230 ELEMENTS OF ELECTRICAL ENGINEERING. 



113. Transformer connections for synchronous converters. An 



n-ring converter must be supplied with alternating current from 

 an ;2-wire system, the supply wires being connected to the 

 rings in proper order. Thus a four-ring converter (sometimes 

 called a two-phase converter) cannot be supplied from a three- 

 wire two-phase system, but the two phases must be entirely sep- 

 arate, each transmitted over a separate pair of wires. 



Three-ring converter. A three-ring converter is supplied with 

 alternating currents from a three-wire three-phase system, the 

 three phases being stepped down to the proper voltage, and the 

 three service wires being connected to the three rings. The 

 order of connections of service wires to rings depends on the di- 

 rection in which the converter is to be driven. If the alternating- 

 current supply is two-phase it is necessary to transform to three- 

 phase as explained in Art. 112. 



The four-ring converter. A four-ring converter must be 

 supplied with alternating currents from a four-wire two-phase 

 system. If the two-phase currents are transmitted over a three- 

 wire line, the step-down transformers must deliver currents to 

 four service wires, two separate wires for each phase. The wires 

 of phase A are connected to two opposite * collectorrings, and 

 the wires of phase B are connected to the other two rings. 

 The reversal of the connections of either phase will reverse the 

 direction of driving. 



If the alternating current supply is three-phase it is necessary 

 to transform to two-phase as explained in Art. 112. 



Six-ring converter. Any converter having 2n rings can be 

 supplied with alternating currents from an ^-phase system, pro- 

 vided the n armature windings of the ^-phase supply generator 

 are not electrically connected with each other, each generator 

 winding must have its own separate pair of collector rings (zn 

 rings in all) and must deliver current over a separate pair of trans- 

 mission wires. If the -phase generator has n collector rings, 



* Opposite collector rings are those which are tapped into opposite points of a 

 two-pole armature winding. 



