The purpose of this paper is to discuss recent practical experience in
external network modeling at a number of utility control centers. Thi
s paper presents a set of short notes that discuss recent practical ex
periences on external network modeling. The introduction provides a fr
amework for the rest of the short notes by discussing network represen
tation, modeling issues, unobservable internal models versus unreduced
external models, and data for the unobservable network. The first sho
rt note discusses the solution methods consisting of power flow, one p
ass SE, and two pass SE. The remaining short notes discuss recent prac
tical experience on external network modeling at a number of utility c
ontrol centers. The last short note describes techniques for developin
g REI equivalents.