The impacts of cold load pickup on the design of power distribution systems.

摘要

This research is aimed at dealing with the problem of cold load pickup from a design point of view. The research covers four major subproblems, namely problem formulation, transformer overloading following extended outages, problem solution and application to actual situations.;Transformer overloading is based on numerically solving the differential equations for top-oil and hottest-spot temperatures, calculating the corresponding loss of life, and determining the transformer peak loading level such that none of ANSI/IEEE C57.92-1981 recommended limits is exceeded.;To test the validity of our optimization problem, we apply it to an actual distribution system. Solving the problem through enumeration, a search technique or a genetic algorithm, the optimal values of the decision variables are obtained such that transformer overloading does not violate ANSI/IEEE C57.92-1981 recommended limits. Transformer load during restoration is determined. A power flow is run for the maximum sustained part of this load with the intent of looking for voltage drop and/or overloading problems.;In the problem formulation, our aim is to select the substation transformer size and number of sectionalizing switches such that they can handle a cold load pickup situation while minimizing a total annual cost function composed of the cost of these components, the net cost of energy interruption (the cost of energy interruption less the revenue of the sold energy during restoration), and the cost of transformer loss of life due to overloading. Transformer cost is approximated by a quadratic function and the cases of a distribution substation with one or more transformers are considered. In the latter case, the optimization problem is formulated based on the worst-case scenario of having one of the transformers out of service.