INSTRUMENT TRANSFORMERS f,9l 



Using the relation 



cos _ i 



cos (0 + |8) ~ cos (1 - tan 6 tan 0) 



and remembering that is a small angle whose cosine is very 

 nearly unity, 1 and 2 give 



(N A )t(N B )? /Rz\ 2 = 1 - 2 tan 8 tan 2 _ 

 (N A ) 1 (N B )i \Ri) ~~ 1 - 2 tan tan fa ~ 



1 + 2 tan 6 (tan ft - tan fa) approximately. 

 tin 8 - tin fl * h WO (#*) /# 2 \ 2 1 



^rsffit 1 -(ra^y J- 



Rotary standard watt-hour meters are convenient for making the 

 tests, for the revolutions may be accurately read from the dials. 



References 

 



1. "Electrical Measurements on Circuits Requiring Current and Potential 

 Transformers," L. T. ROBINSON, Trans. American Institute Electrical Engi- 

 nt'ir*, vol. 28, 1909, p. 1005. 



2. "The Testing of Instrument Transformers," P. G. AGNEW and F. B. 

 HILSBEE, Trans. American Institute Electrical Engineers, vol. 31, 1912, p. 

 1635. 



3. "Potential Transformer Testing," J. R. CRAIGHEAD, Trans. American 

 Institute Electrical Engineers, vol. 31, 1912, p. 1627. 



4. "The Phase Angle of Current Transformers," CHESTER L. DAWER, 

 Trans. American Institute Electrical Engineers, vol. 34, 1915, p. 1585. 



5. "The Calibration of Current Transformers by Means of Mutual Induc- 

 tances," CHARLES FORTESCUE, Trans. American Institute Electrical Engi- 

 neers, vol. 34, 1915, p. 1599. 



6. "The Determination of the Constants of Instrument Transformers," 

 P. G. AGNEW and T. T. FITCH, Bulletin Bureau of Standards, vol. 6, 1909, 

 p. 281, Scientific Paper No. 130. 



7. "The Determination of the Ratio of Transformation and of the Phase 

 Relations in Transformers," E. B. ROSA and M. G.LLOYD, Bulletin Bureau of 

 Standards, vol. 6, 1909, p. 1. 



8. "On the Use of Mutual Inductometers," A. CAMPBELL, Proc. Physical 

 Society of London, vol. 22, 1910, p. 207. 



9. "Determination of the Constants of Instrument Transformers," F. A. 

 LAWS, Electrical World, vol. 55, 1910, p. 223. 



10. "Some Recent Developments in Exact Alternating-current Measure- 

 MM-nts," C. H. SHARP and W. W. CRAWFORD, Trans. American Institute 

 Klrcirn-nl Engineers, vol. 29, 1910, p. 1517. 



11. "A Watt-hour Moter Method of Testing Instrument Transformers," 



