Direct Start-up of the Squirrel-cage Induction Motor at Variable Parameters of the Rotor

Exploitation of squirrel-cage induction motors (SC IMs) is inevitably accompanied by the appearance of the transient processes that critically impact on the condition and operation of electrical machines. The high-power induction motors with a SC rotor have strong starting current and rotation torque; therefore, their starting condition significantly influences the functioning of a power system. In the work, rotor parameters strongly affecting the IM transient processes were analyzed. In particular, its resistance defines the starting current and rotation torque of IM. During the start-up, the rotor resistance and inductance are changing due to the effect of current displacement. This skin effect in the rotor slots is taken into account in the analysis of SCIM direct start-up. In the paper, comparative analysis is given for the method using the equivalent circuit of rotor bar and that based on the resistance & inductance calculations using Fild’s coefficients for differently shaped slots. Comparison is also given for the dynamic characteristics of different power SCIMs with constant and variable parameters of the rotor. The results confirm advantages of the proposed method of equivalent scheme