Transformers and iron cores and frequency

[IWantToLearn]

As far as i understand the thing that matter in all of the process of mutual inductance is the rate of change of the current in the primary coil $$\frac{dI}{dt}$$
butting soft iron core will increase the density of the magnetic field inside the primary coil, but how this will effect $$\frac{dI}{dt}$$ , now the question is "What is the reason we use soft iron core?"

Second using these iron cores will create eddy currents, and causes power losses
but could this effect will also cause increasing the frequency of the secondary voltage ?

 

[EverGreen1231]

As far as i understand the thing that matter in all of the process of mutual inductance is the rate of change of the current in the primary coil $$\frac{dI}{dt}$$
butting soft iron core will increase the density of the magnetic field inside the primary coil, but how this will effect $$\frac{dI}{dt}$$ , now the question is "What is the reason we use soft iron core?"

Second using these iron cores will create eddy currents, and causes power losses
but could this effect will also cause increasing the frequency of the secondary voltage ?

Most power transformer core's are an alloy of Iron and Silicon that has been cold rolled, they're referred to as a "CRGOS" core (Cold Rolled Grain Oriented Silicon Steel). The main goal behind all that is to rid the transformer core of Hysteresis losses: The cold rolling orients the grain of the ferromagnetic material so that hysteresis is kept at a minimum; the addition of silicon was found to also decrease the hysteresis and create a highly permeable material, cutting down on magnetization losses. I've never heard it referred to as "soft iron," but I suppose it could be.

Laminations in the core eliminate much of the eddy currents, but there will always be some present. I view eddy currents as currents that don't really have a rhyme or reason, they're simply a byproduct of losing something from a more useful attribute; they would not add to the voltage of the secondary in any appreciable way.

 

[IWantToLearn]

What about the frequency of the secondary voltage?
it will increase?

 

[EverGreen1231]

What about the frequency of the secondary voltage?
it will increase?

No. In large scale power systems load currents can cause frequency to fall, but this is due to generator operation and not transformer characteristics.