240v debate....

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jim dungar

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Staff member
Location
Wisconsin
Occupation
PE (Retired) - Power Systems
No, let's not ignore mesh analysis....let's embrace it!!

Please tell us how you are able to complete this analysis without having your B-Phase current not contradict your B-Phase voltage! (Watch your minus signs, because you darn well know I will be watching them.)
I believe I asked this question a year or so ago. IIRC, his(?) answer was it didn't make a difference.
 

Jraef

Moderator, OTD
Staff member
Location
San Francisco Bay Area, CA, USA
Occupation
Electrical Engineer
Wow, 27 pages of postings in 12 days on such a simple issue. We are a contentious bunch. I can't take the time to read them all, so I will not join the fray because frankly, I'm confused as to why this is so contested (he says hopefully without divulging his bias so as to avoid being banned or ridiculed, because lord knows I've made enough of my own gaffs in here already).

I would imagine that the poor OP has run the other way by now.
 

jumper

Senior Member
Rick,

Why? You are a smart guy.

Your challenges/threats to Bob are silly-he is a member first and a mod second. As a member you will not rattle him, he is as hard headed as he is stubborn-you seem to imply that dual standards are acceptable-and they are not. I neither defend or support Bob-he does need me to be that presumptuous.

As for calling the other EEs in this thread "old school", I find that funny-especially concerning Mivey (I cannot comment on Bes, David, or Lazlo-I do not know them well enough to comment without their permission, although I have great respect for all three, as I do I for you).

Mivey merely points out the different aspects involved in looking at a particular install. He never thinks inside the box, he makes people think outside it. Mivey-conventional-ya gotta be kidding. He is like no EE I have ever met.

In a nutshell, this is how I see it:

You are doing this:

1sm074hole.gif

to land here:

smiley.jpg

You will not get banned for your previous comments here, that would be too easy at this point and give you a false sense of self-vindication.
 

Rick Christopherson

Senior Member
Actually, even before reading your posting, I was planning on apologizing for allowing myself to get so irritated last night. Besoeker's sudden apparent flip-flop set the stage, when I thought we were making some progress. It spiraled downhill from there.

Bob's posting(s), if they had come from any regular member, would be easy to dismiss. However, he is a moderator and has asserted himself as a moderator in this discussion. He is supposed to be the person preventing that type of behavior, not instigating it. It is the antithesis of a moderator's duties. If he was an active participant in this discussion contributing content, then it would be just fine. However, he is not adding content, but instead, his only contributions to the discussion have been antagonist barbs originating from someone with "moderator" in his moniker. Yes, my comment was made in the heat of irritation, but it was not entirely idle, and I have had moderators removed from their position on other forums for this same behavior.

Nevertheless, I do apologize to everyone reading this discussion for allowing myself to get so irritated last night. I will do my best to keep this in check as this discussion hopefully continues.
 

jumper

Senior Member
Actually, even before reading your posting, I was planning on apologizing for allowing myself to get so irritated last night. Besoeker's sudden apparent flip-flop set the stage, when I thought we were making some progress. It spiraled downhill from there.

Bob's posting(s), if they had come from any regular member, would be easy to dismiss. However, he is a moderator and has asserted himself as a moderator in this discussion. He is supposed to be the person preventing that type of behavior, not instigating it. It is the antithesis of a moderator's duties. If he was an active participant in this discussion contributing content, then it would be just fine. However, he is not adding content, but instead, his only contributions to the discussion have been antagonist barbs originating from someone with "moderator" in his moniker. Yes, my comment was made in the heat of irritation, but it was not entirely idle, and I have had moderators removed from their position on other forums for this same behavior.

Nevertheless, I do apologize to everyone reading this discussion for allowing myself to get so irritated last night. I will do my best to keep this in check as this discussion hopefully continues.

I say we drop the whole mod discussion and let the math and and analysis continue. This really is a fascinating thread.

We all have tempers, we just need to rein them in-easier said than done-I know.
 
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pfalcon

Senior Member
Location
Indiana
If you're really suggesting that Van=120<0 and Vbn=120<0, then how do you get a calculated voltage of 240V across a load connected between A and B using Kirchoff's Voltage Law?

Vl= Van-Vbn = (120<0)-(120<0)
...................= (120+j0)-(120+j0)
...................= (0+j0)
...................= 0 Volts?

Isn't this supposed to be
Vl = Van + Vnb = (120<0) + (120<0) ?
I don't think you get to reverse the direction of your leads when you take the measurements. B > N > A not N > B and N > A
 

cowboyjwc

Moderator
Staff member
Location
Simi Valley, CA
I say we drop the whole mod discussion and let the math and and analysis continue. This really is a fascinating thread.

We all have tempers, we just need to rein them in-easier said than done-I know.

Oh yeah, well, YOU JUST REIN IN YOUR OWN TEMPER MISTER! And don't tell me to have a nice day, I'll have any kind of day I want! :lol::lol::angel:
 

Besoeker

Senior Member
Location
UK
Besoeker, I have been very patient with you for the past couple of days, but that patience has its limits when you keep flip-flopping in what you are saying. If you are unsure about your position, or are unable to communicate it using the English language, then you need to bow out of this discussion.
I'm sure you would like me to bow out of this discussion. Denigrating my grasp of the English language is hardly the way of constructive discourse.
And, for the record, I am totally sure about my position. We design and manufacture things that have to work in the real world. Getting them wrong isn't an option.

You have emphatically stated that you must have a 180? phase shift, but then deny making such a claim.
Yep. I dropped a goolie in post #85 where I did mention a phase shift when I commented "i.e 180 deg phase shifted from each other."
The "from each other" might have been a clue that one is not actually generated by phase displacing the other. Yes, I accept that it wasn't entirely evident from my post. For that, I apologise.
Phase displaced is how I should have put it and indeed did in that and similar terms in a number of other posts.

Post #22 - To get twice the magnitude they have to be 180 degrees apart
Post #34 - If they were all the same and in phase, how would you get 240V end to end on the transformer?
Post #49 - It's what you would see and do see on an oscilloscope using the the neutral as the common point. Each half 0f the 120V-0-120V HAS to be displaced 180deg
Post #66 - *If you don't do so simultaneously, you can't determine the phase relationship.
Post #67 - How else can you determine their phase relationship?
Post #86 - Unless the 120V supplies were in anti-phase i.e. 180deg apart
Post #86 - Note that Ia and Ib are displaced by 180deg.
Post #86 - Note that the two SCRs HAVE to be triggered 180deg apart because the voltages are 180 deg apart.

Getting from that to claiming that I have have emphatically stated that you must have a 180? phase shift is a bit of a stretch.
I should have thought from the above, all previously posted, that my position is perfectly clear and without ambiguity.
You have affirmed that a phase shift is a time shift, but then later deny that.
It is. Where did I deny it?


I cannot carry on a discussion with someone that doesn't even know what their own position is about. If you don't understand what your position is, or can't decide what position you want to take, then leave the discussion to those that do understand.
You are leaving??

Yes, I do have an answer for how neutral currents cancel,
Get on with it then.
 

Rick Christopherson

Senior Member
Yep. I dropped a goolie in post #85 where I did mention a phase shift when I commented "i.e 180 deg phase shifted from each other."
The "from each other" might have been a clue that one is not actually generated by phase displacing the other. Yes, I accept that it wasn't entirely evident from my post. For that, I apologise.
Phase displaced is how I should have put it and indeed did in that and similar terms in a number of other posts.

Post #22 - To get twice the magnitude they have to be 180 degrees apart
Post #34 - If they were all the same and in phase, how would you get 240V end to end on the transformer?
Post #49 - It's what you would see and do see on an oscilloscope using the the neutral as the common point. Each half 0f the 120V-0-120V HAS to be displaced 180deg
Post #66 - *If you don't do so simultaneously, you can't determine the phase relationship.
Post #67 - How else can you determine their phase relationship?
Post #86 - Unless the 120V supplies were in anti-phase i.e. 180deg apart
Post #86 - Note that Ia and Ib are displaced by 180deg.
Post #86 - Note that the two SCRs HAVE to be triggered 180deg apart because the voltages are 180 deg apart.

Getting from that to claiming that I have have emphatically stated that you must have a 180? phase shift is a bit of a stretch.
I should have thought from the above, all previously posted, that my position is perfectly clear and without ambiguity.
Wait, let me get this straight. You are arguing over a "descriptor"?
popcorn.gif
You think a "180? difference" is OK, but if you call it a "180? phase shift" it is somehow not the same thing? It's not about the words that follow the 180? that matter. It is the 180? that matters.

It doesn't matter what you want to label it. When you stick the 180? into your voltage, the effect is the same. It is a "difference", "time shift", "phase shift", "phase relationship", "displacement", or what ever else you want to call it. It is the same thing. Do you honestly believe that giving it less offensive name makes it do something different with your voltage waveform? Shouldn't we be having a Bill Clinton joke in here somewhere?
 

jwelectric

Senior Member
Location
North Carolina
I have a question and I am serious about the question is someone would please take some time and help me.

How can two coils connected in series (or one coil that has a center tap) be 180 degrees in or out of anything?
:?
 

Rick Christopherson

Senior Member
I have a question and I am serious about the question is someone would please take some time and help me.

How can two coils connected in series (or one coil that has a center tap) be 180 degrees in or out of anything?
:?
They can't. That's why I am arguing this topic so strongly.

Edit: Actually, two unrelated coils in series can. Contrary to the posting of Mivey's that I was going to go after a little later, it is the common core flux that prevents it from happening with a center tapped coil.
 
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hurk27

Senior Member
They can't. That's why I am arguing this topic so strongly.

Edit: Actually, two unrelated coils in series can. Contrary to the posting of Mivey's that I was going to go after a little later, it is the common core flux that prevents it from happening with a center tapped coil.

And I also agree, and in a strange way Mivey confirmed for me in post 243 that these two half windings are in fact in-phase, which leads me to what Besoeker stated back in post 32:
Take the instant in time 90 deg into the cycle. At that point, L1 is positive with respect to the centre tap, the neutral, and L2 is negative.
At 90? into the cycle, with L1 positive with N and L2 negative in respect to N then N has to comprise of being a negative and a positive just like in the series batteries, this is how they become an adder to get 240 volts. if you had two negatives at N you would not have 240 from L1-L2 no more then you would have 3 volts with two batteries in series with the negative ends together, so this using of the common point as a reference with both traces negative input leads on the common point is not referencing the two windings in their correct polarity.

If at 90? the correct polarity of each winding is A+---A-N|B+N----B- why would you try to reference the B+ with a black lead and place the red lead on the B- as we know this would reverse your reading the same as it would reverse a DC measurement this and only this is why you see a 180? displacement.

Also bringing in other types of circuits in to a discussion that was only about a transformer on a single phase 120-0-120 system made no sense other then to keep the discussion going.
 

Rick Christopherson

Senior Member
There is a significant difference between changing how one measures a voltage and physically changing what is being measured. When this topic last came up about 3 1/3 years ago, I put together this picture of batteries to help explain the concept. It is very similar to this discussion pertaining to a center tap transformer.

The right hand stack of batteries represents what happens when you "define" the system based on reversing your test leads. The image to the left is what happens when you simply relabel the system with a chosen reference point in the middle.

Batteries.jpg
 
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