Full Title: Coordination Of Transmission And Distribution Operations In A High Distributed Energy Resource Electric Grid
Author(s): Prepared By Staff Of CAISO, PG&E, SCE, SDG&E With Support From More Than Smart
Publisher(s): More Than Smart
Publication Date: June 1, 2017
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The electricity industry is going through a systemic transformation resulting from two major shifts. One is the shift away from traditional fossil-fuel generating resources to renewable resources, particular solar and wind generation. The other is the shift from a highly centralized system powered mainly by large remote generating plants to a more decentralized system, where technological advances and customer adoption are creating a vibrant “grid edge” of diverse distribution-connected or “distributed” energy resources (“DERs”1 ). The second shift is the focus of this paper.
The electricity supply system consists of generating facilities that produce electricity plus transmission and distribution facilities that move it from where it is produced to the energy users who need it. Although the transmission and distribution grids are interconnected they are distinct systems, with inherently different structures, characteristics, functions and operating principles. The primary function of the transmission grid is to deliver bulk electric power from utility-scale generating facilities to transmission-distribution (T-D) substations via interconnected high-voltage power lines organized as a meshed network. High voltage electric substations at numerous locations on the transmission network connect to distribution systems that deliver power to end-use customers via lower-voltage electric distribution lines. The T-D “interfaces” are those substations where the transmission and distribution grids interconnect.