THE TRANSFORMER 



287 



gives approximately the same weight of copper for both 

 coils. 



Transformers designed with this ratio, however, will 

 get hotter in the high-voltage coil than in the low-voltage 

 coil because, owing to the greater thickness of insulation 

 around the high-voltage coil, it is more difficult for the heat 

 to escape from the copper. In practice, therefore, a some- 

 what greater weight of copper is used in the high-voltage 

 winding than in the low-voltage. 



0/ Over 



FIG. 179. Plan of General Electric Type H Transformer, Showing 

 how the Oil May Circulate around and between the Coils. 



Insulation of Windings. The insulation of the windings 

 of a transformer must be very carefully looked after because 

 of the high voltages to which a transformer is subjected. 

 The high-voltage coil must be insulated not only from the 

 low-voltage coil, but also from the core; a breakdown 

 in the insulation in either of these places would connect 

 to the high-voltage line a part of the transformer on which 

 the operator supposes there is either a low voltage or none 

 at all and he would probably receive a fatal shock in work- 

 ing around the transformer. Or a customer touching 

 what he supposes to be a low-voltage line might receive 



