Edimar J. de Oliveira, José Luiz R. Pereira, Leandro M. Riani, André Luis M. Marcato and Leonardo W. Oliveira Abstract--In this paper the influence of a contingency in the Series Compensation (SC) device allocation and size is evaluated. The SC placement and size are determined using an optimal power flow (OPF) program via the Benders cut technique to include the contingency influence. This problem is solved in two steps: (i) The SC size and placement are determined as an investment OPF sub-problem. The SC cost and energy production cost are included in the objective function; (ii) The operation OPF sub-problem is solved considering the specified line and generation outages. The Benders cut are generated according to the outage occurrence probability. In this case the objective function is the minimum load shedding and energy production cost. The OPF sub-problems are solved using linear programming technique. The IEEE-14 bus and IEEE-118 bus test systems are used to show the effectiveness of the proposed methodology. Index Terms--Contingency analysis; Cutting plane methods; Optimal power flow; Series compensation allocation; Transmission congestion management. I. INTRODUCTION N the competitive environment, where the power system expansion planning tends to be more rigorous, the option of increasing the power transfer capability among subsystems, using the SC is an important issue [1]-[2]. The SC is also an attractive option to reduce congestion management through the change of pattern flows on the network [3]. In ref erence [4] the optimal SC allocation on a thermal power system is presented. The hydrothermal coordination associated to SC allocation is treated in [5]-[6]. References [7]-[8] describe the allocation of SC in a competitive environment, considering the transmission charge issues. The common feature of the above publications relies on the DC network modeling, meaning that the reactive power and voltage problems are not considered. This work was supported in part by CAPES and FAPEMIG. E. J. Oliveira is with the Department of Electrical Engineering , Federal University from Juiz de Fora, MG, 36036-330 Brazil (edimar@lacee.ufjf.br). J. L. R. Pereira is with the Department of Electrical Engineering , Federal University from Juiz de Fora, MG, 36036-330 Brazil (jluiz@ieee.org). L M. Riani is currently working towards the M.Sc. Degree in Electrical Engeneering at Federal University from Juiz de Fora, MG, 36036-330 Brazil (riani@eletrica.ufjf.br). A. L. M. Marcato is with the Department of Electrical Engineering , Federal University from Juiz de Fora, MG, 36036-330 Brazil (marcato@pee.ufjf.br). L. W. Oliveira is currently working towards the M.Sc. Degree in Electrical Engeneering at Federal University from Juiz de Fora, MG, 36036-330 Brazil (riani@eletrica.ufjf.br). Reference [9] describes an alternative, which is based on the combination of DC and AC OPF models, to consider the reactive power and voltage effects on the SC allocation problem. In this approach the SC allocation is solved in two steps in a decoupled manner. In [10] a sort of sensitivity analysis is described to place FACTS devices in a power system using the AC model. However the increase of line capacity limit is not considered. In reference [11] the methodology presented in [3] was extended to the full AC network model, in which the line flow limit increasing, for the line where the SC is placed is considered. In this paper the previous experience in both SC allocation [3]-[8] and Benders cut technique [5]-[6] is applied to investigate the former problem under contingency constraints. II. PROPOSED APPROACH The objective of SC reinforcement optimization problem is to determine a minimum cost, which ensures a feasible system operation both in normal state and contingency situations. A hierarchical decomposition approach adopted in this paper comprises two main steps: • The investment sub-problem, where decisions about the location and size of the SC devices are made; • The operation sub-problem, in which these devices are used to optimize the system operation avoiding load shedding. The deficit penalty considered is 400 US$/MWh. In this step the Benders cut is produced [12]. The global results is obtained by the iterative solution of the investment and operation sub-problems, as illustrated in [13] and shown in Figure 1. This Figure shows that whenever the investment OPF sub-problem is executed, the objective is to install new SC equipment or readjust the size of the already allocated in previous iterations, according to the Benders cut, in such a way that these readjustments are sufficient to a guarantee the feasible operation of the system. INVESTMENT SUBPROBLEM OPERATION SUB-PROBLEM Benders cut Decision about SC Fig. 1: Two-level hierarchical approach Series Compensation Device Allocation under Contingency Constraints I 0-7803-7967-5/03/$17.00 ©2003 IEEE Paper accepted for presentation at 2003 IEEE Bologna Power Tech Conference, June 23th-26th, Bologna, Italy