166 TREATISE ON ALTERNATING CURRENTS. 



Fig. 67 shows a starting resistance and switch, for use with a 

 tri-phase star- wound rotor. 



Fig. 68 shows a rotor of a British Thomson-Houston polyphase 



FIG. 67. FIG. 68. Rotor with starting resistance. 



induction motor, with a starting resistance inside the spider, and 

 so arranged that it is automatically cut out when speed is got up. 



PERFORMANCES OF INDUCTION MOTOKS. 



113. The following table gives the results of tests made with 

 monophase motors of the Heyland type : 



Brake horse-power 1 3 5 10 20 30 40 50 



Full- ) at 40 cycles per second 1050 1080 1080 1100 750 760 760 575 575 



load 50 1310 1350 1350 13SO 940 950 950 710 710 



speed) 60 1580 1620 1620 1660 1130 1140 1140 860 860 



Number of poles 4 4 4 4 6 6 6 8 8 



Full-load efficiency per cent. . 65 70 75 80 82 85 87 89 90 



Full-load power factor . . . 0'65 0'70 0'73 0'75 0'80 0'82 0'83 0'85 0'85 

 Full-load current in amperes at 



100 volts 9 15 41 62 113 215 310 394 580 



Approximate weight in Ibs. . 145 154 308 440 660 1100200026403500 



Fig. 69 gives the curves showing the results of a test of 

 a 5 B.H.P. Heyland monophase motor; Fig. 70 gives similar 

 curves for a tri-phase motor manufactured by Messrs. Witting 

 Bros. ; while Fig, 71 gives curves relating to a 1/5 B.H.P. mono- 

 phase motor of the Fuller- Wenstrom Electrical Manufacturing 

 Company. 



