Sharif Digital Repository

This chapter describes performance of the power system stabilizer (PSS) of a large thermal power plant as tuned by the manufacturer. The stabilizer was redesigned based on extended phase compensation of the exciter input-the electrical torque transfer function and root locus analysis; and its effect on local, interplant, and interarea electromechanical oscillations was thoroughly analyzed. Participation factors and mode shapes were effectively employed to identify local, interplant, and interarea modes, as well as their characteristics. The PSS designed with extended phase compensation improves the damping of local and interplant oscillation modes considerably, and has some positive damping... 

The paper presents a new approach that assists power system restoration planning with regards to control of temporary overvoltages (TOVs) due to transformer energization. The frequency-domain analysis in combination with analytical calculations is applied to find an optimum resonance condition. The analytical equations are based on sensitivity analysis for single frequencies and are extended to total sensitivity calculation. After an introduction of the phenomenon of overvoltages during power system restoration and harmonic resonance overvoltages, basic principles of their control are explained. Also, an algorithm is introduced for the results evaluation of harmonic resonance studies where... 

The paper presents a new approach that assists power system restoration planning with regard to control of temporary over-voltages (TOV) due to transformer energization. The frequency domain analysis in combination with analytical calculations is applied to find an optimum resonance condition. The analytical equations are based on sensitivity analysis for single frequencies and are extended to total sensitivity calculation. After an introduction to the phenomenon of overvoltages during power system restoration and harmonic resonance overvoltages, basic principles of their control are explained. An algorithm is introduced for the results evaluation of harmonic resonance studies where it is... 

The reliable design, planning, and operation of power systems are of paramount importance for providing reliable services to customers. This article reviews the different aspects of power system reliability, ranging from planning to operation. Standard benchmarks employed for power system studies are reviewed according to nearly 2,500 IEEE journal papers from 1986 to early 2019. Our overview provides the pros and cons of existing test systems, implying the lack of appropriate benchmarks for future power system studies, including renewable resources and modern technologies. Furthermore, this article presents requirements for updating and modifying the benchmarks for modern power systems... 

This paper presents a dynamic programming methodology for finding the optimum preventive maintenance schedule of generating units of a GENCO in open power systems. The objective function for the GENCO is to sell electricity as much as possible, according to the market price forecast. Various constraints such as generation capacity, duration of maintenance and maintenance crew are taken into account. In a case study, introducing a GENCO with six generating units, and implementing dynamic programming, we obtain the optimal maintenance schedule over the planning period. © 2002 IEEE  

Power system state estimation is a reliable tool used in Energy Management System (EMS) to identify the existence state of the system during its operating hours. The results of this estimation are values for unknown state parameters of the power system. The presence of systematic errors can alter the results of state estimation. The chi-square and normalized residual tests are the common post estimation procedures usually used for detection and identification of gross errors in the estimation algorithm. These tests are based on two separate test statistics and are not so powerful for detection of smaller magnitudes of gross errors. In this paper, an implementation of largest studentized... 

In this paper, an accurate fault location algorithm for series compensated power transmission lines is presented. Distributed time domain model is used for modeling of the transmission lines. The algorithm makes use of two subroutines for estimation of the fault distance - one for faults behind the series capacitors and another one for faults in front of the series capacitors. Then a special procedure to select the correct solution is utilized. Samples of voltages and currents at both ends of the line are taken synchronously and used to calculate the location of the fault. The proposed algorithm is independent of fault resistance and does not require any knowledge of source impedance. The... 

This paper presents a new controller for power system stabilizer (PSS) that, unlike the conventional linear controllers, consists of both a linear and a nonlinear part. The linear part is properly designed to improve the small-signal stability margin and the damping of the local electromechanical modes. The nonlinear part is then designed to improve transient stability margin of the system without violating the features offered by the linear controller. Both parts are designed based on a perspective which attributes the system oscillations to a Hopf bifurcation (HB) phenomenon. More specifically, the design of the nonlinear part is done through the definition of a nonlinear index that... 

In this paper, performance of power system stabilizer (PSS) of a large thermal power plant, as tuned by the manufacturer, is investigated. Then, the stabilizer is redesigned based on extended phase compensation of the exciter input - electrical torque transfer function and root locus analysis; and its effect on local, interplant and inter-area electromechanical oscillations is thoroughly analyzed. As Bisotoun PSS has a special structure with two inputs, frequency and power, its performance is compared with power-speed PSS. The effect of PSS with existing and new tunings on transient stability is also studied. Simulation results are verified by experimental test records. © 2007 JD  

The necessity of dynamic equivalents for power system analysis has been well known since the expansion of large interconnected power networks, and has been discussed during the last decades. The present paper proposes a new method for constructing dynamic equivalents of power systems. In this method, at the first step the "study system" is modeled completely via a single machineinfinite bus modeling procedure. Then the "external system" is identified as a MIMO feedback block of this model in such a manner that can include dynamic effects of the latter on the behavior of the former. The method is successfully experimented on a part of the Iranian southern network. Copyright © 2007 The... 

Application of a fast hybrid transfer switch (HTS) as a suitable tool for protection of sensitive electrical loads against power quality problems has attracted much attentions these days. In this paper, methods for desired control of a HTS which consists of a fast fault-detection method and a suitable firing and transfer strategy are proposed. Simulation results of a HTS under various operating conditions for two types of medium-voltage electrical systems, i.e. grounded (star connection) and ungrounded (delta connection) systems, with respect to total transfer time are presented. The results show the capability of the HTS and the proposed control methods in fast transferring of sensitive... 

In this paper an optimized wind/PV hybrid system with battery and diesel backup is designed. As a result of this study the costs of the hybrid system will be minimized in its 20-year life time. The optimization is done by considering the annual load increase and fuel cost rise. This Optimization is subject to load covering and minimizing the total cost. The total cost entailed maintenance, equipment and diesel fuel consumption substitution. An advanced variation of individual particle optimization algorithm (IPO) is used to solve the optimization problem  

The accurate fault location is an important criterion for protection system. Accurate and fast fault location decreases the outage time, consumers dissatisfaction and operation cost. Different methods have been proposed to determine the fault location. The impedance-based methods are usually used to protect power systems. The accuracy of these methods depends on system parameters and the structure of power systems. Also, these methods require an iterative process, the phase alignment and a high volume of data. Another algorithm has been newly presented based on negative sequence parameters, which is not iterative and the amount of data communicated between relays is small. Besides, this... 

Power system restoration is the procedure of restoring a power system after a blackout and different strategies have developed for it because of its importance. One of the most practical and economical strategies is a "Build-up strategy" that includes the process of restoring separated islands in the power system and interconnecting them after it. The process of Build-up power system restoration is highly affected by power system telecommunication capabilities. Based on the constraints of wide area measurement system (WAMS) operation, each island must be fully observable. This paper provides an approach for power system restoration and observability of these islands. The New England 39 bus... 

With the rapid evolution of electricity markets and the need for higher economic efficiency of power industry, attempts for lowering down the maintenance costs as a large portion of system operation expenses seem imperative. Recognised as a crucial step in practical implementation of modern maintenance paradigms, e.g. reliability-centred maintenance, this study proposes an efficient method to quantify the generating units' criticality on the bulk power system reliability performance. The proposed approach utilises a solution concept of game theory and evaluates the contribution of each generating unit on the overall system reliability when a higher-order contingency occurs. The suggested... 

Nowadays communication and monitoring systems play an important role in power systems security. However, these systems are exposed to bad data injection through attackers. This paper is aimed to propose a priority order list of attacked buses in order to be fully informed about the attacker decision. To do so, system security is evaluated through two well-known risk indices including under voltage risk index and overloading risk index. A genetic algorithm (GA) is employed to determine the most severe attack for each of the security indices. The effectiveness and accuracy of the proposed model are scrutinized through simulations on the IEEE 30-bus network. The paper reveals that knowing the... 

In this paper we discuss an improved method for the calculation of Available Transfer Capability (ATC) in a restructured power system. The ATC calculation is performed through an optimal power flow approach. The objective function is to maximize the sum of the receiving-end load in a specified area as well as to send generation to other control areas while a minimum cost of generation is continuously achieved. The constraints are ac power flow equations and system operation limits. It is assumed that the generation cost curve of each generator is available. A genetic algorithm is used for the optimization process. An IEEE 30 bus test system is used for testing the proposed algorithm and the... 

Electrical power system is subjefcted to disturbances. A large disturbance may bring the system to the complete blackout or partial outage. Restoration of power system to normal state constitutes several stages including transmission line connection. In closing network loops, power system operators sometimes encounter an excessive Standing Phase Angle (SPA) across a line. SPA should be within allowable limits before any attempt is made to close breaker. In this paper, the effect of reduction of SPA in improving transient stability and impact on adjacent generators is discussed. Also, the effect of closing of breakers at two ends of the line is studied. At the end, the effect of loading... 

A special hybrid genetic algorithm (GA) is designed to solve the long-term coordination of hydro-thermal power systems with cascaded reservoirs and stochastic inflows. Since decision variables are continuous, in the proposed GA we employ real number rather than binary encoding. To create superior children we introduce dynamic tuning of the weights of operators. An exponential normalization is also developed such that better chromosomes have more chance to reproduce. To test the proposed method, 16 GAs are investigated which differ based on real or binary encoding, dynamic tuning or fixed weights for operators, inverse or exponential normalization and mixed or pure random initial populations.... 

This paper describes an approach for unit start-up sequence determination during power system restoration. This approach is based on the backtracking search method, which determines the generating starting times to maximize the MWh load served over a restoration period and guarantee optimality of the start up sequence. The dynamic characteristics of different types of units and system constraints have to be considered. The shortest path, i.e., the path that requires the minimal number of switching actions, between the supplying unit and load is selected unless it is not feasible. Simulation tests, carried out on 39-bus New England test system, verify the effectiveness of the proposed method....