How to recognize phase A?
How to recognize phase A?
(OP)
Hi
I am disputing with a colleague:
I say : Phase "A" exists. every 3-phase system has a phase "A"
He says: Phase "A" is random. Important is just the rotation ABC, or BAC. You cant determine which is A.
I believe: every circuit has a phase A, that can be measured, and labeled as A.
If there is another source: transformer, Generator, etc: That has also a phase "A".
If you want to connect the 2 circuits(even through buscoupler), you have to connect A to A.
Question: if i am true, how can one measure which one is phase A ?
I am disputing with a colleague:
I say : Phase "A" exists. every 3-phase system has a phase "A"
He says: Phase "A" is random. Important is just the rotation ABC, or BAC. You cant determine which is A.
I believe: every circuit has a phase A, that can be measured, and labeled as A.
If there is another source: transformer, Generator, etc: That has also a phase "A".
If you want to connect the 2 circuits(even through buscoupler), you have to connect A to A.
Question: if i am true, how can one measure which one is phase A ?






RE: How to recognize phase A?
During Positive sequence phase 'A' will lead Phase 'B' will lead Phase 'C'.
Note: not all utilities refer to the three phases as A, B and C. Where I am now we use Red, White and Blue (which I am still trying to get used to)
Bottom line: Phase 'A' does exist, as does 'B' and 'C'. It is crucially important that you know which is which to determine wheter or not your system is running properlly.
There has been an on going debate regarding system sequence components and whether or not representing a system as either positive, negative or zero sequence is a true representation of what is physically happening in real world or whether or not it is just a convienient representation. Personally, I believe that it is a true representation.
RE: How to recognize phase A?
But how do you measure which is A?
RE: How to recognize phase A?
Like Marks1080 i learned on Red Yellow Blue, there was no possibility of making a mistake with that system, however I also agree with pisimatza unless you trace it all the way back to the point of generation how do you know for sure if your red wire is A,B or C?
Roy
RE: How to recognize phase A?
For some locations with lots of Dy transformers, I see the phase next to the neutral bushing denoted as A or Red. Since lines traverse long distances, it is only fair that a system of reference is developed.
RE: How to recognize phase A?
A is traditionally the reference phase. You need a reference so that you can express other quantities with respect to it. Phase A is important on interconnected systems, but if you were synchronising a generator onto the system, only the rotation would matter (in this context).
Regards
Marmite
RE: How to recognize phase A?
Say that you now have the 3-phase wires labeled 1 2 and 3 and that measuring them you find you get a positive sequence when they are in the order 1 2 3.
You will then also get a positive sequence when the phases are ordered 2 3 1 or 3 1 2. There is nothing you can measure that will tell you if the wire 1, 2 or 3 should be marked as 'A' phase.
If you want to use parallel feeds you always have to measure the phasing between all 3 wires to ensure they are in phase with each other and that you won't be creating a fault when you turn on the second feed.
RE: How to recognize phase A?
I'd say to really know what Phase A is you have to know the standards of the utility and how they define Phase A.
RE: How to recognize phase A?
RE: How to recognize phase A?
Good discussion point. While the rotation sequence (1,2,3 or 1,3,2) would matter inside a system (of having motors and generators), the naming sequence would be definitely important while paralleling with other systems, as marmite says.
I have seen protection & relay testers use what is called 'phasing in' where they connect a voltmeter (via PT's) between the incoming system to the main system and check for zero voltage (?). They do that for all three phases.
RE: How to recognize phase A?
Designations A B C or 1, 2, 3 are arbitrary but once in place you need know physical locations (terminations) at the source if you need to synch with another "fixed" source like another utiltiy feeder. This can be done by chekcing out volatage between phases of the two sources.
If the one of sources is not fixed such as a geneator all you need to know is the rotation of the two sources are same.
RE: How to recognize phase A?
So:
There is no method to find which one is A?
Just to trace the phases all way back to generator.
And more: it doesn't matter which one is A. If u have to connect 2 circuits, just to be sure that there is no phase difference between them.
I have found something, but it is too scientific, it is not a common device: http://www.clarke-hess.com/2500.html
If you see on display, angle 120 deg is shown. This means is phase A, or not?
RE: How to recognize phase A?
I would like ask you: What is a phase A?
Lets start from here.
for my pinion, you can see it only on the generator.
Phisicaly, it's some abstract declaration. important for us only rotation.
Regards.
Slava
RE: How to recognize phase A?
This just means that the measured voltage is 120° ahead of the reference voltage.
RE: How to recognize phase A?
If you were to see BAC rotation on such a system that would be a good indication of a fault, or other non-ideal system operation.
Look up the Two-Lamp method for determining phase sequence. It's easy to understand, and set up.
RE: How to recognize phase A?
It's true: Phase A exists. Phase A is always the phase the utility in question has assigned to be phase A. The same is the case for phases B and C, and with this decision the utility has determined the phase rotation sequence as well, once and forever. And there is no way to argue with the utility. Every single three phase device (generator, transformer, etc.) commissioned at a later stage has to follow this regulation.
Wolf
www.hydropower-consult.com
RE: How to recognize phase A?
Depending on how you lable the three phases determines the phase rotation, ABC, or CBA. (ABC is easer to work with for some reason).
Consiter this: From a new customer point of view, the utility delivers three phases, and a neutral. To see that a motor will rotate in the proper direction you would do a bump test.
The electrtition will add colored tape to the four black wires as a reference (So which is A, or does it matter)?
RE: How to recognize phase A?
RE: How to recognize phase A?
You can't tell the difference between a sine wave or a cosine wave. One starts at voltage zero the other at voltage maximum. Sine or cosine just depends on when you start the stopwatch o trigger the scope.
Same with phasing, you can tell what the phase sequence is (the sequence that the three wires reach their positive voltage maximum) but not which wire is called phase A at the other end.
Instruments are available to inject a signal onto a phase wire at a substation that can be detected out on the line to match the distribution wire to the substation nomenclature. Other fancier instruments use GPS timing and signal injection to measure the phase angle of any voltage or current in the power system against the reference phase at a main substation.
Hydro One in Ontario has a system something like that. But they don't call it A phase, its red, white, blue (?). In our plant it is ABC so we did a conversion A =white, B= blue and C = red. Inside the plant A phase is always on the left when facing the front of the equipment. Helps when starting motors the first time if we keep it straight.
RE: How to recognize phase A?
I just seem to forget which standard it is, but i understand there is a convention as to how to lay conductors such that others who will inherent a certain system will find it easy to determine which is phase A, B, and C (line1, line2, and line3).
It is really a matter of convention as the voltages measured will likely be the same as wellas the phase angles between them.
On bus bars, if arranged from left to right, the first busbar on the left is assigned as Phase A, then Phase B at the center, and the rightmost busbar, Phase C. etc...
Will post back if can find the corrrect doc!
RE: How to recognize phase A?
The longer I think about this thread, the more I believe that it has no practical meaning and is purely academic. Still, here are some more comments:
Before connecting a three phase device (lets say its a three phase electric motor, for instance) to a three phase system, its of paramount importance to check the phase rotation sequence of the latter by using a phase sequence indicator.
Then hook terminal #1 of your motor either to phase A or B or C of the supply system. In case the motor requires the same phase rotation as the feeding system, connect the remaining phases in the same sequence as before, i.e. when the systems phase rotation sequence was determined. And that's it.
For the average consumer its not at all important whether he connects terminal #1 of a three phase device to phase A or B or C, as long as the phase rotation sequence for both is identical. For a manufacturing plant, however, with a complex system of various drives and other consumers, its practical to determine the designation of the three phases at the factories feeder point. It is to the discretion of the plant electrical engineer which phase he names A.
Only at the generator terminals you can be 100% sure that terminal #1 belongs to phase A, #2 is phase B and #3 is phase C, if so specified. The further you move away from the generator, the more chances are that leads are changed by mistake, with the phase rotation sequence still intact. As said before, every consumer can determine which phase he names A, as long as he is consistant within his environment.
Regards
Wolf
www.hydropower-consult.com
RE: How to recognize phase A?
Phase "A" does not exist in principle, but it HAS to exist (as lot of you have mentioned) and the utilities have to define it, hopefully without confusion
I had to "rotate" some GIS because of this confusion, not a cheap confusion.
RE: How to recognize phase A?
The remaining phase is "C" and is on the bottom or on the right.
This works well for tens of thousands of industrial plants. Which is REALLY "A" phase? Who cares and what difference does it make?
Utilities must identify "A" phase and have methods and conventions to do so. For the rest of us, it just doesn't matter. "A,B,C," Left to right or top to bottom.
If you want to split hairs go for it, but don't forget that "A" phase may be displaced 30 degrees from "A" phase in the same system or industrial plant.
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: How to recognize phase A?
So, even if fancy time stamps and other tags are used: Which one of all these generators is the reference generator? No answer provided. No answer needed. No answer possible.
Pisimatza brought up an uninteresting, kind of school-yard, question. He was fully aware of its "thin" nature and said so from the beginning. It has opened for a flood of answers and opinions that some valid and some not so valid. The interesting thing is that we all started thinking about it. That is good!
Gunnar Englund
www.gke.org
--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...
RE: How to recognize phase A?
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: How to recognize phase A?
But let me know one thing, that I never understood? What is this story that in USA (California) they don't use ABC (positive sequence set) but, it seems to me, a "negative sequence set" (ACB). Is that really true?
Since we are looking for phase A...
RE: How to recognize phase A?
Sorry but I tend to lose focus when we play Dueling Definitions.
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: How to recognize phase A?
Why is it that in the USA, we used to have power companies and now we have energy companies? When regulators got rid of vertical integration, did they substitute time integration?
RE: How to recognize phase A?
Whow, 27 replies up to now!
The famous German poet Goethe once said:
Stepped-on cottage cheese becomes wide, not thick.
Regards
Wolf
www.hydropower-consult.com
RE: How to recognize phase A?
To answer 521AB's question, PG&E (Pacific Gas & Electric Company in California) uses ACB sequence and this is indicated on all of their powerhouse one-line drawings, etc (see attached file). I will have to check on SCE (Southern California Edison).
Interestingly enough this became important for me yesterday but see my post entitled "Generator cannot charge UPS".
RE: How to recognize phase A?
In IEC world, transformers are marked as U,V,W as sequence while ANSI calls for H1,H2,H3. The physical position on the transformer will be N,U,V,W as viewed from HV side,from left to right.But in ANSI transformer the order will be as viewed from LV( ie the order will be exactly opposite to IEC!)
IEC will say phase sequence is U,V,W, ANSI will say H2,H3,H1 which we know is same as H1,H2,H3.
So engineers should be extra vigilent in phase sequence issues.
RE: How to recognize phase A?
I for one am shocked as to how many people truly seem to believe there is a difference and that it matters.
"If I had eight hours to chop down a tree, I'd spend six sharpening my axe." -- Abraham Lincoln
For the best use of Eng-Tips, please click here -> FAQ731-376: Eng-Tips.com Forum Policies
RE: How to recognize phase A?
Synchrophasors make it possible to verify that A at one substation is the same (or not) as A at a different substation. For large area grid management it is critical that all synchrophasors reference the same phase, generally A for convenience. When comparing the phase angle of V1 at many locations it is imperative that the sequence component calculation references the same phase at all locations.
RE: How to recognize phase A?
For a customer with a single service, there normally wouldn't be any reason to care, except for correct rotation.
jraef, btw what color are "Moon Unit" and "Dweezle"?
RE: How to recognize phase A?
"Like, you know man, it was like operator error. Like those lights and numbers are real tripy but when your Bonged, it's like to much to cope with. Sort of like "A" phase, If you don't have to care, why sweat it."
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: How to recognize phase A?
I thought they were both Zappapple.
RE: How to recognize phase A?
Unfortunately, bottom line your friend is right and you are not. You cannot measure and detect which phase is 'A'. The important thing as mentioned by many others is that 2 systems are in phase when interconnected.
RE: How to recognize phase A?
RE: How to recognize phase A?
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: How to recognize phase A?
Keith Cress
kcress - http://www.flaminsystems.com
RE: How to recognize phase A?
Going to Montana now, my Dental Floss farm is in need of attention...
RE: How to recognize phase A?
RE: How to recognize phase A?
But I have found out that the colors(!) get mixed as the electrons go through transformers with Delta/Wye windings. And even more so if there are Z connected windings. One would need a considerable apparatus to make a spectral analysis to reconstruct from where the different spectral components (colors) come. It is like trying to find out if the human DNA really comes from the apes or from peanut butter.
Gunnar Englund
www.gke.org
--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...
RE: How to recognize phase A?
*confused from Australia*
RE: How to recognize phase A?
My god pisimatza, you have caused this forum to melt-down.
RE: How to recognize phase A?
RE: How to recognize phase A?
Keith Cress
kcress - http://www.flaminsystems.com
RE: How to recognize phase A?
We do not stem from the Apes! That's for sure. A secret agreement was recently signed between UNAPE (United Nation Alternative Prehuman Exploration) and a hitherto (until tomorrow by noon, probably) secret consortium representing the primates, spokesman Oran Gutang says in a late message found floating around in a cocoanut. "We are glad not to be involved" he adds.
Former president (name witheld) Carter says he will make an announcement tomorrow (by noon, probably).
Gunnar Englund
www.gke.org
--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...
RE: How to recognize phase A?
It makes one wonder how many humans have evolved only half way?
RE: How to recognize phase A?
Sounds like a good Swedish name.
"If I had eight hours to chop down a tree, I'd spend six sharpening my axe." -- Abraham Lincoln
For the best use of Eng-Tips, please click here -> FAQ731-376: Eng-Tips.com Forum Policies
RE: How to recognize phase A?
Gunnar Englund
www.gke.org
--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...
RE: How to recognize phase A?