TRANSFORMER CASES AND TAN 151 



be borne entirely by bolts or massive lifting-hooks. If the eye- 

 bolts or lifting-hooks are not suitably located, then considerable 

 injury may result when lifting, due to buckling of the sides. 

 The >ide^ may be strengthened by providing a light angle-iron 

 framework, placed either inside or outside, and it should be 

 arranged that the weight of the transformer, when lifted, shall 

 come directly on this framework. In some methods of handling 

 tin Wright, the eyebolts are made an integral part of long bolts 

 which extend from the base of the transformer. The entire 

 weight is thus carried by the bottom of the case. Annular 

 ditches may lie provided in the base to catch any dripping or 

 leakage of the oil. The sheet-iron walls vary in thickness 

 from 1,5 mm to 1 mm, according to the size and capacity of 

 the transformer. 



BOILER-IRON CASES. 



Boiler-iron cases are used principally for large water-cooled 

 and forced-oil-cooled transformers (see Chapter \.>, and in 

 special types where great strength is required, as in portable 

 transformers. Their advantage lies principally in the fact that 

 they are stronger and more durable and are cheaper than sheet- 

 iron cases. Ordinary boiler-plates ranging between 7 mm and 

 }~> mm in thickness are used, with thoroughly caulked single- 

 ri\et-d lap-joinN, and the construction provides a very satis- 

 factory and pel-man. -nt oil-tight joint. 



The maximum liz for which a transformer can be built 

 to he self-cooling is limited by the amount of heat-emitting 

 capacity for \\hich the case can be design- -d. Caadfl with 

 corn; e often supplied with transformers up to 



750 kva capacity, hut beyond thi^ si/e, th< and 



dimensions of the case become so great that some method, 

 other than meiv increase in si/e, miM he resorted to in order 

 to pi-,, vide the necessun i 



case has recently b.-. i l.y the 



