• Energy Research

We have applied a multiobjective combinatorial optimization (MOCO) based on a vector immune system (VIS) algorithm to determine the optimal sequence of parallel cables in a multiconductor three-phase system. We build the objective function in a way that minimizes the magnetic stray field and the current unbalance of a bunch of rectilinear power cables. Our principal aim is to extend and verify the ability of the VIS algorithm to solve combinatorial problems represented by nonlinear objectives that are not usually solved in MOCO problems.

A low voltage three phase power line constituted by many single core cables in parallel is analysed. The geometry of the line is referred to IEC and European Standard suggestions and different possible solutions are compared. Rated loads are evaluated both under balanced and unbalanced conditions. Steady state three phase short circuit currents are also examined. The protection of such a line using a set of parallel single core cables by means of one protection under over current condition is discussed, making reference to the actual current sharing among the conductors.

The aim of the work is the optimisation of a rail heater, constituted by a magnetic core supplied by a sinusoidal current, which induces an eddy current in the rail. Optimisation parameters are electrical and geometrical quantities: supply frequency, voltage amplitude, airgaps, and core shape, while objectives are power transferred to the rail, absorbed current, and power distribution index. Optimisation is performed by an accurate field analysis, provided by the finite element method (FEM), coupled to an automated multiobjective procedure based on fuzzy logic. Particular care has been devoted to the FEM model in order to take into account important phenomena as non-linearity magnetic behaviour and non-uniform distribution of current in the rail caused by eddy currents.

In this paper a mixed integer linear model is proposed to solve the problem of the optimal energy management of a system composed by several kind of loads (electrical, thermal, cooling) and energy sources (external network, CHPs, boilers, chillers). The optimizer manages on/off status of CHPs and boilers and their level of power production and power rate of chillers. A realistic scenario of trigenerative plant is studied focusing the attention to the economical analysis of different CHP size.

The refurbishment of historic buildings is a complex task in which the goal of obtaining a more energy-efficient building can conflict with the peculiar characteristics of the building’s environment and its intended use. In this article, the authors address this problem for a very specific type of building: a historic opera house located in northern Italy. The results of energy consumption monitoring and spot measurements on selected loads were used as a basis to propose energy-savings strategies. The objective of this article is to highlight the difficulties in refurbishing historic buildings, particularly regarding the building envelope, in lieu of proposing a new methodology for measurements or a new strategy for energy savings. It is documented that energy savings are obtainable with relatively small investments and low-impact construction work.

The worldwide global market requires electrical engineers to have a deep understanding of the bonding and earthing practices adopted in different countries around the world. This knowledge is essential to obtain effective designs and high safety standards and can promote the elimination of technical obstacles that can still create market barriers. The full comprehension of the “grounding” theory requires the command of key technical concepts regarding the earthing methods, which may cause confusion when used in the North American technical realm rather than in the International Electrotechnical Commission (IEC) world. This issue is further worsened by the lack of literature in this matter, as well as of harmonization documents between national codes and international standards. This paper, by analyzing the protection against indirect contact in ac (50/60-Hz) low-voltage power systems by automatic disconnection of supply, seeks to clarify both the terminologies and each type of grounding system adopted in IEC standards, with the intent to create a common reference for practicing engineers in the matter of bonding and earthing of power systems. Major differences encountered between sizing procedures adopted in IEC standards and the North American National Electrical Code are also examined.

Stray currents leaking from DC and AC electrical installations may flow through buried metal works towards their sources. Such currents may circulate through intentional electrodes, for example dwelling units and railways grounding systems, but also through building and tunnels metal frames, as well as, water and gas utility pipelines. Besides the corrosion phenomena, triggered over the aforementioned metal parts by DC currents, the stray currents may energize these conductive parts, exposing persons to touch voltages. This paper proposes an approach to evaluate the voltage exposure appearing on the aforesaid metal parts, based on the estimation of an appropriate ground-resistance matrix. This matrix, used in conjunction with a system of circuit equations, will yield voltage and current associated to the interfering electrodes. In the case of standard electrode configurations (e.g. spherical, cylindrical, etc.) the evaluation of the above mentioned matrix may be analytically carried out. To take into account complex electrode geometries and/or non-homogeneous soil conditions, numerical elaboration based on the method of the moments will be employed. Historical cases are presented and discussed.

PurposeThe definition of a simple model of low frequency magnetic field created by power industrial installations can be approached by using an equivalent source system (ESS). Given a set of measured magnetic field points, the ESS, made by a limited set of current carrying wires or turns, must be placed and supplied in order to fit the measured magnetic field values. An optimisation procedure can be used to define the current values and the location of the ESS which minimize the error between the measured and computed magnetic field values.Design/methodology/approachA two‐step optimal procedure is defined: in the outer step a stochastic optimisation routine is used to drive the geometric control parameters of the ESS while, in the inner step, the current values flowing through the sources are computed to find the minimization of the error with respect to a set of measured magnetic field values. The optimisation procedure is based on an artificial immune system algorithm which focuses on a deep exploration of the search space and gave interesting results both in terms of accuracy and computational efficiency.FindingsThe results show that the proposed approach is able to reconstruct the magnetic field created by complex source system and give some accuracy measure on the reconstruction error. The optimisation process carried out also on conductor positions has allowed to find out the location of the real sources in an accurate way, also in presence of measurement errors.Originality/valueThe approach proposed uses optimisation procedures to solve the inverse problem of source reconstruction starting by a set of measured magnetic field values. The definition of a simple equivalent source structure, together with an optimisation procedure to set its control parameters, allows to simulate complex magnetic field sources, like power substations or cable systems, in a very efficient and compact way.