318 ELEMENTS OF ELECTRICAL ENGINEERING. 



stator winding / by transformer action just as if the armature 

 itself were included in the primary circuit. 



The simple series motor is different from the repulsion motor 

 in that the transformer flux T does not exist in the simple series 

 motor, and this transformer flux has an interesting effect on the 

 rotating armature conductors as follows : The armature sections 

 which are short-circuited under the brushes have electromotive 

 forces induced in them by the pulsation of the field flux F ex- 

 actly as in the simple series motor, but these short-circuited sec- 

 tions are cutting the transformer flux T at the time of their 

 short circuit, and the electromotive force due to this cutting is 

 opposed to the electromotive force produced by the pulsation of 

 the field flux F. In fact, the electromotive forces due to cutting 

 of the transformer flux T are equal and opposite to the electro- 

 motive forces due to pulsation of the field flux F at synchronous 

 speed and therefore the repulsion motor has no great tendency to 

 spark at synchronous speed. 



146. Repulsion-motor-starting of the single-phase induction 

 motor. The most valuable feature of the repulsion motor is that 

 it can be easily and quickly converted into a single-phase induc- 

 tion motor by bringing a metal ring into contact with all of its 

 commutator bars, thus converting the armature into what is sub- 

 stantially a squirrel-cage rotor. The single-phase induction 

 motor of the Wagner Electric Company, for example, is started 

 and brought up to speed as a repulsion motor, and then con- 

 verted into a single-phase induction motor. 



A general view of a four-pole Wagner motor is shown in Fig. 



273. The commutator is radial so that the brushes can be lifted 

 off the commutator by a movement parallel to the armature shaft. 

 At starting the brushes (which are connected by short heavy con- 

 ductors) rest against the commutator and short-circuit the arma- 

 ture as above explained, and the machine acts as a repulsion 

 motor. When a certain speed is reached the weights V, Fig. 



274, are thrown outwards by centrifugal action, and the connect- 

 ing rods U push the sleeve / along the shaft, bringing the 



