Showing papers on "Power-flow study published in 1985"

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.

Application Of Sensitivity Analysis Of Load Supplying Capability To Interactive Transmission Expansion Planning

Abstract: This paper illustrates the application of sensitivity methods as a tool for long-term transmission expansion planning. Possible investments are ranked in accordance with their effectiveness in increasing the system load supplying capability or reducing the system load curtailment. The calculation of these indices is performed as a special case of the optimal dispatch problem, for which very efficient solution algorithms are available. A case study with the system of Southern Brazil is used to evaluate the performance of the ranking algorithms.

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.

A Method That Combines Internal State Estimation and External Network Modeling

Abstract: A method that combines internal state estimation and external network modeling is developed. The external system is represented by an unreduced load flow model. One state estimation covering both the internal system and the external system is used. The external system operating data on power injections and bus voltages are entered as pseudo-measurements. At each iteration the set of active pseudo- measurements are selected to conform with the specified variables in a load flow program. Because such a set of non-redundant measurements is used, the internal state estimation is not affected by the external system pseudo-measurements. External generation MVAR and controlled bus voltage limits are enforced. A technique is developed to make a pseudo-measurement dormant. Using the dormant-measurement technique, it is possible to maintain the same external system state estimation formulation while the PV-PQ switching takes place from iteration to iteration. The method can easily be implemented by modifying an existing state estimation program. It has been implemented in a fast model-decoupled estimation program. Because of the dormant measurement technique, the constant gain matrix evaluated at flat voltage is used in every iteration. The method has been tested on the IEEE 14- bus, 30-bus, and Brazilian 66-bus systems. Excellent results are obtained. The number of iterations for the method to converge is usually the same as the regular state estimation runs. Thus the method presented here achieves simultaneously the internal state estimation and the external network modeling without adversely affecting the internal state estimation.

Decoupled Economic Dispatch Using the Participation Factors Load Flow

Abstract: This paper presents the concept of the participation factors load flow and applies it to the economic dispatch problem. The participation factors load flow consists of a load flow model where the quantities specified or controlled at the NG generation buses are the NG participation factors instead of NG-1 real generations. This formulation permits us to more realistically model the closed loop mode of generation dispatch used by control centers today. In contrast most modern economic dispatch algorithms based on the conventional load flow produce an open loop dispatch which cannot be directly implemented in the closed loop participation factors dispatch mode without additional computations. The numeric and analytic properties of this new load flow formulation are very similar to those of the conventional load flow with one significant difference, a slack bus need not be defined, a property which has various advantages. The new model permits the development of a decoupled economic dispatch scheme which directly computes the participation factors and separates the dispatching of real power quantities quite naturally from reactive power, voltage variables and transformer parameters.

Application of balanced realizations to power system equivalents

Abstract: An algorithm is presented to accurately estimate the feasible order reduction of dynamic models used in power system analysis. Order estimates obtained by balancing a linear model of the power system are used to determine the proper aggregation level of power system models derived from modal-coherency analysis. Test results for the 39 bus New England system are presented.

User-Friendly Workstation for Power Systems Analysis

Abstract: This paper presents the experimental study of advanced interactive power systems analysis using a-personal scientific computer. The personal scientific computer has new powerful displaying and operating capabilities. Our workstation, called the Advanced Analyzer of Power System (ADAPOS), intends to utilize these capabilities for power systems analysis. In addition our workstation has three features to perform effective human interaction: a supervisory system, database and graphic human interface. The supervisory system controls start and stop of application programs selected from a menu and guides a user to run them successfully according to the rules of analytical procedures. The database facilitates handling of both input and output data of application programs. The graphic human interface is the most important part of our system. Iconic and text menus, instead of a conventional command language, improve operational performance. Graphical presentations of analytical outputs, for example the color animation of power swings, aid understanding of power systems. The experimental results show that the new workstation highly contributes to effective power system analysis, although the computing speed is a little slow for large power systems.

Loss of load probability evaluation based on real-time emergency dispatch

Abstract: The loss of load probability (LOLP) represents an important index in the reliability evaluation of electric power systems. The LOLP denotes the probability of customer demand curtailments due to random outages of various system components. A combined optimization/reliability technique is presented in which the system control parameters are optimized. This simulates practical contingency situations where suitable controls are invoked in order to preserve, as much as possible, the continuity of supply. A DC representation of the power network is used and the optimization problem is solved by linear programming. The active component of the net injected power and the voltage angles at all buses represent the optimization variables of the problem. The optimal solution maximizes the load power supplied subject to the power flow equations as well as upper and lower bounds on the optimization variables. A description of the computerized algorithm developed and numerical results for a test power system are also included.

Planning and operation of electric energy systems

Abstract: This book presents the papers given at a symposium on the design and control of power system by the electric utilities. Topics considered at the symposium included power system state estimation, the scheduling of large hydroelectric power plants, power generation and transmission planning, distribution automation, security analysis and control, static VAR compensation, power plant and generation control, power system control centers, optimal power flow, digital relaying, and microcomputer systems. cc

Stability monitoring on the large electric power system

Abstract: The objective of this work is development of techniques which provide on line decision on the stability of a large interconnected power system faced by assumed or actual disturbances. Since the system is very large and nonlinear and the time scale only a few seconds at best the only hope for results which are mathematically honest, computable on line, and of sufficient accuracy lies in a set of carefully coordinated approximations founded on precise mathematical theory. Such an approach is discussed in this paper. It divides the problem into four segments in order to narrow down those parts of the system which are actively involved and then represent the critical elements by using approximate transformations and graded precision for remote elements.

Lyapunov function for power system with transfer conductances

Abstract: A method is given for deriving a Lyapunov function for a two-machine power system with nonzero transfer conductances. The assumptions required are only mildly restrictive and are likely to be satisfied for practical values of machine parameters. The method shows promise for extension to systems of more than two machines.

Decomposed load-flow algorithm suitable for parallel processor implementation

Abstract: The paper presents a new method for load-flow analysis which is particularly appropriate for very large power systems. The objective has been to reduce the computation time for the analysis of a given system by tearing the network into a number of independent subsystems. The subsystem programs may be executed in parallel, resulting in a considerable time saving for on-line system control. The main advantage of the new algorithm is that the computation efficiency of the main or co-ordinating program is significantly improved. Results are presented which indicate that, for average to very large systems, the net solution time using the suggested technique is less than half of that required by a centralised decoupled method to achieve the same accuracy.

Voltage Stability Analysis in Electric Power Systems by Nonlinear Programming

Abstract: Voltage instability phenomena in electric power systems are characterized by a progressive lowering of receiving end voltages beyond their nominal values.Particularly, a voltage collapse occurs at a load node when the active power fed from the load reaches a maximum value. On the basis of this observation a new method for the analysis of the voltage stability in power systems is presented.The suggested approach derives the critical voltage stability conditions for the system through the solution, by non linear programming techniques, of a non linear constrained optimization problem which considers as objective function the active power demand at a prefixed load node and as constraints the active and reactive power balance equations at the system nodes and the practical operating capabilities of generators. The method proves suitable for a rigorous individualization of the factors which affect voltage instability phenomena and can advantageously be used for planning and operation of electric power...

Analysis of orthogonal-core type transformer for DC-AC interconnection system

Abstract: This paper presents the quantitative analysis of the orthogonal-core type transformer used in a converter for dc-ac interconnection system. The power versus phase angle relation of the transformer is calculated by using the flux-MMF relationships of the orthogonal-core. The analytical results agree well with the experimental ones. The analysis presented here is useful for development of the dc-ac interconnection system.

Natural modes and their stability in power systems

Abstract: In this paper we investigate a special type of power system trajectories called natural modes. We show that the stability of the natural modes can be determined from an equivalent single machine infinite bus system. A series expansion technique is proposed for computing natural modes and is illustrated with a small example.

Leasecraft Power System Leasecraft Power System

Abstract: Various building blocks of the Fairchild Leasecraft Power System are described in detail after a brief description of the evolution of the Leasecraft spacecraft. The principle of maximum power transfer from a solar cell array has been employed in the power system advantageously. Results of detailed tradeoff studies are presented which led to the selection of the decentralized regulation concept utilizing a nondissipative unregulated main (power) bus approach. Finally the main features of the Leasecraft Power System, i.e., flexibility, reliability, input and output electrical characteristics, etc. are presented.

Power System Measurements Using Microprocessors

Abstract: Developments in power system measurements starting from the conventional analogue, through digital to microprocessor based measurements are reviewed. Then is presented a microprocessor- based power system monitor (μPSM) that scans the three phase voltages and currents and computes therefrom RMS voltages and currents, average active, reactive and complex power, as well as power factor and maximum demand. Our μPSM is thus meant to replace the conventional analogue meters and recorders on control panels used in generating, receiving and sub stations, load despatch centres, control rooms of bulk power consumers, etc. μPSM can also find application in power system data loggers, alarms and annunciators, power system relaying, load frequency control, etc, as the basic data acquisition unit.

Stabilization and voltage regulation of electric power systems with (P,Q) load buses preserved

Abstract: The mathematical model for the power networks we are considering consists of the electromechanical dynamic equations at generation buses and the nonlinear algebraic active and reactive power equations at (P,Q) load buses. The resulting nonlinear model is treated as such; no resort to linearization around operating points is taken. The control strategy we propose is, in fact, meant for true emergency situations when large variations in reactive power demand and structural changes in the network occur. We stress, however, that the resulting nonlinear controls coincide around stable operating points with linear controls designed on the basis of linearizations around those points.

Adjoint modeling of electrical networks based on generalized tellegen's theorem

Abstract: The method fo r consistent adjoint siniulation of various e lec t r ica l systems (e.g. , lumped or distributed c i r cu i t s , power systems) i s introduced i n the paper. Sens i t iv i t ies of any function of system vdriables are obtained via adjoint aridlysis. The method presented i s bdsed on a generalized form o f Tellegen's theorem and i t uses the concept o f system secondary variables in the derivation of adjoint models. Adjoint elements are not defined in a unique way. A particular form of an adjoint element depends on the selection of secondary variables describing the original element. The method includes the case O F coniplex secondary variables as well as the case o f real seconddry vdriables. Adjoint models of some elements a re developed in t h e pdper t o i l l u s t r a t e the method.