• Energy Research

In low-voltage systems, ground-faults do not necessarily involve the actual earth, but fault currents may return to the source via conductors; such conductors, which provide a clear path toward the source, are defined in applicable codes and technical standards as equipment grounding conductors or protective conductors. The above situation is for example typical of the North American low-voltage multiple grounded distribution systems, also referred to as TN-C-S, in international standards (IEC). In this paper it is substantiated that under ground-fault conditions even healthy equipment, sharing the same protective conductor with faulty equipment, as well as any metalwork in the building, acquire electrical potentials. Such potentials have a decreasing magnitude toward the electrical source and keep the same constant value on equipment located downstream the ground-fault location. The presence of non-zero potential differences between exposed-conductive-parts is a salient trait of TN systems and may constitute a hazard particularly in special locations, such as bathrooms with showers or bathtubs. In such areas, in fact, the resistance-to-ground of persons may be greatly reduced by moisture, water or the absence of clothing. This paper illustrates the advantages of supplementary equipotential bonding connections in such locations as a possible solution in the reduction of latent potential differences.

The purpose of this paper is to analyze the behavior of residual current devices at frequencies higher than the rated one. Many experiments are carried out by measuring tripping current and time of devices of different typology, produced by different manufacturers. The attention is mainly devoted to verify the satisfaction of the current-time safety curve at high frequency and experiment tripping and immunity to unwanted tripping in the presence of harmonics. Conduced tests show that the behavior of residual current devices at high frequency is strongly influenced by their typology rather than the values assumed by their physical parameters. In addition, a mathematical model is developed, and simulations are compared with measurements showing satisfactory agreement in the entire frequency range under study.

In this paper earthing systems under lightning conditions are studied by means of the cell method. Strong ionization and deionization phenomena are included together with their hysteretic behavior. The model of soil resistivity during ionization and deionization proposed by Liew and Darveniza is integrated into a 3D current field code. The simple test case of a hemispherical rod is used as a reference case for tuning space and time discretizations of the 3D approach. An earthing system including an horizontal square grid with four vertical rods at its corners is analyzed and the computed waveforms of earthing voltage and resistance are evaluated and compared with a linear model that neglects ionization phenomena.

The European Union funded project MICEV aims at improving the traceability of electrical and magnetic measurement at charging stations and to better assess the safety of this technology with respect to human exposure. The paper describes some limits of the instrumentation used for electrical measurements in the charging stations, and briefly presents two new calibration facilities for magnetic field meters and electric power meters. Modeling approaches for the efficiency and human exposure assessment are proposed. In the latter case, electromagnetic computational codes have been combined with dosimetric computational codes making use of highly detailed human anatomical phantoms in order to establish human exposure modeling real charging stations. Detailed results are presented for light vehicles where, according to our calculations, the concern towards human exposure is limited. Currently, the project has reached half way point (about 18 months) and will end in August 2020. 2019 AEIT International Conference of Electrical and Electronic Technologies for Automotive, 2-4 July 2019, Torino (Italy)

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.

The purpose of this paper is to analyze the main techniques for magnetic field mitigation at power frequency and assess their effectiveness presenting two real applications used as case studies. Some mitigation techniques presented in the literature are reviewed and discussed. The result of the preliminary numerical design is compared with results of measurements on real installations, showing that the available methods are mature instruments for the design of mitigation measures.