THE TR.\\sr<>h>MKR 



213 



The delta- Y connection shown in Fig. 203 is a very useful 

 connection for stepping up the voltage. It is not open to the 

 objection of a "floating neutral" and of wave distortion, such 

 as the Y-Y connection involves. Another distinct advantage of 

 delta-Y connection over the delta-delta connection is that for 

 high voltages the transformers need not be so well insulated. 

 For a 100,000-volt system, the Y-connected transformers need 

 be insulated only for 58,000 (100,000/\/3) volts, whereas delta- 

 connected transformers must be insulated for 100,000 volts. 

 The Y-delta system is often used for stepping down the voltage. 



The ratio between line voltages in these two systems is not the 

 individual transformer ratio, for the line voltage on the Y-side is 

 \/3 times that given by the transformer ratio. A delta-Y bank 

 cannot be paralleled with a Y-Y or a delta-delta bank, even al- 

 t hough the voltage ratios are correctly adjusted, as there will be 

 a 30 phase difference between corresponding voltages on the 

 ndary side. 



Transformer primaries may be connected in either Y or delta 

 without any attention being paid to phase relations. The 

 secondaries must be phased like the alternator coils in Par. 59, 

 1 25. The primaries of three-phase transformers, however, 

 must be correctly connected as regards phase relations. The 

 actual phasing is often avoided as the primary and secondary 

 connections are brought out of the case symmetrically. 



92. The V-connection. It was pointed out in Par. 59, pa ire 

 125, that line voltage must exist between the open ends of the 



Primaries 



-V or open-<l'lt:i 



f t r.-m-fr.rmers. 



two coils of the delta before the third one is eonnected. At no 



load, with only 1 ^< i ransformen, t h !<, eipial three-pha.-e voli 



iround the BeOOQdAliefl and a three-phase Iran-formation is 

 therefore |>os>ible with only two transformers. This is called the 



