TRANSFORMERS 



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connection is much simpler, and it would be quite permissible to 

 use it for transformers of small capacities where the direct current 

 circulating in the neutral is less than 30 per cent (10 per cent per 

 transformer) of the rated transformer current. 



When three-phase core-type transformers are used, it is not 

 necessary to resort to the zig-zag connection, as in such trans- 

 formers the direct current flows along the core from end to end in 

 the same direction on all three legs, and since the direct mag- 



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netism must find its return path through the air and the case 

 outside of the core, its effects are practically negligible. 



On account of the 30 displacement between the voltage from 

 line to neutral and that across each half of the transformer legs 

 of the zig-zag connected windings, the low-voltage side operates 

 only at 86.6 per cent of the normal capacity, which it would have 

 if operated straight Y. 



Y-Y. This connection is not ordinarily to be recommended 

 for a bank of three single-phase transformers or a three-phase 

 shell-type unit. This is due to the fact that the triple frequency 

 component of the exciting current necessary for normal magnet- 

 ization cannot flow, which results in a third harmonic and its 

 odd multiples appearing in the e.m.f. from line to neutral, and 



