This paper presents a method and the mathematical formulation for large scale optimal power flow sensitivity analysis. The method has been implemented in a computer program presently in use in the Pacific Gas and Electric Company. Some of the results of the sensitivity calculations are also presented.
KEYWORDS;Large scale optimal power flow, Sensitivity analysis.Techniques and software for solving Optimal Power Flow (OPF) problems have attained a fair level of maturity ([1].[2],[3]). OPF packages are available which can reliably find a steady-state operating point (e.g. generation dispatch, voltage profile, and transformer tap settings) which minimizes some criterion such as system real power losses or real power generation costs while enforcing a variety of operational constraints such as limits on bus voltages, generator outputs, or flows on individual transmission lines. While knowledge of the optimal operating point for a given set of conditions (e.g. loads and equipment limits) is very useful, for some purposes knowledge of how the optimal operating point changes as conditions change may be more useful. That is, an analyst may wish to determine the sensitivity of the optimal operating point to a change in some parameter such as real or reactive load at a specific bus or a change in an operating limit such as the limit on the flow on a transmission line. We show how such sensitivity analyses can be efficiently performed for large-scale OPF problems once the optimal operating point is known. We also identify some application areas for such types of analysis.We developed the program OPSENS based on this method. The program is used to perform sensitivity analyses for PG&E's 1700 bus transmission network. The results of using the OPSENS program for calculating the sensitivity of system losses for a 34 bus and a 1700 bus transmission network to bus load changes are reported in this paper and compared to the results of multiple OPF studies.
METHODWe shall use a parametric optimal power flow formulation in our analysis. The implementation of this method or the optimal power flow model used for obtaining the optimal operating point, however, need not use this formulation.
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