Operating Conditions Of Power System Research Articles

Out-of-Step Relays Testing Procedure

Out-of-Step Relays Testing ProcedureThe paper presents out-of-step (OOS) protection device testing methodology under close-to-real power system operation conditions. The power system stability modelling software is used as source of test signals. The accurate modelling of power system in conjunction with dynamical modelling features allows the correct choice of the most reliable OOS protection scheme. Methodology was applied for out-of-step relay "AGNA" testing and device settings verification.

Fixed order controller design subject to engineering specifications

This paper analyzes and extends the simple and efficient low-order controller design method proposed in 1999 by O.N. Kiselev and B.T. Polyak, as applied to the stabilization of normal operating conditions of electric power systems. Within this approach, the complete set of feasible regulators of given structure is composed (or generated in a random way) and a desired controller is then chosen according to one or another performance index formulated in engineering terms. A robust version of the method is also analyzed and a generalization to higher-order controllers is discussed.

Adaptive neuro-fuzzy inference system based representative quality power factor for power quality assessment

Under sinusoidal operating conditions of electric power system, the classical definitions of apparent power and power factor work well as long as the loads are linear and the source voltage waveform is sinusoidal. Increase in use of power electronic devices, adjustable speed drives and other nonlinear loads cause the voltage and current waveforms to become non-sinusoidal and highly distorted. A new adaptive neuro-fuzzy inference system based representative quality power factor (ANFIS RQPF) is proposed in this paper to represent the existing different power factors—displacement power factor, transmission efficiency power factor and oscillation power factor. The ANFIS RQPF can represent an essential module for evaluating and amalgamating the three power factors. The ANFIS RQPF was applied to different cases—linear, nonlinear, sinusoidal and non-sinusoidal considering lagging and leading power factors. It is shown that the ANFIS RQPF is expressive and accurately represents the existing power factors in all cases and in all situations. Taking into consideration the advantages of the ANFIS such as simplicity, ease of application, flexibility, speed and ability to deal with imprecision and uncertainties, this factor can be useful for power quality assessment, cost-effective analysis of power quality mitigation techniques, as well as billing purposes, in these situations.

An Affine Arithmetic-Based Methodology for Reliable Power Flow Analysis in the Presence of Data Uncertainty

Power flow studies are typically used to determine the steady state or operating conditions of power systems for specified sets of load and generation values, and is one of the most intensely used tools in power engineering. When the input conditions are uncertain, numerous scenarios need to be analyzed to cover the required range of uncertainty. Under such conditions, reliable solution algorithms that incorporate the effect of data uncertainty into the power flow analysis are required. To address this problem, this paper proposes a new solution methodology based on the use of affine arithmetic, which is an enhanced model for self-validated numerical analysis in which the quantities of interest are represented as affine combinations of certain primitive variables representing the sources of uncertainty in the data or approximations made during the computation. The application of this technique to the power flow problem is explained in detail, and several numerical results are presented and discussed, demonstrating the effectiveness of the proposed methodology, especially in comparison to previously proposed interval arithmetic's techniques.

Dynamic and Steady Behavior of Harmonic Filter for Compensating Resonance in Mining Systems

Process integration and automation in mining facilities require systems engineering involving electronics, information technologies, telecommunication, computer-based devices and power electronics control for a broad range of functions. Electronics controllability has evolved with power converter-based systems for material handling and mineral ore processing. However, power converters introduce harmonics and EMC/EMI emissions, affecting the reliability of sensitive and important electronic systems, stating a current challenge for a proper design of electrical systems in mining facilities, because increasing complexity due to combination and interaction of weak networks, high-power equipment, variable structure and non-linear loads with harmonic current injections. Harmonic filters are commonly used to provide power factor correction and limiting the harmonic distortions. This paper highlight the capability of harmonic filters to give a stationary and dynamic behavior that can be employed for compensating resonances of electrical systems in order to avoid unwanted transient phenomena like overvoltages. Modeling and simulation results obtained for a typical system with switching operations depict the good correlation between steady and transient behavior, supporting the results given by tools intended for stationary analysis of harmonics performance. Different operating conditions of an industrial power system given by variable topology, multiple harmonic injections and loading factor should be taken into account for the proper design of harmonic filters systems. This work presents a methodology for supporting the risk assessment and decision making process at the design stage of power systems, in order to avoid failures, improving design and reliability.

Simulation of the first-loop water chemistry regime of a nuclear power system with a two-phase water coolant

An approach to simulating the water-chemistry regime for transient and stationary operating states of a nuclear power system is proposed. The approach is based on the designer’s philosophy. The first loop of the nuclear power system is divided into standard units. The special features of the reactor design and the crux of the problem being solved determine the number of units and the interaction between them. The units can be structural components of the loop as well as coolant components. The thermochemical and radiation-chemical transformations of the components of the water coolant are simulated at each unit. The interaction between the physicochemical processes at the units is expressed in the flow of the coolant components between them. The approach developed is illustrated on the analysis of the water-chemistry regime in implementing a passive safety system — a promising solution geared toward increasing the operational safety of the first loop of a nuclear power system.

ART artificial neural networks based adaptive phase selector

This paper introduces a new phase selector based on adaptive resonance theory (ART). Because conventional phase selector cannot adapt dynamically to the power system operating conditions, it presents different characters under different power system conditions. To overcome the disadvantage, an adaptive phase selector, which utilizes artificial neural network based on ART, is designed. ART based neural network (ARTNN) has some advantages such as no local extremum, quickly convergence and so on. Therefore, the proposed ARTNN based phase selector has better performances compared with other neural networks based phase selector, and the new selector can adapt dynamically to the varying power system operation conditions. Furthermore, the phase selector can be trained and learned on-line. A lot of EMTP simulations and experimental field data tests have illustrated the phase selector's correctness and effectiveness.

Decentralized Nonlinear Adaptive Control for Multimachine Power Systems Via High-Gain Perturbation Observer

This paper presents two novel decentralized nonlinear adaptive controllers (DNAC) for large-scale interconnected power systems, via state-feedback and output-feedback strategies respectively. In the both controllers, system perturbation, which includes all subsystem nonlinearities and interactions between subsystems, is estimated by a high-gain observer and then involved the decentralized adaptive feedback linearizing control law. For the first DNAC, when all subsystem states are available, a second-order high-gain perturbation observer is designed to estimate the system perturbation, which leads to a decentralized nonlinear adaptive state-feedback controller. For the second, a decentralized nonlinear adaptive output-feedback controller is designed using a high-gain states and perturbation observer, when only one subsystem state is measured. The stability of the closed-loop controller/observer system is analyzed by the Lyapunov direct method. Both the controllers have been evaluated in a simulation study based on a three-machine power system. The results show that with a simple structure, both the controllers have robust performance of improving the transient stability and damping of multimode oscillations, under different power-system operation and fault conditions.

On-site safety evaluation for earth fault in mining power systems

Many mining power systems utilize ineffectively grounded sources to restrict the residual current of single-phase earth fault in order to reduce outage and shock hazard. In practice, with the system expansion, topology changing, and insulation aging, the potential residual current and zero-sequence voltage for earth fault vary dynamically and some arcing earth faults can easily cause over-voltage and induce multiple faults. In order to improve the system safety, on-site condition monitoring, safety evaluation, and preventive maintenance for earth fault are proposed in this paper. Some techniques for online parameters measurement based on resonance-measurement principle are presented. Power system operation states are classified into normal secure state, alert state, incipient fault state, and fault state. Some security enhancement methods (preventive action and remedial action) for each state are implemented. The prototype for safety evaluation has been developed and installed in industry power systems for several years.

Experimental study on on-line grasp of operating condition of longitudinal power system by use of SMES

SMES (superconducting magnetic energy storage) system has excellent ability as not only an energy storage system but also a power system stabilizer, a load fluctuation compensator and so on. A new application of SMES in a power system has been proposed, that is, for on-line grasp of power system operating conditions. This paper shows the possibility and validity of the proposed application of SMES by use of a small SMES system and power system simulator of rotating machine type. The experimental system is a longitudinal four machine power system. It was confirmed the SMES can give a small power swing of known pattern without affecting operating conditions of the power system. On-line data of response due to the small power disturbance of SMES were analyzed to obtain natural frequencies and eigenvectors of the power system operated. The power system operating condition was estimated by these data. This application can be easily used with a SMES of small size.

Robust observer-based nonlinear control of multimachine power systems

A novel robust observer-based nonlinear controller (RONC) for excitation control of synchronous generators interconnected in a multimachine power system is presented. The RONC is developed based on a feedback linearising control strategy for nonlinear systems and it employs estimation of system states and perturbation. A sliding-mode observer is designed to estimate system states and perturbation which encompasses all the system nonlinearities and uncertainties. The successful estimates of states and perturbation are involved in the feedback control law, which enables a real-time compensation of system nonlinearities, to realise the feedback linearisation of the nonlinear power system. The RONC is robust in performance as its design does not require the exact knowledge of the power system. Moreover, the RONC is easy to be implemented as only one state is measured. The simulation study is carried out based on a three-machine power system. The results show that the RONC has better performance and robustness, under variations of power system operation conditions and disturbances, in comparison with a conventional nonlinear state feedback linearising controller (NFLC).

Artificial neural network based contingency ranking method for voltage collapse

The paper presents a neural network-based approach for contingency ranking of voltage collapse. By using the singular value decomposition method, a Radial Basis Function (RBF) neural network is trained to map the operating conditions of power systems to a voltage stability indicator and contingency severity indices corresponding to transmission lines. The advantages of RBF neural network are demonstrated by applying it to contingency ranking and voltage stability assessment. Tests carried out on the IEEE 57-bus system are reported.

Object-oriented methods drive protective relay system

China is a developing country, and shortages in electrical power supply exist in most provincial power systems. Stability margins are always very limited, which requires operators to run the system carefully. With each change in either the power system configuration or operating conditions, a series of actions must be taken to guarantee the safety of the power system. The actions adopted for the protective relays include arranging protective devices appropriately and setting relays at their appropriate values for all elements involved. In addition, as power systems are developing very fast in China, the number of skilled operators available is far less than required. Expert systems are urgently needed. This article describes the use of object-oriented (OO) methods to develop expert systems and, in particular, features the object-oriented expert system for the power system protective relay operation and management (OOPRES). The article covers knowledge acquisition and representation, knowledge management, and inference engine.

Probabilistic three-phase load flow

In actual systems unavoidable uncertainties affect the steady-state operating conditions of a power system: these uncertainties are mainly due to changes of load demands and of generation system. Taking into account the uncertainties, it is most useful to introduce random variable and to apply probabilistic techniques of analysis. Up to now probabilistic power flows neglect the unbalances of the loads and of the other components and consider adequate single-phase model of the whole power system. In this paper the probabilistic power flow is extended to the three-phase field to evaluate the uncertainties which affect the steady-state operating conditions of an unbalanced power system. Both Monte Carlo procedure and a linearized form are proposed. A numerical application to a test system is also discussed.

Experimental verification of multi-input PSS with reactive power input for damping low frequency power swing

A multi-input power system stabilizer (MPSS) is developed to improve damping of low frequency power swing in long distance power system and to emphasize robustness for changing power system configuration and/or operating conditions. In the MPSS, the deviation of reactive power /spl Delta/Q, changing rates of terminal voltage and active power output are added to a /spl Delta/P+/spl Delta//spl omega/ input type PSS. In this paper, the AVR with the MPSS is applied to 100 kVA micro generator in CRIEPI's Power System Simulator and is compared with the /spl Delta/P+/spl Delta//spl omega/ PSS. The MPSS is verified through linearized system analysis and experiment to damp low frequency power swing and to have better performance than the /spl Delta/P+/spl Delta//spl omega/ PSS.

Rule-based variable-gain power system stabiliser

The paper presents a rule-based variable-gain power system stabiliser (PSS) for power systems, which has been implemented in the laboratory by transputers for real-time control tests. This stabiliser has been developed from the conventional PSS, but with a variable gain, which is adjusted on-line to meet the damping requirement of power systems. The real-time adjustment of the stabiliser gain is based on two control rules by detecting the oscillation status in the systems. The object of this arrangement is to achieve a stabiliser which is robust to the changes of the operating conditions of power systems and can suppress the oscillation detected in the system more effectively and with less detrimental influence on the transient performance of power systems. Results of laboratory tests are presented in the paper to show the effectiveness of this rule-based variable-gain power system stabiliser.

Discussion on “Determination of optimum power-system operating conditions under constraints”

Discussion on “Determination of optimum power-system operating conditions under constraints”

Power-system load scheduling with security constraints using dual linear programming

The optimisation of power-system operating conditions is formulated as a dual linear programming problem. This suboptimal model allows fast solutions to be obtained dependably by applying the revised simplex l.p. method to the problem of minimising total generation costs subject to the constraints imposed. These constraints include the network equations, the inequalities restricting generator loading, runningspare capacity and transmission-line loading under normal and outage conditions. The fast speed of solution and low computer-storage requirements result from the reduced mathematical model developed by means of the variable eleimination and the computing strategy used. The computational procedure automatically adjusts the size of the problem to be solved according to indications obtained of the likely critical lineoutage security constraints, a small number in relation to the prohibitively large number of possible outage constraints. A sample application of the method is given for a 2700MW, 275/132kV system of 23 busbars, 30 lines and transformers, supplied by 24 generators. Using ALGOL 60 on the Atlas computer, solutions were obtained in 5s neglecting line-outage security, and 11.5s including security under all possible single-line-outage conditions. For accuracy, comparisons are also made with the network-flow technique and the full nonlinear programming solutions.

Determination of optimum power-system operating conditions under constraints

The optimisation of power-system operating conditions is formulated as a general mathematical programming problem. All the system voltages, active and reactive generations and transformer tap settings are considered as independent variables, with network equations represented by equality constraints, and system operating limits by inequality constraints. An iterative indirect approach to the problem based on the Lagrange-Kuhn-Tucker conditions of optimality is presented, and the computer program is described briefly. A small sample system of part of the British 275/132kV network is solved.

Aids in the calculation of transient stability

An abrupt change in the steady operating conditions of a synchronous power system may produce transient-stability problems. A study of these is of great importance in electrical engineering. This account reviews the application of various computational aids to the solution of these problems.The authors are in the Department of Electrical Engineering, King's College, University of Durham.