Phase question

[DanZ]

Hey everybody. I got in a discussion the other day with someone about 2 phase alternating current. He told me (in great length, at great detail) how he defined 2 phase alternating current as taking two phases from three phase a/c transformers. I want to try to correct him about 2 phase, but I want to make sure my understanding of it is correct before I attempt to explain it. I have also googled it, but it's not used quite enough to be a major find. So, here's how I understand it.

-Single phase, generally a residential a/c electrical service (that can be found in commercial applications) whose sine wave is a single line between -170V RMS and 170V RMS.

-2 Phase, not broadly used, created (discovered?) by Tesla and used to make more efficient motors. Sine wave is two lines 90 degrees offset from one another. Can be derived from three phase with the use of a Scott T transformer or Scott Connection.

-Three Phase, generally a commercial or industrial a/c electric service with two major transformer types (Delta and Wye). Sine wave is three lines that are 120 degrees offset from one another. When properly used, this allows there to be no zero moment in voltage, considered the most efficient service for motors.

-Split Phase, Connection that uses the system ground and one other live conductor to mimic a single phase system. I'm unsure of how the sine wave looks. Technically referred to (according to wikipedia) a 3 wire, single phase, mid point neutral system. Erroneously referred to as 2 phase.

Do I have it down, or am I missing something?

Please remember:

I have read the battle of the phases, I just want to make sure I have it down.

This is not the battle of the phases, please don't turn it into it.

Leave the horse alone.

 

[jim dungar]

Yes, you have the basics down. Except the voltage is 120V RMS.

The biggest problem people have is wanting to call a conductor a phase.

My primary method of describing the number of phases has to so with the number of L-L combinations. I do not feel that the presence or absence of a neutral/common point should affect the number of phases in a system/circuit.

 

[quogueelectric]

Hey everybody. I got in a discussion the other day with someone about 2 phase alternating current. He told me (in great length, at great detail) how he defined 2 phase alternating current as taking two phases from three phase a/c transformers. I want to try to correct him about 2 phase, but I want to make sure my understanding of it is correct before I attempt to explain it. I have also googled it, but it's not used quite enough to be a major find. So, here's how I understand it.

-Single phase, generally a residential a/c electrical service (that can be found in commercial applications) whose sine wave is a single line between -170V RMS and 170V RMS.

-2 Phase, not broadly used, created (discovered?) by Tesla and used to make more efficient motors. Sine wave is two lines 90 degrees offset from one another. Can be derived from three phase with the use of a Scott T transformer or Scott Connection.

-Three Phase, generally a commercial or industrial a/c electric service with two major transformer types (Delta and Wye). Sine wave is three lines that are 120 degrees offset from one another. When properly used, this allows there to be no zero moment in voltage, considered the most efficient service for motors.

-Split Phase, Connection that uses the system ground and one other live conductor to mimic a single phase system. I'm unsure of how the sine wave looks. Technically referred to (according to wikipedia) a 3 wire, single phase, mid point neutral system. Erroneously referred to as 2 phase.

Do I have it down, or am I missing something?

Please remember:

I have read the battle of the phases, I just want to make sure I have it down.

This is not the battle of the phases, please don't turn it into it.

Leave the horse alone.

I am with you so far.
most of the confusion/interpretation disputes occur over where the references of measurement is taken from Both time and voltage(amplitude).
Where are you placing the leads black and red as this will determine what your waveform looks like

 

[gar]

080613-1224 EST

DanZ:

A single phase power source will consist of 2 wies and and one voltage source. Thus, there is only one voltage waveform.

A multiphase power source will have at least 3 wires and at least 2 voltage sources. You can also read voltage as current. If we exclude degenerate cases, then in a multiphase phase system each voltage source will have at least a slightly different phase angle from any of the other sources.

In the real world a 2 phase system would usually have a 90 deg shift of one source relative to the other. And a 3 phase system 120 deg shift.

A single phase system can not produce a rotating magnetic field without some additional means to created a second phase.

A multiphase phase system can produce a rotating magnetic field.

Is a brush type DC motor always less efficient than an AC motor? Not necessarily.

.

 

[mivey]

Good luck . You are not going to correct definitions that have been scrambled over many decades. As "right" as you think you might be, someone else will find a reference to dispute your definition. As you know from your readings, your post has what can be called "errors" depending on what standard you choose.

You may not want a battle of the phases here but that is what you are starting with your referenced discussion (not here but off-site). It may be fun for discussion, but you can't "fix" the world. The person you are talking with could dispute with you until one of you gives in. You will have proved only who is more stubborn, not who is "right".

A fight will prove who is stronger, not who is right.

The reason you will never prove who is "right" is because there is no such thing for some of this stuff. The best you can hope for is to agree on a common terminology for your current task, recognize that it may not be the "right" terminology for a future task, and accept that you may have to use different terminology in the future to facilitate communication with someone else.

My advice would be to not worry about the definition but focus on communication. The important thing is when you are talking about a system is that you both understand what you are talking about, even if you both have different terminology. You can certainly agree on terminology for the task at hand.

 

[jim dungar]

In the real world a 2 phase system would usually have a 90 deg shift of one source relative to the other. And a 3 phase system 120 deg shift.

In the real world a 2-phase system WILL ALWAYS have a 90? shift of one source relative to the other. The fact that this is a very rare, if not obsolete, system does not change what it is called nor how it is created.

 

[mivey]

In the real world a 2-phase system WILL ALWAYS have a 90? shift of one source relative to the other. The fact that this is a very rare, if not obsolete, system does not change what it is called nor how it is created.

DanZ, see what I mean? This absolute statement by Jim has been disputed before with many references, and can always be debated, but will solve nothing. Focus on the task at hand and what you hope to accomplish with the debate. If it is debate for the fun of it, so be it. If it is not just a debate for fun, will it help you get the primary task completed?

 

[DanZ]

If it is debate for the fun of it, so be it. If it is not just a debate for fun, will it help you get the primary task completed?

It started as a just for fun general knowledge thing. Then became several stories of how he used 1-2-3 phase definitions when he was in communications, and the arguments he had with EEs about the terms, which led to his explanation of why he wanted to use those terms. It made trouble shooting over the phone easier ("Did you check the fuses?", "Yep, both of em." , "Uh, there's three.").

I know correcting definitions isn't easy, but I want to make sure I'm at least using the terms properly.

Jim, I think the reason it gets so misused is that it's not common anymore. Then again, engines and motors are common and the terms get misused as well.

Gar, I wasn't trying to knock DC at all! I was just comparing 2 phase A/C and 3 phase A/C.

Quogue, (How do you pronounce that?) I wasn't actually taking measurements, just going by "accepted common standards"

 

[coulter]

Dan -
Lots of screwy terms in semi-common use. Beats me where they come from and even more bafling is why they persist.

1. Split Phase (refering to 1ph, 120/240): Uhhh this isn't a motor, it's a panel (service, feed).

2. This isn't Europe. 110, 220, 440V hasn't been around since the 60's.

3. Noodle?

4. 2Phase (speaking of two legs and neutral of a 208/120V)

5. 2Phase (speaking of single phase 120/240V)

:-?And the beat goes on (1967)

I agree with mivey. Make sure you understand the context when the wise, knowledgable, old timers use their mis-guided slang.

I also agree with Jim (in the following post)

The only way that we can "fix the world" is to put a stop to the incorrect words, slang, and the misleading use of electrical terms.

(edited right at the end of the time limit)


carl

 

[jim dungar]

DanZ, see what I mean? This absolute statement by Jim has been disputed before with many references, and can always be debated, but will solve nothing. Focus on the task at hand and what you hope to accomplish with the debate. If it is debate for the fun of it, so be it. If it is not just a debate for fun, will it help you get the primary task completed?

When were references provided that said that a 2-phase system did not have a 90? phase difference? Previous discussions, on this website, about the method of describing voltages in single phase 120/240V 3-wire systems regularly agreed that they were not 2-phase systems.

The only way that we can "fix the world" is to put a stop to the incorrect words, slang, and the misleading use of electrical terms. The NEC specifically mentions 1-phase, 2-phase, and 3-phase supply systems as each being unique (see table 430.37), it is a shame that so many people that use the NEC insist on ignoring this fact when describing residential services.

How do people learn about Scott-connected transformers if they do not agree what 2-phase means.

How do we explain the difference between NEC tables 430.248 and 430.249 if we do not know the difference between 1-phase and 2-phase motors?

 

[iwire]

The NEC specifically mentions 1-phase, 2-phase, and 3-phase supply systems as each being unique (see table 430.37), it is a shame that so many people that use the NEC insist on ignoring this fact when describing residential services.

I am with you Jim and I tried bring up the fact that there are real 2-phase systems and they are not the 120/240 systems that you see at a house.

But I simply gave up as it seemed many wanted to over complicate this subject. :grin:

I believe I even read about an area that at one time had a four or five phase system.

 

[jim dungar]

I am with you Jim and I tried bring up the fact that there are real 2-phase systems and they are not the 120/240 systems that you see at a house.

But I simply gave up as it seemed many wanted to over complicate this subject. :grin:

I believe I even read about an area that at one time had a four or five phase system.

Bob,

Are you talking about 2-phase systems with 3W, 4W (the most common), and 5W? Many people have incorrectly called these individual phase conductors as system phases (looks like part of our problem comes from not using all the words in a description).

 

[iwire]

Bob,

Are you talking about 2-phase systems

I was referring to the two phase systems referenced in the NEC that you had mentioned.

 

[mivey]

...I also agree with Jim (in the following post)

The only way that we can "fix the world" is to put a stop to the incorrect words, slang, and the misleading use of electrical terms.

I wish it were that easy but I think there are too many holes in the dike. Who gets to decide the right and the wrong? Remember the saying: "that is the nice thing about standards, there are so many to choose from".

IEEE is the largest organization of technical professionals in the world so what do happens when the standards IEEE sets forth conflict with the NEC or some other standard?

In this forum, I would suspect the NEC to take precedence (then why do we debate the things it says?). In another forum, the NEC would take a back seat and IEEE standards would prevail. In another forum, common convention would prevail and the NEC and IEEE standards would both be thrown out. I have seen many posts from members here (other threads) that would indicate that they see the "standards setting" organizations as just being full of themselves.

 

[jim dungar]

IEEE is the largest organization of technical professionals in the world so what do happens when the standards IEEE sets forth conflict with the NEC or some other standard?

Are you aware of any IEEE definition that conflicts with any NEC definition? Standards values are different than standard definitions (definitions are different than simply words). For example: in the US we have a protection standard of 5mA for faults to ground and in Europe they have a standard of 30mA for faults to earth. The standards use different words and have different values but their "electrical" definition is the same. And we should not forget that the context in which a phrase is used is also very important. Phase is used in AC power systems differently than in audio circuits, even though both are areas of study in electrical engineering.

 

[coulter]

I wish it were that easy but I think there are too many holes in the dike. ...

Yes

... Who gets to decide the right and the wrong? ...

You, me and Jim.

...so what do happens when the standards IEEE sets forth conflict with the NEC or some other standard? ...

Stick with the law. IEEE is rarely the law.

... I have seen many posts from members here (other threads) that would indicate that they see the "standards setting" organizations as just being full of themselves.

And this group isn't? M's at the top, selected e's in the middle - You and me at the bottom, of course

Disambiguate Acluistic Anacronyms

carl

 

[hardworkingstiff]

OH Boy!

OH Boy!

How many hundreds of posts will this thread go?

:smile:

 

[K8MHZ]

One phase - no phase shift

Multi phase - one or more phase shifts.

Simple, ain't it?

 

[winnie]

I believe that the 'battle of the phases' disagreement is not quite applicable to the original poster's question, however during that discussion we raised many relevant points.

The 'battle of the phases' disagreement was about the meaning/value/interpretation of a '180 degree phase difference'.

However it sure sounds to me as though the original poster is discussion a situation where there is a 120 degree phase difference. "how he defined 2 phase alternating current as taking two phases from three phase a/c transformers ".

In this case, there are clearly _two_ separate phases present, and you clearly do have a polyphase system

Having said that, describing a supply with two separate phases 120 degrees apart is not one of the classic usages of the term 'two phase power'. All of the classic usages involve a 90 degree phase difference. So while there are two phases present, using the term 'two phase power' would be misleading.

If it is appropriate to identify this as a subset of a three phase system, then it should not be called 'two phase', but should instead be described in some fashion that names the three phase system. For example 'open wye'. But often it is not necessary to identify this as a polyphase system. If you are talking about service into a home, with two hots and a neutral from a _wye_ secondary, that service is _called_ a single phase service. (The name does not describe the phase angle differences present...but it does describe the usage!)

-Jon

 

[frizbeedog]

.....I want to try to correct him about 2 phase, but I want to make sure my understanding of it is correct before I attempt to explain it. I have also googled it, but it's not used quite enough to be a major find. So, here's how I understand it.

An Interesting History of 2 Phase