Three winding transformer

[ranju]

while studying the purpose of tertiary winding in the this 3-winding transformer , I'hv gone through a statement that " the zero sequence component caused by line-to-neutral load on secondary side cannot be balanced by primary currents as the zero sequence currents cannot flow in isolated neutral star connected primary".
Now first of all I wanted to know that the currents in secondary are balanced by primary as this is the basic thing I am not getting this and why can't primary currents balance the zero sequence component ??
And secondly why can't the zero sequence current flow in star-primary??
I am missing some basics , so please elaborate it..??

 

[jim hardy]

zero sequence currents cannot flow in isolated neutral star connected primary"

Isolated neutral... hmmmmm,,, you already know the answer...

What is phase relation between zero sequence currents?

What does KCL tell you about currents into that neutral node?

 

[ranju]

What is phase relation between zero sequence currents?

the zero sequence are all in same phase with each other & there's a zero phase displacement between them .. I am not getting why the primary currents can't balance the zero sequence current??

 

[jim hardy]

the zero sequence are all in same phase with each other & there's a zero phase displacement between them .. I am not getting why the primary currents can't balance the zero sequence current??

hmmmmm. all in phase? Do they all flow into or out of the the neutral in phase?

seems there's no way back out of neutral? You said it's not connected ... Kirchhoff says what goes in must come back out?