Coordination of Transmission Line Transfer Capabilities

This is a project report from the Power Systems Engineering Research Center (PSERC). PSERC is a multi-university Center conducting research on challenges facing a restructuring electric power industry and educating the next generation of power engineers. More information about PSERC can be found at the Center's website: The project has been carried out in collaboration between the Washington State University team and Richard Goddard of Portland General Electric, and we thank Portland General Electric for their support of this work. The maximum power that can be transferred over any transmission line, called the transfer capacity, is limited by constraints on thermal limits, voltage bounds, and security considerations. As the power system gets more stressed with increasing loads, the need to transfer power over long transmission lines is becoming very important. This is especially the case for deregulated markets where it is attractive to minimize costs by buying power from remote generators with lower generation costs. In the present power system operation, the transfer capacity studies of transmission lines are carried out separately by their owners with little coordination. The objective of this project has been to propose a global framework for coordinating the capabilities of several transmission paths, while also meeting the regulatory requirements on voltage security and dynamic security. As an example, we focus on maximizing the transmission capacity of the California-Oregon AC Inter-tie (COI), by coordinating other path-flows that have an impact on the COI capacity. We show that substantial improvements in the COI MW transfer can be achieved with reasonable rescheduling of neighboring tie-line flows using the optimization algorithms presented. These coordination algorithms would be of vital importance in stressed power-flow scenarios when there is a need to increase the capability of one or more critical transmission lines by rescheduling of other paths, while also satisfying strict requirements on system security. The optimization results could suggest operating procedures which could be entered into the transmission contracts appropriately. Also, by introducing the economic costs associated with specific path-flows, the optimization can be used for maximizing the profits of a specific path owner by approaching the problem in a global sense. This is because the optimization specifically points to those neighboring path flows which are limiting the capacity of the critical transmission path under consideration. The computations involve four commercial software engines: 1) Bonneville Power Administration (BPA) Power-flow program pf; 2) Electric Power Research Institute (EPRI) midterm transient stability …