502 



ELECTRICAL MEASUREMENTS 



control arrangement. Machine A energizes the potential coils 

 of the meters while machine B supplies the current coils; B is 

 either of low voltage and large current capacity or else works 

 through a step-down transformer. Both machines should give 

 sinusoidal waves, for the operation of induction meters, especially 



Phase Shifting . 

 Transformer TraU8 ? ormeu 



PhaseLJ ~U~Pressu re 



Regulating Rheostat 

 or Choking Coila 

 It 



3 Phasef 



Transformers 



Current 

 Transformers 



FIG. 289. Drysdale phase-shifting transformer. 



at low power factors, is greatly influenced by wave form. To 

 obtain good wave forms, specially designed three-phase machines 

 with Y-connected armatures are necessary. 



A much simpler and less expensive device for accomplishing 



