1 Sensitivity Analysis For Overload-Relief In Transmission Lines Using An Implicitly Coupled Method (CRIC) E. S. Hoji, Student Member, IEEE, and A. Padilha-Feltrin, Senior Member, IEEE Index Terms-- Power Transmission Lines, Reactive Power Control, Sensitivity. I. INTRODUCTION HE restructuring of energy markets in order to increase its competition and to supply free access to the networks had as consequence the increase of the number of power transactions. If it is necessary to violate any network security level in order to supply the demand, the system is under congestion. Network congestion may prevent the use of lowest-priced resources to meet the demand besides allows the sellers to exercise market power. As consequence, the networks have been suffering overloads in the lines in a more frequent way [1]. In emergent countries, this situation is worsened by the increase of demand and the restrictions to install new transmission lines. Many authors deal with this problem through generation rescheduling and load shedding, although in restructured environments, the control of the system is unbundled. So, the transmission companies are not able to take decisions about generation and loading levels. In this way, the overloads must The first author would like to thanks to FEPISA – Fundação de Ensino, Pesquisa e Extensão de Ilha Solteira for the financial support. E. S. Hoji and A. Padilha-Feltrin are with Department of Electrical Engineering, Universidade Estadual Paulista, Câmpus de Ilha Solteira, Ilha Solteira – SP – Brazil (e-mail: shigueo@aluno.feis.unesp.br, padilha@dee.feis.unesp.br). be alleviated by reducing of reactive power flow in the overloaded line. It can be done changing the parameters of some network devices, as transformer ratios and reactive power injections in buses. Once overloads imply in emergency situations, it’s necessary that the decision-making processes be fast. One efficient tool for defining which are the best actions to be taken in order to alleviate a line overload is the sensitivity analysis. It provides the system behavior when one of its parameter varies. Besides, linear sensitivity factors calculation is sufficient quick for real-time applications. Then, it is possible to establish a relation between the reactive flow in the overloaded line and some parameters of network devices, providing a set of possible actions to alleviate an overload, in a safe time. This paper presents an application of sensitivity factors for overload alleviation. The idea of this methodology is to calculate, in a fast way, sensitivity factors related with the reactive flow of the overloaded line for buses and transformers of the transmission network, and presents capable devices for alleviating a line overload, by reducing its reactive flow. So, it’s possible to take decisions in order to alleviate the overload and avoid additional problems, as contingences. For buses, the sensitivity factors are related with their reactive power injections and for transformers they are related with the transformer ratios. The present methodology starts at the Lc matrix of the Implicit Coupled Power Flow method (CRIC) [2], and it was implemented in [3]. With some algebraic manipulations and using this matrix is possible obtaining the desired sensitivities. II. TRANSMISSION LINE OVERLOADS Network congestion can be defined as the incapability of the transmission system in supplies the demand. Under commercial consideration, buyers look for the lower price. But, when the security limits are considered, the system can be unable to accommodate these transfers. In this way, congestion is caused by the lack of sufficient transfer capabilities to simultaneously transfer energy between the various selling and buying entities [4]. In these environments, sudden demand variations, equipments failures and contingencies may cause overloads in some lines of the transmission system. An overload is defined T 1-4244-0288-3/06/$20.00 ©2006 IEEE 2006 IEEE PES Transmission and Distribution Conference and Exposition Latin America, Venezuela