T1IK HKATIXG OF TRANSFORMERS 



alter the j>eriod corresponding to the term of full load. In this instance 



the t-t l.u'l should not bo applied until tin- transformer has been in 



it for a sufficient time to attain the temperature-elevation due to 



Lots, Wi'h : i-.;!. -formers for commercial lighting,' the duration of 



the full- may be taken as three hours, unless otherwise 



-}><; 



If it is deriniti-lfi known that a transformer, while in circuit 

 continuously, will only be loaded lor short periods and that 

 tli >( periods will In- followed hy considerable intervals of no 

 load or of only small loads, then obviously it is not appropriate 

 to provide a transformer capable of dealing with the maximum 

 load for the entire twenty-four hours. On the contrary, the 

 results will be obtained by employing a transformer which 

 will jxrt'onn tl rinir<'l tcrvici without ever exceeding a 



liable temperature-rise, say 40. But commendable 

 rll'orts t<> provide the most suitable transformer should not 

 be confused with the inelination of some manufacturers of ba si ng 

 their designs on the assumption that their transformers will, 

 in a very large percentage of instances, never be called upon to 

 (Miry the rated load for periods of more than a very few hours 

 each. TheM- firms may designate as of 20 kw rated capacity 

 a transformer which will be decidedly smaller than another 

 firm's standard-rated transformer and consequently having a 

 \crv much smaller core-loss, and in the few instances in which 

 there are complaints, these firm* are well able to afford to 

 ivplurr their misleadinL'ly-rated trail-former by a very liberal 

 transformer. It is not for the manufacturer, but f<>r the 

 purchaser or his adviser to decide whether a certain trans- 

 form, r will sutlice for some particular conditions of service. 

 NYheii the manufacturer represent- hi> ti-an>form-r al being 

 of 20 kw capacity lie is undertaking (unless it is oilier 



:cssly specified i that the trail-former \\ill can \ -JO kw con- 

 tinu-'Usly without exceeding a temperat mv rise of 10 or 45 



(according to the stipulation! above the room temperature, The 



purchaser may analyse the condition, and himself that 



according to the amount and duration of the peak lot 



