This paper presents the new shape of a rotor bar improving the starting performances in a double-cage induction
motor (IM). The rotor bar of a doble-cage IM is composed of a working bar, neck, and starting bar and
each part has different effects on the characteristics of a motor. In this paper, it is confirmed that a starting bar
has a dominant effect on the starting performances. The shape of a starting bar is designed by using the two
ratios of the depth to width and the lower to upper width, respectively. The starting performances are closely
analyzed by estimating the reactance and resistance of a rotor bar with respect to the depth through multi-layer
method and FEA. Finally, by applying both the ratios to the starting bar, their mutual influence is scrutinized
by using a response surface methodology and three models satisfying both starting torque and current aimed in
this paper is proposed.