;><MI ELECTRICAL MEASUREMENTS 



(N A )i and (N A )z = number of revolutions made by meter A when connected 



to transformers 1 and 2, respectively. 

 (NB)I and (Nn)-2 = number of revolutions made by meter B when connected 



to transformers 1 and 2, respectively. 



pi and 02 = phase angles of the transformers 1 and 2, respectively, 

 taken + when the current or voltage in the secondary 

 lags the primary current or voltage reversed. 

 Ri and R z ratios of the transformers 1 and 2. 



Suppose that meter A is connected to transformer No. 1, and 

 that the phase of the auxiliary voltage is adjusted so that is 

 large. The watt-hours registered on the meter dials are given 

 by (K h )(N A ) which, when corrected for the rate of the meter, is 



(Kk)(N A ) (' ) As the meter is operated through a trans- 

 former of ratio Ri., this quantity must be multiplied by Ri. 



giving (Kh)(N A )i(Ri) To obtain the true watt hours by 



m A 



. . cos 6 cos 



meter A this result must be multiplied by- - a , = 



cos coa(0-\-p) 



(see page 577). Therefore from meter A, 

 corrected watt-hours = (K h )(N A )i(Ri) 



m A cos (0 

 Similarly for the meter B connected to transformer 2, 



corrected watt-hours = ( 



m B cos pi 



/ 1 \ 

 ' 



m B cos (0 

 cos 1 cos 



A cos . 



and when the meters are interchanged, 



If the test is made at unity power factor, = 0, and since is a 

 small angle, 



= (N B )*(Rjm A (la) 



= (N B ) 1 (R l )m A (2a) 



Si fi 



s~.~\i 



To determine the difference of the phase angles of the trans- 

 formers, a test is made at low power factor. 



