## 6 Congestion Management  
Congestion management is one of the technical challenges facing deregulated power networks [186, 187]. Rapid energy demand and uncertainty in available resources cause  
problems like outages and disruption of electrical power. Therefore, electrical power transmission capacity is unable to transmit sufficient electrical power under these constraints. This technical phenomenon in deregulated networks requires congestion management. [PERSON] et al. [155] describe that, in a deregulated market environment, electrical power companies ensure maximum utilization of transmission lines during high-demand periods. This transmission behavior reduced the security margin of the entire system. Also, the presence of any constraints in power networks limits the power transfer capability. In practice, it may not be possible to deliver all bilateral and multi-lateral contracts in full and to supply the entire pool demand at low cost, as it may lead to violations of operating constraints such as voltage limits and line overloads [188; 189]. Such transmission limitations are referred to as congestion. Therefore, congestion occurs due to the results of contingencies or lack of coordination between generation and transmission companies. Congestion management is generally approached by two methods, i.e., cost-free means (CFM) and non-cost-free means (NCFM). The CFM method is called cost free because it has no marginal cost and it includes the operation of power electronics devices or FACTS devices, network configuration, etc. Conversely, the NCFM method takes into consideration the security constraints, generation, redispatch, network sensitivity factor methods, congestion pricing, market base methods, and application of FACTS devices [190]. FACTS controllers play a significant role in the reduction of transmission congestion and allowing better utilization of electric grid infrastructure [191]. Several methods for congestion management in deregulated environments are presented in [192; 193]. However, several issues related to FACTS devices are control interactions, modeling, cost, size, optimal location, etc. [191]. Therefore, the authors of [194; 195; 196] proposed new methodologies for the placement of series FACTS devices to reduce congestion in deregulated networks. To validate the results, proposed methods were tested in IEEE-14, IEEE-30, and IEEE-57 bus systems using TCSCs. Another approach to solving congestion in the IEEE-14 bus network, by optimal placement of TCSCs, is presented in [197]. Furthermore, congestion management is provided by optimal placement of TCSCs in deregulated networks (IEEE-30 and IEEE-57 bus systems) using the gravitational search assisted (GSA) algorithm [198]. However, two methods, i.e., optimal power flow (OPF) and available transfer capability (ATC)-based GSA, are used in this study. Results show that GSA-based OPF reduced congestion in deregulated networks compared to GSA-based ATC, OPF-based GA, and PSO. Similarly, research to reduce congestion (by finding an optimal location) using TCSCs and SVCs in a deregulated environment is presented in [199]. The authors further conclude that locations which present a favorable solution with respect to one of the objectives (branch loading, voltage stability, and loss minimization) are not effective with respect to other objective functions. Later, these objective functions are simultaneously optimized using the strength Pareto evolutionary algorithm (SPEA) and tested in the IEEE-30 bus system. Furthermore, a combination of FACTS devices, i.e., SVC and TCSC, is implemented in restructured networks to provide congestion management [200]. In the literature [201], congestion is reduced by using individual or combined FACTS devices (TCSC and SVC). It is observed that FACTS devices reduced congestion, but a TCSC with an SVC is more effective compared to their individual usage. It is further concluded that the SVC improved the voltage profile of restructured power systems, but the TCSC has more control of line loadings.