Method of Calculation of Transient Skin-Effect in Conductors Embedded in Slots for Cage Windings

Skin- effect has a marked influece on the steady-state performance of electrical machines. In order to study the phenomenon of skin-effect during transients, the general partiaf differential equation of the vector potential is developed on the basis of two-dimensional analysis. Numerical techniques for solving the field equations obtained from two-and single-dimensional analyses are presented. With the consideration of single-dimensional analysis, a transient analytical solution is derived for the case of a sinusoidal total current applied to a rectangular bar embedded in a slot. The two specific cases of a step total current and a sinusoidal total current applied to a rectangular bar are considered to investigate the skin-effect during transients. The excellent agreement between numerical and analytical results verifies the correctness of the two-dimensional analysis and the accuracy of the numerical techniques presented in the paper. The results show the skin-effect during transients and the need for its incorporation in the transient analysis of electrical machines.