Starting disc rotor for high-output two-pole induction motors

The starting torque of an induction motor is defined by the loss arising in the rotor at standstill. To increase the starting torque, a configuration should be used that results in a surplus loss in the rotor upon starting, but this loss should disappear at operating speed. This requirement has long been met by the double-cage and deep-bar rotors, although their application was accompanied by some compromise. Both rotor types use the rotor slot leakage flux for reaching uneven current distribution, resulting in surplus loss. It is obvious that the depth of the rotor slot should be considerably increased; however, this takes room, and thus the utilizability of the machine decreases. A new solution to this problem is presented. The so-called starting disc rotor is described. This is an electrically conductive disc fixed to a squirrel-cage rotor. At standstill, the rotating field induces eddy currents in the disk, which results in loss and therefore increases the starting torque of the machine. However, there is practically no loss at operational speed.<>