Till-: IMH'CTIOX MOTOR 253 



to thoir corresponding lines, Fig. 239 (c), and at the same time 

 the compensator is entirely disconnected from the line. One 

 advantage of this type of starter is that it can be readily used 

 on two-phase as well as on three-phase circuits. 



Practically all starting compensators have a no-voltage release 

 as indicated in Fig. 238. When the line voltage decreases to a 

 low value, a solenoid plunger drops, releasing the starting handle 

 which springs hack to the "off" position. 



107. The Wound-rotor Induction Motor. If resistance be 

 int induced in the rotor circuit of an induction motor, the slip for 

 any given value of torque will increase. 



i ven value of torque requires a definite value of flux and a 

 definite value of current. The flux of the induction motor is 

 practically constant, since the back emf. is practically constant. 

 If resistance be introduced in the rotor circuit, the rotor impe- 

 dance is increased. (At slips which give the ordinary values of 

 torque, the armature reactance is small as compared with its 

 a nee, hence the armature impedance is practically all 

 ance.) If the slip remains constant, the induced emf. of 

 the rotor does not change. The armature current, which is 

 equal to thi< emf. divided by the rotor impedance, decreases. 

 The torque therefore decreases. 



To bring the torque back to its original value, the armature 

 current must be increased. To increase the armature current, 

 the armature induced emf. must increase. Since the flux is 

 constant, the increase in the induced emf. may be obtained only 

 by this tlux cutting the rotor conductors at a greater rate. 

 for a given value of torque, the slip must increase 

 when resistance is introduced in the rotor circuit. 



The slip-torque curve will he changed from curve (1) to curve 

 _'!(). It will be noted that full-load torque is obtained 

 at increased values of slip as the rotor i increased. 



The value of the maximum or break-down torque will not be 

 affected, but the point of maximum torque mvcs toward the 

 point of d. ( 1.0.) That is. the maximum torque 



occur- at \ -alue .it 'slip. The rotor now runs at reduced 



. but the reduced ^]H; <\ fa obtained at the e\pcM>e of rtll- 



ciencv. for I he rotor / /.' ' ised. 



- evident th. brol may be obtained by the intro- 



