  The primary objective of this paper is to highlight the need for and benefits
of studying the steady state and dynamic response of power systems using three
phase integrated transmission and distribution (T&D) system models (hereafter
referred to as hybrid models). Modeling and simulation requirements for
building and analyzing hybrid models are also discussed. Finally, results from
steady state and dynamic simulations of a large hybrid model are presented to
demonstrate insights that can be obtained from hybrid models which cannot be
obtained from the study of transmission and distribution systems separately.
