418 



ELECTRICAL EQUIPMENT 



on account of the fact that the third harmonic voltage is made 

 use of to obtain the direct-current voltage regulation and in such 

 a case the windings must be insulated for double line voltage to 

 ground and 3.46 times normal Y-voltage across windings, due to 

 the presence of the third harmonic e.m.f s. The middle points of 

 the diametrical windings can readily be connected together and 

 brought out for three-wire Edison service, the unbalanced three- 

 wire direct current having no distorting effect. Arrangements 

 should then be made for opening the neutral connections during 



a b 



WVWWW 



\c d\ \e f 



WWWWV WvVVWW 



Collector Rings 



FIG. 262. 



starting to avoid short circuit. When used with regulating pole 

 converters the neutral must be isolated. 



The current in each coil on the low-voltage side is equal to 



T output of transformer in watts 



/= ovx j- rr ~ assuming the load is balanced 



3 X diametrical voltage 



and that the power-factor is unity. 



With six-phase diametrical connection with common neutral, 

 one-half the output can be taken from the low-voltage side for 

 operating three-phase without change of diametrical voltage. 

 If full three-phase output should be desired, the coils can be con- 

 nected in delta in which case the diametrical voltage is increased 

 14 per cent. The full three-phase output at 1.73 times the dia- 

 metrical voltage may be obtained by connecting the coils in Y, 

 in which case the neutral should be grounded and if the high 

 windings are Y-connected the system is subject to the dangers 

 of the third harmonic e.m.f s. as previously explained. It must 

 also be ascertained if the insulation of the windings can withstand 



