Application of the duplex reactor - an unusual and forgotten technique to reduce short circuit duty

The duplex reactor is a center tapped, three-phase, current-limiting reactor that can benefit power system operation when connected in certain configurations between two utility-fed distribution system buses and a local generator source. Its use was fairly common in the 1940s and 50s. This paper discusses the physical and mutual-inductance characteristics of the duplex reactor, its equivalent-circuit model, and revisits its potential application to limit the three-phase short circuit duty on medium-voltage industrial systems. Its use can also, result in beneficial system voltage support of local distribution buses during severe "remote" system faults. Results of simple system simulations using short circuit and load flow programs are explored on example systems.