INSTRUMENT TRANSFORMERS 58 9 



of the transformer ratios would be found by taking the ratio of the 

 numbers of revolutions made by the two watt-hour meters in the 

 same time. If the power factor were other than unity, the ratio 

 of the revolutions would be affected by an amount dependent on 

 the difference in the phase angles of the transformers. 



Voltage 

 Supply 



Arrangement for Testing Current Transformers 



Uo-Q-Oj 



Aux.Current Supply Meter A 



Meters 



Arrangement for Testing Voltage Transformers 



FIG. 36G. Connections for Agnew method of comparing instrument trans- 

 formers by use of watt-hour meters. 



To eliminate differences in the calibration of the meters two 

 runs are made, the meters being interchanged. 



Let = power factor angle or the phase difference of the current (or 



voltage) in the primary of the transformer and the 



auxiliary voltage (or current) applied to the watt-hour 



meter. 6 is taken + for lagging current. 



m A and ////, = the rates of meters A and B respectively, that is, the 



Watt-hours registered 

 values of the ratio ^ watt . hours - 



K h = watt-hour constant of the meters as marked on the discs. 



