Transformer when output circuit is open

[ahmadriaz]

can u explain what hapens output circuit is open and no current is flowing through output coil? isn't it that a large current flows through the input?and the wire burns...i know it doesn't hapen...but why?when there is no back emf in primary?

 

[berkeman]

can u explain what hapens output circuit is open and no current is flowing through output coil? isn't it that a large current flows through the input?and the wire burns...i know it doesn't hapen...but why?when there is no back emf in primary?

When the secondary is open, all you see is the magnetizing inductance (and the leakage inductance) of the primary. As you add impedance to the secondary so that some secondary current starts to flow, that secondary impedance is reflected back to the primary, where it appears in parallel with the magnetizing inductance of the primary.

Quiz Question -- What is the magnitude of the transformed secondary impedance, as seen in parallel with the primary magnetizing inductance, in terms of the number of turns on the primary and secondary coils?