Bar Diagnostics of Double Cage or Deep Bar Rotor of an Induction Motor

Abstract

The mathematical model of a deep bar or double cage rotor of an induction motor is developed, the differential equations for which are written with respect to flux linkages in stator and rotor phase coordinates with the phase number in starting and working rotor windings equal to the number of short-circuited bars. Using measurement data from stator phase voltages and currents simulation as well as online calculations of the torque and power consumed, the most informative parameter for short-circuited rotor bars diagnostics, defined as a product of inverse stator reactive power and its time derivative, is obtained. The excess of this parameter over the inverse reactive power derivative is the criterion for the damage to rotor bars. To eliminate the influence of asymmetry in stator circuit the inverse reactive power of positive phase sequence is used. The results of detecting damage to one or more bars in rotor windings using the developed algorithm are presented. The algorithm adequacy is confirmed by simulation results and the experimental study of a phase-wound induction motor, in which different values of phase resistances have been set.