374 Report S.A.A. Advancement of Science. 



E.M.F.s. induced are given by Fig. ii, if fixed as illustrated in Fig, 

 12, by Fig. 13. In the former case, the resultant E.M.F. has a 

 peaky appearance, and its formfactor is greater than that of curve 

 I. ; consequently, the total hysteresis losses are reduced. In the 

 latter case, the resultant E.M.F. curve is flatter than that of I, and 

 the total hysteresis losses are increased. This arrangement has, 

 however, the advantage of producing less strain on the insulation, 

 and this is usually of greater importance than the reduction in the 

 iron losses. 



In the systems described so far, we cannot join the consuming 

 devices of both kinds of currents to the same mains, and we require 

 bifilar wound choking coils or motors to separate the currents. In 

 D.R.P. 128406. Arnold-Bragstad-la Cour gives, however, a 

 modification of their original systems, which makes the joining of 

 both kinds of consuming devices to the same mains possible. The 

 connections of such a modified three phase single phase polycyclic 

 system are shown in Fig. 14, in which one main of the distributing 

 network is common to both systems. These are now, however, no 

 longer independent of each other, because the currents of each system 

 have two circuits through which to pass. For all practical purposes, 

 however, the drop caused in one system by large variations of the 

 currents in the other system is negligible. In Fig. 15, 

 both primary and secondary circuits are of the modified type, in Fig. 

 16 the primary circuits are independent, the secondary modified, and 

 in Fig. 17 both are again of the modified type, for a two phase 

 single phase polycyclic system. The various diagrams are self- 

 explanatory. 



Difference of Potential Between the Mains. 



Consider a two phase single phase polycyclic system with both 

 circuits independent, such as is illustrated in Fig. 18. If E2 be the 

 R.M.S. P.D. between two leads of the two phase system, then — 

 assuming a similar R.M..S. P.D. between conductors a and b of the 

 single phase circuit — the P.D. of the single phase generator must be 



^2 



The amplitude of the P.D. between wires a and d, or b and c, is 



'V/2E2, 



if we assume sine waves, but that between a and b will be greater, 

 and will depend upon the position of the two pressure curves relatively 

 to each other. In fact, in the most unfavourable position, see Fig. 

 II, it is 2E2. If the periodicity of one system is an uneven mutiple 

 of that of the other, it is advisable to fix the poles in such a manner 



