CHAPTER VIII 



THE HEATING OF TRANSFORMERS 



the efficiencies of static transformers are generally 

 high ami the losses consequently small, nevertheless, owin.u 

 to the absence of any ventilating effects from moving parts, the 

 proM.-m of limiting the temperature rise is one of considerable 

 difficulty. The difficulties encountered are greater the greater 

 the rated capacity of the transformer. In the early days when 

 th. d.mand for transformers was confined to small sizes, the 

 pr. >ldem of limiting the temperature rise would hardly have 

 arisen except for the fart that the material employed for the 

 magnetic circuit was at that time very poor and the losses in 

 it were high. If the active material in a transformer only 

 amounts to some two or three KILOGRAMS, the surface per 

 kilogram of material will, with ordinary forms, be far greater 

 than in u transformer containing two or three TONS of active 

 mat. iiieiitly while in the former size it suffices 



that tin transformer n.-.-d simply be surrounded by air, and 

 will he maintained cool by natural processes of heat emission, 

 it becomes necessary in th. latt.-r case to resort to additional 



IDS, such as immersing the transformer in a tank of oil and 

 abstracting the heat in>m the oil and its contents by the 

 eureolatioD of water through pipes immersed in the oil. 



In Pig. 72 is shown a design for an air-cool, d transformer 

 in winch thr million >!' IP at !r-m the active material is very 

 cialdy increased by the various ways in which additional 

 surface is provided. 'I'll.- windings are sub-divided into a 

 numher <.f small r..iU, and cooling ribs of sheet copper aliout 

 0,5 mm. thick are arranged betwe nt coils. It will In- 



seen .< core is also of such a shape as to have a large 



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