Addition of a small per cent of silicon 3% to iron will increase the ________ significantly; by that ________ will be reduced.

Concept:

Losses in a transformer

Iron loss: Losses that are generated in the conducting core laminations by the alternating magnetic field due to hysteresis and eddy currents.         

These losses are constant at all load variations.

Hysteresis loss: When the core of the transformer is applied to an alternating magnetizing force and for each cycle of emf a hysteresis loop is traced out. Power is dissipated in the form of heat known as hysteresis loss.

P_h = K_η B_mⁿf V

Where, P_h = Hysteresis loss (W)

η  = Steinmetz hysteresis coefficient, depending on material (J/m³)

B_m = Maximum flux density (Wb/m²)

n = Steinmetz exponent, ranges from 1.5 to 2.5, depending on material

f = Frequency (Hz)

V = Volume of magnetic material (m³)

Eddy current losses: When an alternating magnetic flux links with a conducting surface, it induces electric currents in this surface as currents can’t go anywhere, but as the potential across the surface is continuously changing, the currents tend to circulate through the surface these are known as eddy currents and heat generated by it is known as eddy current losses.

P_e = K_eB_m² f² t² V

Where, P_e = Eddy current loss (W)

K_e = Coefficient of eddy current.

B_m = Maximum value of flux density (wb/m²)

t = Thickness of lamination  (m)

f = Frequency (Hz)

V = Volume of magnetic material (m³)

Copper losses: Losses that are caused by currents flowing in the primary and secondary windings.

 These losses changes with change in loads.

Hysteresis losses can be minimized by

• Choosing a material with less hysteresis loop area.
• Core stamping

Eddy current losses can be minimized by

• Cores are cut into thin laminated sheets.
• The resistance of the core should be increased, Therefore by adding 3% silicon to the iron core its resistance is increased.
• The laminations are thin with relatively high resistance.