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Integrated system preventive maintenance is an exigent job in both regulated as well as deregulated utility systems that must be carried over by the utilities in order to extend their continuation and performance. The generator maintenance scheduling is commonly focused, but the line flow limits in the transmission lines, which are connected to the generating units may violate due to the outages. Thus, maintenance planning of generators and transmission lines has become indispensable and the Integrated Maintenance Scheduling (IMS) addresses alike. Inclusion of transmission lines and line flow constraints in generating unit maintenance will increase intricacy of the problem that enforces IMS for secure and economic operations. As an efficient optimization tool is necessary, the modern bio inspired algorithm, Ant Lion Optimizer (ALO) has been intended for the first time to address the IMS problem. The well-known / standard test systems are used for demonstration and the attained numerical results by simulation are compared with other meta-heuristic methods. The comparison reveals that the ALO is a positive choice for solving IMS problems.

This paper describes a method for alleviation of line over load in a line by regulation power flow in another line having Series Power Flow Controller (SPFC). For this purpose, the sensitivity relations between the line flow of the line with SPFC and the over loaded line are determined. These sensitivity relations are used to determine the required amount of change in power flow at the line with SPFC to reduced power flow of the over loaded line. IEEE 30 system is used to verify the applicability of the proposed method.

Line flow is one of the key factors which dominate the power system security. To deal with this problem, this paper proposed a method of power system assessment and control based on power system Line flow risk. Probabilistic power flow (PPF) is used to analyze the random of system statuses. The severity function is used to describe the impact of the transmission line load. Line flow risk is defined as the result of the probability multiplying the severity of Line flow. It is an indicator of power system security. This reduces the system line flow risk and increases the system security.

This paper investigates voltage stability of the power system during steady state and transient conditions. The voltage stability enhancement is achieved by utilizing FACTS devices at the best location of the system. The weakest bus in the system is the best location to implement shunt compensation device. In this paper, the weakest buses are identified via a fuzzy technique that utilizes two critical indices: Line Flow Index (LFI) and Voltage Profile Index (VPI) during normal and fault conditions. These indices are used to evaluate Criticality Index (CI) using Fuzzy rules, and thus, the system buses are ranked. Remedial actions are discussed to enhance the power system voltage stability by using FACTS devices (SVC and STATCOM) at the most vulnerable system buses. The results of this study show that the (STATCOM) performance is preferable to that of the (SVC) during fault conditions.

Under open access, market-driven transactions have become the new independent decision variables defining the behavior of the power system. The possibility of transmission lines getting over-loaded is relatively more under deregulated operation because different parts of the system are owned by separate companies and in part operated under varying service charges. This paper discusses a two-tier algorithm for correcting the lone overloads in conjunction with the conventional power-flow methods. The method uses line flow sensitivities, which are computed by the East Decoupled Power-flow algorithm and can be adapted for on-line implementation.

This paper presents a new decoupling strategy by strengthening P – δ and Q – V relationships based on line flow and voltage magnitude measurements in order to obtain a reliable convergence and higher computational speed. The real and reactive set of measurements are combined using simple multiplying factors such that the modified set is decoupled into two set of equations without making any assumption on r / x ratios. The resulting Jacobian matrices that contain only line parameters are sparse and constant. The technique is applied on three test systems and is solved by WLS and WLAV methods to illustrate its superior performance.

In this paper, a new algorithm based on sensitivity method for alleviating overloads in power networks is presented to find the switching branches effectively. By applying the new sensitivity of the line flow with respect to the change of the branch impedance, both on and off switchings for alleviating overloads in power networks are performed systematically at once and an effective scheme for drawing up a plan to alleviate overloads of the lines is presented through screening a large number of line switching cases easily. The ranking of switching branches is calculated according to the new switching algorithm based on sensitivity method and the switching of the ranked branches is performed in the order of ranking until overloads are eliminated. In order to show the effects of this algorithm, it is applied to a small scale power system of IEEE 39-bus test system.

This paper develops a test bed based on the Northeastern Power Coordinating Council (NPCC) 48-machine, 140-bus power system model for simulating cascading failures. Then, the paper uses the test bed to demonstrate the interaction model recently proposed by [1] for analyzing cascading failures, identifying key linkages between component failures, and predict propagation of failures. For the NPCC test bed, a new efficient method is proposed to determine line flow limits as critical parameters in cascading failures simulation. Then, those limits are utilized in AC-OPA to generate a database of cascades. Finally, the interaction model is derived based on the database to extract key knowledge on cascades, which can be used for online analysis and simulation of cascading failures.

In this paper, the risk of coming across flow neck in electric power systems is considered, and a computational example on expenses required in order to control the risk is shown. Total fuel cost increases by setting a margin which controls the risk. This cost is the necessary cost for the risk hedge. The uncertainty of load demand is assumed to be normal distribution. Then charge of the line flow which is calculated from changes of each load demand is assumed by using sensitivity coefficient. The risk of arising uncertainty of load line flow is shown. In order to control this risk, a margin is introduced, and the relation between this margin and the incremental fuel cost is calculated. This calculation technique can estimate expenses required in order to control the risk arising from uncertainty of load. © 2008 Wiley Periodicals, Inc. Electr Eng Jpn, 164(3): 42–49, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.20480

This paper presents principles about installation and operation of flexible ac transmission systems (FACTS) devices to enhance the steady-state security of power system. Three generic types of FACTS devices are introduced and the proper location of each kind of FACTS devices is determined in accordance with the individual purpose of use. It is desirable to install shunt controllers where there is a need for voltage support according to V – Q sensitivity analysis and to install series controllers where line flow control is required to increase system loadability. It is also important to install combined series–shunt controllers such as UPFC in order to get most of their merits, that is, to control both the active and reactive power flow. An algorithm to minimize simultaneously and iteratively both kinds of security indices such as J P relating to line flow and J V relating to bus voltage is proposed in this paper. For minimization of security indices, each sensitivity vector of both indices is derived analytically. Results from the minimization show that optimal operating points of FACTS devices under various conditions of power system have been achieved. The proposed methodology to install and operate FACTS devices properly is verified on the IEEE 57-bus system where FACTS devices were operated under normal condition and in a line-faulted contingency.

Line flow constraints or transmission capacity constraints are among the most important constraints in power systems generation scheduling and system reliability evaluation problems. For real world systems, there are usually a very large number of transmission capacity constraints and this is one of the main difficulties in solving the related problems. However, it has been found that many of the transmission capacity constraints are redundant, i.e., feasible region and optimal solution of the related problem will not be changed if the redundant constraints are eliminated from the problem formulation. The solution efficiency of any method, whereas, will be greatly improved when the redundant constraints are removed. Approaches for identifying the redundant constraints have been reported in literature and a revised method is established in this paper. The new method can be used to quickly identify the redundant constraints in systems with changeable power and load injections. Compared with the reported methods, the new method is much easier to be understood and implemented. Numerical testing is performed and it is found that the new method is efficient.

This paper presents a detailed formulation and implementation of a fast program for power system available transfer capability (ATC) calculations. The formulation is based on the linear incremental power flow to account for the line flow thermal loading effects. An efficient linear ATC implementation enhances speed in processing a large number of contingencies to determine ATC for each specified transfer. Test and performance results for practical power system models are presented.

Optimum power flows and security constrained power flows assume that customer demand is a fixed quantity. In the new competitive environment, it is necessary to assume that demand is elastic and will vary as a function of price. A critical element in any competitive model, whether it be a PoolCo or a multi-lateral contract model, is for a system operator to ensure reliability and feasibility of the power system operating point. Security pricing for feasibility was first advanced by Schweppe et al for the case of line flow constraints for a PoolCo model. Using geometry, this paper generalizes the approach to include any security constraint for a general competitive model. The paper discusses interpretations of security pricing and its possible implementation in energy management systems.

The practical power system operation criterion along with short term and long term expansion planning are most important parameter to be factored into the decision of the optimal location of FACTS controllers for achieving the maximum benefit of FACTS controllers. This paper proposes the optimal location of TCSC controllers in the power transmission system to eliminate or alleviate line overloads in the system based on practical power system operation criterion. The concept of line flow overload sensitivity index (LFOSI) of the system lines with reference to real time generation mix strategies based on conventional and nonconventional generation, seasonal load pattern, peak and off-peak conditions, adhering grid discipline, permitting power transactions, future projected demand, network modification and capacity addition have been developed. The proposed concept of FACTS placement using LFOSI based on practical operation criterion and expansion planning approach has been extensively analyzed and implementation methodology is also developed to decide the optimal location of FACTS controllers so as to consider practical operation criterion and expansion planning systematically.

This paper presents an enhanced expert system for line flow control in power systems. The preventive mode dealing with both pre-contingency and post-contingency constraints is considered in this enhanced expert system. The presented expert system is achieved through integration of an existing expert system and the fuzzy set theory. The IEEE 30-bus system and a practical 265-bus system in Taiwan are used to serve as samples to show the applicability of the proposed expert system in this paper.

Fast, accurate algorithms to compute network capabilities are indispensable for transfer-based electricity markets. Available Transfer Capability (ATC) is a measure of the remaining power transfer capability of the transmission network for further transactions. Transmission System Operators (TSOs) are encouraged to use the existing facilities more efficiently. One of the limitations of reactive ATC is the error produced by neglecting the effect of reactive power flows in line loading. This paper presents the determination of shunt reactive power compensation with Flexible AC Transmission System (FACTS) devices, the Static Synchronous Series Compensator (SSSC) to improve the transfer capability of a power system incorporating the Linear and Reactive power flows in ATC calculations. By redistributing the power flow, the ATC is improved. Studies on a sample 5-bus power system model are presented to illustrate the effect of shunt compensation along with line flow control.

This paper presents an on-line economic power dispatch method by calculating the B -coefficients from the network sensitivity factors. The sensitivity factors are established from a new line flow solution based on the DC load flow model. The derivation of a new loss coefficient formula is performed and the solution algorithm is described. Many assumptions in the use of the conventional loss coefficients are eliminated. Example systems are tested to demonstrate the performance of the proposed method. Compared with the exact solution of the optimal load flow method and the computational rapidity of the base-case database method, the proposed method has good accuracy and a fast execution time. This method is very suitable for on-line application in the economic operation of power systems.

This paper proposes a new evolutionary approach named as multi agent particle swarm optimization (MAPSO) algorithm for solving economic dispatch with security constraints (line flow and bus voltage). This method integrates multiagent systems (MAS) and particle swarm optimization (PSO) to form a new algorithm, multiagent particle swarm optimization algorithm. In MAPSO, an agent represents a particle to PSO and a candidate solution to the optimization problem. All agents live in a lattice like environment, with each agent fixed on a lattice point. In order to obtain optimal solution, each agent competes and cooperates with its neighbor and it can also learn by using its knowledge. Making use of these agent-agent interactions, MAPSO realizes the purpose of minimizing the objective function value. MAPSO is applied to two representative systems i.e. IEEE 14 bus and IEEE 30 bus systems. Simulation results show that proposed approach gives better solution than earlier reported approaches.

Summary form only given. Research effort has been given to locate the optimal locations of thyristor-controlled series capacitor (TCSC) and their initial compensation levels using mixed-integer programming (MIP). As a useful technique for combinatorial optimisation over integer and continuous variables, the MIP approach can provide robust performance as well as high computational efficiency while solving complex optimal problems. Previous work using MIP employed DC load flow model ignoring reactive power balance, power loss and transformer tap ratios. In this paper, a new planning method is developed based on recently reported line flow equations and basic linearisation of binary-continuous products. The objectives of the planning strategy are to improve system loadability, voltage profile in the network, as well as to minimise the investment cost by choosing proper locations and settings of devices. Simulation results are presented and discussed for IEEE 9-, 57-, 118-, and 300-bus systems.

A power system state estimation algorithm using line flow measurements only is presented. The algorithm estimates the state of only one node at a time using measurements in the electrical vicinity of that node. Before any measurement is used, it is passed to a subroutine that tests for bad data. Thousands of tests were performed on the IEEE 14-bus and the IEEE 30-bus systems; results are compared with the line flow only (LFO) method. It is concluded that the proposed method is much faster than the LFO method and it can identify almost all bad data having an error greater than four times the maximum expected normal error.

As a useful tool for combinatorial optimisation over continuous and discrete variables, the mixed-integer linear programming (MILP) approach can address complex control and planning models providing high computational efficiency as well as robust behavior. On power system planning, previous work using MILP employed conventional dc load flow model neglecting reactive power, power loss and transformer tap ratios. In this paper, a novel thyristor-controlled series compensator (TCSC) allocation model is proposed based on recently reported line flow equations and basic linearisation rule of binary-continuous products. The objectives of the planning strategy are to improve system loadability by choosing proper locations and settings of devices. Simulation results are presented and discussed for IEEE 9- and 118-bus systems.

This paper discusses the concept of state forecasting and estimation in power systems. A method of forecasting bus injective power and line flow power which makes use of the current information and the historical data from run patterns is presented and the results of state forecasting and estimation are compared with those of static state estimation. >

This paper presents an efficient bounding method suitable for fast contingency screening. It is based on real power flow distribution factors relative to selected network branches of an interest area centered around the outaged branch. The maximum amount of real power flow leaving the interest area serves as a bound on the change in line flow across the branches outside the area considered. The implementation of the proposed approach exploits the method's ability to keep the number of endangered branches limited to any preselected value. The proposed method is validated by extensive testing with reference to both IEEE test networks and actual power systems of Italian, European and North American origin.

Application of FACTS devices in power systems is promising new and more efficient operating scenarios for implementing the transfer of power in a bulk grid or RTO (regional transmission operator). With FACTS devices installed in a power system, methods based on traditional busbar-oriented power flow methods need substantial modifications for handling series line flow control as well as shunt injection powers, as evidenced in the many approaches proposed in the literature. Traditional busbar-oriented power flow algorithms use busbar voltage magnitudes and phase angles as independent variables. An alternative line-flow-and-busbar-voltage-magnitude-based formulation is shown to be more useful in solving the power system with FACTS devices under steady state conditions. Such a formulation permits much greater flexibility in evaluating the FACTS device ratings. All the common FACTS device models are easily incorporated in the new framework. The potential of the alternative formulation is demonstrated through the solution of examples with FACTS devices.

A ranking method is a means of reducing the prohibitively large computational burden involved in the conventional exhaustive contingency analysis which is carried out for assessing the steady-state security of a power system. This paper summarizes the theory and compares the accuracies and efficiencies of various MW ranking methods which utilize the criteria of line flow problems for achieving a ranked list of all the proposed contingencies. The original forms of all the methods as well as the modified forms of a number of them are tested on a 275 kV power system assuming primarily single line contingencies. The effect of the higher values of the exponent(s) of the performance index on the accuracy and efficiency of several of the methods is also illustrated.

The paper presents the implementation of the fast decoupled load flow technique for the inclusion of a multiterminal HVDC link in a large AC system. It is shown in the paper that reliability, computational speed and storage advantages, offered by the basic fast decoupled algorithms are preserved as far as the AC network is concerned. The method described in the paper is versatile to include any particular control mode of the HVDC link by changing some of the elements associated with the DC Jacobian matrix. Further tha outages of ac and dc lines are simulated by modifying the power injected to the affected buses using the fast decoupled line flow algorithms. A test example is worked out to highlight the formulas presented in the paper. The dynamic stability mcdeloof the multiterminal HVDC system is then attempted by using the linearised version of the DC Jacobian matrix and replacing the AC network by equivalent generations and loads.

Extending the theoretical foundations established in Part I(1), this paper further describes this efficient method of computing the real-time load flow solution for a power system network. An efficient numerical solution technique particularly applicable to this problem is outlined. Relative weighting of the measurements is analyzed in terms of the measurement accuracies. A method is given for dynamic determination of the frequency of the state estimate calculations. The effects of real-time changes in the network are discussed.

Under open access environment in the era of deregulated power industry, transmission loss allocation to various transactions is one of the important issues to be solved exactly. Because of the non-linear nature of power flow and power loss, it is very difficult to segregate and to allocate losses among the participants properly. This paper presents a New DC method (NDC) where an efficient loss allocation algorithm has been applied. Considering the impact of every line flow in a network, the loss allocations to the loads have been computed at first and finally the total loss has been allocated to the generators. The effectiveness of this procedure has been studied for the 6-bus and IEEE 118-bus model power systems. Several numerical analyses implicate that the proposed loss allocation procedure including the DC load flow model is reasonably acceptable. Keywords: Transmission loss allocation DC load flow model, Deregulated power market Bangladesh J. Sci. Ind. Res. 42(3), 257-268, 2007