2-A] 



SPEED CHARACTERISTICS. 



33 



(The possible method of control by brush-shifting, 8, is not 

 used.) 



(2) Speed control by varying reluctance is obtained in certain 

 shunt motors by varying the air-gap. 



A limit to speed control by a variation in flux (by varying 

 either excitation or reluctance) is reached on account of arma- 

 ture reactions; a considerable reduction in flux causes bad com- 

 mutation. For varying the speed through a wide range, there- 

 fore, these methods can only be used if the effects of armature 

 reactions are overcome. 



This Was first SatisfaC- Constant Potential Supply 



torily accomplished by the 

 compensated winding of 

 Prof. H. J. Ryan, which 

 was placed in slots in the 

 pole faces. This compensa- 

 tion is now generally ac- 

 complished by the more 

 easily constructed inter- 

 poles or commutating poles 

 of the inter pole motor. /^^X" 8HUNT nFLD /^~N 



' fj HTnrowffip / A \ 



o 



STARTING BOX 



FIG. i. Connections for operating a 

 shunt motor. 



PART II. OPERATION. 

 ii. Shunt Motor. If 



the motor is compound, cut 

 the series coil out of the 

 circuit. Connect the sup- 

 ply lines to the main terminals of the motor and complete the 

 connections, as in Fig. i. Note the queries, 15. 



To start the motor, have all the starting box resistance in cir- 

 cuit and all the field rheostat out of circuit ; make sure that the 

 field circuit is complete. The circuits should be so arranged 

 that closing the supply circuit will excite the field (which takes 

 4 



