An Integrated Tool for Analysis of Power System Constraints in the Spanish Electricity Market E. Lobato, L. Rouco Universidad Pontifica Comillas C. Alberto Aguilera, 23 28015 Madrid, Spain M. I. Navarrete, R. Casanova Indra SSI C. Velázquez, 132 28002 Madrid, Spain J. García Castillejo, G. López Red Eléctrica de España P. Conde de los Gaitanes, 177 La Moraleja, 28019 Madrid, Spain Abstract- The role of the System Operator in the Spanish electricity market, as it started on January 1 st 1998, is to determine the technical feasibility of the generation dispatch provided by the Market Operator. The security criteria of the Spanish power system require that branch power flows and bus voltages are within their limits, not only in normal operating conditions but also when any credible contingency occurs. This paper presents an integrated tool for analysis of power system constraints in the Spanish electricity market. The components of this tool are: a power system scenarios builder, contingency analysis routines and preventive dispatch algorithms (active and reactive power). The tool addresses separately the overloaded branches and the bus voltage violations. The performance of the tool will be illustrated using an actual scenario of the Spanish power system. Keywords - Load flow analysis, contingency analysis, power system dispatch, security assessment, congestion management, deregulation. I. INTRODUCTION Competitive electricity markets can be organized and operated in different ways. The Spanish electricity market, as it started on January 1 st , 1998, is based on two separate entities: the Market Operator and the System Operator. The Market Operator receives the bidding of generation and demand for each hour of the following day and clears the market according to economic criteria. The System Operator is on charge of determining the technical feasibility of the generation dispatch provided by the Market Operator. The technical constraints imposed by the transmission system to the generation dispatch are solved by increasing and decreasing the generation of several units. Therefore, the adequate treatment of the technical constraints is very important for the fair operation of an electricity market. The security criteria of the Spanish power system require that branch power flows and bus voltages are within their limits not only in normal operating conditions but also when any credible contingency occurs. The contingencies under consideration are the loss of any generator, transmission line or transformer, the loss of the double circuits that share more than 30 km and the combined loss of key generators and transmission lines [1]. It should be noted that the branch and bus voltage limits in case of n-1 and n-2 contingencies are different from the limits under normal operating conditions. A power system can be operated under two security levels: (a) preventive and (b) corrective. A preventive operation requires that, for every contingency postulated, all system variables are within limits without making any action. A corrective operation requires that, if any of the contingencies postulated occurs, all variables can be brought within their limits taking appropriate control actions. Therefore, a preventive operation is more restrictive than a corrective operation. The operational procedure of the Spanish power system imposes a preventive operation of the power system. Technical constraints can be separated into two types: (1) active power constraints and (2) reactive power constraints. Active power constraints correspond to violations of the branch power flows. Reactive power constraints occur when the bus voltages are not within their admissible ranges. This paper presents an integrated tool for analyzing and solving technical constraints in a competitive electricity market operated with preventive criteria. The tool addresses separately active and reactive power constraints. However, the effect of the branch reactive power flows is approximately taken into account in the solution of the active power dispatch. The components of the tool are: a power system scenarios builder, contingency analysis routines and preventive active and reactive power dispatch algorithms. Power system scenarios are obtained as converged load flow solutions from topology, demand and generation data. A contingency analysis routine is firstly used to identify the contingencies that result in overloaded branches. The preventive active power dispatch modifies the generation dispatch to alleviate them. The modification of the generation dispatch consists of increasing and decreasing the generation of the on line generators and connecting off line ones. A contingency analysis routine is again applied to find the contingencies that result in non-admissible bus voltages. The preventive reactive power dispatch connects new generators to solve them. The