How to recognize phase A? 5

[pisimatza]

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 ?

 

[wolf39]

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

http://www.hydropower-consult.com

 

[521AB]

Interesting discussion.
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.

 

[waross]

A lot of plants label either the top device or the left device as "A" phase. From that, the next phase in sequence is "B", in the center.
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

 

[Skogsgurra]

I think that rcwilson and 521AB have the best comments. It is all very uninteresting. There is no answer. And there is no reason to look for the answer. As soon as you leave the substation (upstreams), you will never know what phase is what. There are transformers with different connections and, to make the question really meaningless, there are tens, hundreds or thousands of generators connected to the grid - also using transformers with different connections.

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

http://www.gke.org

--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

 

[waross]

Right on Gunnar.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[521AB]

By the way, I call them L1, L2 and L3 or W1, W2 and W3.
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...

 

[waross]

Are you confusing California with Australia where the water also swirls the other way going down the drain?
Sorry but I tend to lose focus when we play Dueling Definitions.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[jghrist]

In the southeast USA, Duke Power (sorry, Energy) and Georgia Power use reverse phase rotation. Duke calls the phases XYZ instead of ABC.

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?

 

[wolf39]

Whow, 27 replies up to now!

The famous German poet Goethe once said:

Stepped-on cottage cheese becomes wide, not thick.

Regards

Wolf

http://www.hydropower-consult.com

 

[gepman]

I have been an engineer for many years and not paid much attention to phase sequence, just connected A to A, B to B, and C to C. Of course motor and equipment rotation direction is important.

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".

 

[prc]

Phase sequence can be a serious issue as practices differ in various regions.Fiascos are not rare in real world.Some twenty years back I supplied a 3 phase Generator transformer bank ( 4 single phase units including spare)to a 500 MW generator.When the transformers reached site, it was found that with the bus duct connections arranged, the phase sequence will become RBY while the sequence of generation was RYB.Since the mistake was from client side,he agreed to modifications at site.A special intermediate oil filled box was provided on each transformer over the LV 12.5 KA bushing mounting box to interchange the LV terminals from 2.1-2.2 to 2.2-2.1( ANSI world X1-X2 to X2-X1)Otherwise alternative was to transport all units (each weighing nearly 180 Tonnes) back to factory,2000 Kms away,change the LV lead connections inside transformer,retest,delaying the project by atleast one year.

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.

 

[jraef]

I live in PG&E country, and for sure, there is a "Phase A". It is imperative that all sensing equipment be connected to Phase A only because with all of the cutbacks and financial problems we have now, that is the only one we can afford to keep constant. The other two phases (which by the way are called "Moon Unit" and "Dweezle" out here) are a little flakey so we don't rely on them for anything other than providing power to our guitar amplifiers and fan-forced bongs.



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

 

[davidbeach]

Within a single system it can matter, a lot. What is phase A in one system vs. what is phase A in a different system don't make a hill of beans. And where it does matter the determination will alway be made by bringing the two systems to an open switch and then measuring voltages across the open; always starting with a measurement that should show voltage (A-B', etc.) followed by what should be zero volts (A-A', etc.) and back to a voltage.

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.

 

[alehman]

As david says, it is very important for a utility that operates interconnected systems. Dweezle must match Dweezle across the system or things get ugly. And as has been stated, the definition of Dweezle is totally arbitrary. For two utilities or generators that are not interconnected, there is no relationship. Once they interconnect, then their Dweezles must match or someone must keep track of which is what.

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"?

 

[waross]

There were reports of the newer fan-forced bongs suffering erratic performance issues when connected to Dweezle phase. After an in depth investigation it was determined that the issues were not related to Dweezle, but were:
"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

 

[sibeen]

jraef, btw what color are "Moon Unit" and "Dweezle"?

I thought they were both Zappapple.

 

[etronics]

Pisimatza,
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.

 

[alehman]

sibeen, if that's true waross is likely to get his bong fan blowing backwards.

 

[waross]

My fan blowing backwards?? That really sucks!!

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[itsmoked]

Wasn't Skogs on about the A phase electrons being red?

Keith Cress
kcress -

http://www.flaminsystems.com