opinion that information on it should be footnoted in the NEC (and its derivatives such as Ugly's) because it causes more confusion than anything else. A LOT of people misconstrue 2-phase with 1-phase 2 wire systems, because they see 2 hot legs and assume they are 2 phases.

 

[frenchelectrican]

Here the link for 2? transformer connection diagram

http://www.electrical-contractor.net/forums/ubbthreads.php/ubb/showflat/Number/148672/page/3#Post148672



Here is for the 2? motor connecton diagram

http://www.electrical-contractor.net/forums/ubbthreads.php/ubb/showflat/Number/148645/page/4#Post148645


Hope that will help answer some question which I know it will come up from time to time.

Merci,Marc

 

[quogueelectric]

I know you meant single phase 3 wire systems the centertap being grounded and the reference for most people does cause a lot of confusion.

 

[Sharpie]

Do I remember correctly that 2-PH are 180 Deg. out of phase with each other?

 

[LarryFine]

Did someone say TWO PHASE??

Yes, two phase. Picture two typical center-tapped 120/240v secondaries, with the two windings placed in an X, i.e., at 90? timing-wise, with the center taps connected together.

Now you have a four-point star (like a 3-ph Y), with four line conductors (instead of three), and a single common neutral. The timing between adjacent line conductors is 90? instead if 120?.


Added: Note: Rattus might refer to this configuration as four-phase.

 

[LarryFine]

I know you meant single phase 3 wire systems the centertap being grounded and the reference for most people does cause a lot of confusion.

Picture two of these placed at 90? with the center taps connected together. Now you have four hots and a single neutral.

Do I remember correctly that 2-PH are 180 Deg. out of phase with each other?

It would be more accutare to say 90? than 180?.

 

[rattus]

Now I wouldn't say that!

Now I wouldn't say that!

Yes, two phase. Picture two typical center-tapped 120/240v secondaries, with the two windings placed in an X, i.e., at 90? timing-wise, with the center taps connected together.

Now you have a four-point star (like a 3-ph Y), with four line conductors (instead of three), and a single common neutral. The timing between adjacent line conductors is 90? instead if 120?.


Added: Note: Rattus might refer to this configuration as four-phase.

I have seen it described as four-phase, but as Mr. Wimple of the Fibber shows used to say, "Now I wouldn't say that".

 

[mivey]

Do I remember correctly that 2-PH are 180 Deg. out of phase with each other?

The old 2-phase system was 90 degrees out of phase and was a non-uniform polyphase system.

A lot of people don't like to call a system with a 180 degree difference 2-phase because the vectors of the two voltages are on the same axis. You will see that notation in some reference material but it causes confusion because of the old 90-degree 2-phase system. If you feel froggy, read: http://forums.mikeholt.com/showthread.php?t=96673

 

[jim dungar]

The systems were "generated" as 2-phase 4 wire without any common connection. One set of conductors were usually labeled as L1-L2 and the other set were L1'-L2'. The next common connection was 2PH 3W where L2 and L1' were connected together in a configuration that looked like the letter L. The common connection was not a neutral point and in fact carried 1.41 times the current of the other conductors so it did not always "save" on wiring costs. The final, rare, connection was a 2PH 5W, which was created by connecting a midpoint from each phase L1-N-L2 and L1'-N-L2' together into a configuration that looked like a + sign. Regardless the number of conductors, loads were never connected across phases (i.e. from L1' - L2)