What do you call this voltage

[Jim Dungar]

So you’re saying that as the magnetic field passes through a wire as it does in a generator winding, the phase relationship between the ends of the wire is that they are in phase? Is that the correct terminology?

Yes, that is what we say in power systems analysis.

I was under the impression that the “other end” would swing both positive and negative and not just in a single direction, and if we are talking 60 Hz, the positive and negative peaks would be 8.3 mS apart.

Yes, this is what a sine wave looks like. But in power systems we do not deal with the peaks of the wave form. We use average RMS values to represent the length of our "voltage" line (you should find information on phasor and vector analysis). If we have multiple waveforms the difference in the zero crossing points (negative going to positive) becomes our phase difference. One voltage waveform means one phase.

I was also under the impression that “choosing a reference point” shouldn’t “force the other end” to change in any way. Can you give me some insight on what exactly you meant?

Choosing a new reference point somewhere along a single straight line does not change the relationship between the the end points of the line. Given the two ends of a line as B and E, their relation ship doesn't change simply by adding a new point M between them. Yes, there is now a B-M and a M-E but they must still equal the original B-E result.

I didn’t understand your comments about a battery or power supply either. I was under the impression that to have a phase relationship, at least one entity has to go “Full Circle” and return to it’s starting point on a consistent basis as the waveforms from a generator or transformer might do. I didn’t understand why you were using DC components in a discussion about AC phasing. Can you tell me why you used those examples and how they relate to AC phasing?

There is very little difference in the analysis of DC and single phase AC circuits.

If you have multiple voltage waveforms then you may have a poly-phase voltage system. This is one use of the word phase.

If your voltage waveform and your current waveform have a time difference in their zero crossing points, you have another use of the word phase. Can you have a this type of phase relationship in a DC circuit?

 

[STEMAPPLICATIONS]

Load doesn't change the nature of the supply

If it's a 3 phase supply, then why would connecting a load change the supply?

It's still a 3 phase supply whether you connect a single phase load from a single leg to neutral or to another phase.

 

[Roy Matson]

Its only 2 phase if you also have a neutral, with only 2 wires it's not possible to have two phases (different phase angles).
Roy

 

[Jim Dungar]

Its only 2 phase if you also have a neutral, with only 2 wires it's not possible to have two phases (different phase angles).
Roy

No it is not.
Adding a new reference point (the neutral) does not create a new phase. Adding a neutral point allows you to talk about (2) L-N voltages but they still must combine to the SINGLE L-L voltage that was present originally. If you added (2) more midpoints (so you have L1, tap1, tap2, tap3, tap4) do you say you now have a 4-phase system? The physics have to stay the same when you are using a single core transformer regardless if it has 2 wires, 3 wires, or multi-taps.

It is only 2-phase if there are two sets of voltages that are 90° apart. This is a unique (and antique) voltage system.

 

[Roy Matson]

Jim,
I think we are both saying the same thing.
220 tapped at 110 is single phase with a center tap, do you agree?
L1 - L2 is single phase.
I meant L1 - N - L2 is 2 phase, that is 2 phases 120° apart not single phase center tapped
Regards
Roy

 

[OZEE]

No, Roy, that's not 2 phases. Center-tapped 110 is the same phase as the 220 it's tapped off of...

 

[HJTRBO]

American voltage distribution systems. Man, tough work.

Hey i got an idea, scrap the 110V system and save the world of the high copper price.

240V Star, 415V Delta.

Childs play.

 

[Roy Matson]

I have been telling them that for years, It's unbelievable the number of transformers they use here.
Ex Mangaweka, now Vancouver
Roy

 

[Gil47]

If you draw a graph of the sine waves from the supply of your choice, then count the number of times the poles, North and South cross each other in the 360 degree rotation, and then divide that answer by 2 you will see how many phases you have.

Try it, single phase and thee phase are all I could get.


Also follow this link http://www.nojolt.com/three_phase_and_single_phase_electric.shtml

 

[Gilbert W]

Jim,



I’m trying to understand the Power Systems concept a little better so I’m going to ask you some more questions and give you the way that I look at things, weather the way I look at things is right or wrong. I looked a little at the phasor method for power systems and I’m starting to understand it a little better even though I might not like it. Again, I am no expert on any of this.

Yes, this is what a sine wave looks like. But in power systems we do not deal with the peaks of the wave form. We use average RMS values to represent the length of our "voltage" line (you should find information on phasor and vector analysis). If we have multiple waveforms the difference in the zero crossing points (negative going to positive) becomes our phase difference. One voltage waveform means one phase.

Why only negative to positive? What do you mean by Average RMS?

There is very little difference in the analysis of DC and single phase AC circuits.

If you have multiple voltage waveforms then you may have a poly-phase voltage system. This is one use of the word phase.

If your voltage waveform and your current waveform have a time difference in their zero crossing points, you have another use of the word phase. Can you have a this type of phase relationship in a DC circuit?

As far as I understand it, current and voltage in a PURE DC circuit are not out of phase nor are they in phase. There is no cyclic activity to compare the relationship to. They just exist.







Here are some questions on phase difference for you…



If I wind a piece of wire around a core in a clockwise direction, and I wind another in a CCW direction and pass a cycling magnetic field through the windings, what is the phase difference in the windings and does the right hand rule have any relevant meaning in this case?



How come I get double the output of an individual winding between the tops of the windings when I connect the bottoms together? How come when I do the same thing with 2 wires wound in the same direction, the output between the tops is 0?



If, in a generator with a rotating magnetic field, I wind a piece of wire around a core at the top, and another winding at the bottom, what’s the phase difference between them?



Are they in phase and just opposite in polarity?



When the magnetic field rotates 90 degrees and there is no potential across one of the windings at that instant, are the 2 ends of that winding opposite in polarity?



I forgot to tell you, I was sloppy in building this so my bottom winding is actually located 178 degrees from the top. Is there a 2 degree difference form being in phase? Can I say this winding is 2 degrees out of phase with the top winding?



OK … I got really sloppy with my location on the bottom winding, so it is located 120 degrees from the top winding. If a bottom winding location is in phase with the top and the location is 60 degrees from being in phase, then does that make the winding 60 degrees out of phase with the top winding?



If 2 objects that are located with 180 degrees difference in a circle are in phase then how does 181 degrees to 360 degrees exist?



If they are in phase, then shouldn’t the windings at 120 degrees and 240 degrees be EXACTLY the same as far as phase?



If I had the bottom winding located 178 degrees from the top and I shifted the physical location of the magnetic field off center but still attached to the center rotating point so the N-S line intersects both the top winding and bottom winding in the center of each winding at the same time does that make the windings in phase?





If I have a gear with 5 teeth rotating inside a circle, since a tooth of the gear touches at 0, 72, 144, 216, & 288 degrees, does that make all those points in phase?





And Finally, these are the most important questions for you…..



I have 3 phase 480 volts as is typical here in the USA and I label them A, B, & C. The phase relationship is A-B leads B-C by 120 degrees and A-B leads C-A by 240 degrees. I connect 2 single phase step down transformers one primary to phase A&B (I’ll cal this transformer 1) the other primary to phase B&C (I’ll call this transformer 2). The secondary output of these transformers is 277 volts RMS. I have a dual channel oscilloscope with isolated commons so they can be hooked anywhere. I hook the common of channel 1 to phase A and the probe of channel 1 to phase B. I hook the common of channel 2 to one of the wires on the secondary of transformer 1. I connect the probe to the other secondary wire of transformer 1. The channel 1 and 2 waveform positive peaks, negative peaks and zero crossings are perfectly in sync . Now I connect one of the secondary leads of transformer 2 to the lead on transformer 1 that the channel 2 scope probe is hooked to. I move the channel 2 scope probe to the wire on transformer 2 that is not connected to transformer 1. The commons on channel 1 & 2 have not changed.



What is the phase difference between channel 1 and 2 on the scope now? What is the output voltage between the 2 points that the channel 2 scope leads are connected to?



Now I remove the probe of channel 2 but leave the common still connected. I reverse the 2 secondary leads of transformer 2 so that the end that wasn’t connected to the first transformer is now connected and the other lead of that secondary is not connected. I connect the scope probe of channel 2 to the second transformer’s secondary lead that is not connected to the first transformer.



What is the phase difference between channel 1 and 2 on the scope now? What is the output voltage between the 2 points that the channel 2 scope leads are connected to?













Thanks,

Gil

 

[leitmotif]

Gil W
I applaud you for your desire to learn.
I censure you for trying to do it the hard way with people that are not instructors. Also on this thread there will be conflicting opinions that will only confuse you.

Your question "what is RMS" shows the need for a good class with a good instructor. You need an organized systematic learning method to get the basic theory well understood. You will not get that here.

Yes you can treat any AC circuit as DC - basically you take an instantaneous shapshot of what is going on and analyze as if it were DC.

IF you really want to get a good understanding of how 3 phase is generated, the theory of inductance / capacitive reactance, power factor, delta, wye, and a whole bunch of other stuff then you really need a class with an instructor who has good movies and good demo equipment and stuff you can put your hands on. Even with all this it is still hard to get a good grasp because you just cannot see electrons go this way and that way.

If you cannot get a good class then you will have to drop back to a mail course or something off the web.
Dan Bentler

 

[Jim Dungar]

I meant L1 - N - L2 is 2 phase, that is 2 phases 120° apart not single phase center tapped

It is much easier to understand poly-phase systems if you do not try to include a neutral in your basic terminology. This is why I try to teach people to count the number of different L-L voltages.

There are many different systems that do not use a neutral point. We cannot be changing our system definitions simply be adding or removing a reference point. For example, a 600V delta supply does not have a neutral point but a 600Y/347 supply does: the only similarity is the number of L-L voltages.

Yes, I wish our industry had a unique name for a 3-wire circuit (2 lines and a neutral)fed from a wye connected system, but it does not.

 

[leitmotif]

I learned 3 phase in the Navy we did not have grounded distribution on 3 phase and of course no neutral either 440 main distribution or 120 lighting. We did not have grounded DC either. It all floated. Was definitely much easier to learn.

When I became a civilian the neutral threw me for a loop for a while.

Recommend
1. Learn basic 3 phase.
2. Learn the neutral connections later. If you know 3 phase well then the neut will not be so bad.

In industry I have not seen two phases and a neut brought out. If you had 3 phase then you used a 3 phase motor (either 208 or 480).

Basically the only time I have seen the neut used on 3 phase 4 wire wye is to get lighting single phase (either 277 from 480 or 120 from 208)

Dont worry too much about grounded delta either corner ground or center ground. It is becoming a thing of the past. If you work in an old plant or do a lot of old church or medium commercial you may need to know about it. Have worked in places where both existed - delta installed in 1948 and wye installed in an upgrade 1960?
Dan Bentler

 

[Gilbert W]

Gil W
I applaud you for your desire to learn.
I censure you for trying to do it the hard way with people that are not instructors. Also on this thread there will be conflicting opinions that will only confuse you.

Your question "what is RMS" shows the need for a good class with a good instructor. You need an organized systematic learning method to get the basic theory well understood. You will not get that here.

Yes you can treat any AC circuit as DC - basically you take an instantaneous shapshot of what is going on and analyze as if it were DC.

IF you really want to get a good understanding of how 3 phase is generated, the theory of inductance / capacitive reactance, power factor, delta, wye, and a whole bunch of other stuff then you really need a class with an instructor who has good movies and good demo equipment and stuff you can put your hands on. Even with all this it is still hard to get a good grasp because you just cannot see electrons go this way and that way.

If you cannot get a good class then you will have to drop back to a mail course or something off the web.
Dan Bentler

Dan,

Thanks for the advice. I guess I'm just trying to understand the "New Math" that's being used here because it's a conflict from what I learned.

Actually I didn't ask "what is RMS". I think Root Mean Square is a formula to convert an AC wave to it's DC equivelent. It takes the full 360 degree circle rotation into account. Average on the other hand is another way to look at an AC cycle. I asked the question what is "average RMS" because to me that statement is like asking what is the distance in Kilometer-Miles. Again, I don't understand how you can assign a phase angle to an RMS voltage if, by converting to RMS you take into account the full 360 rotation. Must be the new math again.

Did you do the math on the must answer questions I had at the bottom of my last post? I think you'll find that the sum of the instantanious voltages you're talking about will give you a wave that is the combination of the Phase refrence and the 120 degree coil on the first instance. The second instance will give you a sum that is equal to the refrence and a 300 degree coil (120+180). The phase angle changed and shouldn't have if the 2 ends of the coil are in phase. The voltage level should change but the phase angle shouldn't if polarity is the only thing different between the 2 ends of a winding. That's the way I've always looked at it and understand it. I'm just trying to understand the new terminology and concepts.


Thanks,
Gil W.

 

[leitmotif]

I do not believe the utilities have anything new for 3 phase. It is the same 3 phase as I learned almost 40 years ago.

There is no new math. It is still basic algebra and trig. Nothing new since Pythagorus.

Phase A voltage still = X x sine(theta)
B = X x sine (theta +120)
C = X x sine (theta +240)

RMS is an average. I forget the calculation BUT I remember 1.414 and .707. I also remember 1.73

Please describe the difference between getting shocked on 277 to ground as opposed to one leg of 480 wye to ground.

Please describe the difference between getting shocked from L 1 to ground on Edison 3 wire residential service as opposed to getting shocked from one leg of 240 to ground -- Edison 3 wire again.

Please describe phase differences -- bonus question.

Dan Bentler