ALTEENATORS. 



201 



current attained its maximum value as the centre of the coil 

 passed the centre of a pole, the armature currents would 

 exert a direct strengthening or weakening effect on the main 

 field. In a machine of the usual type, the maximum electro- 

 motive force is induced in a winding when it is situated 

 mid-way between two poles, i.e., when the conductors com- 

 posing the winding are directly under the poles. If the current 

 is in phase with the voltage, the maximum current will neither 

 strengthen nor weaken the field. Before the coil gets to this 

 symmetrical position the current will be smaller in value and 

 will tend to strengthen the pole opposite to the coil. After 

 passing the central position, the current will tend to weaken 

 the next pole to the same extent. The result is, that with 

 the current in phase with the voltage, neither strengthening 

 nor weakening as a whole takes place. The result of a lagging 

 or leading current is discussed later. 



EXPERIMENT XXXV. DETERMINATION or MAGNETISA- 

 TION CURVE OF AN ALTERNATOR AT FULL NON-INDUCTIVE 

 LOAD. 



DIAGRAM OF CONNECTIONS. 



o M/V 



M 2 R 



FIG. 93. 



M t , M., Source of direct current. 



G Alternator armature. 



F Alternator field windings. 



j?j Variable non-inductive load resistance. 



R 2 Field regulating resistance. 



A l Ammeter for measuring load current. 



A 2 Ammeter for measuring exciting current. 



V Voltmeter for measuring alternator voltage. 



S Switch for breaking load circuit. 



Instructions. Connect the alternator field windings to 

 a source of continuous current through an ammeter and 



