three-phase model is as follows: (a) each power line has been
replaced with a three-phase physically based model with
positive sequence parameters approximately equal to that of
the original system tm and(b) ech noe (bu) of the orginal
system has been replaced with a substation with specific bus
arrangement (ring, breaker and a half, and so on). The bus
arrangement at each node and the location of each circuit
breaker become the explicit part of the network model.