How will the ideal transformer will behave in the presence of Vr=20 Vdc

When S2 is open.

Let V1,V2 be the voltages drop on the ideal transformer sides respectively then

V1=-(N1/N2)V2

THEN I think that V2=0? because of the open-circuit.

Someone can verify or defy that.

a.jpg:

 

Are you sure Vr is DC? If Vs is also DC, then with S2 open (as you described) there will be no voltage on N2:

1. because S2 is open
2. because Vs is DC, so there will be a DC current through N1 but no energy transfer from N1 to N2.

Where does this picture come from? Isn't this for dynamic analysis, like what happens when I close / open this switch? In this case it'd be a different story.

 

Are you sure Vr is DC? If Vs is also DC, then with S2 open (as you described) there will be no voltage on N2:

1. because S2 is open
2. because Vs is DC, so there will be a DC current through N1 but no energy transfer from N1 to N2.

Where does this picture come from? Isn't this for dynamic analysis, like what happens when I close / open this switch? In this case it'd be a different story.

thanks dude.

but vs is AC...didn't thought it's matter at all.

This is actually a question from a test i'm practicing too...The task is to calculate IL for t>10ms when in t=10ms the switchs are switching.

So If Vs is AC what can you say on V2?

 

If one assumes the circuit is at steady state when the switch S2 is closed then there will be a transient condition which can be solved. If S2 is opened or closed when the circuit is not at steady state this can also be solved but the different initial conditions would need to be taken into account. You haven't given the complete picture so it's difficult to comment on what will happen. If you also state the switching regime to be applied to S1 & S2 then this might be more informative as well.

You haven't given all the circuit values or stated which current is IL (i.e. not shown on your schematic).

Otherwise the solution can only be given as two general differential equations which may only be solved when circuit values are substituted and initial conditions known.