21 THE DESIGN OF STATIC TRANSFORMERS 



electrical design has been shown by A. P. M. Fleming and 

 Faye-Hansen l in a paper recently read before the Institution 

 of Electrical Engineers. 



ILLUSTRATIVE EXAMPLE IN TRANSFORMER DESIGN. 



For the purpose of explaining designing principles I propose 

 to make calculations for a single-phase 50-cycle transformer of 

 the rectangular-core type for a rated output of 20 kilovolt- 

 amperes. I shall work out the design for a primary pressure of 

 5000 volts and for a secondary pressure of 200 volts. Let it be 

 required that the regulation at full load shall be within 2,0 per 

 cent. The transformer is to be designed for use on circuits having 

 a periodicity of 50 cycles per second, and supplies a load con- 

 sisting exclusively of incandescent lamps. Consequently the 

 power factor of the load is 1,00, and the output of the trans- 

 former is in this instance not only 20 kilovoltamperes, but also 

 20 kw. Let us denote the power factor by G. Thus we have 

 G = 1,00. When the nature of the load to be put on the trans- 

 former is not stated or known, it is safer, in order to prevent mis- 

 understanding between the customer and the manufacturer, to 

 rate the transformer in kilovoltamperes. If, however, it were 

 known that the power factor would be, say, 0,80 and the output 

 20 kw., then the transformer must be designed for a current 



corresponding to an output of (^ ~ =) 25 kilovoltamperes. 



MJjbO / 



From the curves in Fig. 7 a rough preliminary estimate of 

 the full-load efficiency for the transformer to be calculated, 

 may be obtained. These curves may in a general way be taken 

 as representative for all types of single-phase oil-cooled trans- 

 formers up to the outputs shown, whether of the shell type or 

 of the core type, and, in fact, no error of consequence will be 



1 " Transformers : Some Theoretical and Practical Considerations," A. P. M. 

 Fleming and K. M. Faye-Hansen, Jour.I.E.E., Vol. XLII., p. 373. 



