284 ALTERNATING CURRENTS 



advantage that the direction of rotation is easily reversed, by a simple 

 reversal of the connections of one of the stator windings. In order 

 to reverse the simple form of repulsion motor, it becomes necessary 



FIG. 176. Connections of Atkinson's Motor. 



to rock the brushes to the other side of the line OF of the impressed 

 field (Fig. 170). 



A variety of Atkinson's motor is one in which only the transformer 

 winding TW is connected across the mains, the exciting winding EW 

 being across the brushes. The exciting winding then forms a load 

 for the armature winding, regarded as the secondary of a transformer, 

 of which TW is the primary. 



169. Mixed=action Commutator Motors 



The single-phase commutator motors which we have so far con- 

 sidered are chiefly of interest in connection with railway work ; they 

 are variable-speed traction motors. For stationary work requiring 

 approximately constant speed, the simple single-phase induction 

 motor is capable of giving good results. The inherent weakness of 

 this motor is its poor starting torque. Now, the repulsion motor is 

 capable of exerting a powerful torque. If the good starting qualities 

 of the repulsion type of motor could be combined with the satisfactory 

 running qualities of the induction type, a motor would be obtained 

 satisfactory from every point of view. Several forms of such com- 

 pound or mixed-action commutator motors have been devised. 



In the Wagner motor,* the rotor is provided with an ordinary con- 

 tinuous-current winding having a commutator, and at starting the 



* The Electrician, vol. li. p. 743 (1903). 



