24 Proceedings of the Royal Society of Victoria. 



In open-circuit transformers, on account of the great reluctance 

 of their magnetic circuits, the magnetizing ampere turns are 

 necessarily high, and neither of the two conditions stated above 

 are approximately fulfilled unless over a small range near full 

 load. 



If we neglect leakage, or be satisfied with the rough approxi- 

 mation to its eflfects that the present method aflFords for open- 

 circuit transformers, then the theory given — as it is equally valid 

 in other particulars for the two types — will apply with fair 

 approximation to accuracy to the open-circuit type, especially in 

 the neighbourhood of full load. 



There will be considerable difference, however, in the values of 

 the constants and other characteristics of transformers of equal 

 capacity of the two types. 



Let us assume that we have two transformers, one of each 

 type, in which the cores, of the same iron, have the same cross 

 section and volume. Let tj, t^, S, cr, 6 i efer to the closed, and 

 Ti", T.2, 8°, (T°, 0° refer to the open circuit one. Then if they are 

 so wound that when working under similar conditions their 

 resultant fluxes F and F" are equal, 



F 



(a) Since - ~Siimp.{n^Ci + ^i^C^) 



(where o- = 47r permeance of magnetic circuit) their magnetizing 

 ainpere turns will be inversely proportional to the permeances 

 of their magnetic circuits. 



(b) Their iron losses will be equal or 



P2 JP02 



iw— 8inS = |z£^— flSind" (see § 14) 



and as F = F« 



Sin8_8in8» 

 o- "^^ 

 or the sines of the angles of magnetic lag of the tzvo transformers 

 are proportional to the pertneafices of their magnetic circuits. 



Again if the two cores, carrying equal fluxes, have their 

 secondary coils such that the outputs and .secondary voltages are 

 equal, the sections of their secondary wires and the numbers of 

 their secondary turns will be equal, and hence the conductivities 

 of their secondary copper belts will be equal, so that 



