The goerges phenomenon: Induction motors with unbalanced rotor impedances

THE INDUCTION motor with unbalanced rotor resistances was first studied by Hans Goerges more than 50 years ago.1 Early investigations were concerned with one particular phase of the problem: the single-phase rotor. It was found that the wound-rotor motor with one rotor phase opened could be operated stably near half-speed, either as motor or generator. A singular feature noted by Goerges was that the efficiency of the motor with single-phase rotor was much higher than that of the balanced motor operated at the same speed with external resistances. Subsequent study of the problem has been motivated by the need for a simple method of speed control. Rotor unbalance has had to be considered in the application of resistance controllers for speed variation and starting, because this equipment usually is unbalanced at many of the stepped positions.