Computer calculations of pulsatory torques of three-phase induction motors for diagostics purposes

The paper deals with the problems of the mathematical modelling of the damaged three-phase induction motors. Analysis of internal asymmetries of the induction machine comprises the internal short-circuit, lack or inversion of a winding part and break in the parallel path of the winding. As a result of failures, pulsatory electromagnetic torques appear. At a defect in the stator winding, they have the double frequency in relation to the frequency of the supply network however for the damage in the rotor the frequency of the additional pulsatory torques is equal to double network frequency multiplied by the rotor slip. Existence of the pulsating torques can be treated as a diagnostic signal informing about appearance of the winding failures. This method can realize non-invasive diagnostics of induction motors. Calculations for the cases of internal asymmetries are simplified within the new modelling method by assumption of the equivalent structure of the damage induction machine with two parts: the symmetrical three-phase machine connected with additional electrical circuit.