310 



THE POLYPHASE CIRCUIT. 



Enter the results of the readings thus : 

 DETERMINATION OF POWEH-FACTOR IN S-PHAKE CIRCUIT. 



Measurement in Unbalanced Circuit with Two Wattmeters. 

 Two wattmeters connected as shown in Fig. 156 suffice 

 to measure the power in an unbalanced 3-phase system. 

 The sum of the readings of the two instruments is equal 

 to the total power transmitted. Sometimes the two 

 volt coils are mounted on a single spindle, and the two 

 current coils act on their respective volt coils in a single 

 instrument. In this way the deflection of the needle is 

 the sum of the deflections due to each pair of coils, and 

 the instrument then reads the total watts of the circuit 

 directly. 



The proof that the sum of the readings of wattmeters 

 W l and PT 2 in Fig. 156 gives the true watts of the 

 circuit may be stated as follows. 



Referring to Fig. 156, it is desired to measure the 

 power delivered to the three branch circuits, a, 6, and c. 



C 



- c 



FIG. 156. MEASUREMENT OF POWER IN AN UNBALANCED CIRCUIT. 



