Can someone tell me how the soft iron core can be responsible for execssive heating??

And how the heating can be reduced??

 

in a transformer heating occurs due to the formation of "eddy currents".
eddy currents are induced in a bulk mass of metal when the magnetic flux through it continously varies.
eddy currents are induced currents and obey both faraday's laws and lenz's law of electromagnetic induction.

eddy currents are called so because their direction of motion in the bulk metal is circular-`like eddies on the surface on water`

generation of eddy currents in a core hence results in a loss of energy with appears in the form of heat-useless energy in a transformer
eddy currents can be reduced by laminating the soft iron core. soft iron sheets in the form of "I" & "E" shaped laminates are laminated so as to increase resistance and decrease currents.
other techiques for reducing eddy currents are cutting tracks in the bulk metal making so as to make the current folow a longer path and hence increase net resistance.

 

hi,

here's some additional input on heat generation by a power transformer.

we all know that a transfo works on the basic principle of magnetic coupling, that is the transfer of energy from the primary side to the secondary side and vice versa.

an ideal transfo does not impose load on the supply unless there is load on the secondary side. these power transfo are usually rated in Volt-Ampere (VA). so if you connect a reactive load it would dissipate no power but you still have the voltage and the current. what is important is the result of real voltage and current thereby the transfo gets hot or warm due to internal losses regardless pf the power.

as to eliminating heat, there's nothing you can do about that but rather you can only minimize the heat generated. heat generation is cause by magnetizing loss which is the current that is needed to maintain the design value of magnetic flux in the transfo core. likewise losses is dependent on the size of the core and the design of the transfo.

another aspect about losses is that bigger transformer have higher magnetizing loss than small ones. how ever the big ones are not affected so much by this due to its large surface area thereby allowing it to remain cool w/no load small ones incur more losses per VA, that's why they run hotter that big ones.

another contributing factor on heat generation is copper loss. when you have a high iron loss, copper loss is reduced resulting to improved regulation. but if the iron loss is set too high the transfor will overheat even without a load connected.

this is just an overview of transfo heat generation.