476 



ELECTRICAL MEASUREMENTS 



is closed a magnetomotive force proportional to and in phase with 

 7 2 is introduced. The leakage flux <t> L2 will be in time phase with 

 and substantially proportional to / 2 ; likewise the leakage flux 

 <i>Li will be in time phase and substantially proportional to /i. 

 The mutual flux $ M is proportional to and in phase with I , Io 

 being the vector sum of I\ and 7 2 as in any transformer. $1 is 

 the vector sum of <b M and <>LI, and < 2 is the vector sum of $ M 

 and 4>L2. Eij the induced voltage in the primary, will obviously 

 be 90 ahead of $1. By the proper adjustment of 7 2 , $ L 2 may be 



Secondary Closed 

 FIG. 272 A. Diagram for lag adjustment of induction watt-hour meter. 



made of such magnitude that <f> 2 , the total flux cutting the disc, 

 is swung clockwise so that angle A is made 90. In order to make 

 the adjustment, one must have at command a source of sinu- 

 soidal current which has the voltage and frequency for which the 

 meter was designed and from which loads can be taken at unity 

 power factor and some lower power factor, 0.5, or thereabouts. 

 One must also know whether the power factor is due to a lagging 

 or a leading current. 



The meter is set up and adjusted by moving the drag magnets 

 so that it registers correctly at unity power factor. If the 

 registration is correct the constant K, calculated by the formula 



K = 



Pt 



#3,600 



will agree with that stated by the makers. (P is the power, t is 

 the time in seconds required for N revolutions.) The light-load 

 adjustment is now made. 



