Reduction of the starting losses of the wound rotor induction machine

Wound rotor induction motors are used in heavy duty drives in the range of hundreds kW, like cement and minerals industries. Important users make use of hundred of such drives, summing hundreds of MW. Despite their technical capabilities to easily operate at variable speed, the large amount of losses which occur at low speeds determine the users to use the facility given by the wound rotor only for starting. Even so, the losses specific to the additional rotor resistors are quite important, given the range of power. The paper discusses the existing technologies involved in the variable speed drives based on wound rotor induction machines and proposes a technique for starting which avoids the use of additional rotor resistors and consequently it eliminates the corresponding losses. The simulations confirm the viability of the technique.