Paired-Phase Bus Bars for Large Polyphase Currents

With the paired-phase arrangement, many of the difficulties associated with the transmission of large alternating currents are minimized. Nonuniform current density, including ``skin effect´´ and ``proximity effect,´´ is greatly reduced. This results in low a-c energy losses which combines with effective heat dissipation to produce low and uniform temperature rise. Both resistance and reactance voltage drops are very small, and voltage drop is almost perfectly balanced. Furthermore, the dimensions that produce all these desirable electrical and thermal characteristics lend themselves to convenient structural designs wherein the problems of joining adjacent bus-bar lengths, making tap-offs, support against mechanical and short-circuit forces, and insulation are greatly simplified. There are several specific features which particularly adapt the paired-phase arrangement to prefabricated enclosed bus-bar systems. Enclosure, of course, impedes heat dissipation, but the low heat generation minimizes this effect. Metallic or magnetic enclosures cause no additional losses and no increase in reactance. Structural designs are possible which facilitate erection in the field and the adaptation of standardized constructions to special installation conditions. The paired-phase arrangement has several unique properties that distinguish it from previously known arrangements. Its low voltage drop and low losses depend largely upon close intrapair spacing, dimension s in Figure 1. The interpair spacing d, or different relative pair locations, as illustrated by the three variations of Figure 1, have no appreciable effect upon voltage drop and, therefore, may be varied to obtain low temperature rise and convenient structure.