Showing papers on "Electric power system published in 1985"

Power System Harmonics

Abstract: Preface Introduction Harmonic Analysis Harmonic Sources - The Static Convertor Other Harmonic Sources Harmonic Effects: Within the Power System Interference with Communications Power System Harmonic Measurements Transducers and Data Transmission Standards for the Limitation and Control of Power System Harmonics Harmonic Penetration in A.C. Systems Harmonic Elimination Index.

A United Approach to Optimal Real and Reactive Power Dispatch

Abstract: This paper presents a unified method for optimal real and reactive power dispatch for the economic operation of power systems. As in other methods, the problem is decomposed into a P-optimization module and a Q-optimization module, but in this method both modules use the same generation cost-objective function. The control variables are generator real power outputs for the real power module; and generator reactive power outputs, shunt capacitors/reactors, and transformer tap settings for the reactive power module. The constraints are the operating limits of the control variables, power line flows, and bus voltages. The optimization problem is solved using the gradient projection method (GPM) which is used for the first time in the power systems study. The GPM allows the use of functional constraints without the need of penalty functions or Lagrange multipliers among other advantages. Mathematical models are developed to represent the sensitivity tivity relationships between dependent and control variables for both, real and reactive power, optimization modules, and thus eliminate the use of B-coefficients. Results of two test systems are presented and compared with conventional methods.

Electric load model synthesis by diffusion approximation of a high-order hybrid-state stochastic system

Abstract: A statistical approach is used to model the dynamics of the electric demand of large aggregates of electric space heaters or air conditioners. The importance of such loads is twofold. First, they account for a significant portion of power system dynamics following a power outage. Second, because they are associated with energy storage, they are often selected for load shedding within a load management program. The derivation of the aggregate electrical dynamics is considered first for a homogeneous group of devices. Subsequently, a perturbation analysis yields the dynamics for a nonhomogeneous group. The homogeneons group aggregrate load model is a system of coupled ordinary, and partial differential equations (Fokker-Planck equations). It is obtained by writing evolution equations for the probability density of a hybrid-state Markov system used to model the switching dynamics of individual devices. This result is new and could give a clue to the analysis of a broad class of hybrid-state stochastic systems. In turn, this could provide a new impetus not only in the area of electric load modeling but other areas such as power system reliability and the design of relay control systems, where stochastic hybrid-state models occur frequently. Simulation results which illustrate the dynamical properties of the model are presented.

Direct methods for transient stability analysis of power systems: Recent results

Abstract: Transient stability analysis of a power system is concerned with the system's ability to remain in synchronism following a disturbance In utility planning, transient stability is studied by numerical simulation The long CPU run times for simulation preclude their use for on-line security analysis Interest has therefore shifted toward the Lyapunov direct method of stability analysis This paper provides a critical review of research on direct methods since 1970 Considerable progress has been made on both theoretical properties of energy functions and on criteria suitable for on-line implementation Current theory provides a satisfactory treatment of voltage-dependent reactive power demand, transfer conductances, and flux decay However, it cannot incorporate the exciter control Proposed on-line criteria appear to work very well on sample examples; but, they still lack rigorous justification Finally, recent work has shown that power systems can exhibit chaotic behavior This surprising fact demonstrates that our understanding of the dynamics of power systems remains incomplete

Transmission Network Planning Using Linear Programming

Abstract: In long range transmission planning, where new load growth, new generation sites and perhaps a new voltage level are to be considered, a computer aided method of visualizing new circuits in a network context is needed. The new method presented meets this need by the combined use of a linear (dc) power flow transmission model and a transportation model (also known as a trans-shipment model). The dc transmission model is solved for the facilities network by obeying both of Kirchhoff's laws, flow conservation at each bus and voltage conservation around each loop. The transportation model is solved for the overloads by obeying only the bus flow conservation law while minimizing a cost objective function.

Electrical Engineer's Reference Book

Abstract: General principles materials power generation transmission and distribution power systems electricity utilization - power control and conversion electricity utilization - materials treatment electricity utilization - environmental electricity utilization - transportation.

Reliability Modeling of Generation Systems Including Unconventional Energy Sources

Abstract: A method for reliability evaluation of electric power systems with unconventional energy sources, such as solar power plants and wind turbine generators, is presented. The fluctuating nature of energy produced by such unconventional units has a different effect on the overall system reliabilitv than conventional units. Methods described in the published literature appear to have several deficiencies. The method presented in this paper combines conventional and unconventional units into separate groups. The analysis proceeds by creating a generation system model for each group. The models of the unconventional groups are modified hourly depending on the limitations of energy. All the models are combined hourly to find the loss of load expectation and the frequency of capacity deficiency for the hour in question. This procedure is accomplished using a discrete state algorithm as well as the method of cumulants. Results obtained in a case study using the proposed method are described.

The Effects of Power System Harmonics on Power System Equipment and Loads

Abstract: This report is intended to present a summary of current knowledge regarding the effects of power system harmonics on system equipment and loads. The purpose of this summary is two-fold: first, to lay a groundwork for the study and control of system harmonics; and second, to promote a discussion with those closely involved with each of the various load types.

Commissioning Tests Of The Bonneville Power Administration 30 MJ Superconducting Magnetic Energy Storage Unit

Abstract: A 30 MJ (8.4 kWh) Superconducting Magnetic Energy Storage (SMES) unit with a 10 MW converter has been installed and commissioned at the Bonneville Power Administration (BPA) substation in Tacoma, Washington. This is the first large-scale application in the US of superconductivity in an electric utility system. The unit, which is capable of absorbing and releasing up to 10 MJ of energy at a frequency of 0.35 Hz, was designed to damp the dominant power swing mode of the Pacific AC Intertie. This paper describes the electrical characteristics of the magnetic energy storage unit, its modes of operation, results of device tests, means for controlling real and reactive power, and some initial power system response tests. A short summary of the operating history of the unit over the first eleven months is also presented.

Bad Data Identification Methods In Power System State Estimation-A Comparative Study

Abstract: The identification techniques available today are first classified into three broad classes. Their behaviour with respect to selected criteria are then explored and assessed. Further, a series of simulations are carried out with various types of bad data. Investigating the way these identification techniques behave allows completing and validating the theoretical comparisons and conclusions.

A Decomposition Approach To Automated Generation/Transmission Expansion Planning

Abstract: This paper describes a model for automated generation/transmission expansion to be used in longterm system planning studies. The network is represented either by a transportation model or by a linearized power flow model. The solution technique is based on Benders decomposition, maximum flow algorithms and linear programming/optimal dispatch models. Case studies with the system of Southern Brazil are presented and discussed.

Kalman Filtering Applied to Power System Measurements for Relaying

Abstract: Digital protection algorithms are becoming more complex as the cost of computational equipment continues to decrease. In particular, optimal response digital filters, such as Kalman filters, can be implemented on presently available devices. Optimal filters are not yet extensively applied because they appear complex and engineers have not become familiar with their use. This paper presents the basics of the Kalman filtering technique in power systems terminology and illustrates its use for estimating rotating phasors. Sample designs are presented for voltage and current phasor estimation during system transients. A method for including decaying dc and harmonic frequency components in the filter design is also described and sample results are presented.

Optimal Scheduling Of Large Hydrothermal Power Systems

Abstract: In this paper we present a new algorithm to find the optimal unit commitment and economic dispatch (UC/D) for a large hydrothermal power system. Mathematically, this is a large nonlinear, mixed integer optimization problem involving over 16,800 integer variables for a system having 100 thermal units with a 1-week scheduling horizon. We use a dual programming approach to solve a separate optimal control problem for each thermal unit and for each set of coupled hydro units. The algorithm has been tested on a 100 thermal unit/6 hydro unit system having a 168-hour scheduling period, and will find solutions that are within 0.1 to 0.25 percent of the optimal dual cost. We report computational results for a system modeled after the New York Power Pool.

Hachtel's Augmented Matrix Method - A Rapid Method Improving Numerical Stability in Power System Static State Estimation

Abstract: In this paper we apply the so-called Hachtel's augmented matrix method for solving linear least squares problems to static state estimation. This method does not seem to have been applied in power system state estimation by others. The test system is the 99-bus main Norwegian grid. Hachtel's method is compared to two versions of the normal equations approach and is found to greatly improve numerical stability, which is important for ill-conditioned systems. It requires less computing time than the standard normal equations method, while needing somewhat more computer storage.

Variable-structure-system control applied to AGC of an interconnected power system

Abstract: A control scheme based on a variable-structure-system concept is applied to the problem of automatic generation control of interconnected power systems. The proposed algorithm is simple and easy to implement. The effect of generation-rate-constraint nonlinearity on the dynamic performance of the system for reheat- and nonreheat-type steam turbines is also studied. A comparison of the conventional and the proposed variable-structure control strategies shows that, with the application of the proposed algorithm, the system performance is improved significantly.

A Solution of the Unit Commitment Problem Via Decomposition and Dynamic Programming

Abstract: Each day power generating units have to be selected to realize a reliable production of electric energy with the fewest fuel costs. This paper proposes decomposition and dynamic programming as techniques for solving the unit commitment problem, a high- dimensional non-linear, mixed-integer optimization problem. Experiments indicate that the proposed methods locate in less time a better solution than many existing techniques.

The Effect of Photovoltaic Power Generation on Utility Operation

Abstract: This paper presents an evaluation of the effect on utility operation of photovoltaic (PV) generation that is interconnected to an electric utility grid. Various PV concentrations and performance characteristics are examined and the effect on utility generation control performance is evaluated.

Effect of Station Originated Outages in a Composite System Adequacy Evaluation of the IEEE Reliability Test System

Abstract: The reliability evaluation of a bulk power system normally includes the independent outages of generating units, transformers and transmission lines. Station originated outages, can, however, also have a significant effect on the composite system adequacy indices. Terminal station related failure events such as failures of breakers, transformers and bus sections are a major cause of multiple outages of major cxxponents (generators and/or transmission lines etc.). This paper illustrates the effects of terminal stations in composite system reliability evaluation by using the IEEE Reliability Test System (RTS). The paper also provides a valuable extension of the original RWS by including switching configurations at each bus.

A probabilistic mechanism for small disturbance instabilities in electric power systems

Abstract: Unstable, oscillatory behavior has been observed on several occasions in electrical power systems operated in an unfaulted, normal state under moderate load. In some cases system failure has resulted from this behavior. In this paper, we report on some recent results in the mathematics of stochastic processes which suggest a mechanism leading to small disturbance instabilities of this type in power systems. Unstable oscillations in power angles may be produced in a system consisting of a synchronous machine with negligible damping weakly coupled through randomly fluctuating links to other machines each with positive damping. The assumptions necessary to structure the model to produce this behavior are simple, flexible and consistent with possible operating conditions in an electrical power system.

Advanced secondary power system for transport aircraft

Abstract: A concept for an advanced aircraft power system was identified that uses 20-kHz, 440-V, sin-wave power distribution. This system was integrated with an electrically powered flight control system and with other aircraft systems requiring secondary power. The resulting all-electric secondary power configuration reduced the empty weight of a modern 200-passenger, twin-engine transport by 10 percent and the mission fuel by 9 percent.

A Hierarchical Approach to Reactive Volt Ampere (Var) Optimization in System Planning

Abstract: A two-level hierarchical approach for optimum allocation of reactive volt ampere (VAR) sources in large scale power system planning is presented in this paper. The approach takes advantage of the natural distinction between var dispatch in system operation (Level 1) and var allocation in system planning (Level 2). The two levels are related together using the Generalized Benders Decomposition. The methodology has been implemented in the form of a prototype computer program which can be applied to large scale power systems with up to 1500 buses. The results of testing the package with practical power systems of different sizes and characteristics indicate that the technique is a valuable tool for reactive source allocation.

Decentralised load-frequency control

Abstract: In the paper we propose a numerical procedure to determine the load-frequency control of a power system composed of several interconnected areas. In order to decrease the associated implementation cost, the control law is constrained to have two different special structures: decentralised feedback and/or output feedback control. The procedure is based on a new property of the classical Riccati equation which is analysed in two different aspects: closed-loop asymptotic stability and suboptimality degree. An example of two interconnected areas is solved and comparisons are made in order to evaluate the performance of the closed-loop system.

Probabilistic load flow considering network outages

Abstract: Many techniques have been proposed to solve the load flow problem probabilistically. The great majority have only accounted for load and generation data uncertainties, and therefore, the network configuration has been considered fixed. So far, the effects of the configuration uncertainties due to the probabilistic nature of the network have not been deeply analysed. The paper presents a new method for obtaining a probabilistic load flow solution when network outages are modelled as a random variable. The proposed technique is applied to a typical power system and the results discussed.

Control of Reactive Power in Distribution Systems with an End-Load and Varying Load Condition

Abstract: The flow of the reactive power in utility systems produces losses which utility engineers attempt to keep at a minimum level by the installation of capacitor banks. Previous work focussed on obtaining the optimal conditions for a fixed load level. The present paper deals with the conditions of fixed load, growth in the load and the presence of end-load in the feeder. A mathematical analysis of shunt capacitor application for the reductions of peak power loss and energy loss for a uniform feeder with an end-load condition is presented. Generalized equations for calculating the reductions of peak power and energy losses in a feeder are derived. The optimum location and the rating of the capacitor banks on feeders with uniformly distributed loads and end-load injection are developed. A method to assess the economical effectiveness of whether or not to install capacitor banks in a condition of load growth is also given. The method is applied to a test case of a practical system.

Modeling and analysis of spacecraft power systems

Abstract: A comprehensive large-scale power system modeling using the multi-port coupling method is developed to facilitate design and analysis of present and future spacecraft power systems.