In transformer core,etc the eddy current path is assumed to be purely resistive in nature, but there must be some inductance due to self linkage of the eddy current generated flux with the core itself.The value of this inductance must be very less .Thats why purely resistive eddy current path is assumed.My question is why this inductance is very less?
The eddy current is not purely resistive.
To check if the eddy current is resistive, you should calculate the skin depth (due to the skin effect) of the material subject to eddy current. (look up on the Internet about skin effect.)
I did this for electrical steel, and then I come at a skin depth of 4.2 mm. Its the inductive contribution of the eddy current that causes the skin effect. As electrical steel is usually laminated in thickness of about 0.3 mm, and this is way less than twice the skin depth, you can see that indeed for an electrical machine, neglecting the inductive part is acceptable.
This method is only an approximation, as the (resistive) eddy current distribution is different from the (resistive) current flowing in a conductor wherefor the skin effect is calculated. However, I am quite sure that if you want to calculate eddy current crowding due to inductive part (skin effect), you need to use same calculation techniques that are used for skin effect.
Of course the eddy current is not purely resistive, as has been pointed out, the eddy current flux couples with the original flux. Placing a coil next to a conductive non-permeable plate will reduce the apparent coil inductance. As the frequency is increased, Re(Z) scales as sqrt(frequency) while Im(Z) scales as frequency. As frequency is increased, the inductive part becomes more and more important compared to resistive part. A permeable plate changes the numbers, but not the physics. So the question really comes down to numbers: what is your frequency, what is your geometry, and what are your materials?
Eddy current is a loss in the core losses estimated assuming that the operating frequency is constant.So it is for the purpose of calculation ,directly proportional to leakage of flux in turn converted to heat.as the loss is directly proportional to eddy current it is assumed as resistive.
Dear Tauseef,
Although there are four factors which are very important and change quite a lot the expression of the skin effect respect to eddy currents : type of material (mainly, ferromagnetic and good or bad metal), geometrical shape, thickness and frequency. Your question can be simplified in one idea. As the skin effect increases (due to different factors), the current density decreases at the bulk of the conductor and it reaches a minimum at the center of the conductor (almost zero if the frequency is very high).
Thus this effect is equivalent to a reduction of the cross-section area of the conductor and, therefore the effective resistance (no resistivity) of the conductor is increased with respect the inductive effects due to the change of the magnetic field, as can be calculated easily.
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