Tranformer flux is said to be constant but it is sinusoidal in nature. how?

Question

Tranformer flux is said to be constant but it is sinusoidal in nature. how?

Answer 1

In a transformer when the primary winding is excited with sinusoidal current and the secondary is open, the core flux is sinusoidal.  When a load is connected to the secondary winding, current flows and produces additional magnetic flux in the core.  But, by the Lenz Law, the primary winding will also draw additional current and produce flux that is 180 degrees out of phase with the secondary current to oppose any  change in magnetic flux.  The end result is that the exciting flux of the transformer remains unchanged or constant in value.

Answer 2

Flux is the changing magnetic field.

In a (mains electicity) transformer, say in your iPod charger, the ac current coming in from the plug is converted into alternating magnetic field by the windings in the Primary coil.

Another coil, the Secondary, picks up this flux and has a EMF induced in it proportional to the number of turns it has. The current is sinusoidal (60 Hertz in US, 50 Hz in Europe) but has a constant rate of change - flux. Imagine the Flux as the effort your legs make cycling up a gentle hill! The gears are the transformer windings, with primary the front gear and the secondary the rear!

Answer 3

What they mean here is that the magnetic flux in the core of the transformer has a sinusoidal time-dependent nature, but the magnitude (i.e. the peak value) of the sine wave is the same from cycle to cycle.

This assumes that the voltage applied to the transformer coils is also of constant magnitude and constant frequency.