I know how to calculate current in delta connection but just for knowledge purpose I wanted to know from basics why this method(in image) of calculating phase and line current is completely wrong even for balanced load and so for unbalanced load also, so here is a circuit enter image description here

Of unbalanced load and that is my calculation of phase and line current (which is obviously wrong) enter image description here

So why this method(method of potential difference) of calculation don't work here, even though in all dc circuits this method works always so why not here?
And what is best approach to solve these types(varying magnetic flux) of complex circuits

  • \$\begingroup\$ Ohm's law doesn't apply when there's non-constant magnetic fields involved. \$\endgroup\$
    – Hearth
    Jul 13, 2020 at 14:22
  • \$\begingroup\$ Yeah but, can you give a detailed answer so that I doesn't make such mistakes afterwards? \$\endgroup\$
    – user215805
    Jul 13, 2020 at 14:28

1 Answer 1


So why this method(method of potential difference) of calculation don't work here

It doesn't work like that because you haven't considered the two other currents, \$I_{BY}\$ and \$I_{YB}\$. You can't just conveniently forget about them. Some part of the content of those currents flow into the load. The load is not exclusively fed a current \$I_{RB}\$.

  • \$\begingroup\$ OK, but if we apply same method to circuit where only dc source is present and we know potential difference across aa' and resistance of coil aa' that's enough to calculate the current i(RB) and we don't care what other currents are but that's my question why in this case other two currents required? \$\endgroup\$
    – user215805
    Jul 13, 2020 at 15:20
  • \$\begingroup\$ @user215805 The DC load current will be sourced from two parallel batteries that have the same terminal voltage. In effect, your analysis fails to account for both currents. You are considering the the whole current is supplied from one of the two parallel batteries. \$\endgroup\$
    – Andy aka
    Jul 13, 2020 at 15:34
  • \$\begingroup\$ So basically what I understand by your comment that potential difference across terminal a and a' keep changing as we changing the load and doesn't behave like a ideal voltage source, so if I wanted to analyse this same circuit to an ideal dc or ideal ac voltage sources(just to make circuit more simple for understanding) , so how exactly their equivalent circuit looks likes?or this type of circuit cannot be modelled as ideal ac voltage sources instead of varying magnetic fields? \$\endgroup\$
    – user215805
    Jul 13, 2020 at 16:00
  • 1
    \$\begingroup\$ Eh? You asked me to consider a DC case in your top comment and that is what I commented on. This means that the potential difference between a and a' cannot keep changing. Remember that this site is not a forum or talking shop. Let me make it simple. Put two identical 9 volt batteries in parallel across a 9 kohm load and the load current is 1 mA. That current is split equally between both batteries hence each battery supplies 0.5 mA. Your actual question made the mistake of thinking that all the current is supplied by one battery. \$\endgroup\$
    – Andy aka
    Jul 13, 2020 at 16:06
  • \$\begingroup\$ I was hoping for some more detailed explanation but looks like I have to close it \$\endgroup\$
    – user215805
    Jul 17, 2020 at 8:57

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