bsoeker single or two phase

[Jraef]

in the US (elsewhere?) there is actual 2 phase power dist (90 deg)
the first generation from Niagra Falls was like this
iirc some inner cities still use it
this is what most would traditionally call 2 phase

but yes, if you have 2 sinusoidal (not exclusively) waves of primarily the same fundamental freq and they differ in phase you would have 2 phases

And that takes us back to the semantics issue. I have seen this semantic battle play out time and time again when I worked for EU electrical equipment mfrs (Siemens and Klockner Moeller) when they would use the term “2 phase” in a product description, meaning what we refer to as “1 phase”.

Here in North America, where true “2 phase” polyphase systems still exist, we must differentiate between this and “2 out of 3 phase” power. So for us, if we have “2 out of 3 phase” used for something, we call that “single phase”. So the power fed to your house is derived from 2 phases of a 3 phase distribution system, but we still call that single phase. Then those two phases are fed to a transformer with a center tap that is grounded as a neutral, hence the term “split phase”, but it is still single phase power.

Pretty much everywhere ELSE in the world, “2 out of 3 phase” distribution is often called “2 phase”, but because the TRUE 2 phase polyphase systems like those in Niagara don’t exist, there is no need to differentiate.

I don’t know of anyone that still makes a true 2 phase polyphase motor any more, so discussing how it is started etc is pointless. It’s just that when people NOT from North America mention having to have “starting sparatus” for “2 phase motors”, they are referring to what WE call a “single phase motor”.

 

[Ingenieur]

And that takes us back to the semantics issue. I have seen this semantic battle play out time and time again when I worked for EU electrical equipment mfrs (Siemens and Klockner Moeller) when they would use the term “2 phase” in a product description, meaning what we refer to as “1 phase”.

Here in North America, where true “2 phase” polyphase systems still exist, we must differentiate between this and “2 out of 3 phase” power. So for us, if we have “2 out of 3 phase” used for something, we call that “single phase”. So the power fed to your house is derived from 2 phases of a 3 phase distribution system, but we still call that single phase. Then those two phases are fed to a transformer with a center tap that is grounded as a neutral, hence the term “split phase”, but it is still single phase power.

Pretty much everywhere ELSE in the world, “2 out of 3 phase” distribution is often called “2 phase”, but because the TRUE 2 phase polyphase systems like those in Niagara don’t exist, there is no need to differentiate.

I don’t know of anyone that still makes a true 2 phase polyphase motor any more, so discussing how it is started etc is pointless. It’s just that when people NOT from North America mention having to have “starting sparatus” for “2 phase motors”, they are referring to what WE call a “single phase motor”.

not saying 120/240/1 is 2 ph power
only that it has 2 distinct electrical signal 'phases' referenced to neutral
to 'split' something, in this case a 'phase', means a number of 2 items (phases) result
there is no 'correct' answer, depends on context

the power to my house is from 1 ph (and n/g)

 

[ggunn]

... the power fed to your house is derived from 2 phases of a 3 phase distribution system, but we still call that single phase.

Not usually. Most household power is derived from a single phase with a center tapped (and grounded) transformer. Hence the name.

 

[gar]

180721-1316 EDT

kiwred:

If you take a true single phase motor with no starting system, then it is unlikely that the motor will randomly self start before burnout. This has an oscillating single angle magnetic vector.

Next take a two phase motor where the physical stator coils are physically spaced 90 deg apart and apply the same source AC power to both coils. Same as the single phase motor except that the oscillating single angle magnetic vector is now shifted in spatial position by 45 deg.

Next take the input to one stator coil and interchange its leads. This is an electrical phase shift of 180 deg. Now the physical position of the oscillating magnetic vector is shifted back to -45 deg relative the original single phase motor.

Neither of these two phase motor connections will be self starting.

But if the two stator coils are excited by signals electrically 90 deg apart, then we create a rotating magnetic vector in space that pulls the rotor around. Thus, no additional started mechanism is required.

,

 

[Besoeker]

in the US (elsewhere?) there is actual 2 phase power dist (90 deg)

Yes, the Scott and Le Blanc connections are considered to be examples of that. Not that I, to my knowledge, have enountered either.

but yes, if you have 2 sinusoidal (not exclusively) waves of primarily the same fundamental freq and they differ in phase you would have 2 phases

Thank you.
We have occasionally used 55-0-55V control transformers where specified in the RFQ. Usually not more than 1 kVA supposedly to reduce the risk of fatal electrocution. Not something I was ever keen on. It can make faultfinding more complex as you guys would know with the loose neutral issue often mentioned here.

 

[Tony S]

Yes, the Scott and Le Blanc connections are considered to be examples of that. Not that I, to my knowledge, have enountered either.

Have you travelled by train in the UK? Both Scott and Leblanc transformers are used for 25kV feed in points.

Some parts of London and Bristol up until a few years ago used 90° 2Ø so that the old DC distribution cables could be reused.

 

[ActionDave]

What you're saying is, people who nitpick are unreasonable.

Nitpicking is not always being unreasonable that often conjure fatous, illogical reasoning. It is often the vehicle that leads to constructive criticism.

Although it (nitpicking) can demonstrate both negative and positive criticisms, they both have their appropriate uses.

It basically offers an option for putting something right. . . which in many cases shows up, starting in the wrong track.

What's the difference between a nitpicker compared to somebody who is trying to bring a better understanding of a subject? I think it is mostly attitude. Nitpickers are arrogant.

 

[gar]

180721-1509 EDT

buffalonymann:

I ran some experiments on a ferromagnetic core that I made into a simple current transformer. This core is a tape wound toroid with a cross sectional area of about 1 sq-in, open hole about 2" id dia, a high peramabilty square loop materia; about 50 years old. Off hand I don't know the material. Primary is one wire turn, and secondary is 8 turns.

My current generators were 15 W, 75 W, and 250 W incandescents, and a 1500 W space heater. Currents are about 125 mA, 625 mA, 2.1 A, and 10.2 A.

Turns ratio is 1 to 8. Current measured with a Fluke 27 in mA or A range, Output noise level reading with no input current was about 0.01 mA.The output measured values were estimated for input and measured on output as:

15 W ------ 0.63 to 1.5 mA over a time period, input 0.125 mA, ratio 125 to 1.

75 W ----- 10.8 mA, input 625 mA, ratio 58 to 1.

250 W ---- 73.8 mA, input 2.1 A, ratio 28 to 1.

1500 W --- 1.25 A, input 10.2 A, ratio 8.2 to 1.

The nonlinearity at low levels is obvious. This is probability mosty from core losses.

Since you have a single threshold need the nonlinearity at low currents may be of no concern. But what might be a concern is threshold stability. Likely a temperature problem. The core area I played with may be much larger than what you need.

You need to define the constraints you are working under. Cost might be one. Even more important what are the whys that are driving the need, and is it a safety critical application.

.

 

[buffalonymann]

180721-0754 EDT

buffalonymann:

You are the one that clearly does not not understand electrical circuit theory.

It does not appear you have electrical engineering training from a major university, and you are not broad minded enough to be able to work with how the same word may be used with somewhat different meanings.

In electrical circuits and analysis the word phase is used in many ways and context will probably provide information on what its meaning is.

In general phase is used to describe the relationship between two or more different items. This could be the difference between two or more points in a waveform, or the relationship between two or more waveforms.

A circuit powered from one single phase two wire source can have multiple phases of various phase shift angles.

Broadly there are two types of AC motors excluding universal. These are a true single phase with a pulsating but not rotating magnetic field that requires some mechanical or electrical means to get it rotating. This operates like someone pumping a swing. Self starting single phase motors are at least multiphase for a short time to get rotation initiated. Multiphase motors have rotating magnetic fields that drag the rotor around, and thus are self starting. Proper magnetic phase relationships are required to produce the rotating field. A 180 degree shift does not produce this result. You could probably usefully use any shift angle from 30 to 150 degrees to start a two phase motor.

A pulsating and non-rotating magnetic field motor after being started has substantial torque ripple. While a rotating magnetic field motor with a constant amplitude rotating vector has no torque ripple. Very important difference in a machine used to test bearing life.

For convenience two separate synchronized AC sources can be classified as two different phases and can have any phase relation between - infinity to + infinity. Just because you pass thru 0, 180, 360 should not make them, from a broad perspective, something different than phases.

A resolver is a nice electromechanical device with with AC electrical input, and output. The position of a mechanical shaft can produce the output at any phase angle from 0 thru 360 relative to the input reference. So I have an input phase and an output phase. Broadly speaking I have a two phase system no matter what the phase angle is.

.

You're right about one thing, I'm not open minded to anybody's intellectual dishonesty. You've been filed into the snowflake box

 

[buffalonymann]

a 2 phase 4w motor will start if wired with L1-n and L2-n pairs

and 240/1 can be derived as 2 'phases', on at 0 deg, one at 180 deg, or opposite polarity

:lol:

 

[buffalonymann]

Yet, you have two supplies L1-N and L2-N that are not in phase.
Yes, I know it is generally called single phase or split phase but if you have two supplies is it reasonable not to recognise them as different phases.
That's why I mentioned hexaphase. It is a three-phase implementation of what is NOT being called two phase.

Besoeker

you have just one xfmr the current always flows in the same direction, even when you tap it. Therefore the two split phases ARE always in phase. The diagram the snowflakes offered in the other thread is not what happens in a split phase xfmr.

 

[buffalonymann]

And that takes us back to the semantics issue. I have seen this semantic battle play out time and time again when I worked for EU electrical equipment mfrs (Siemens and Klockner Moeller) when they would use the term “2 phase” in a product description, meaning what we refer to as “1 phase”.

Here in North America, where true “2 phase” polyphase systems still exist, we must differentiate between this and “2 out of 3 phase” power. So for us, if we have “2 out of 3 phase” used for something, we call that “single phase”. So the power fed to your house is derived from 2 phases of a 3 phase distribution system, but we still call that single phase. Then those two phases are fed to a transformer with a center tap that is grounded as a neutral, hence the term “split phase”, but it is still single phase power.

Pretty much everywhere ELSE in the world, “2 out of 3 phase” distribution is often called “2 phase”, but because the TRUE 2 phase polyphase systems like those in Niagara don’t exist, there is no need to differentiate.

I don’t know of anyone that still makes a true 2 phase polyphase motor any more, so discussing how it is started etc is pointless. It’s just that when people NOT from North America mention having to have “starting sparatus” for “2 phase motors”, they are referring to what WE call a “single phase motor”.

I think the power company uses autotransformers derived from 1 phase of the bank for residential distribution

 

[ActionDave]

You're right about one thing, I'm not open minded to anybody's intellectual dishonesty. You've been filed into the snowflake box

That says more about you than it does about him.

 

[Besoeker]

Besoeker

you have just one xfmr the current always flows in the same direction, even when you tap it. Therefore the two split phases ARE always in phase. The diagram the snowflakes offered in the other thread is not what happens in a split phase xfmr.

When L1-N is max positive L2-N is max negative. That's how they work. That's how you get 120V-N on each side and 240 V L1 to L2. Put a scope on them and you will see.

 

[winnie]

IMHO if you are going to have an argument about _terminology_ you had better be able to listen to, and understand, different perspectives, rather than simply flat out stating that others are wrong.

This is not physics where ideas are subject to experimental verification; these are words where the meaning is in people's head.

You can explain why different terminology would be better or clearer; and if you do a good job in that explanation you can convince others and change the meaning of the words in their head. But if you simply call people 'snowflakes' they will ignore you.

On the physics: You can clearly define a 180 degree phase difference.

Consider a 2 pole alternator designed with adjustable stator coils, so that you can change the mechanical angle between them. Since there are 360 degrees in a complete rotation you can clearly define 360 degrees of phase relation.

Similarly, in _3_ phase machines we describe the phase angles as 0, 120, and 240 degrees.

Now, in a single frequency pure sine wave situation you cannot distinguish between a true '180' degree phase offset generated by that adjustable alternator and a simple inversion. For purpose of generating a rotating field, such a phase difference (by inversion _or_ 180 degree mechanical rotation) is effectively single phase. Since this simple inversion looks like the 180 degree rotation of the adjustable output, it seems reasonable to use the term 180 degree phase difference.

If you are going to argue that a 180 degree phase difference is meaningless, then I expect you to try to convince the engineering community to describe three phase power using the phase angles 0, 120, 60.

If the adjustable alternator output was somehow not a pure sine wave, then it might be possible to distinguish between the 180 degree rotation of the adjustable coil and a simple inversion.

And just to keep things amusing, in the US, for large residential applications such as apartments, each individual dwelling will be supplied with 2 legs plus neutral of a 208/120 system. This is _called_ single phase because of how it is used, even though there is a real phase difference that can be used to generate a rotating field.

-Jon

 

[gar]

180722-0801 EDT

buffalonymann:

See https://en.wikipedia.org/wiki/Autotransformer for definition of an autotransformer.

.

 

[buffalonymann]

That says more about you than it does about him.

To some, perhaps; to others no

 

[mivey]

He certainly doesn't sound like he is totally clueless either so what is wrong with helping him understand an area he is maybe a little weak on?

Because he did not come to learn but came to argue. Little value in that.

 

[mivey]

180721-0754 EDT

buffalonymann:

You are the one that clearly does not not understand electrical circuit theory.

It does not appear you have electrical engineering training from a major university, and you are not broad minded enough to be able to work with how the same word may be used with somewhat different meanings.

In electrical circuits and analysis the word phase is used in many ways and context will probably provide information on what its meaning is.

In general phase is used to describe the relationship between two or more different items. This could be the difference between two or more points in a waveform, or the relationship between two or more waveforms.

A circuit powered from one single phase two wire source can have multiple phases of various phase shift angles.

Broadly there are two types of AC motors excluding universal. These are a true single phase with a pulsating but not rotating magnetic field that requires some mechanical or electrical means to get it rotating. This operates like someone pumping a swing. Self starting single phase motors are at least multiphase for a short time to get rotation initiated. Multiphase motors have rotating magnetic fields that drag the rotor around, and thus are self starting. Proper magnetic phase relationships are required to produce the rotating field. A 180 degree shift does not produce this result. You could probably usefully use any shift angle from 30 to 150 degrees to start a two phase motor.

A pulsating and non-rotating magnetic field motor after being started has substantial torque ripple. While a rotating magnetic field motor with a constant amplitude rotating vector has no torque ripple. Very important difference in a machine used to test bearing life.

For convenience two separate synchronized AC sources can be classified as two different phases and can have any phase relation between - infinity to + infinity. Just because you pass thru 0, 180, 360 should not make them, from a broad perspective, something different than phases.

A resolver is a nice electromechanical device with with AC electrical input, and output. The position of a mechanical shaft can produce the output at any phase angle from 0 thru 360 relative to the input reference. So I have an input phase and an output phase. Broadly speaking I have a two phase system no matter what the phase angle is.

.

Well said.

To discuss phase, it is better to start with a definition of phase. There are too many versions of the term. Depending on the definition basis, you could argue either side of multiple phases.

"Two phase" is a term reserved for a quadrature phase displacement. "Two phases" is descriptive and could mean two signals with any phase displacement, even 180 degrees.

Two different signals. Meaning at least three terminals being involved. Not just two terminals where you might be limited to a discussion of only polarity.

The OP has clearly little EE training and exposure to the term across multiple disciplines.

 

[mivey]

semantics

but for someone to make an assertive declaration, and in doing so impung the understanding of others, by stating 120/240/1 definitely cannot be considered to be comprised of 2 phases says more about them than those he ridicules

For once I totally agree with you.