S-C] CIRCLE DIAGRAM. '9 1 



would complete the semi-circle and assume the position P'", the 

 current in this case (E^-^-X) being limited only by the leakage 

 reactance, X. The short-circuit current of a transformer oper- 

 ated at full voltage would be, however, greatly in excess of the 

 carrying capacity of the transformer windings, and, in actual 

 operation, the point P does not go far beyond the full-load point 

 P'. See also Fig. 12, which is more nearly to scale. 



25. Data Necessary. The data necessary are the values of 

 7 , /H and /M, to locate the point A, and the leakage reactance 

 X, to determine the diameter of the semicircle. f 



These data are obtained from the open-circuit / 



and short-circuit tests of Exp. 5-6. 



All quantities are to be in terms of the pri- 

 mary (high-potential) side; thus, in Fig. 2. 

 Exp. 5-B, the values of 7 , /H and /M, meas- 

 ured on the loo-volt coil, are divided by 20 to 

 obtain the corresponding values for the 2,000- 

 volt primary. This gives us : 



A> = -03025 ; /H = .0208 ; /M = .0220. 



The reactance X for the same transformer, is 

 35.2 ohms; see Fig. 7, Exp. 5-6. 



26. Construction of Diagram from Experi- 

 mental Data. From the data given above, lay 



off (Fig. 12) : v 



\ FIG. 12. Con- 



r\n T -DA T s\ A T struction of cir- 



OB = Iu; BA=Iu', OA=I Q . dc diagram. 



The diameter of the circle is E 1 -t-X = 2,000-^-35.2 = 56.8 

 amperes. The radius P = E^ -+- 2 X = 28.4. These values are 

 large compared with 7 = .O3 and full-load current / (2) = i 

 ampere. It is, accordingly, not practicable to construct the 

 whole semicircle, as in Fig. n, which is not at all to scale. 



