Single phase 240v and double phase 240v

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looking for someone that can explain to me the phase shift on a single phase 240v system. I just read in a book that the phases in a TWO phase system are 180 degrees out of phase from each other. i guess i have misunderstood this for years. i always thought that the phases in a single phase system were 180 degrees out of phase. i never really researched two phase since it is not really used.
 

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  • #2
davenn
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in a singe phase system there is only 1 phase so not sure why you are saying phases

there is a positive and negative half of the cycle that is 180 deg out of phase.

two phase systems.. from wiki....
Two-phase electrical power was an early 20th century polyphase alternating current electric power distribution system. Two circuits were used, with voltage phases differing by 90 degrees. Usually circuits used four wires, two for each phase. Less frequently, three wires were used, with a common wire with a larger-diameter conductor. Some early two-phase generators had two complete rotor and field assemblies, with windings physically offset by 90 electrical degrees to provide two-phase power. The generators at Niagara Falls installed in 1895 were the largest generators in the world at the time and were two-phase machines.
now thats different than 2 phases of a 3 phase system. In a normal 3 phase power system, the phases are 120 deg out of phase, adding up to a total of 360deg.
Any 2 phases are 120 deg out of phase

am sure there are some more informed guys out there that will put you straight ( and me too haha)

Dave
 
  • #3
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relationship between electrical angle and mechanical angle

i wanna know the relationship between electrical angle and mechanical angle with derivation...
 
  • #4
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please someone help me and its so important to me (relationship between electrical angle and mechanical angle with derivation)
 
  • #5
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I am saying "phases" because there are 2 hots and a neutral coming into your house right? My understanding was that there were two sine wave
 
  • #6
davenn
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no not that this....

i always thought that the phases in a single phase system were 180 degrees out of phase.
you said about phases (plural) in a SINGLE phase system that was the contradiction ;)

Dave
 
  • #7
davenn
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please someone help me and its so important to me (relationship between electrical angle and mechanical angle with derivation)
Hi maddy,
dont hijack someone elses thread, its rude, start your own thread :)

Dave
 
  • #8
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I am saying "phases" because there are 2 hots and a neutral coming into your house. "Single" phase right? Each hot is 120v to neutral or ground. 240v between hots. Same results you would get with a "TWO" phase system. "TWO"phase makes complete sense, but how is it possible to get the same result with only one phase. I think a picture on an oscilloscope would really clear things up. Anyone know of any links online?
 
  • #9
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Dave the key word in my first post was "thought". All that I thought I knew about single phase has gone out the window. thanks for the jab at maddy
 
  • #10
davenn
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I am saying "phases" because there are 2 hots and a neutral coming into your house. "Single" phase right? Each hot is 120v to neutral or ground. 240v between hots. Same results you would get with a "TWO" phase system. "TWO"phase makes complete sense, but how is it possible to get the same result with only one phase. I think a picture on an oscilloscope would really clear things up. Anyone know of any links online?
Ahhh ok.... I'm not totally up with the USA system and how they split the phases.
Others on here will help with that one :)

Here in Australia ( and back in New Zealand, my home country) we have a single 240V phase coming into the house. Out on the pole in the street there are 3 phases. 240V between any phase and neutral ( ground) (Neutral is tied to ground at the house meter/fuse board). and ~400V between phases.

Dave
 
  • #11
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Consider 2 nos., 1.5V DC batteries connected in series. The +ve terminal (polarity) of cell 1 is 180 deg. out of phase with -ve terminal (polarity) of cell 2. 180 deg. out of phase means both the hot lines have opposing polarities.

DC system could be considered being limited to 180 deg phase angle as there cannot be intermediate phase angle difference as is case with AC system.

P.S. Above example does not signify phase angle concept in DC. It is just to draw an analogy betwn the 2 systems to explain concept of phase difference
 
  • #12
dlgoff
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I am saying "phases" because there are 2 hots and a neutral coming into your house. "Single" phase right? Each hot is 120v to neutral or ground. 240v between hots. Same results you would get with a "TWO" phase system. "TWO"phase makes complete sense, but how is it possible to get the same result with only one phase. I think a picture on an oscilloscope would really clear things up. Anyone know of any links online?
There is only one phase that is split by using a center tap ground on the secondary of a transformer as shown below (Fig. 1).

Split_phase2.png


A transformer supplying a 3-wire distribution system has a single-phase input (primary) winding. The output (secondary) winding is center-tapped and the center tap connected to a grounded neutral. This 3-wire system is common in countries with a standard phase-neutral voltage of 120 V. In this case, the transformer voltage is 120 V on either side of the center tap, giving 240 V between the two live conductors, shown as V1 and V2 in Fig. 1. The two outputs are properly called "legs", not "phases".
Bold type by me.

http://en.wikipedia.org/wiki/Split_phase
 
  • #15
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Ref Page 265 in said PDF - as soon as you discuss "phases" you need to see the difference between 3 phase and single ( split ) phase systems.
 
  • #16
dlgoff
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Ref Page 265 in said PDF
Which is what I posted in post 12; to keep things simple without bringing all the 3 phase circuits up, which may confuse the OP further IMO.
 
  • #17
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So would I be correct in saying that the "LEGS" of a single (split) phase sys. and the "PHASES" of a two phase sys. are both 180° apart and oppisite in polarity? ultimately the same when you compare them on an oscilloscope?
 
  • #18
dlgoff
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So would I be correct in saying that the "LEGS" of a single (split) phase sys. and the "PHASES" of a two phase sys. are both 180° apart and oppisite in polarity? ultimately the same when you compare them on an oscilloscope?
No.

Two-phase electrical power was an early 20th century polyphase alternating current electric power distribution system. Two circuits were used, with voltage phases differing by 90 degrees. Usually circuits used four wires, two for each phase.
Bold by me.

http://en.wikipedia.org/wiki/2_phase_power
 
  • #19
jim hardy
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Digoff has it -- your house is fed with SINGLE PHASE , center-tapped.

to call the two hot wires "phases" is misleading as it infers a multiple phase system, which it really isn't.

Lavoisier would have named them better.
http://web.lemoyne.edu/~giunta/ea/lavprefann.html
""The impossibility of separating the nomenclature of a science from the science itself, is owing to this, that every branch of physical science must consist of three things; the series of facts which are the objects of the science, the ideas which represent these facts, and the words by which these ideas are expressed. Like three impressions of the same seal, the word ought to produce the idea, and the idea to be a picture of the fact. And, as ideas are preserved and communicated by means of words, it necessarily follows that we cannot improve the language of any science without at the same time improving the science itself; neither can we, on the other hand, improve a science, without improving the language or nomenclature which belongs to it. However certain the facts of any science may be, and, however just the ideas we may have formed of these facts, we can only communicate false impressions to others, while we want words by which these may be properly expressed.[3]""
 
  • #20
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Thanks alot dlgoff. That wiki picture really helped. I've never seen the sine waves of a two phase sys. And I always thought the phases(of any system) had to add up to 360° I guess I need to look up single and three phase alternators now. Thanks again
 

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