i have been carefully studying controll techniques used to control the speed of wound rotor induction motors. mostly this motors are controlled by inserting external resistance via the slip rings.But since losses are directly proportional to the square of the current times the resistance. i was thinking if its possible to conttrol the this motor by using switching capacitance connected through slip rings.

Kind regards
Elvis

I would not recommend it. The effects of adding capacitance will not be the same as the effects of adding resistance. Further depending on your selection of capacitance you might create a resonant circuit in the rotor resulting in very low impedance (high current flow) which can overheat the rotor.

Off the top of my head, I can't come up with a math description of what would be expected response with varying capacitance. If it were a good idea, I suspect someone would have done it a long time ago.