76 



POWER AND POWER-FACTOR. 



Instructions. Connect in series an inductive and a non- 

 inductive resistance, ammeter, the series coil of a watt- 

 meter and switch. Connect a voltmeter and the shunt 

 coil of the wattmeter across the two resistances, so as to 

 read the total voltage of the circuit. 



Take readings on the ammeter, voltmeter, and watt- 

 meter for several values of the resistances. 



For each set of readings determine graphically the 

 idle and energy current and angle of lag as described 

 below, and tabulate the results as shown in the following 

 table: 



Determination of Idle and Energy Currents. 



To separate the idle and energy currents, proceed as 

 follows : 



Draw a horizontal line OC (see Fig. 36) to represent the 

 total current of the circuit to a scale of amperes. Describe 

 a semi-circle on C as diameter. Determine the value of 

 the energy current by dividing the measured watts by 

 the voltage, and describe a circle with centre C and radius 

 equal to the energy current on the scale of amperes, 



SCALE: or 

 PIG. 36 DIAGRAM OF CURRENTS. 



