-POLYPHASE SYSTEMS 77 



The same machine operating throe-phase or six-phase has about 

 50 per cent, greater capacity than when operating single-phase. 

 A machine has the same capacity whether connected three-phase 

 or six-phase, because the same windings are used in the same 

 manner for each. (The foregoing table does not apply to syn- 

 chronous converters. The ratio of polyphase to single-phase 

 capacity in converters is much greater than that shown in the 

 above table. See page 355.) 



A minor consideration in favor of three-phase power is the fact 

 that with a fixed voltage between conductors, the three-phase 

 system requires but three-fourths the weight of copper of a single- 

 phase system, other conditions such as distance, power loss, etc., 

 being fixed. 



43. Symbolic Notation. The solutions of problems involving 

 circuits and systems containing a number of currents and volt- 



- a 



oo 



I I.,. 7 .",. Symbolic notation applied to voltage and current VIM- tors. 



ages are simplified and are less susceptible to error if the current 

 and voltage vectors are designated by some systematic notation, 

 of which the following is one type: If a voltage is acting to 

 send current from point a to point 6, Fig. 73 (a), it shall be de- 

 noted by Eob. On the other hand, if the voltage tends to send 

 current from b to a it shall be denoted by Eba. Obviously, 

 Eab = Eka. It may seem as if alternating current- cannot be 



iered as having direction since they are undergoing con- 

 tinual reversal in direction. The assumed direction of a current, 

 however, i.- determined by the actual direction of the How of 

 In an alternator the energy comes out of the armature 

 and the current is considered as flowing out of the armature. 



ilthou^h it ifl actually flowing into the anna lure for half the. 



time. 





