THREE-PHASE CURRENT MOTOR. 



The Starting Resistance. 89. In order to calculate the resistance 

 of the starting box, it is advisable to plot a curve representing the 

 torque, the amperes and the volts in the armature as a function 

 of the resistance of the starting box.* This can easily be done if we 

 remember that at starting the energy available at the shaft of the 

 motor, when running with the same torque, must be dissipated into 

 heat. We find, therefore, the starting resistance necessary to enable 



300 



600 



OHMS PB PHASE. 

 FIG. 26. 



the same torque to be generated in the motor, by dividing the output 

 by the square of the armature current. In this way the curve for the 

 torque, in Fig. 26, has been drawn. From this curve we can find the 

 starting current, the torque, and the voltage at the slide rings of the 

 armature. The latter is considerable at a small starting torque, and 

 the armature conductors must, therefore, be carefully insulated. 



This method was first recommended by Dr. Behn-Eschenburg, Oerlikon. 



Si 



