A. Gomes Martins

Simulation-based assessment of electric load management programs

The paper describes a methodology for assessing the contribution of storage type loads to an electric energy systems load curve and for evaluating the impact of load shedding actions, as part of load management programs, on the systems load curve. The methodology uses physically based individual load models and an aggregation procedure that accounts for both statistical reference patterns of the energy service demand and for the random nature of load use. A simulation case study of electric water heaters fed by a single transformer station is presented, to illustrate the effects of load control. The proposed methodology presents the possibility of evaluating-both at individual consumer level and at system level-the impacts of load management (LM) on the quality of service provided, besides anticipating the impact on the systems load curve. It allows an effective design of LM programs through variables such as the number of different load shedding schedules and their frequency of use by the utility.

Design of an adaptive mutation operator in an electrical load management case study

An adequately designed and parameterized set of operators is crucial for an efficient behaviour of Genetic Algorithms (GAs). Several strategies have been adopted in order to better adapt parameters to the problem under resolution and to increase the algorithms performance. One of these approaches consists in using operators presenting a dynamic behaviour, that is displaying a different qualitative behaviour in different stages of the evolutionary process. In this work a comparative analysis of the effects of using an adaptive mutation operator is presented in the operational framework of a multi-objective GA for the design and selection of electrical load management strategies. It is shown that the use of a time/space varying mutation operator depending on the values achieved for each objective function increases the performance of the algorithm.

Energy planning in urban historical centres A methodological approach with a case-study

Abstract The paper aims at the presentation of a methodology for energy planning in urban historical centres, using the historical centre of Coimbra, an old Portuguese city, for illustrating purposes. The paper starts with a general perspective of the problems associated with planning activities in historical centres. It describes a methodological approach and general procedures used in the formulation of a mid-term energy plan and presents its main prospective items – identification of objectives and recommended measures, and evaluation of measures’ impacts. It also draws a picture of the standard steps to be given and procedures to be adopted in similar plans. It then presents the formulation of the mid-term energy plan for the historical centre of Coimbra. Difficulties found and anticipated are listed and directions for circumventing them and for future methodology improvements are also presented.

Multi-Objective Evolutionary Approaches for Reactive Power Planning in Electrical Networks - an Overview

Since the 1960s a great deal of attention has been paid to the problem of reactive power compensation in electrical networks. This problem consists in providing the appropriate location and sizing of compensation devices, aimed at ensuring satisfactory voltage profile and reduce power losses, while minimizing the compensation cost. In recent years the methodologies to solve this problem shifted from mathematical programming algorithms to metaheuristics and, in particular, to Evolutionary Algorithms (EAs). EAs can provide good quality solutions without requiring mathematical model simplifications. Moreover, EAs are well suited to multi-objective problems because they work with a population of solutions. This paper makes an overview of the application of multi-objective EAs to the reactive power planning problem.

Assessment of the behavior of protection systems in radial networks with distributed generation

This paper evaluates the behavior of electricity distribution networks protection systems, through a systematic short-circuit analysis, as a means of characterizing the behaviour of protective devices in distribution systems. A comparison is made between two of the most common protection schemes, the first one using recloser and fuses and the second using overcurrent relays, with distributed power injections, in one of the IEEE publicly available radial test feeders. All simulations are performed using the Power Factory software package from DigSILENT. From the simulation results, conclusions are drawn that provide insights into the behavior of protection systems, highlighting the limitations of the original protections, and devising strategies to meet quality assurance, coordination and selectivity of proposed modified protection schemes.

Next hour load forecast in medium voltage electricity distribution

Purpose – The purpose of this paper is to assess next hour load forecast in medium voltage electricity distribution.Design/methodology/approach – The methodological approach used in this paper, is based on a regressive method – artificial neural network. A real life case study is used for illustrating the defined steps and to discuss the results.Findings – The presence of a de‐regulated environment reinforces the need of short‐term forecast algorithms (STLF). Actions like network management, load dispatch and network reconfiguration under quality of service constraints, require reliable next hour load forecasts. Methodological approaches based on regressive methods such as artificial neural networks are widely used in STLF, with satisfactory results. The construction of an “efficient” artificial neural networks goes through, among other factors, the construction of an “efficient” input vector (IV), in order to avoid over fitting problems and keeping the global simplicity of the model. The explanatory vari...

MEASUREMENT OF ACTIVE AND REACTIVE POWER FOR REAL-TIME POWER SYSTEMS CONTROL

Real-time control of power systems requires a fast evaluation of the active and reactive power balance within the system. It is therefore very important to obtain accurate and rapidly updated values of the active and reactive powers, P and Q. A system is described that takes approximately 100 ms to perform the whole computations of active and reactive powers with a maximum error of 0.04% on P and 0.06% on Q irrespectively of the presence of harmonics of the fundamental frequency on the voltage, the current or on both. A simple time-domain algorithm is applied with a 16 bit microprocessor to achieve high-speed calculations in spite of the high-precision provided by the floating point arithmetic used. The data acquisition process is accomplished on a stand-alone basis, allowing the full microprocessor time utilization for the numeric computations. A 12 bit ADC is used to convert the samples of voltage and current obtained simultaneously. A FIFO is used to store the converted values later accessed by the microprocessor. A serial communications channel allows direct interface with large control systems.