TH1-: TRANSFORMER 



203 



tank and circulate cooling water tlinmgh the coil. This coil is 



d when 4 it is in contact with the hot oil (Fiji. 193). Careful 



-hould l>e made at regular intervals for leaks in the cooling 



coils, as the presence of a very slight amount of water in the oil 



greatly impairs its insulating and dielectric properties. 



:irnl \virnlirms of tin- nnliator typr of t r:m~t"onnr: -hown 

 in Fin. ! 



89. Three-phase Transformers. Three-phase transformers 

 have coiiHderahly leflfl weight and occupy much less floor space 

 than thi-ee single-i >rmers of equal capacity. For this 



reason they are commonly used in practice. The principle of 

 the three-phase cure-type transformer is illustrated by l'i-. M>1 

 (a). Three single-phase transformers secondaries not >ho\vn) 

 have each a primary winding upoi , These tran.-formers 



are symmetrically wound and each \\inding \ connected to one 

 lirei -phase system. Th are placed 120 apart 



