OPTIMAL TRANSMISSION DISPATCH USING FACTS DEVICES IN OPEN POWER MARKET

Abstract

This thesis focuses on reporting the research study on a problem area relating to the use of Flexible AC Transmission System (FACTS) devices in open power market. With open access to the transmission system by competing generators, the pattern of generations and flows can change drastically over a few hours. Under such circumstances, the operator needs more direct means of controlling the flows. Flexible AC Transmission Systems (FACTS) is the name given to the application of power electronics devices to the control of flows and other quantities in power system. The ancillary function required for smooth operation of the networks in open power market, such as congestion management, increasing available transfer capability, frequency control, optimal load-flow control, reactive power and voltage stability, as well as security are being assumed by the operators. These additional requirements for power system can be effectively met by using FACTS equipments. Thyristor controlled series compensator (TCSC), thyristor controlled phase angle regulator (TCPAR), unified power flow controller (UPFC) as well as generalized unified power flow controller (GUPFC) are considered as promising devices for implementing the FACTS concept. The development of TCSC and TCPAR is quite ahead but the development of UPFC, GUPFC is still in an infant stage, probing into its impact on power system operation is actively pursued and significant effort has been devoted to put it forward as a practical FACTS devices and as a challenging academic research object. FACTS devices by controlling the power flows in the network without generation rescheduling or topological changes can improve the performance considerably. The insertion of such devices in electrical systems seems to be a promising strategy to decrease the transmission congestion and to increase available transfer capability (ATC). Using controllable components of these devices, line flows can be changed in such a way that thermal limits are not violated, losses minimized, stability margin increased, contractual requirement fulfilled etc. without violating specified power dispatch. Increased interest in use of these devices is due to two reasons: development in high powerelectronics devices and increased loading of power systems combined with deregulation of power industry. Tighter control of power flow and increased use of transmission capacity are key benefits of new thyristor based controllers. In other words, future power system development depends much on how to make it more flexible to meet all sorts of control requirements. Essentially contribution of present research study is posed to investigate some of its aspects along the line to make deregulated power system operating in more flexible, secure and economic way. For about the last one hundred years the electricity supply industry in nearly every country has been a natural monopoly and as a monopoly attracted regulation by government. Without exception, the industry has been operated as a vertically integrated regulated monopoly organization that owned the generation, transmission and distribution facilities. It was also a local monopoly, in the sense that in any area one company or government agency sold electric power and services to all customers. Since 1980, the electricity supply industry has been undergoing rapid and irreversible change reshaping an industry, which for a long time has been remarkably stable and had served the public well. A significant feature of these changes is to allow for competition among generators and to create market conditions in the industry, which are seen, as necessary to reduce costs of energy production and distribution, eliminate certain inefficiencies, shed manpower and increase customer choice. This transition towards a competitive power market is commonly referred to as electricity supply industry restructuring or deregulation. Technically, the greatest challenge facing the deregulated and unbundled electricity supply system is the operation of the grid. There are some important issues that the system operator will face in routine system operation, and how these issues can be resolved in a market environment. Some potential technical problems of open power market are: Congestion management, Available Transfer Capability, Security, Market power, Pricing and Economic and environmental issues. Locations of FACTS devices in the power system network are obtained on the basis of static and dynamic performances. There are several methods for finding optimal location of FACTS devices in vertically integrated systems but little attention, however, has been devoted to unbundled power system. The optimal locations of FACTS devices are obtained by solving the economic dispatch problem plus the cost of these devices making the assumption that all lines, initially, have these devices. In the presence of open power market it would be difficult to use these objectives because other aims should be taken for successful operation of the market. Congestion in a transmission system, whether vertically organized or unbundled, cannot be permitted except for very short duration, for fear of cascade outages with uncontrolled loss of load. Some corrective measures such as outage of congested branches (lines or transformers), using FACTS devices, operation of transformer taps, redispatch of generation and curtailment of pool loads and/or bilateral contracts can relieve congestion. If there is no congestion, the placement of FACTS devices, from the static point of view, can be decided on the basis of reducing losses but this approach is inadequate when congestion occurs. Electric power utilities, throughout the world, are undergoing considerable change in regards to structure, operation and regulation. Under these conditions, either due to increased loading or due to severe contingencies, system no longer may remain in the secure operating region. The primary objective to the independent system operator (ISO) is to apply suitable control action to bring the power system into the secure region. Flexible AC transmission systems (FACTS) devices can play very important role in power system security enhancement. In deregulated power systems, total transfer capability (TTC) analysis is presently a critical issue either in the operating or planning because of increased area interchanges among utilities. Utilities, therefore, would have to determine adequately their ATCs to ensure that the system reliability is maintained. FACTS devices can be an alternative to reduce the flows in heavily loaded lines, resulting in an increased transfer capability, low system loss, improved stability of the network, reduced cost of production and fulfilled contractual requirement by controlling the power flows in the network. This thesis proposes a systematic method to determine the suitable locations of FACTS devices, with static point of view. The method is based on the sensitivity evaluation with respect to control parameters for two objectives: the reduction in total system real power loss and reduction in the real power flow performance index to manage the congestion, enhancing security and TTC of the power system network. The injection model of FACTS devices has been proposed. The proposed method of location has been demonstrated on 5-bus, IEEE 14-bus, IEEE 30-bus and UPSEB 75-bus Indian systems. In view of fact that power systems nowadays are becoming more openly accessible, maneuverability of their power flow continues to be a general concern in the coming decade. Hopefully, power systems can be made more controllable and flexible due to development of computing and power electronic control technology. Apparently, power flow control within the transmission system still remains as one of the main hurdles. Power flow (or load flow) analysis involves the calculation of power flows and voltages of a power system for a given set of bus bar loads, active power generation schedule and specified bus bar voltage magnitude conditions. Such calculations are widely used in the analysis and design of steady state operation as well as dynamic performance of the system. The in power flow problem is formulated as a set of nonlinear equations. Many calculation methods have been proposed to solve this problem. Among them, Newton-Raphson method and fast-decoupled load flow method are two very successful methods. In general, the decoupled power flow methods are only valid for weakly loaded network with large X/R ratio network. For system conditions with large angles across lines (heavily loaded network) and with special control devices (FACTS devices such as UPFC) that strongly influence active and reactive power flows, N-R method may be required (Kundur 1994). Therefore, when the AC power flow calculation is needed in systems with FACTS devices, Newton- Raphson method is used. A Newton-Raphson load flow program has been developed which includes comprehensive control facilities and yet exhibits very strong convergence characteristics. The UPFC model is incorporated into an existing Newton-Raphson load flow algorithm. The modified Jacobian matrix and power mismatch equations are deduced based on the injection model of UPFC to control active and reactive powers and voltage magnitude and load flow calculation have been performed on test systems. The proposed method is also used to see the effect of change of parameters of UPFC on power system performances. An essential requirement of any modern society is the economic, secure operation of its power systems. This important objective needs many powerful technologies, such as advanced system analysis tools, optimization and control methods. After the concept of FACTS emerged, link up of FACTS to OPF is logical as reviewed from the research output. Series compensations and phase shifters are incorporated in traditional OPF. An Optimal Reactive Power Planning (ORPP) problem covering some FACTS devices like TCSC and SVC is addressed in few papers. Its objective function takes into account, the network real power loss and the constraints are load flow equations and variables limitation. Some contributions towards OPF, which maximize social benefit satisfying constraints, have been undertaken with FACTS devices to find out their optimal parameters using sequential quadratic method in this thesis. NAG FORTRAN library (E04UCF) has been used as optimization tool to optimize the parameters and generation schedule with and without FACTS devices. The minimum generation cost price may be another approach to locate these devices in open power market. Results and discussions are demonstrated on various tests systems. From the literature it is found that generalized unified power flow controllers (new emerging FACTS controller) are very powerful and can give flexible and effective power flow control in power system. Their modeling and incorporation in load flow is very much IV required. Due to high costs, it is necessary to know the optimal sitting and sizing of these devices. Therefore, emphasis has been given on development of a suitable model of GUPFC on two objectives: 1) to optimally locate them in power system for total system loss reduction and congestion management using sensitivity based method and 2) to modify the N-R load flow method to incorporate GUPFC and analyze the effect of their parameters variation on system performance of the power system. Numerical results and discussions have been given on practical test systems. Transmission pricing has been an important issue on the ongoing debate about power system restructuring and deregulation. Purpose of pricing is to recover cost of transmission, encourage efficient use and investment. Hence, location based pricing concepts has been suggested and nonlinear programming problem formulation has been developed to determine real and reactive power prices, with an objective to maximize the net social welfare within the system constraints. Impacts of FACTS devices on transmission pricing have been studied and different conclusions have been drawn on various test systems. To conclude, following issues are investigated using FACTS devices in this dissertation: • Optimal locations of FACTS devices for required objective using sensitivity approach (a) For managing congestion in open power market (b) For enhancing security of the power system (c) For enhancing Total Transfer Capability (TTC) of network • Power Flow Control using UPFC • Optimal Power Flow control using FACTS devices for parameter determination • Location and Power flow control of GUPFC • Impact of FACTS devices on pricing /wheeling of transactions.