ACTUAL LOAD TESTS 



43 



field of one machine be reversed, a still further dis- 

 placement of 180 degrees is made. With the connection 

 which gives the nearest value of armature current to 

 that required, a further adjustment may be made by 

 shimming the stator of one or both machines up on 

 one side and taking shims out on the other side. The 

 circuits should then be closed and the heat run made 

 for the specified time. Even with the angles of phase 

 displacement possible with the various combinations 

 of connections and field rheostats it may not be prac- 

 ticable to get the desired armature current. In this 



Fig. 16. Full Load Test on Induction Motors 



case, unbolt the coupling and shift the rotor of one 

 machine around one or more bolt holes. The "cut 

 and try" operations should then be repeated. 



Although the method employed in this test may 

 seem long and tedious, the results obtained are very 

 satisfactory, especially where it is necessary to make 

 an actual full load test. 



The induction generator method is sometimes em- 

 ployed in making full load tests on induction motors. 

 Two similar induction motors are belted together 

 and run in parallel from the same alternator which 

 supplies the losses. (Fig. 16.) In order to get full 

 load on both machines, the diameter of the pulleys 

 must differ by a percentage equal to double the full 

 load per cent slip. 



