A Comparison of three resilient HVAC Switchyards: Moebius-Strip, Crossed-Ring and Breaker-and-a-Half

Existent switchyard designs such as Ring- or Breaker-and-a-Half-configurations try to fulfill this requirement. Another design – the Crossed-Ring configuration – is to be counted into this category too. It also needs 1½ C.B.s (circuit-breakers) per feeder – three parallel C.B.s each connect a feeder to the switchyard - and has the physical appearance of a closed strip. By twisting this strip into a Moebius-Strip configuration some qualities of the switchyard are improved. A previous publication presented an analysis for these three switchyard configurations with up to 6 feeders, how feeder availability depends on unavailable C.B.s and feeders respectively. The result was that the Moebius-Strip configuration clearly provides the best feeder availability, followed by Crossed-Ring – and at a great distance - Breaker-and-aHalf configuration. The aim of the present paper is to extend the number of feeders in the analysis to a maximum of 12. It is shown that the superiority of the Moebius-Strip also exists in this range. In addition, other switchyard qualities, such as operational flexibility, busbar failures, switchyard extendibility, reduction of short circuit current per C.B. by partitioning and considerations of CIGRE Green Books Substations are discussed and compared too. The analysis demonstrates that Moebius-strip and Crossed-Ring are superior to Breaker-and-a-Half in many respects, clearly in feeder availability if C.B.s are unavailable. Moebius-strip configurations, therefore, are an advantageous solution for substations with high demands on feeder availability.