SWITCHING EQUIPMENT 



569 



2 Bars per phase 



4 Bars per phase 



somewhat below the permissible temperature rise of buses in the 

 open. 



Skin-effect can best be taken care of by arranging the bus-bars 

 so as to simulate a cylinder or tube, and this is done by running 

 the laminations as much as possible in pairs, as shown in Fig. 350. 

 The distance between the pairs should then 

 be as great as the space of the bus-bar com- 

 partments will permit. 



With the bars run flat in the compart- 

 ments, the connections can, as a rule, be 

 made easier, but, as previously stated, the 

 ventilation becomes poorer than if run on 

 edge. On the other hand, installing them 

 on edge gives a more substantial construc- 

 tion in that it increases their strength and 

 ability to withstand short-circuit stresses. 



With alternating current bus-bars run 

 flat, the reactance of the laminations in 

 the outside phases varies quite consider- 

 ably, this effect being more noticeable the 

 less the distance between phase centers. 

 The effect of this difference of the inductive 

 reactance in the bars, due to the different 

 distance between the middle phase and the 

 individual laminations, will cause the lami- 

 nation nearest the middle phase to develop 

 the least reactance, and the lamination 

 farthest away from the middle phase to develop the highest 

 reactance. Therefore, the lamination nearest the middle phase 

 will carry the highest current and the bar farthest away from the 

 middle phase the lowest current. If the bus-bars are placed on 

 edge this difference of inductive reactance in the laminations 

 disappears, and the only effects to be looked out for on A.C. 

 bus-bars is then the matter of ventilation and skin-effect. 



Both the buses and the connections should be securely sup- 

 ported and the insulators should be bolted or clamped to the wall 

 or slab and not cemented, since this construction causes consider- 

 able inconvenience when it becomes necessary to exchange an 

 insulator. Several different lines of bus-bar supports are now on 

 the market, two typical types being illustrated in Figs. 360 and 



1 



C Bars per phase 



FIG. 359. Method of 

 Pairing Bus-bars to 

 Reduce Skin Effect. 



