Eddy-current effects in slot-bound conductors

In most electrical machines, current-carrying conductors appear in slots in one or more areas. The highly permeable material into which the slots are formed focuses the magnetic field generated by current flow in the conductors. This focused field increases the resistance and decreases the inductance of the conductors as the frequency of excitation increases. Although this phenomenon has been known for approximately a century and has led to the use of individually insulated stranded conductors (e.g. Litz wire), analytic resistance and inductance expressions for multi-turn, slot-bound conductors have not been reported. These expressions are developed and analysed. It is shown that the slot resistance increases with the square of the slot depth. Experimental results are presented which confirm the trends noted in the expressions developed