single vs. 3 phase

[Rick Christopherson]

Rattus, I don't need to try to embarrass you. You do that just fine on your own. I was going to point out how short your memory was, but you just demonstrated that yourself by posting two near identical posts 15 minutes apart. :grin: :grin:

Go back and begin reading with post #328. Your statements are quite clear.

Now you are changing your story because you ran out of arguments, but you are trying to convince everyone that you never stated these things to begin with. Well you did say this, and here are the quotations to back up that assertion.

Because the zero crossing point is at the same point in time.
And each leg is in phase with the other, just equal and oposite voltage.

This is an excelent answer, and you can proof it with math.

I can't see that, so let's see the proof. Maybe you can add something new.

..... It is fine if you choose to call them out of phase, but it is not fine that you imply that they cannot be in-phase, but inverses.

I don't see any proof, therefore I will prove my own point with a paraphrased reference:

'Two sinusoidal waves, of the same frequency, are said to be in phase if their positive peaks occur at the same instant.'

[Tang, K. Y., "Alternating Current Circuits," Intl. Textbook Co., 1960]

The positive peaks of a wave and its inverse do not occur at the same instant, therefore, they cannot be in phase. They are 180 degrees out of phase.

Never, ever said that. In a nutshell, I am claiming V1n and V2n are inverses of each other which is equivalent to a 180 degree phase difference.

They are either in-phase and inverses, or 180 degrees out of phase. They can't be both, because that would be a double-negative. This is the first time in this discussion that you have acknowledged that they can be inverses. I am sure this is the closest thing I will ever see as being a concession from you, or admitting error, so I guess I should accept it and be happy. Case Closed.

 

[dwcaveney]

n+1 and n+2 models

n+1 and n+2 models

delete.......

 

[dwcaveney]

n+1 and n+2 models

n+1 and n+2 models

dwcaveney, put down the beer and step away from the cooler. :grin:

I did not follow your discussion. I guess I'm going to have to read it when I have more time/patience. I read some on the law of phases, equilibrium with n components in n+1 phases, or n components in equilibrium at n+2 phases under certain conditions...what? I can't go there right now. Maybe I need to raid your cooler 1st.

Sounds like you're talking heat

Sensible Heat - heat that when added to or removed from a substance causes a change of temperature and not a change of state.

Latent Heat- Heat that when added to or removed from a substance causes a change of state but not a change in temperature.

 

[rattus]

Yes, but:

Yes, but:

Phase angles are regularly and properly applied to many non-sinusoidal waveforms.

For example, a quadrature encoder is described as having two outputs 90 degrees out of phase. These outputs are square waves.

-Jon

Perhaps so Winnie, but strictly speaking, from a purist's standpoint, the phase shift applies only to the 1st harmonic. Why? Because a degree of phase shift in the 1st corresponds to 2 degrees in the 2nd, 3 degrees in the third, etc., etc., etc. Of course you knew that already.

 

[rattus]

Huh?

Huh?

They are either in-phase and inverses, or 180 degrees out of phase.

How can they be in phase if the positive peaks do not occur at the same instant? That was my objection to pshycojohn's statement in the first place.

 

[winnie]

They are either in-phase and inverses, or 180 degrees out of phase. They can't be both, because that would be a double-negative.

IMHO _inverse_ explicitly means _not in phase_. You could thus never be both in-phase and inverse, excluding the trivial case of zero amplitude. To my mind, 'inverse' means maximally out of phase, and is equivalent to 180 degrees out of phase.

When a generator is synched to the mains, it must be at the same frequency and phase at the time of connection. You would _never_ say, 'okay, the generator is perfectly inverse to the mains, throw the switch'.

-Jon

 

[dwcaveney]

Test for an apprentice

Test for an apprentice

If you have a generator with 3 outputs at 120 degress apart spinning at 3600 RPM, that is 60 cycles per second. Now assume the output is 120V each leg. Each leg is 60hz, 120V to ground. Now assume each leg (maybe its not called leg, but I don't know what to call it) produces 10,000 watts.

Now take the voltage of two legs and add them together=240V, take the square root of 3 divide by 2 and multiply by 240=207.8 Volts.

So if you have two of those hots going to your service the voltage across the hots will be 208? The voltage from each hot to ground is 120V? This is a single phase 120V/208V, _________Amp Service?

So if you have three of those hots going to your service, the voltage across any two hots will be 208? The voltage from each hot to ground is 120V? This is a three phase 120V/208V, _________Amp Service?

 

[rattus]

The Oregon Fudge Factor Again:

The Oregon Fudge Factor Again:

It occurs to me that the single phase service is an example of the application of the O.F.F. (1.154) which is the ratio of the apparent power provided by the transformers to the apparent power delivered to the load--for line to line loads.. That is,

O.F.F. = 240xI/208xI = 1.154

 

[mivey]

it's settled

it's settled

If you have a generator with 3 outputs...

:grin: There it is boys...the missing link!!! If we had only known earlier how currents actually flow through a wye-connected service. And the whole 207.8 volt thing ties up the rest of the loose ends since we have been thinking it was 208 all along. I'd say case closed, wouldn't you?

As for the test, since we have 120 volts from leg to ground I would say we may need the paramedics because we appear to have some sort of line to ground fault flowing through somebody. Or is it hot to ground? I guess at 10 kW per leg, something would be hot. Maybe we just need to call Quincy, M.E.

 

[dwcaveney]

Mivey,

Please explain.

Would the paramedics be bringing the valium and Quincy the thorzine?

EDIT:
Oh I get it, a hot leg is not a hot leg, it is an energized electrical conductor. Sort of like the red hot wire isn't refered to as a phase, and the black hot wire isn't refered to as a phase. But neither is a hot leg, because in all cases, a hot leg is a sunburned human being's over heated lower extremity? Is that what you meant?

 

[dwcaveney]

It occurs to me that the single phase service is an example of the application of the O.F.F. (1.154) which is the ratio of the apparent power provided by the transformers to the apparent power delivered to the load--for line to line loads.. That is,

O.F.F. = 240xI/208xI = 1.154

Sorry I don't understand, Must you have a transformer to get 3 phase 120/208, or can you get it from one generator?

 

[hardworkingstiff]

And I'll bet the OP thought he was asking a simple question.....

I'm not sure what the answer is to the OP question. :-? Was there ever an agreed upon definition?

 

[rattus]

No and yes:

No and yes:

Sorry I don't understand, Must you have a transformer to get 3 phase 120/208, or can you get it from one generator?

The same argument would apply to two phases of a 3-ph wye connected alternator, but the original question from an older thread specified transformers.

 

[winnie]

Sorry I don't understand, Must you have a transformer to get 3 phase 120/208, or can you get it from one generator?

You can get 120/208 from a transformer, a generator, or from a suitably designed inverter system, and probably a few other places.

The 'Oregon Fudge Factor' that Rattus mentions is a 'feature' of single phase loads connected to certain three phase sources. The single phase load is supplied by the voltage Vab, but the transformer coils develop Van and Vbn. Vab is not in phase with Van or Vbn. If you presume a resistive load, the Iab is similarly not in phase with Van or Vbn.

This means that even with a purely resistive load, the _three phase_ transformer coils will see a non-unity power factor. The KVA produced by the transformer coils is of necessity greater than the watts consumed by the load, and this remains true even for a perfectly resistive load.

-Jon

 

[rattus]

Agreed to disagree:

Agreed to disagree:

I'm not sure what the answer is to the OP question. :-? Was there ever an agreed upon definition?

Stiff, we have agreed to disagree.

 

[dwcaveney]

It occurs to me that the single phase service is an example of the application of the O.F.F. (1.154) which is the ratio of the apparent power provided by the transformers to the apparent power delivered to the load--for line to line loads.. That is,

O.F.F. = 240xI/208xI = 1.154

Rattus,
Could you develope that a little further, and apply it to the post "test for apprentice" (#387 this thread) I am having problems getting the picture.
Thanks

 

[coulter]

I'm not sure what the answer is to the OP question. ...

Good point. That should have happened.

why is 2 phase - 240 volt - called single phase???

Cause it is generated (created?) using just one centertapped winding (or two windings connected to form a CT). There is no appreciable phase angle difference between the two 120V halves, so the two halves add to 240V. This is opposed to 3 phase which takes thee windings spaced 120 deg apart. And I couldn't tell you about 2 phase - never seen one, just pictures.

And this is the TRUMTH.

carl

 

[dwcaveney]

You can get 120/208 from a transformer, a generator, or from a suitably designed inverter system, and probably a few other places.

The 'Oregon Fudge Factor' that Rattus mentions is a 'feature' of single phase loads connected to certain three phase sources. The single phase load is supplied by the voltage Vab, but the transformer coils develop Van and Vbn. Vab is not in phase with Van or Vbn. If you presume a resistive load, the Iab is similarly not in phase with Van or Vbn.

This means that even with a purely resistive load, the _three phase_ transformer coils will see a non-unity power factor. The KVA produced by the transformer coils is of necessity greater than the watts consumed by the load, and this remains true even for a perfectly resistive load.

-Jon

Thanks Jon,

Could you answer post #387 this tread. The question may not be phrased correctly. If I got a number I could work backwards to "prove" it? I'm having problems with the theory and the math!

 

[mivey]

Mivey,

Please explain.

Would the paramedics be bringing the valium and Quincy the thorzine?

EDIT:
Oh I get it, a hot leg is not a hot leg, it is an energized electrical conductor. Sort of like the red hot wire isn't refered to as a phase, and the black hot wire isn't refered to as a phase. But neither is a hot leg, because in all cases, a hot leg is a sunburned human being's over heated lower extremity? Is that what you meant?

Not sure about the meds but yes to the rest.

 

[dwcaveney]

Not sure about the meds but yes to the rest.

Mivey,
OK, can you answer #387? Or a least phrase it so it could be understood?