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?

 

[sir-pinski]

When the output circuit of a transformer is open, it means that there is no closed loop for the current to flow through in the secondary coil. This results in no current flowing through the output coil. In this situation, the transformer is not able to step down the voltage and provide power to the load.

If there is no current flowing through the output coil, then there is also no back emf (electromotive force) in the primary coil. Back emf is the opposing voltage that is generated in the primary coil due to the changing magnetic field caused by the alternating current. This back emf helps to limit the current flowing through the primary coil.

Without the back emf, there is no limitation on the current flowing through the primary coil. This can lead to a large current flowing through the input, which can cause the wire to overheat and potentially burn. However, most transformers have protective measures in place to prevent this from happening, such as fuses or circuit breakers.

In summary, when the output circuit of a transformer is open and there is no current flowing through the output coil, it can result in a large current flowing through the input. This can potentially lead to overheating and damage, but proper safety measures are in place to prevent this from happening.