  This paper analyses the impact of conservation by voltage reduction (CVR) on
voltage stability margin (VSM) considering transmission and distribution (T&D)
systems. VSM is determined by P-V curve analysis using PSSE and GridLAB-D
solvers to co-simulate the T&D systems under CVR and No CVR conditions. ZIP
loads with profile [ZIP] = [0.4 0.3 0.3] are used to model the load. The paper
discusses the counterintuitive result: under CVR, the VSM is reduced.
Theoretical justification for the reduced VSM under CVR is the increase in the
effective impedance between generation and load and this is proved using an
extended 2-bus system. The paper shares T&D co-simulation results with IEEE
9-bus transmission system and a larger 123-bus distribution system and with
distributed generation (DG) in unity power factor (UPF) and volt-VAR control
(VVC) mode.
