THE INDUCTION MOTOR 277 



primary flux does not link the secondary so that the induced 

 olectromotivo force in the secondary is zero. As the mutual 

 inductance of the windings is zero under these conditions, the 

 secondary acts like a choke-coil of very high impedance. To 

 prevent this, a short-circuited tertiary winding is placed on the 

 stator. This acts like a short-circuited transformer secondary, 

 and therefore reduces the inductance of the regulator secondary 

 to a very small amount. The primary winding is shunted across 

 the line as shown in Fig. 254 (6) and the secondary is connected 

 in series with the lino (compare with Fig. 200, Chap. VII, page 

 210). When the secondary is in the plane of the primary in one 



_ 



Primary Co bit 



"ij. General Electric 2,300-vnlt, (i()-cyclr. feeder volta^' regulator, 

 disassembled. 



pOtttion, it- induced electromotive force is a maximum and it is 



connected to act as a booster. When the secondary is turned 

 180 degrees from this position, its electromotive force i- also a 

 maximum, but it now bucks the line voltage. Any value of 

 voltage between that corresponding to these two positions i> 

 obtainable by varying the portion of the secondary. 



The secondary is turned by a small motor, controlled by relays, 



_'.",.. Tin- relays are actuated by a contact-making volt- 



If the volume i.. too lii:h. one set of contacts causes the 



motor to turn in such a direction as to make the secondary 



reduce the lim- voltage. If th- e is too low. another set of 



cont- i i he motor to reverse its direction and the second- 



