# KVL and Dot Convention



## Phatso86 (Sep 9, 2016)

I am having trouble understanding this.

So I know that both currents entering dots mean that M is additive.

But I keep seeing examples where:

1 - one current enters dot, other current leaves dot

2 - KVL is performed so the loop current always ENTER each dot

3 - during KVL equations, the voltage drop at inductor is negative and drop @ M due to other inductor is also negative. (this makes M additive)

(for example. the equation would be, " - I1*100 - I1*100j - I2*50j = 0")

Is this the ONLY way to perform this problem? When I simply choose clockwise loop currents, the Ms are subtractive, which is how I thought its meant to be. I keep getting the wrong answer this way.

(for the equation above, I would obtain, " - I1*100 - I1*100j + I2*50j = 0")


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## Phatso86 (Sep 13, 2016)

anyone?


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## cupojoe PE PMP (Sep 13, 2016)

Current flows into the dot on primary side and out of the dot on the secondary side. 

As I recall for circuits class, this makes sense, since you always do loop analysis using the clockwise (or less common counter-clockwise) orientation.

You are going to have to post a circuit diagram, having trouble following what you are saying here.

IMHO, relearning circuit analysis is not going to help you much on the PE.


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## Phatso86 (Sep 14, 2016)

cupojoe PE PMP said:


> Current flows into the dot on primary side and out of the dot on the secondary side.
> 
> As I recall for circuits class, this makes sense, since you always do loop analysis using the clockwise (or less common counter-clockwise) orientation.
> 
> ...


ok, so here is what I know (these are professor notes).

if both currents enter the dot, mutual inductance is additive

if one enters and the other leaves, mutual inductance is subtractive.

my problem is that when there is a circuits with multiple panes and you do loop analysis, the solutions always shows additive mutual inductance due to direction that loop currents are chosen. Meaning that currents are always chosen to ENTER the dot and the KVL always shows additive inductances.

But when I choose clockwise (leading to one entering, one leaving - subtractive inductances) I obtain the wrong answer every time.

View attachment 8600


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## Phatso86 (Sep 14, 2016)

I need to start proof-reading what I type :reading:


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## Phatso86 (Oct 15, 2016)

anyone have any tips on this?


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## knight1fox3 (Oct 15, 2016)

Have a look at this to see if it helps at all:

http://faculty.citadel.edu/potisuk/elec202/notes/xformer.pdf


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## Phatso86 (Oct 15, 2016)

knight1fox3 said:


> Have a look at this to see if it helps at all:
> 
> http://faculty.citadel.edu/potisuk/elec202/notes/xformer.pdf


it's been a while. I'll try those problems I had issues with again. maybe I kept missing a negative somewhere.


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