INDUCTION MOTORS 



137 



Calculation of Impedance Test on Induction Motors 



Table XVII shows the form used in calculating an 

 impedance test, and Fig. 40 the method of plotting it. 



Torque 



Two methods are used for measuring torque on induc- 

 tion motors, one employing a spring balance and the 

 other a special torque indicator. 



50O 



Fig. 40. Impedance Curve on a 100 H.P., 2080 Volt, 1200 

 R.P.M., 60 Cycle, 3-Phase Induction Motor 



In the first method a wooden brake lever is clamped 

 around the pulley as shown in Fig. 41. The size and 

 length of lever depends on the size of the motor, the 

 length being chosen to give a maximum reading at one- 

 half or two-thirds the capacity of the spring balance 

 used. Let the point of attachment to the lever be at X\ 

 then the length of the lever arm = XY. On the frame of 



