THK BEATING OF TRANSFORMERS 



141 



11 in Fig. 83 temperature curves for a 10-kva 50-cycle 

 2000 : 210-volt single-phase oil-immersed transformer which 

 was test, d ut full load in two different sizes of case. The 

 ivlutive sizes of the two cases are shown in Fig. 84. The 

 heating .iata for these two tests are as follows : 



From these figures it is seen that for this particular trans- 

 former (or these particular tests) the temperature rise was 



halved hy increasing the radiating surface by tin per cent. The 

 specific temperature rise is 13 and 11 respectively, the higher 

 li'jmv relating to the higher temperature. The results mu-t 

 be taken as liable to quantitative error, hut as strongly con- 

 tinuing the correctness of the principle. 



In the above tests the temperature was thermmnctrically 

 determined ;it a point near the top just below tin- surface of 

 the nil. The temperature at such a point is usually the 

 maximum which occurs in an oil-immersed transformer. 

 Indeed the temperat ure at all points in the oil above the top of 

 the core is usually quite uniform. The tempeiatme at other 

 the transformer usually varies greatly and is a 

 minimum at tin- bottom of the case. 



Fig. 85 shows t I. mperatmv curves for the same 



10-kva single phase nil-immersed transformer, hut loaded to only 



:ions of the time thermometers Tl. I _ and 



PS, sho\\n in Iiif. si. These curves show dearly the 



temp, Tallin- di^l rihut i. >n and also the rate at which the 



temperature increase^ at diuVn-nt prl , 'I 1 . at the top of 



the , nd then rate 



