Power utilities are increasingly being interconnected to improve the reliability of power supply ... more Power utilities are increasingly being interconnected to improve the reliability of power supply and achieve economy of operation. Optimal load-flow analysis of such interconnected power systems, in general, results in complex large scale nonlinear programming problem, the direct method of solution of which requires huge amounts of core and computer time. Decomposition techniques have been extensively investigated in the power system literature to alleviate these difficulties. A piecewise method based on graph 'theoretic concept is proposed in this paper. The decomposition of the optimal load-flow into an additively separable nonlinear programming problems is achieved through the artifact of equivalent networks which were introduced in the piecewise load-flow problem. Lasdon's decomposition technique is adapted for its solution. The optimization of subsystems is carried out using a shifted penalty function• algorithm imbedded with a recent Fletcher's unconstrained function minimization routine. Few example~are presented to demonstrate the effectivenes's of this approach ' over the others.
As more and more systems get interconnected in order to improve operational efficiency and reliab... more As more and more systems get interconnected in order to improve operational efficiency and reliability, piecewise techniques for power systems analysis are gaining wider acceptance. Here an attempt is made to summarize various piecewise methods that are available and relate them to similar methods when a system is solved as a single network. Different piecewise methods differ mainly in the way they consider the effect of the rest of the system on a given subsystem. In this paper a common frame of reference is considered, so that the various methods could easily be compared and contrasted. This should also provide a basis for any future work in this area. Not only the mathematical model but also the solution procedure used to solve the model influence the final solution obtained, the number of iterations required for convergence, the computer time required and the storage requirement. Here, distinction is made between modelling difference and difference in solution techniques. The differences among the solution methods arise mainly because of the inherent non-linearity in the load flow problem.
greater than unity) the estimator can still give an estimation pro vided that the system is not i... more greater than unity) the estimator can still give an estimation pro vided that the system is not ill-conditioned Ill-condition can be caused by one or more of the following reasons (1) position of the slack bus, (2) existence of the negative line reactance, (3) improper choice of metering The first and the second are related to the network structure and parameters, and the third is related to the
This paper presents HYDSIM (Hydro-electric Simulation), a new versatile computer model developed ... more This paper presents HYDSIM (Hydro-electric Simulation), a new versatile computer model developed to simulate the hourly or daily operation of a large network of multi-purpose reservoirs and river systems. The salient features of HYDSIM include computational efficiency and accuracy of results. To achieve computational efficiency, calculations are carried out in two phases. In the first phase, the program develops a set of feasible hourly hydro plant generation schedules based upon the availability and cost of fuels for thermal generation, unit maintenance schedules, flow forecasts, etc. In the second phase, the program optimally dispatches the scheduled hourly plant outputs among the units available in each plant. The paper includes computational results obtained from an application of this model to an existing hydro-thermal system.
Proper management of multi-purpose hydro systems requires to take into account the largely stocha... more Proper management of multi-purpose hydro systems requires to take into account the largely stochastic nature of water inflows, electric loads, and water demands, as well as the often conflicting objectives of different water users. The paper outlines an integrated approach used to solve this problem. It consists of dividing the problem into several sub-problems, each covering different planning horizons. A set of computer programs was developed to solve the sub-problems. These programs, and the computational experience obtained with them, are briefly reviewed.
This paper presents a reliable and computationally efficient method for solving the optimal hydro... more This paper presents a reliable and computationally efficient method for solving the optimal hydro dispatch problem. Moreover, this method guarantees a true optimal solution when the units' 'discharge-power' relations are characterized by quadratic polynomials. Based upon this method a computer program has been developed and was tested on a sample system published elsewhere. The test run results proved to be better than the published ones. In order to illustrate the effectiveness of the proposed method as an operating tool for dispatch, it was applied to Alcan's hydroelectric system (installed capacity 2 687 MW) and the paper discusses the computational results obtained thereof and the expected potential benefits to the utility.
Power utilities are increasingly being interconnected to improve the reliability of power supply ... more Power utilities are increasingly being interconnected to improve the reliability of power supply and achieve economy of operation. Optimal load-flow analysis of such interconnected power systems, in general, results in complex large scale nonlinear programming problem, the direct method of solution of which requires huge amounts of core and computer time. Decomposition techniques have been extensively investigated in the power system literature to alleviate these difficulties. A piecewise method based on graph 'theoretic concept is proposed in this paper. The decomposition of the optimal load-flow into an additively separable nonlinear programming problems is achieved through the artifact of equivalent networks which were introduced in the piecewise load-flow problem. Lasdon's decomposition technique is adapted for its solution. The optimization of subsystems is carried out using a shifted penalty function• algorithm imbedded with a recent Fletcher's unconstrained function minimization routine. Few example~are presented to demonstrate the effectivenes's of this approach ' over the others.
As more and more systems get interconnected in order to improve operational efficiency and reliab... more As more and more systems get interconnected in order to improve operational efficiency and reliability, piecewise techniques for power systems analysis are gaining wider acceptance. Here an attempt is made to summarize various piecewise methods that are available and relate them to similar methods when a system is solved as a single network. Different piecewise methods differ mainly in the way they consider the effect of the rest of the system on a given subsystem. In this paper a common frame of reference is considered, so that the various methods could easily be compared and contrasted. This should also provide a basis for any future work in this area. Not only the mathematical model but also the solution procedure used to solve the model influence the final solution obtained, the number of iterations required for convergence, the computer time required and the storage requirement. Here, distinction is made between modelling difference and difference in solution techniques. The differences among the solution methods arise mainly because of the inherent non-linearity in the load flow problem.
greater than unity) the estimator can still give an estimation pro vided that the system is not i... more greater than unity) the estimator can still give an estimation pro vided that the system is not ill-conditioned Ill-condition can be caused by one or more of the following reasons (1) position of the slack bus, (2) existence of the negative line reactance, (3) improper choice of metering The first and the second are related to the network structure and parameters, and the third is related to the
This paper presents HYDSIM (Hydro-electric Simulation), a new versatile computer model developed ... more This paper presents HYDSIM (Hydro-electric Simulation), a new versatile computer model developed to simulate the hourly or daily operation of a large network of multi-purpose reservoirs and river systems. The salient features of HYDSIM include computational efficiency and accuracy of results. To achieve computational efficiency, calculations are carried out in two phases. In the first phase, the program develops a set of feasible hourly hydro plant generation schedules based upon the availability and cost of fuels for thermal generation, unit maintenance schedules, flow forecasts, etc. In the second phase, the program optimally dispatches the scheduled hourly plant outputs among the units available in each plant. The paper includes computational results obtained from an application of this model to an existing hydro-thermal system.
Proper management of multi-purpose hydro systems requires to take into account the largely stocha... more Proper management of multi-purpose hydro systems requires to take into account the largely stochastic nature of water inflows, electric loads, and water demands, as well as the often conflicting objectives of different water users. The paper outlines an integrated approach used to solve this problem. It consists of dividing the problem into several sub-problems, each covering different planning horizons. A set of computer programs was developed to solve the sub-problems. These programs, and the computational experience obtained with them, are briefly reviewed.
This paper presents a reliable and computationally efficient method for solving the optimal hydro... more This paper presents a reliable and computationally efficient method for solving the optimal hydro dispatch problem. Moreover, this method guarantees a true optimal solution when the units' 'discharge-power' relations are characterized by quadratic polynomials. Based upon this method a computer program has been developed and was tested on a sample system published elsewhere. The test run results proved to be better than the published ones. In order to illustrate the effectiveness of the proposed method as an operating tool for dispatch, it was applied to Alcan's hydroelectric system (installed capacity 2 687 MW) and the paper discusses the computational results obtained thereof and the expected potential benefits to the utility.
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