Abstract: A slip recovery system for a wound rotor induction motor is disclosed in which first and second inverters, connected in series, are coupled to the rotor of the induction motor. A switch is arranged in parallel with the second of these inverters, the switch being in the open position during starting and stopping of the motor, and being closed to short out the second inverter during normal running conditions. Thus, the first inverter need have only a voltage rating of such magnitude so as to satisfy the expected operating range for the wound rotor, while the second inverter need have only a voltage rating of sufficient magnitude to satisfy the additional capacity requirements for stopping and starting service. Thus, lower rated inverter components may be used with lower initial costs as well as concomitant lower operating costs.

Abstract: This disclosure relates to an electric arc furnace control system for positionally displacing the consumable furnace electrodes. Each electrode is coupled to an electric motor and arranged for vertical height displacement in relation to the material in the furnace. An arc current control signal is derived by comparing the actual arc current with a reference electrode arc current. In addition, a reactive power control signal is also derived by comparison of the (actual reactive power/actual real power) with a desired ratio of (reactive power/real power). The arc current control and the reactive power control signals are algebraically summed to provide an output error signal which is sent to the respective electric motors to provide rectilinear displacement of the electrodes.