THE HEATING OF TRANSFORMERS 1-J7 



rable periods together without any apparent deterioration, 

 and yet transformer experts in America and Germany have found 

 that even so low a temperature as 70 C. rise is detrimental to 

 certain oil-varnish insulations. Mica and compound insula- 

 tions with mica as a basis are very often capable of resisting far 

 higher temperatures than those specified." 



As opposed to tin- above loaning toward permitting high 

 temperatures I would recommend to the reader's attention the 

 following leading article from the Kl>'<-(ri<-al 1\< r/Y/r of August 

 isth, 1905 (Vol. 57, p. 246). I am of opinion that, nowithstand- 

 ing the live years which have elapsed since it was written, tin- 

 article is exceedingly appropriate to the present transformer 

 situation. 



" Th>- />')</ of T> niju-ratnrc mi Insulating Material*: The 



i net-ring Standards Committee recently issued Report 



22 entitled, * Report on the Effect of Temperature on 



Insulating Materials.' The report consists of three section-. 



The first section comprises the investigations carried out by 



Mr. E. H. Rayner, which, as an institution paper (Proceedings. 



tution of Electrical Engineers, Vol. 84, p. 618, March 9th, 



I'.H I.".), has already received consideration in the columns of the 



Priori /,' In the second and the third sections are 



given the results of tests of insulating materials employed in 



the manufacture of dynamo-electric machinery at the works of 



Messrs. Orompton & Co., Ltd., and of Messrs. Siemens Bros. 



& Co., respectively. These la>t two sections contain a mass 



of useful results set forth in a series of carefully-prepared 



tables. In spite of the fact that >tat. ments as to the conditions 



of test are exceedingly mea-jrc, the iv>ulN are very inter, sting. 



MIL! the publication of results, of really exhaustive 



tical tests, made with a full appreciation ,.f the nature 



and ieope \\hich should obtain in such investigat MII-. it is 



believed that the data published in this report will be widely 



consulted, and with advantage to the industry. It i-, however 



remarkable that at so advanced a stage in the develops 



