Unbalanced 3phase system

alim

Joined Dec 27, 2005
113
So, you're saying mathematics is incorrect?



I don't know what measuring line-to-line voltages has to do with line-to-neutral voltages.



I have extensive practical knowledge. I'm an industrial electrician and have been working with, and studying 3 phase power systems nearly 30 years.



So it's true for everyone but you? Seems to me you're the one having difficulty understanding!



Note that there are two kinds of 3 phase distribution systems: wye and delta. For systems where a neutral is used, the wye is more common since it allows for the possibility of a balanced system, whereas a grounded delta system (be it corner-grounded or center-grounded) will be unbalanced by design.

In the case of a center-grounded delta system, the line-to-neutral voltage readings from 2 of the phases will result in half the line-to-line voltage (that is, 240V line-to-neutral on a 480V system). However, the 3rd leg will measure approximately 208V to neutral.

On a grounded 480V wye system, the line-to-line voltages will, of course, measure 480V. But measure any one of the phases to neutral, and you will see that it is 277V, not 240V.


If you're getting something other than these readings, you're either doing something wrong, or you have a bad meter.
I You are correct with your voltages except on the the center grounded delta system you will get 416 volts on the high leg, it is 216 volts on a 240/ 120 volt system.
 

zgozvrm

Joined Oct 24, 2009
115
In the case of a center-grounded delta system, the line-to-neutral voltage readings from 2 of the phases will result in half the line-to-line voltage (that is, 240V line-to-neutral on a 480V system). However, the 3rd leg will measure approximately 208V to neutral.
You are correct with your voltages except on the the center grounded delta system you will get 416 volts on the high leg, it is 216 volts on a 240/ 120 volt system.
Yes, you are correct. I mistakenly gave the high leg voltage for a 240 volt center-grounded delta, while referring to a 480 volt center-grounded delta.

To clarify: On any center-grounded delta system, the 2 legs nearest the grounded (neutral) wire when measured to neutral will be 1/2 the the line-to-line voltage. The 3rd leg (the one opposite the grounded wire) is the "high leg" and will measure approximately 1.73 (the square root of 3) times those voltages.

So, as alim pointed out, on a 240 volt center-grounded system, line-to-line voltages will be 240V, line-to-neutral voltages will be 120V (half the L-L voltage) for the 2 legs closest to the neutral wire. The 3rd (high leg) will measure 1.73 x 120 V = 208 V to neutral.

On a 480 volt system, you have 240 V for the "low legs" and 1.73 x 240 V = 416 V for the "high leg."
 

zgozvrm

Joined Oct 24, 2009
115
And to continue...

For any grounded 3 phase wye system, the line-to-neutral voltage will always be 0.577 times the line-to-line voltage (that's \(\sqrt3 / 3\))

Of course, these measurements assume that you have a good power source to start with (meaning the L-L voltages are all equal). If the L-L voltages are NOT equal, then you either have a bad transformer, or it is being over-loaded and the voltage is being pulled down on one or more phases.
 

R!f@@

Joined Apr 2, 2009
9,920
So, you're saying mathematics is incorrect?
I donno how u came to believe tht. Did I say tht?

I don't know what measuring line-to-line voltages has to do with line-to-neutral voltages.
Oh really...And u say are an industrial tech.

I have extensive practical knowledge. I'm an industrial electrician and have been working with, and studying 3 phase power systems nearly 30 years.
This may be true or not.

So it's true for everyone but you? Seems to me you're the one having difficulty understanding!
I understand everything perfectly. I see what I believe too.

In the case of a center-grounded delta system, the line-to-neutral voltage readings from 2 of the phases will result in half the line-to-line voltage (that is, 240V line-to-neutral on a 480V system). However, the 3rd leg will measure approximately 208V to neutral.
Are u saying I am wrong and right at the same time.
The third leg u are talking abt, is something I haven't seen here.


If you're getting something other than these readings, you're either doing something wrong, or you have a bad meter.
I am not doing any thing wrong and My instruments are Fluke devices.
Get that into ur head before thinking abt wht others use.

I am not just a guy from the corner or tech assistant.
What I do and what I can do is enuf to prove what I am capable of.
 

zgozvrm

Joined Oct 24, 2009
115
So, you're saying mathematics is incorrect?
I donno how u came to believe tht. Did I say tht?
Yes ...
This might be true for mathematical proof. But as for me, I have measured line to line of 400VAC thru 440VAC here, and a line of voltage of 200VAC to 230VAC.


I don't know what measuring line-to-line voltages has to do with line-to-neutral voltages.
Oh really...And u say are an industrial tech.
You don't need a neutral to measure L-L voltages. In fact there are several ungrounded systems (both wye and delta) in existence. Therefore, there is no line-to-neutral voltage in those cases.



I believe what I see, and no one can convince me otherwise.
...so you believe in magic? That pretty much explains your misunderstanding.



I understand everything perfectly.
Wow! You should receive a Nobel prize!



The third leg u are talking abt, is something I haven't seen here.
Which not only proves you don't understand everything, but that you don't know what you are talking about.



I am not doing any thing wrong and My instruments are Fluke devices.
Get that into ur head before thinking abt wht others use.
That may be. But even Flukes go bad. Also, just because you own and use a Fluke, doesn't mean you know how to use it. So, like I said,
If you're getting something other than these readings, you're either doing something wrong, or you have a bad meter.
 
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R!f@@

Joined Apr 2, 2009
9,920
I donno how to use a fluke... hahahahahah.. u crack me up.

Brag all u want. I could not care less.
Good luck
 

zgozvrm

Joined Oct 24, 2009
115
I donno how to use a fluke... hahahahahah.. u crack me up.

Brag all u want. I could not care less.
Good luck
I never said that you didn't know how to use a Fluke (or any other meter).

What I was saying was: just because you have a Fluke, doesn't necessarily mean that you know how to interpret the readings correctly (one does NOT imply the other).

There is obviously something you're not understanding concerning the measurement of 3-phase systems. Therefore, either:
1) you don't know (or you don't understand) what you are measuring,
2) your meter is faulty or out of calibration (and yes, even Flukes can go bad),
3) you are misreading your meter, or
4) the laws of physics don't apply in your corner of the world.


... and I'm not bragging. It is clear that you don't fully understand 3-phase power systems and I (along with others in this post) are trying to help you to understand.

Instead of being receptive to facts that have been proven many times over, you continue to act like a child with his hands over his ears, saying "na-na-na, I'm not listening!"

The fact remains that a grounded 480 volt wye system measures 277 volts line-to-neutral (NOT 240 volts as you have indicated). Also, the neutral will, in fact, carry NO CURRENT if the system is perfectly balanced.

Believe what you will, but thousands of people have been able to show that both of the above statements are true (both mathematically and practically), myself included.
 

alim

Joined Dec 27, 2005
113
There was a long thread on moderators intervening on threads, while it may not be a desireable thing sometime it maybe necessary, as in the case of this thread,in my opinion. This thread is one which deal with three phase voltages and measurements, the science and facts have long been established. Zvozgrm has been making all the correct statements, but then you have another member making statements which are incorrect and is adamant about them. I would suggest the administration seek the input of tnk who seems to me to be eminently qualified, or any other member to give an input, my view is this unnecessary back and forth is not useful.
 

R!f@@

Joined Apr 2, 2009
9,920
By the way, that statement means that you DO care.
You probably meant to say, "I could care less."

...but then again, you've already told us that you "understand everything perfectly!"
U are right, I do care..:p.
I tend to get on ppl's nerve when I want to find how good they are. I not trying to prove u wrong, I have a nature of doing things differently.

One more thing abt this corner of the world is this place is very different.
Before I get to know most of the things learned from here tend to be some what different from the rules and practice that are practiced here. So I tend to find the truth by trying to argue, which in any way is not unfriendly. I am cool and smiling as I type. Please do not take me wrong. Sometimes acting like this has benefited for me.
In the end I am always happy,that I learned something new.
And if I am wrong, I admit it, and I always apology's. Like now, if u felt uncomfortable. I am sorry.
This is just a friendly argument. This always been my nature.

@alim
What does tnk has to do with this, This is something I like to know abt our new member zgzvrm.

Anyways. I am going to do a little testing on our 3 phase in a recently finished building to make sure about our voltages and connections.
Till then
cheers
 
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