THE INDUCTION MOTOR. 411 



When the motor is overloaded until it stops, the 

 slip becomes equal to 1, and under these conditions the 

 output of the motor is nil, and the line N P must become 

 a point on the line a b. The line B will then be in 

 a position B 1 such that the line B 1 A is a tangent to 

 the output semi-circle A N F, and B 1 A f is consequently 

 a right angle (see Fig. 198). 



Draw from B 1 a line B 1 T perpendicular to A f\ 

 which is the radius of the circle A H F, T being its inter- 

 section with A 0, and so obtain the line V T. This line 

 will be proportional to the slip, because angle B 1 T A = 

 angle A H F, and consequently in the similar triangles 

 AHF, ATV 



H F V T 

 blip cc oc r-jp , or since A T is constant 



slip oc FT. 



The various quantities represented by the diagram 

 may be summarised as follows : 



Phase of terminal pressure by line O E. 



No-load magnetising current by line O F. 



Stator current by line O B. 



Power factor by cos <P which is a maximum when 



O B is a tangent to the semi-circle A B F. 

 No-load current by the line K. 

 No-load power factor cos <P". 

 Energy component of no-load current by F K. 

 Rotor current proportional to F B. 

 Input of ^ motor (C^xE x 1.73 x cos <P) directly pro- 

 portional to B G. 



Torque of motor by line H L, maximum torque which 

 motor can exert before pulling up being represented 

 by eg. 

 Output of motor proportional to N P, the maximum 



output being represented by e h. 



Percentage slip of motor by line V T, line B 1 T repre- 

 sents 100 per cent, slip, in position shown Fig. 198. 

 Starting torque proportional to line H 1 L l in Fig. 198, 

 the corresponding starting current being the line 

 O B 1 and the power factor at starting cos -0 1 . 

 EXPERIMENT LIII. EXPERIMENTAL DERIVATION OF 

 HEYLAND DIAGRAM FOR AN INDUCTION MOTOR. 

 (a) Run the motor without load with current of 

 normal voltage and frequency. Measure the current 



