Design of an optimized defence plan for a power system

This paper presents a novel optimization technique for determining the setting of various emergency power system controls. This will allow for the production of a comprehensive defence plan, against events such as cascading blackouts. The goal of this technique is to retrieve a new equilibrium operation point following a severe contingency. In general, the emergency controls used to prevent cascading blackouts are generator tripping, fast-valving, load shedding, excitation controls and system islanding. However, generator tripping, load shedding and system islanding are the most effective control actions. As such, these are considered as the main emergency control actions in the proposed optimization technique described in this paper. This problem is a complex nonlinear problem and it is very difficult to solve using ordinary numerical optimization method such as mixed integer linear programming. Since Genetic Algorithm approaches are very successful at solving nonlinear combinatorial optimization problems, these have been applied in this work to produce an optimized defence plan. Genetic Algorithms are search algorithms based on the mechanism of natural selection and natural genetics subject to survival of the fittest among string structures that identify possible solutions to a problem. A Genetic Algorithm approach is used to find the optimal combination of generators and loads to be tripped as the best solution for the network to regain a new state of equilibrium that is operationally stable, whilst maintaining supply to as many consumers as possible. System islanding may also be applied if a satisfactory state of equilibrium can not otherwise be obtained. The optimization technique uses transient stability evaluation algorithms, based on timedomain simulation, to assess the fitness of the potential solutions. The test case, presented in this paper, for the optimization technique was the Libyan power system network. In order to show the validity of the optimized defence plan, a comparison between the existing Libyan power system defence plan and the optimized defence plan is presented for the case of a major blackout in the western part of the Libyan power system that took place on 8th November 2003. The results presented in this paper show that a robust defence plan with a satisfactory amount of load shedding and system islands can be obtained by the new technique. The paper also demonstrates that the new defence plan outperforms the existing Libyan power system defence plan.