Evaluation of the variations of short-circuit capacities along a feeder due to distribution system-type upgrading

The variations of short-circuit capacities (SCC’s) along a feeder while a primary network is upgraded from original radial to normally closed loop arrangement is essential for examining the protection system of the network after upgraded. The increments of SCC’s along a feeder may cause the existing protection devices installed at the original network and its customers’ distribution systems becoming inadequate. Hence, a simple, systematic and straightforward evaluation method is required, especially in the planning stage. To meet these requirements the short-circuit MVA method was adopted in this paper. Based on the adopted method, the variations of SCC’s along a primary feeder before and after the network upgraded were represented by simple formulas and illustrated by figures that make the variations more easily be recognized. The results not only are useful for engineers of utilities to better realizing the impact on the SCC’s along feeder during the planning stage of network upgrading, but also confirm that the short-circuit MVA method is quite suitable for evaluating the variations of SCC’s along a feeder.