MV system design: A paradigm shift

This paper will present new techniques that are advantageous to MV distribution design configurations (specifically Main-Tie-Main) for large industrial and power station installations. Sixty years of traditional low cost design approaches are re-evaluated to demonstrate that initial low capital cost misses opportunities. Many designers may not have considered the component interrelationships and/or their tradeoffs when in an integrated system. The designer and/or user should consider the advantages of higher short circuit capacity (SCC) systems by integrating fault current limiters (FCL) and MV switchgear. Utilizing higher SCC systems permits the power system designer optimization opportunities not possible before using conventional design methods. This paper will provide documentation of substantial savings of capital investment and energy under higher SCC conditions. The savings in one system component will offset another´s increased cost. An obvious benefit of stiffer systems is ease of direct-online starting (DOL) of large motor driven compressor trains. The future need for motor soft starters minimizing system impact will be challenged. This paper may change fundamental system design methodology for system designers by removing several performance tradeoffs.