Comparison of CVR impact on transmission system load margin with aggregated and de-aggregated distribution system

In this paper, emphasis is laid on the importance of modeling de-aggregated loads in form of a whole distribution systems rather than aggregated loads while assessing the impact of changes in distribution system on the transmission system performance. This paper is an attempt to develop an accurate analysis of impact of conservation by voltage reduction (CVR) in distribution network on the transmission system voltage stability margin (VSM) or loadability. The intention is to develop analysis with de-aggregated loads and compare it with traditional aggregated load analysis. Detailed literature review related to CVR and VSM is performed that includes various adjacencies on CVR and its effects. It is observed that CVR impact on voltage stability margin has not been explored much in the literature. The present paper considers a IEEE 9-bus test system for the transmission network that is modified to include distribution system transformer with secondary taps and aggregated lumped load to perform CVR. These results are then compared with a decoupled partial co-simulation that involves an accurately modeled 123-bus distribution network with various profiles of loads in the form of ZIP parameters for CVR. The resulting net real and reactive power reductions at the substation are translated to the VSM at transmission network load. The simulation results and observations suggest that involving the distribution system analysis gives a more accurate understanding of the change in VSM with CVR and how location of performing CVR impacts the transmission system stability margin. At the end, impact of CVR with distributed generation (DG) penetration in form of solar PV is also investigated. It is observed that increase in load margin due to CVR improves with DG penetration.