What does single and 3 phase really mean?

Loading thread data ...

medium voltage has one called "V" phase. At least that is what we called it when working on the REA lines in the Midwest some 30 years ago. Never seen it since leaving the Midwest.

Reply to
Zathera

V phase is an open delta 3 phase. Saves on buying the third can.

Reply to
jak

isn't 2 phase, the normal domestic supply in north america? phase to phase 230volt and phase to neutral 115v

Reply to
obsidian

Yes, but it's single phase center-tapped, not two phase. Any integral multiple of 180 degrees phase difference doesn't count- the voltages are linearly dependent.

Best regards, Spehro Pefhany

Reply to
Spehro Pefhany

formatting link

Reply to
Matt

Mathematically, yes. Electrical supply engineers don't like refering to it as such though, and this has been the cause of much heated debate in the past ;-).

Reply to
Andrew Gabriel

Some folks often confuse the 'Edison' supply of typical US households with 2 phase. The US residential supply is actually just a single phase with a center tap.

That being said, there have been a few 2-phase systems. IIRC, some early traction (street-car) schemes were two-phase.

A true 2-phase system would have two voltages that are generated ninety degrees out of phase with each other. At first glance, this would require four wires, but can be simplified somewhat by tieing one leg of each phase together and only using three wires. But the common wire would have to be larger than the outer two.

So now, compared to a single phase system of the same voltage and current per phase, you can transmit twice the power, but need three conductors and one conductor larger than the others.

Compare this with three-phase systems, where for the same three conductors (all the same size) and the same phase voltage and current, you can transmit three times the power of single phase.

Three-phase is superior when it comes to long transmission costs.

Unbalanced systems like 2 phase are also bad about noise on adjacent telephone lines. And I'd hate to think about the line reactance calculations for such an unbalanced system.

daestrom

Reply to
daestrom

formatting link

Reply to
Steve Alexanderson

Thanks for jogging the memory cells. I have not done that kind of work in ages and in my lifetime never will again.

I remember doing 2 conductors with 3 transformers for the farms. We called it V phase probably one of those........ greenfeild or flex issues.

Reply to
Zathera

Two phase (voltages 90 degrees out of phase) is often used for control motors. Three phase has economic and technical advantages. More bang for the buck. In many parts of the world, particularly where it is not used, the common

120/240V 3 wire "edison" schem used for residential supply is called "2 phase" . Technically it may be considered so but is generally called single phase 3 wire.

-- Don Kelly snipped-for-privacy@peeshaw.ca remove the urine to answer

Reply to
Don Kelly

in article 3f79e7cf$0$31723$ snipped-for-privacy@reader1.news.skynet.be, obsidian at snipped-for-privacy@leuven.vlaanderen.belgium.europe.terra.sol wrote on 9/30/03 1:30 PM:

What is called two phase and may still be in use somewhere is really a four-line, four phase system plus neutral, EXCECPT that two of the lines are missing. That is enough to get rotating fields to drive motors. Three-phase is able to get more power into the same size frame.

It is possible to convert from one to another using a "Scott-T connection." Two phase power systems are probably very rare. There are some servo control systems that use Scott-T connections.

Bill

Reply to
Repeating Decimal

Zathera,

I have read a number of your posts offering advice to others connected with serious electrical safety issues. My suggestion is that you get off crack or whatever mind enhancing drugs you are using. If it is not drugs then you need to complete high school.

Regards,

John Phillips

Reply to
John Phillips

Zathera,

I have read a number of your posts offering advice to others connected with serious electrical safety issues. My suggestion is that you get off crack or whatever mind enhancing drugs you are using. If it is not drugs then you need to complete high school.

Regards,

John Phillips

Reply to
John Phillips

PolyTech Forum website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.