The exploitation of the squirrel-cage induction motors (SCIM) is impedingly accompanied by the emersion of the transient processes that critically impact on the condition and operation of electrical machines. The high powered induction motors with the squirrel-cage rotor have the powerful starting current and rotation torque, therefore, their starting regime exercises a significant influence on the electrical power system regime. The rotor’s parameters are very essential when analysing the transient processes in the induction motors. The rotor’s resistance defines the starting current and the rotation torque of the induction motor. During the start-up the resistance and the inductance of the rotor change under the current’s displacement effect. The current paper is dedicated to the research of the direct start-up of the SCIM with due account for of the current’s displacement in the rotor’s slots. The paper displays the equivalent circuit of rotor bar and the calculations of its resistance and inductance that change under the skin effect for free form slots. Moreover, the paper presents the calculation and the comparison of the dynamic characteristics of the SCIM with the constant and variable parameters of the rotor.