I have found it very difficult to find what actually happens with primary and secondary generated flux in transformers, I understand the normal transformer theory but it doesn't add up in reality! I am hoping someone can shed some light. Simply put, if magnetic lines of flux cannot cross or actually cancel does this mean that the secondary coil is an air core?
You could begin an argument about transformers like this: -
- A transformer has magnetizing flux due to current flowing into the whole of the primary winding when the secondary is open circuit i.e. the transformer is an inductor.
- When extra current flows in the primary due to loading of the secondary this flux increases
- The current flowing in the secondary winding also increases flux (incorrect, it totally cancels the ampere turns in the primary due to loads on the secondary)
However, the massive flux generated by the primary due to loading the secondary is totally cancelled by the reverse magnetic flux due to current flowing in the secondary. Consider these scenarios: -
- Scenario 1 is just the primary winding with Imag flowing
- Scenario 2 is two windings wound close together - Imag (the same as above) is shared by the two windings
- Scenario 3 is the 2nd winding open circuit - it has the same voltage as the primary winding
- Scenario 4 is the secondary load - Iload currents are in opposite directions and their fluxes cancel.
The flux lines (mostly) link the two coils- lines pass through the primary and through the secondary. The closed loops are a consequence of the lack of magnetic monopoles- unlike electric charges there are no sources and sinks of magnetic fields. Real transformers have a certain amount of flux that does not link the coils- that is called leakage inductance.
Magnetic field lines are a visualization aid to help understand intuitively a vector field. The flux line density is related to the magnitude of the field and the tangent to the field direction is the line direction.
Another way to visualize this in situations where most of the field is within a core is to think of it like current in a circuit- like a loop with a certain voltage applied (magnetomotive force) through an impedance (reluctance) or conductivity (permeability) and results in a current (flux) and current density in the conductor (flux density).