Solution Of Network Problems Research Articles

The Effect of Load Modeling on Load Flow Results in Distribution Systems

Effective utilization of power distribution networks requires extensive studies in such areas as using of capacitors, voltage regulators, network reconfiguration, and so on. Indeed, achieving to accurate answers, and managing appropriate solutions for network problems requires a detailed modeling of the network in the process of the above studies. Among the elements that are important for modeling in network research is network loads. Loads are generally being modeled such as constant power. While load nature is often widespread and different. Failure to have a detailed modeling can lead to non-optimal and even wrong answers, and will result in waste of costs and investments. Since the load flow is the basis of any research in distribution networks, in this paper the effect of load modeling on load flow results which can clarify the importance of the load modeling for other network studies are investigated. What can be inferred from this study is that any study in distribution networks can only lead to optimal results if the load model is accurate. Therefore, attempting to measure necessary load parameters and using their exact modeling methods in distribution networks should be done in order to obtain more accurate results and more savings.

System aspects of 1100 kV AC transmission technologies in Japan

AbstractThis paper describes the system aspects of 1100 kV AC transmission technologies with the UHV transmission project in Japan. For realization of technical and economical optimization throughout the design of the transmission line and the substation, solutions for network problems and insulation coordination specific to UHV AC transmission systems were studied in Japan. They include fast multiphase reclosing systems by HSGS (High Speed Grounding Switch) and overvoltage control by the application of surge arresters and circuit breakers with closing/opening resistors. These sophisticated technologies provide highly reliable and economical 1100 kV substations and transmission lines. Copyright © 2009 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.

Efficiency of Algorithms for Solution of Network Problems with Tree-Like Data Structure

It is shown that the running time of a special simplex algorithm for solution of practical network problems is improved if a tree-like structure is used to store data.

A restricted branch-and-bound approach for generating maximum bandwidth signal timing plans for traffic networks

The synchronization of traffic signals located along the urban/suburban arterials in metropolitan areas is perhaps one of the most cost-effective methods for improving traffic flow along these streets. The main objective of synchronized signal timing is to keep traffic moving in platoons throughout the signal controlled system, by setting the signals along the arterials/networks to provide maximum bandwidth progression. A popular technique for generating signal timing plans formulates the problem as a mixed-integer linear program and uses the Land and Powell branch-and-bound search technique to arrive at the optimal solution. Due to numerical instability of the solution technique and the exhaustive nature of the search procedure, the current implementation tends to be computationally inefficient and infeasable for realistic network problems. Furthermore, numerical instability results in suboptimal or no solutions for network problems with a range of variable cycle times. This paper presents the development of a fast and numerically stable heuristic for the maximum bandwidth signal setting problem. The heuristic is computationally efficient, can generate optimal/near-optimal solutions, and is implemented on a PC. It is based on restricted search of the integer variables in the solution space. The efficiency of this heuristic is supported by computational results for a number of test problems. 1998 Elsevier Science Ltd. All rights reserved

Integrating network optimization capabilities into a high-level modeling language

Research in network optimization has reached the stage where large-scale problems-linear or non-linear, pure or generalized-are solved very efficiently with minimal computing resources. Representing such problems for solution on the computer, however, remains a rather cumbersome task. Taking advantage of developments in high-level modeling languages, we design and implement integrated systems to facilitate the representation and solution of network problems. Such systems integrate the flexibility and robustness of modeling languages with the efficiency of network optimizers. We describe two alternative modes for this integration, which can be achieved for linear and nonlinear problems alike. The use of the resulting systems is demonstrated with the solution of large-scale problems from diverse applications and with the implementation of network decomposition algorithms.

Methods for routing with time windows

Consider a set of trips where each trip is specified a priori by a place of origin, a destination, a duration, a cost and a time interval within which the trip must begin. The trips may include visits to one or more specific points. Our problem is to determine the number of vehicles required together with their routes and schedules, so that each trip begins within his given time interval, while the fixed costs related to the number of vehicles, and the travel costs between trips are minimized. The problem is a generalization of the m-travelling salesman problem. We compare numerical results for 3 algorithms developed by our research team: 1. (1) Column generation on a set partitioning problem solved by simplex and branch-and-bound; columns are generated by a shortest path algorithm with time constraints on the nodes. 2. (2) Adaptation of the Carpaneto-Toth algorithm for the asymmetric travelling salesman problem: solution of network problems by relaxing scheduling constraints, and branch-and-bound on flow variables. 3. (3) Solution of network problems by relaxing scheduling constraints and branch-and-bound based on dividing the time windows.

Duality in network problems

Network modeling of industrial processes is now widely used in various branches of the mining industry. As a result, intensive research is being done on new formulations and methods of solution of network problems. Many processes in mining can be represented by network models which have the property of duality. This property can in many cases simplify the solution of a class of network problems. We give a method of constructing dual networks for certain problems which can be represented as networks with a continuous current of a component (as in distribution of homogeneous resources without storage, ventilation, hydraulics, etc.). We describe the algorithms and properties with reference to ventilation networks; however, all the results are also applicable to a broad class of similar problems. The methods of construction of dual networks and their properties can be used to solve a wide range of problems. Many plans can be represented in the form of dual network models (networks), one of which represents the flows of resources, the other the time parameters for completion of operations. Thus a number of methods used to solve problems on ventilation networks can also be used to solve the problems with convex dependences of themore » times of completion of the operations on the quantity of utilized resources. If, with a given time of completion of the project we need to minimize the costs, this problem is also simpler to solve if we use the properties of duality of networks. By analogy with dual problems in optimal programming, the development of specific methods of realization of dual network models in individual cases can simplify the formulation of the problems and reduce the times taken to solve them.« less

Digital calculation of network functions used in loss formula studies

A complete matrix of self and mutual drops, with respect to a single reference point, will completely describe the constraints of a network as far as the significant points are concerned. Thus, these drops are a useful tool in the solution of network problems and have long been recognized as such. Previous to the days of the a-c network calculator, they were in widespread use for the calculation of losses, regulation short-circuit currents, etc. With the advent of the loss formula,1 these drops assumed a new role. Ironically the a-c network calculator, which once subjugated these drops to a relatively minor role, now permitted their economical use by providing a means of obtaining them by direct measurement. For some time now the network calculator has been used quite widely to determine these drops; however, this method still involved considerable time and patience, and there was a serious question as to whether the accuracy obtained was sufficient for all purposes.

The Solution of Network Problems by Determinants

The Solution of Network Problems by Determinants