DIMENSIONS OF A TRANSFORM!: I; 41 



whirh, in tlu- design -iiMdt -rin-j', is nil. \Vitli natural 



1 transformers the magnetic density must, i 

 --a.se with increase of output, as shown in Table ;3, and this 

 for the reason that the output, and therefore (roughly) the 

 s as the ctihe of the linear dimensions, 

 ivas tin- cooling surface only varies as the square ofth- 

 r dmirii-ions. If, therefore, the same <1< 



, the li. ; uld rith.-r be excessive with the 



large outputs, or needlessly low with tin- small outputs. This 

 : any rat., not to so great an < xtnit) to 

 oil-cooled tran^fornirrs. since the heating is then no loi 

 exclr : ot thf roolin'_: surface of th. m r 



f, but also of the surface of the containing case, and ' the 

 quantity of oil per kilowatt of total lo core density in 



sformers must also decrease with increase of out- 

 although not to so large an iral air- 



cool- . rs. The reason of this will be apparent h.-iu 



.aturr ..f the ;iir-blast cooli '.<-m as discussed in 



i Tabl- '1, we find that for our 20-kw transform 



should employ a CO] . of 11.-" Kih-lin. s | BID. 



y fouml that by Bub in tin- f.rmiihi 



!' = 0,0 111 7 M M, 5000 = 0,0444 X 8100 X T,o x M, th. 



ks out at 37 = 0,7:30 megnline. ( ntly tli. 



Iron n '|uir, d in tin- nnigiietic circuit U 



1 =0,,.^.. 



built up ..f ' a tbi. Kn, v, M| (.:, nun. 



ii b" 



our, thu 

 ! 



then . ces of opinion as 



itnti..n .-f tbi^ insnlati 

 i>v aniM-alin 



