408 ELECTRICAL EQUIPMENT 



winding. The three-phase capacity of the T connection as is 

 shown in the table is the same as for the open-delta connection, 

 that is, 86.6 per cent of single-phase capacity, but on account of 

 the fact that the teaser operates at a lower flux density, the ef- 

 ficiency of the T connection is somewhat greater than In the open- 

 delta or V connection. 



Two ordinary transformers may also be used with T connec- 

 tion provided a 50 per cent tap is available. It is also more 

 economical to operate with T connection than with V connection, 

 when one transformer has burned out. 



The T connection, as shown in Fig. 250, can also be used for 

 three-phase synchronous converters, and the neutral point can 

 readily be brought out for Edison three-wire service. The neutral 



FIG. 250. 



is then brought out from a point at one-third the height of the 

 teaser winding and the m.m.f. of the direct current i will balance, 

 as shown in the diagram. 



For T connection with ungrounded neutral the voltage stress 

 is the same as for the- delta system, and with grounded neutral 

 the voltage stress between line and ground is limited to 58 per 

 cent of normal,.' ' 



Assuming again that as with the open-delta connection the 

 two transformers shall be capable of supplying a load equal to 



o TJ1J 



- = 1.5127, the Kv.A. rating of the main transformer must, 

 L 



therefore, be equal to 1.73EI, while the Kv.A. of the teaser trans- 

 former only is equal to 1.737X0.866# = 1.5#7. The two trans- 

 formers are, however, designed to carry the same currents and are 

 generally made identical, so that the single-phase ratings of either 



