would someone help me understand this system and how it operates? everyone that i talk to says don't worry about it you will probably never see it. Boy what an attitude. I'm not worried about it but I am interested in it? why might this be selected over 3phase or single phase? what is the thoery behind it?
2 phase
- Thread starter plt
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Ed MacLaren
Senior Member
Re: 2 phase
Here is an excerpt from an article about the history of two-phase systems in England, that I found on the web.
I'm sure that "Googleing" for "two-phase electrical systems" would come up with others.
"In the 1890s there was a reluctance to consider three-phase systems, principally because the currents must of necessity be interconnected. It was mistakenly believed that it would present some difficulty in regulation. On the other hand with two phases the currents could be independent and were regarded as easily regulated.
Dr John Hopkinson approved the adoption of a two-phase transmission system by the Metropolitan Electric Supply Company in 1899 as it appeared to
permit simpler cables and balancing of the two phases was easier. A textbook of 1904 refers to three-phase as a curious arrangement of currents.
However, by 1907 attitudes were changing and two-phase generation became regarded as obsolete and a survival of the transition period from single phase to multi-phase when the industrial supply of power as distinct from lighting began to
assume prominence. In 1907 it was judged that two-phase systems are little likely to be utilised in any new works, as they had no advantages over threephase and have several disadvantages.
When two-phase generation ceased extensive two-phase distribution systems were maintained for many decades from three phase sources by Scott connected transformers. Two-phase distribution originally associated with two-phase generation was employed in areas of the West Midlands until 1972."
Here is a link to the complete article -
http://www.iee.org/OnComms/pn/History/HistoryWk_Single_&_2_phase.pdf
Ed
Here is an excerpt from an article about the history of two-phase systems in England, that I found on the web.
I'm sure that "Googleing" for "two-phase electrical systems" would come up with others.
"In the 1890s there was a reluctance to consider three-phase systems, principally because the currents must of necessity be interconnected. It was mistakenly believed that it would present some difficulty in regulation. On the other hand with two phases the currents could be independent and were regarded as easily regulated.
Dr John Hopkinson approved the adoption of a two-phase transmission system by the Metropolitan Electric Supply Company in 1899 as it appeared to
permit simpler cables and balancing of the two phases was easier. A textbook of 1904 refers to three-phase as a curious arrangement of currents.
However, by 1907 attitudes were changing and two-phase generation became regarded as obsolete and a survival of the transition period from single phase to multi-phase when the industrial supply of power as distinct from lighting began to
assume prominence. In 1907 it was judged that two-phase systems are little likely to be utilised in any new works, as they had no advantages over threephase and have several disadvantages.
When two-phase generation ceased extensive two-phase distribution systems were maintained for many decades from three phase sources by Scott connected transformers. Two-phase distribution originally associated with two-phase generation was employed in areas of the West Midlands until 1972."
Here is a link to the complete article -
http://www.iee.org/OnComms/pn/History/HistoryWk_Single_&_2_phase.pdf
Ed
- Location
- Lockport, IL
- Occupation
- Semi-Retired Electrical Engineer
Re: 2 phase
The only thing I know about 2-phase systems is that the two phases are offset from each other (i.e., in time, or if you prefer, in phase) by 90 degrees, or one quarter of a cycle. I can?t shed any light of why they might be used, but I can give you two good reasons why they are not used. That is, I can give you two great advantages of a 3-phase system. The first is that when you apply 3-phase power to the stationary part of a motor, you get a rotating magnetic field, without using any moving parts. The only moving part is the rotor, which spins in reaction to the rotating magnetic field.
The second reason is that power is constant in a 3-phase motor. It?s tricky to explain without using math and showing pictures. But imagine this: Contemplate running a race around a track. Suppose that you start slow, then speed up, then reach a top speed, then slow down, then stop, then sit, then have someone hand you a drink, then you stand up, then you start moving, and then you start the pattern all over again. The rate at which you are burning up your internal energy (i.e., the rate at which you are consuming ?power?) is constantly changing. That is the fate of all single phase motors (and I suspect all 2-phase motors as well). But a 3-phase motor consumes power at the same rate at every instance in time. It is like running at a constant speed around the track. I would call that the single greatest advantage of a 3-phase system.
By the way, I have a couple of Word files that show the math (i.e., trigonometry) for the power consumed in a single phase motor and a 3-phase motor. If anyone wants to see them, send me a PM with an email address.
The only thing I know about 2-phase systems is that the two phases are offset from each other (i.e., in time, or if you prefer, in phase) by 90 degrees, or one quarter of a cycle. I can?t shed any light of why they might be used, but I can give you two good reasons why they are not used. That is, I can give you two great advantages of a 3-phase system. The first is that when you apply 3-phase power to the stationary part of a motor, you get a rotating magnetic field, without using any moving parts. The only moving part is the rotor, which spins in reaction to the rotating magnetic field.
The second reason is that power is constant in a 3-phase motor. It?s tricky to explain without using math and showing pictures. But imagine this: Contemplate running a race around a track. Suppose that you start slow, then speed up, then reach a top speed, then slow down, then stop, then sit, then have someone hand you a drink, then you stand up, then you start moving, and then you start the pattern all over again. The rate at which you are burning up your internal energy (i.e., the rate at which you are consuming ?power?) is constantly changing. That is the fate of all single phase motors (and I suspect all 2-phase motors as well). But a 3-phase motor consumes power at the same rate at every instance in time. It is like running at a constant speed around the track. I would call that the single greatest advantage of a 3-phase system.
By the way, I have a couple of Word files that show the math (i.e., trigonometry) for the power consumed in a single phase motor and a 3-phase motor. If anyone wants to see them, send me a PM with an email address.
- Location
- Wisconsin
- Occupation
- PE (Retired) - Power Systems
Re: 2 phase
The line current in a 4 wire two phase system can be less then in a three phase system.
Two phase
Full load current =(746*hp)/(2*eff*pf*voltage)
Three phase
Full Load current =(746*hp)/(1.73*eff*pf*voltage)
The line current in a 4 wire two phase system can be less then in a three phase system.
Two phase
Full load current =(746*hp)/(2*eff*pf*voltage)
Three phase
Full Load current =(746*hp)/(1.73*eff*pf*voltage)
Re: 2 phase
Hey PLT -
Great question, with a possibly MUCH more intriguing set of applicable information than just "early historical installations," like most of Chicago was originally wired early 1900's or so. In fact, until more recent power supplies and technology problems, it really was considered an interesting, though unlikely to be used again, possibility.
What you may well be considering is currently already being done, safely, though "outside" of official recognition by the NEC, since it addresses only niche markets. This is a "balanced" 120V AC system, and is the PREFERRED power for ANY space intended for the specific application of sound or audio recording and performance. The reasons for this are, of course, solidly grounded in physics, but it is fairly simple to understand based on what you likely already know, and can find out more by a simple Google search, but ADD the words "sound audio noise" to your "two phase balanced power" search. You'll likely find many sound specialists and studio links, including the famous Zoo Studio in California, who have installed balanced power circuits to their audio facility.
Basically, it eliminates "hum" right at the source, the power supply & EM/RFI filters prior to amplification circuits. I believe the idea is to provide 60V out-of-phase to the two current-carrying ungrounded conductors. Yes, all two-pole breakers must be used, as there is no neutral. I visualize it as similar to wiring something like a hot water heater at 240V from a typical single phase panel; i.e. two "hots" and a safety ground, to provide 240V via two out-of-phase 120V legs - except now you're doing it for a final 120V.
It completely meets the "spirit" of the NEC, and really does result in a nearly hum-free zone for audio equipment.
*This is NOT the same as lifting the ground for a split-phase AC system with all the monitoring and potential for chassis-short shock hazards and GFCI requirements that then must be applied.
Keep a good bookmark-library of links to others who have done it, and when the need arises, you'll have the tools and the contacts to educate clients (and inspectors...), as well as ensure a safe installation!
Good Luck
!
Hey PLT -
Great question, with a possibly MUCH more intriguing set of applicable information than just "early historical installations," like most of Chicago was originally wired early 1900's or so. In fact, until more recent power supplies and technology problems, it really was considered an interesting, though unlikely to be used again, possibility.
What you may well be considering is currently already being done, safely, though "outside" of official recognition by the NEC, since it addresses only niche markets. This is a "balanced" 120V AC system, and is the PREFERRED power for ANY space intended for the specific application of sound or audio recording and performance. The reasons for this are, of course, solidly grounded in physics, but it is fairly simple to understand based on what you likely already know, and can find out more by a simple Google search, but ADD the words "sound audio noise" to your "two phase balanced power" search. You'll likely find many sound specialists and studio links, including the famous Zoo Studio in California, who have installed balanced power circuits to their audio facility.
Basically, it eliminates "hum" right at the source, the power supply & EM/RFI filters prior to amplification circuits. I believe the idea is to provide 60V out-of-phase to the two current-carrying ungrounded conductors. Yes, all two-pole breakers must be used, as there is no neutral. I visualize it as similar to wiring something like a hot water heater at 240V from a typical single phase panel; i.e. two "hots" and a safety ground, to provide 240V via two out-of-phase 120V legs - except now you're doing it for a final 120V.
It completely meets the "spirit" of the NEC, and really does result in a nearly hum-free zone for audio equipment.
*This is NOT the same as lifting the ground for a split-phase AC system with all the monitoring and potential for chassis-short shock hazards and GFCI requirements that then must be applied.
Keep a good bookmark-library of links to others who have done it, and when the need arises, you'll have the tools and the contacts to educate clients (and inspectors...), as well as ensure a safe installation!
Good Luck
!
physis
Senior Member
Re: 2 phase
This is an extraordinary thead. I have a couple of questions.
Am I undertanding this right? 2 phase is 2 single phases 90 degrees out of phase.
If that's correct then, are the two single phases independent of each other? I'm picturing two ways to do this. What seems most likely to me would be essentially two generators on one armature. The two phase are connected at a neutral.
I summed two 120 voltages 90 degrees out of phase and I get 169.7
This whole thing is just really intesting to me.
The "Hum-Free zone" is also very interesting but why not just use DC for that? Like the phone company.
This is an extraordinary thead. I have a couple of questions.
Am I undertanding this right? 2 phase is 2 single phases 90 degrees out of phase.
If that's correct then, are the two single phases independent of each other? I'm picturing two ways to do this. What seems most likely to me would be essentially two generators on one armature. The two phase are connected at a neutral.
I summed two 120 voltages 90 degrees out of phase and I get 169.7
This whole thing is just really intesting to me.
The "Hum-Free zone" is also very interesting but why not just use DC for that? Like the phone company.
charlie
Senior Member
- Location
- Indianapolis
Re: 2 phase
I know a little bit about the system and how the Scott connected transformers work with the 86.7% tap. It's pretty weird but it works.
I know a little bit about the system and how the Scott connected transformers work with the 86.7% tap. It's pretty weird but it works.
bphgravity
Senior Member
- Location
- Florida
Re: 2 phase
Shouldn't that "2" be 1.414 or the square root of 2 for a two-phase system?
- Location
- Wisconsin
- Occupation
- PE (Retired) - Power Systems
Re: 2 phase
I know the factor is 2. Two phase has a greater efficacy than does three phase. I don't know if it is actually the square root of 4, but I have never seen it put that way.
Scott Tee transformers for 2 phase should not be confused with normal Tee transformers for 3 phase. They only look and sound alike.
2 phase systems can also be found in some motion control devices like resolvers and servos.
I know the factor is 2. Two phase has a greater efficacy than does three phase. I don't know if it is actually the square root of 4, but I have never seen it put that way.
Scott Tee transformers for 2 phase should not be confused with normal Tee transformers for 3 phase. They only look and sound alike.
2 phase systems can also be found in some motion control devices like resolvers and servos.
physis
Senior Member
Re: 2 phase
Here's a schematic of a Scott connected configuration.
http://www.lcmagnetics.com/scott.htm
[ November 23, 2004, 07:10 PM: Message edited by: physis ]
Here's a schematic of a Scott connected configuration.
http://www.lcmagnetics.com/scott.htm
[ November 23, 2004, 07:10 PM: Message edited by: physis ]
hbiss
EC, Westchester, New York NEC: 2014
- Location
- Hawthorne, New York NEC: 2014
- Occupation
- EC
Re: 2 phase
Mrsandman, I believe what you are talking about- a balanced power system- is not 2 phase but single phase just like 120/240 single phase. It is derived from a 120 volt center tapped secondary transformer where the center tap is grounded. The phase relationship between the two "phases" and ground is 180 deg consequently with a voltage of 60 volts to ground.
-Hal
Mrsandman, I believe what you are talking about- a balanced power system- is not 2 phase but single phase just like 120/240 single phase. It is derived from a 120 volt center tapped secondary transformer where the center tap is grounded. The phase relationship between the two "phases" and ground is 180 deg consequently with a voltage of 60 volts to ground.
-Hal
john m. caloggero
Senior Member
Re: 2 phase
I did quite a bit of work on 2-phase, 400 and 1200 hertz generator and power installations for missile systems for planes and ground installations. Two-phase systems are similar to 3-phase systems, except that there are 2 voltages that are displaced by 90 degrees instead of 3 voltages displaced 120 degrees. The voltage in the two windings are 90 degrees apart so that if the windings are connected in series, and 100 volts is developed in each winding the voltage across the two windings is sq root of 2 or 1.41 times 100v = 141 volts; similar to 1.l73 x 120v = 208v for a 3-phase system. It is the vector sum of the voltages because they are not in phase with each other. A common neutral can be derived from the common connection point of the two windings to provide, for example 100 volts from neutral to either phase line conductor or 141 volts across the two phase line conductors. If you draw two windings at right angle to each other and connect one end together and derive a neutral from that point, you will have a 3-wire 2-phase system.
I did quite a bit of work on 2-phase, 400 and 1200 hertz generator and power installations for missile systems for planes and ground installations. Two-phase systems are similar to 3-phase systems, except that there are 2 voltages that are displaced by 90 degrees instead of 3 voltages displaced 120 degrees. The voltage in the two windings are 90 degrees apart so that if the windings are connected in series, and 100 volts is developed in each winding the voltage across the two windings is sq root of 2 or 1.41 times 100v = 141 volts; similar to 1.l73 x 120v = 208v for a 3-phase system. It is the vector sum of the voltages because they are not in phase with each other. A common neutral can be derived from the common connection point of the two windings to provide, for example 100 volts from neutral to either phase line conductor or 141 volts across the two phase line conductors. If you draw two windings at right angle to each other and connect one end together and derive a neutral from that point, you will have a 3-wire 2-phase system.
scott thompson
Senior Member
- Location
- Anaheim, California
Re: 2 phase
Here is a link for some 2? Schematics + information (I'll try to insert one image to this message,but not sure if it will remain!):
2 Phase Transformer Schematics
Let's see if this Schematic will appear (image is 3? Delta primary to 2? 4 Wire Taylor Secondary):
Scott35
Here is a link for some 2? Schematics + information (I'll try to insert one image to this message,but not sure if it will remain!):
2 Phase Transformer Schematics
Let's see if this Schematic will appear (image is 3? Delta primary to 2? 4 Wire Taylor Secondary):
Scott35
Re: 2 phase
I was going to ask why 3-phase was more efficient than 1-phase. It would seem that the natural rotating field in 3-phase motors is smoother shall we say, than in 2-phase equipment. Of course, 1-phase motors must somehow create a second phase to start, and this requires start windings, centrifugal switches, start caps, relays, etc.
Distribution should be more efficient as well, since there would be zero neutral current in a balanced 3-phase system.
Having said that, I must dig out my "Puchstein, Lloyd, and Conrad" to see if I am just babbling.
I was going to ask why 3-phase was more efficient than 1-phase. It would seem that the natural rotating field in 3-phase motors is smoother shall we say, than in 2-phase equipment. Of course, 1-phase motors must somehow create a second phase to start, and this requires start windings, centrifugal switches, start caps, relays, etc.
Distribution should be more efficient as well, since there would be zero neutral current in a balanced 3-phase system.
Having said that, I must dig out my "Puchstein, Lloyd, and Conrad" to see if I am just babbling.
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