Why transformer is called constant flux machine?

when a load is connected to a transformer current(say I2) flows through secondary coil thus an M.M.F (N2I2) is produced ,this produces the secondary flux.

This flux reduces the the main flux induced in the primary & also reduces E.M.F E1 in the primary

As a result more current is drawn from the supply. This additional current drawn is due to the load component(say I2' )

This I2' is anti-phase with I2.This I2' sets a flux which opposes the secondary flux & helps the main flux.

The load component flux neutralises the secondary flux produced by I2 .The M.M.F N1I2' balances N2I2.Thus the net flux is always at constant level.

As practically flux is constant,the core loss is constant for all loads.

Hence a transformer is always called a Constant Flux Machine.