414 



ELECTRICAL EQUIPMENT 



from the two-phase side. When balanced three-phase voltages 

 are applied the voltages on the two-phase side will be unequal. 



The connections and voltage relation of this system are shown 

 in Fig. 257. With equal currents in the two-phase system, the 



FIG. 257. 



currents in the three transmission wires will be the same as in the 

 coils, namely: a =112 amperes, 6 = 112 and d = 100, with the 

 voltages as indicated in the diagram. 



An unbalancing of the two-phase distributing network affects 

 the currents in the three transmission wires, in that an increase of 

 the load on phase D further increases the unbalancing, while, if 

 phase E be loaded in the neighborhood of 15 per cent in excess of 

 phase D, the transmission line currents become practically bal- 

 anced. 



With no neutral the maximum insulation stress under all con- 

 ditions arising from a permanent ground would be 1.12 times V. 



Symmetrical or Woodbridge Connection. In the previous two 

 T-connected methods, the two-phase windings are electrically 

 distinct. There are, however, a number of schemes in which the 

 windings on the two-phase side are electrically interconnected 

 in one way or another. 



Such a system of connections is shown in Fig. 258. It con- 

 sists of three windings, one for each phase. Two of the phases 

 are identical, each consisting of two coils, wound for 0.577 times 

 the two-phase line voltage and having a current capacity of 0.577 

 times the two-phase line current. The third phase consists of 

 three coils, one being wound for 0.577 times the line voltage and 

 the other two being identical and wound for 0.212 times the line 



