Is this calc right?

[Ingenieur]

If you really think that is what Smart$ has calculated then you are not getting it.

apparently I'm not the only one
all 4 of these use the same convention

please consider:
wye-wye with n xfmr-load connection
current convention as follows:
xfmr Xabc OUT and IN to load
load center node OUT and IN to the xfmr X0
this forms a current loop which KVL can be applied with proper sign
if the n was OUT of the X0 and IN to the load nod the loop would have the current convention/loop opposing

we are discussing a wye-wye based on the OP spreadsheet, not some theoretical connection in space without context

I'm done
let the reader decide, he has enough crap to sift thru :lol:

 

[wwhitney]

please consider:
wye-wye with n xfmr-load connection
current convention as follows:
xfmr Xabc OUT and IN to load
load center node OUT and IN to the xfmr X0
this forms a current loop which KVL can be applied with proper sign
if the n was OUT of the X0 and IN to the load nod the loop would have the current convention/loop opposing

I agree with everything above except the word "proper". The choice of positive sense for the neutral current is arbitrary. With the choices above, then KCL takes the form Ia + Ib + Ic - In = 0. If you flip the sense of In, so that positive current is from the X0 to the load centerpoint, then KCL takes the form Ia + Ib + Ic + In = 0.

The upshot is that the power engineering textbooks discussed use one convention, and the physics texts discussed use the other convention. Neither one is "right" or "wrong".

Cheers, Wayne

 

[Ingenieur]

I agree with everything above except the word "proper". The choice of positive sense for the neutral current is arbitrary. With the choices above, then KCL takes the form Ia + Ib + Ic - In = 0. If you flip the sense of In, so that positive current is from the X0 to the load centerpoint, then KCL takes the form Ia + Ib + Ic +In = 0.

The upshot is that the power engineering textbooks discussed use one convention, and the physics texts discussed use the other convention. Neither one is "right" or "wrong".

Cheers, Wayne

no it isn't
based on current flow and power flow and continuity of the loop convention

show me one example in a text book please

 

[wwhitney]

no it isn't
based on current flow and power flow and continuity of the loop convention

What is the "loop convention"? It is apparently a convention that not everyone follows.

show me one example in a text book please

I already gave you two physics references.

Cheers, Wayne

 

[Ingenieur]

What is the "loop convention"? It is apparently a convention that not everyone follows.


I already gave you two physics references.

Cheers, Wayne

EVERYONE follows it, including Kirchhoff who defined it

where? can't find a post with a page out of a physics textbook


let the reader decide
both cases have been made ad infinitum
or ad nauseam
:lol:

 

[wwhitney]

where? can't find a post with a page out of a physics textbook

See http://forums.mikeholt.com/showthread.php?t=182037&p=1807266#post1807266

Cheers, Wayne

 

[Ingenieur]

See http://forums.mikeholt.com/showthread.php?t=182037&p=1807266#post1807266

Cheers, Wayne

physics TEXTBOOK
come on, get a real source, IEEE, etc.

that reinforces MY position

The current entering any junction is equal to the current leaving that junction. i₂ + i₃ = i₁ + i₄


current entering AND leaving

not all entering
opposite sign

 

[Smart $]

physics TEXTBOOK
come on, get a real source, IEEE, etc.

You're one to talk. All you've posted is a picture of IEEE book covers.

 

[Ingenieur]

You're one to talk. All you've posted is a picture of IEEE book covers.

really?

forget about this one, did you now?
:lol:

 

[Ingenieur]

in case your eyes ain't what they used to be



let the reader decide
they are not morons

 

[wwhitney]

So here's a substantive question. If I understand correctly, with a MWBC, combinations of linear loads can cause current on the neutral exceeding the phase current.

E.g. on a split single phase system, a capacitor L₁-N and an inductor L₂-N would cause I_N = I_L1 + I_L2 (in magnitudes).

On a 3 phase system, a 0.5 power factor leading load L_A-N and a 0.5 power factor lagging load L_B-N can cause I_N = I_LA + I_LB (in magnitudes), depending on the phase rotation (with I_N = 0 for the other phase rotation).

Does the NEC address these possibilities? Or are they just so unlikely in practical applications that they are ignored?

Cheers, Wayne

 

[wwhitney]

physics TEXTBOOK
come on, get a real source, IEEE, etc.

OK, so your position is that if EE and physics have a difference in conventions, EE is right and physics is wrong.

That's a good point to end this subsconversation, since the parochialism of that statement speaks for itself.

Cheers, Wayne

 

[Ingenieur]

OK, so your position is that if EE and physics have a difference in conventions, EE is right and physics is wrong.

That's a good point to end this subsconversation, since the parochialism of that statement speaks for itself.

Cheers, Wayne

you have not shown a difference in convention
1 page, Halliday and Resnick, any textbook
insults and quips do not your argument make

let the reader decide, they are not morons

 

[jumper]

Ahem.

View attachment 16778

 

[mivey]

I agree with everything above except the word "proper". The choice of positive sense for the neutral current is arbitrary. With the choices above, then KCL takes the form Ia + Ib + Ic - In = 0. If you flip the sense of In, so that positive current is from the X0 to the load centerpoint, then KCL takes the form Ia + Ib + Ic + In = 0.

So simple. Should not be so hard to accept.

The upshot is that the power engineering textbooks discussed use one convention, and the physics texts discussed use the other convention. Neither one is "right" or "wrong".

Cheers, Wayne

Exactamundo! Engineering and physics texts use both conventions.

No need to limit oneself to a limited set of references and try to conclude that they are the same as all other references. That is just not logical.

 

[mivey]

So here's a substantive question. If I understand correctly, with a MWBC, combinations of linear loads can cause current on the neutral exceeding the phase current.

E.g. on a split single phase system, a capacitor L₁-N and an inductor L₂-N would cause I_N = I_L1 + I_L2 (in magnitudes).

On a 3 phase system, a 0.5 power factor leading load L_A-N and a 0.5 power factor lagging load L_B-N can cause I_N = I_LA + I_LB (in magnitudes), depending on the phase rotation (with I_N = 0 for the other phase rotation).

Does the NEC address these possibilities? Or are they just so unlikely in practical applications that they are ignored?

Cheers, Wayne

Highly unlikely scenarios. While there are exceptions, most loads tend to be more inductive.

 

[mivey]

All righty then,

While I have references showing both conventions, I tried to focus on the sum to zero in one direction convention since that was the disputed convention. Also, I had issues with my scanner so I resorted to phone camera shots so there may be a decrease in quality and a couple wound up rotated for some reason. I don't feel like working with them anymore if they are at least readable so here we go if I can beat the timer and format errors.

Speaking of which, let me drop in a text box then post here so I don't lose my typing. I'll see if I can drop in this post but it may have to go to the next. I have some more but am tired of messing with pics.

Just found there is a limit of 8 and I have 14 so I'll post in two parts:

 

[mivey]

Part 2:

 

[Ingenieur]

Most of those show the accepted convention
positive in
negative out
the ones that don't are being applied to machines or transmission lines
oy a wye source to wye load

Reinforcing my position
eq 4.2
Eq 3-4
Eq 22-16 show a current as negative
Eq 168 shows a current of oppossite sign, ie, other side of =
Fig 235 a shows line out x0 in, opposite for, EXACTLY AS I DESCRIBED
2.2.4 opposite signs, see the - in front?

let the reader decide

 

[Ingenieur]

The very first sideways one n = a + b + c !!!
2-44 show nothing about sign convention: only that sum = 0 at node
abc pos and n neg
15 is the same
4.1 and 4.2 oh bidirection transmission line, NOT load and source


let the reader decide