TRANSFORMERS 



413 



Each of the two halves of the three-phase winding should further- 

 more be distributed over the entire winding length of the core in 

 order to prevent flux distortion and poor regulation. The T 

 connection requires 6.7 per cent more copper than single-phase 

 transformers delivering the same power on account of the idle 



V\M^WAA/ 



W\/Wvw 



V 





It/, 



FIG. 256. 



copper in the teaser and also on account of the fact that wattless 

 currents flow in the three-phase side of the main winding. 



The neutral of the three-phase side, which is one-third the 

 height of the teaser winding, can be brought out for four-wire 

 operation although the transformer construction is somewhat 

 complicated thereby. When operating without the neutral point 

 grounded on the three-phase side, the maximum insulation 

 strain, if a permanent ground occurs, is equal to the line volt- 

 age V. 



Unbalanced T. This connection may sometimes be of use in 

 emergency conditions where a transformer with an 86.6 per cent 

 tap is not available and a teaser transformer of the same voltage 

 as the main transformer must be used. 



In this connection two transformers of exactly the same 

 capacity and voltage are used. The phases, however, are no 

 longer strictly 120 apart, and it is assumed that the same con- 

 nection is used at each end of the line. As it is not a true three- 

 phase system, any attempt to operate in multiple with a three- 

 phase system or three-phase apparatus will cause serious unbal- 

 anced currents. 



The unbalanced T connection occurs when voltage is applied 



