Carlos M. P. Cabrita

Proactive reliability maintenance: a case study concerning maintenance service costs

Purpose – The purpose of this paper is to emphasize that the choice of the most appropriate maintenance model and policies is the best way to reduce significantly the maintenance costs as well as to optimize the useful Key Performance Indicators – failure rates, reliability, mean time between failures, mean time to repair, and equipment availabilities.Design/methodology/approach – In order to implement the Asset Effectiveness Optimization AEO as well as the Overall Equipment Effectiveness OEE, improving productivity in a complex food‐products plant, the paper presents a theoretical and experimental study related to the maintenance costs directly associated with the equipment used in production tasks.Findings – The developed tool is an efficient method of calculating the maintenance costs and allows one by means of computational simulation to define the most advisable maintenance policy. On the other hand, the proposed relationships are universal and could be used as an economic evaluation indicator for ot...

New Multistage and Stochastic Mathematical Model for Maximizing RES Hosting Capacity—Part I: Problem Formulation

This two-part work presents a new multistage and stochastic mathematical model, developed to support the decision-making process of planning distribution network systems (DNS) for integrating large-scale “clean” energy sources. Part I is devoted to the theoretical aspects and mathematical formulations in a comprehensive manner. The proposed model, formulated from the system operators viewpoint, determines the optimal sizing, timing, and placement of distributed energy technologies (particularly, renewables) in coordination with energy storage systems and reactive power sources. The ultimate goal of this optimization work is to maximize the size of renewable power absorbed by the system, while maintaining the required/standard levels of power quality and system stability at a minimum possible cost. From the methodological perspective, the entire problem is formulated as a mixed integer linear programming optimization, allowing one to obtain an exact solution within a finite simulation time. Moreover, it employs a linearized ac network model which captures the inherent characteristics of electric networks and balances well accuracy with computational burden. The IEEE 41-bus radial DNS is used to test validity and efficiency of the proposed model, and carry out the required analysis from the standpoint of the objectives set. Numerical results are presented and discussed in Part II of this paper to unequivocally demonstrate the merits of the model.

New Multi-Stage and Stochastic Mathematical Model for Maximizing RES Hosting Capacity—Part II: Numerical Results

A new multistage and stochastic mathematical model of an integrated distribution system planning problem is described in Part I. The efficiency and validity of this model are tested by carrying out a case study on a standard IEEE 41-bus radial distribution system. The numerical results show that the simultaneous integration of energy storage systems (ESSs) and reactive power sources largely enables a substantially increased penetration of variable generation (wind and solar) in the system, and consequently, reduces overall system costs and network losses. For the system, a combined wind and solar PV power of up to nearly three times the base-case peak load is installed over a three-year planning horizon. In addition, the proposed planning approach also considerably defers network expansion and/or reinforcement needs. Generally, it is clearly demonstrated in an innovative way that the joint planning of distributed generation, reactive power sources, and ESSs, brings significant improvements to the system such as reduction of losses, electricity cost, and emissions as a result of increased renewable energy sources (RESs) penetration. Besides, the proposed modeling framework considerably improves the voltage profile in the system, which is crucial for a normal operation of the system as a whole. Finally, the novel planning model proposed can be considered as a major leap forward toward developing controllable grids, which support large-scale integration of RESs.

On the influence of the pole and teeth shapes on the performance of linear switched reluctance actuator

Purpose – The purpose of this paper is the evaluation of the influence of pole and teeth shapes on the behaviour of a linear switched reluctance actuator (LSRA). The study was carried out through the application of a finite element static analysis and the application of a new method for dynamic analysis. Those studies are thereafter evaluated with experimentations.Design/methodology/approach – The paper characterizes the performance of an LSRA for different polar geometries. A finite element tool is used at an early research stage. Results are then used to build a dynamic numerical model. Obtained data allow the construction of a laboratory prototype.Findings – Polar shape has great influence in actuator behaviour. Different geometrical polar configurations are evaluated and their influence is observed. The obtained data allow attraction force minimization with minimal penalty in the thrust force. A numerical dynamic model is used to evaluate actuator movement with different polar shapes, without taking i...

Characterization of a new linear switched reluctance actuator

This paper presents the electromagnetic analysis of a new designed and constructed prototype of a single-sided linear switched reluctance actuator. First, a brief consideration on the adopted analytical design methodology, establishing some desired electrical and mechanical parameters, is stated. After, a characterization of the actuator is made, analyzing the distribution of magnetic fields and connected translation forces, through the determination of energy and co-energy variation, performing a numerical analysis based on Finite Element Method. A saturation factor is then introduced, corresponding to the magnetic circuit saturation level, allowing the knowledge of the actuator thrust development performance, as well as the definition of proper relative positions for coils excitation, and respective current intensities, in specific practical motion applications. The influence of saturation factor in the actuator mechanical force development, for different positions and excitations, is established and connected with thermal, electrical and mechanical constraints. The paper is illustrated with experimental tests carried out by the authors.

Novel Multi-Stage Stochastic DG Investment Planning with Recourse

This paper presents a novel multi-stage stochastic distributed generation investment planning model for making investment decisions under uncertainty. The problem, formulated from a coordinated system planning viewpoint, simultaneously minimizes the net present value of costs rated to losses, emission, operation, and maintenance, as well as the cost of unserved energy. The formulation is anchored on a two-period planning horizon, each having multiple stages. The first period is a short-term horizon in which robust decisions are pursued in the face of uncertainty; whereas, the second one spans over a medium to long-term horizon involving exploratory and/or flexible investment decisions. The operational variability and uncertainty introduced by intermittent generation sources, electricity demand, emission prices, demand growth, and others are accounted for via probabilistic and stochastic methods, respectively. Metrics such as cost of ignoring uncertainty and value of perfect information are used to clearly demonstrate the benefits of the proposed stochastic model. A real-life distribution network system is used as a case study and the results show the effectiveness of the proposed model.

Design of a tubular switched reluctance linear generator for wave energy conversion based on ocean wave parameters

This work presents a procedure for the design and analysis of a linear tubular switched reluctance generator for wave energy conversion. The generator is meant to be applied to a direct drive wave energy converter, namely a point absorber. The device is modeled according to wave climate conditions at Esposende site in the Portuguese coast. The procedure starts with statistical analysis of the local random ocean behavior in order to determine most likely values of occurrence for the wave parameters in question. Based on that, the generator is analytically designed. With the proper dimensions calculated, a numerical simulation is performed and the magnetic flux path and density values are determined.

Linear switched reluctance motor. A new design methodology based on performance evaluation

This paper concerns the design of linear switched reluctance machines (LSRM), by evaluating the traction forces under defined speed operation conditions. A new methodology concerning optimised design of LSRM, for urban systems of electric traction at low and medium speeds, is proposed. This methodology, supposed to be original, is based on the systematic use of a known and fast processing calculation process, in which some changes are made in order to turn it more generic. For each one of the several design machines the respective magnetization curves are calculated, based on the B=f(H) characteristic of the used material, as well as on the calculated machine dimensions. This calculation was made through the linearization of the airgap length mean value between the unaligned and aligned positions. The simulation of different machines permits the selection of proper model for specific requested application. Simultaneously, machine simulation allows to define the best control strategy for continuous operation. The developed software, for machine simulation, still allows to simulate any LSRM with known magnetization curve I=f(/spl psi/,x).

Impacts of Operational Variability and Uncertainty on Distributed Generation Investment Planning: A Comprehensive Sensitivity Analysis

This paper presents a comprehensive sensitivity analysis to identify the uncertain parameters which significantly influence the decision-making process in distributed generation (DG) investments and quantify their degree of influence. To perform the analysis, a DG investment planning model is formulated as a novel multistage and multiscenario optimization problem. Moreover, to ensure tractability and make use of exact solution methods, the entire problem is kept as a mixed-integer linear programming optimization. A real-world distribution network system is used to carry out the analysis. The results of the analysis generally show that uncertainty as well as operational variability of the considered parameters have meaningful impacts on investment decisions of DG. The degree of influence varies from one parameter to another. But, in general, ignoring or inadequately considering uncertainty and variability in model parameters has a quantifiable cost. Hence, the analysis made in this paper can be very useful to identify the most relevant model parameters that need special attention in planning practices.

Analysis and position control of a linear switched reluctance actuator based on sliding mode control

This paper presents the finite elements analysis and the control of a linear switched reluctance actuator (LSRA). The energy conversion process is described, and based on a finite elements analysis, both traction and attraction maps are derived. This information is useful to understand the device working principle and its performance for different excitation and position conditions. The proposed control strategy, based on sliding mode control techniques, and the electronics used to proper drive the actuator are described and implemented with the TMS320F2812 eZdsp Start Kit. Control implementation takes advantage of the microprocessor internal peripherals and resources. Finally, experimental results are presented and discussed for the validation of proposed control strategy.