Roberto Benato

Distribution Line Carrier: Analysis Procedure and Applications to DG

The paper deals with analysis of carrier signals transmission in MV distribution networks. A multiconductor matrix procedure based on bus admittance matrix, which accounts for the earth return currents, allows predicting the high frequency behaviour of distribution networks and hence the effectiveness of transmitted signals. To this aim suitable models have been implemented based of the Carsons theory for overhead lines with ground return and Wedephols theory for cable lines. A comparison with the modal analysis demonstrates the advantages of multiconductor matrix algorithm with respect to modal analysis. In order to validate the theoretical results two measurement campaigns have been carried out on real MV networks. A good agreement between measured and computed values has been verified. Since distribution networks are generally unlike each other, the procedure becomes a valuable tool, which makes it easy to assess the feasibility of distribution line carrier (DLC) applications in any given system. In particular a protection system to prevent islanding of dispersed generators is proposed. In addition, in a foreseeable hypothesis of allowed islanding operation of portions of distribution networks (microgrids), DLC are proposed as communication control of the interface device at the point of common coupling

Proximity effect and magnetic field calculation in GIL and in isolated phase bus ducts

This paper deals with an integral numerical method suitable to predict the current density distribution in typical multiconductor systems represented by gas-insulated lines (GIL) or by isolated phase MV bus ducts, highlighting their proximity effect. Besides the prediction of power density distribution due to Joule losses, the integral approach makes the evaluation of the external flux density easy. The simplicity of the approach, the conciseness of the matrix algebra applied, and the close-to-reality procedure make this method extremely attractive for self-made software implementation on any commercially available math packages such as Matlab. For the sake of comparison, a finite-element method (FEM) model of the system has been implemented. In this model, a coupling between electric circuit and electromagnetic model has been used in order to take into account the real power supply conditions.

High Capability Applications of Long Gas-Insulated Lines in Structures

This paper deals with the possibility of installing gas-insulated transmission lines (GILs) in dedicated or shared structures. The applications involve railway galleries (both in the proper galleries and in service or pilot tunnels), highway networks, and gas lines. The high GIL power capability together with very low power losses configures these applications as high transmission efficiency corridors. Some issues of this application will be shown in this paper (steady-state regime of the line, voltage drops, power losses, voltage unbalance factor, ampacity, electromagnetic field impact, and limit lengths). Moreover, this paper discusses the necessary studies to be carried out and the problems that have to be faced in order to develop this kind of application toward a feasible technical solution

Solution of coupled electromagnetic and thermal problems in gas-insulated transmission lines

Gas-insulated high-voltage and extra high-voltage transmission lines are a new technology for transmitting high-power ratings over long distances. A previous paper was devoted to predict the current distribution along with the external flux density in this multiconductor system, highlighting its proximity effect. It served as the vehicle for the present further research taking into account the thermal problems coupled to the electromagnetic field. The aim of the present paper, therefore, is to show the concordance between literature analytical formulas and the finite-element method (FEM) approach considering the concrete tunnel installations. The FEM model is able to study the precise thermal distribution inside the phase and enclosure thickness both in the steady-state regime and transient condition due to the phase-to-ground short circuit.

Application of distribution line carrier-based protection to prevent DG islanding: an investigating procedure

The paper deals with the possibility of using the distribution line carrier (DLC) in order to prevent dispersed generation islanding. The feasibility of this technology applied to MV networks has been investigated from a theoretical as well as experimental point of view. A multiconductor matrix procedure based on bus admittance matrix allows us to predict the high frequency behaviour of MV lines (overhead and cable): the signal strength can be verified at any section of MV networks. Moreover two measurement campaigns have been performed on real MV networks in order to validate the theoretical results.

Gas insulated transmission lines in railway galleries

This paper deals with the possibility of installing a double-circuit gas insulated transmission line (GIL) in the pilot tunnel of the planned new railway galleries Bolzano (Italy)- Innsbruck (Austria). This EHV transmission line could represent a new fundamental step in reconstructing the transnational networks. The high GIL power ratings together with very low power losses would be a strong and highly efficient transmission tie between Italy and Austria particularly useful for the future European Market. The steady-state regime of the line and the electro-magnetic field impact are analyzed. Moreover, the paper discusses the necessary studies to be carried out and the problems that have to be faced.

Application of PLC for the Control and the Protection of Future Distribution Networks

The paper shows the great possibilities offered by PLC applied to the medium voltage power networks. The paper focuses the attention on the need for new strategies of control and protection of future distribution networks with high penetration of distributed generator (DG) and points out how PLC could have a key role among the technologies that are expected to be applied. In the paper, three chief proposals of application of PLC will be illustrated: the co-ordinated voltage control, a protection system to prevent dispersed generation islanding and the control of the interface device at the point of common coupling for a micro-grids distribution structure. By means of multiconductor matrix procedure already presented by the authors in previous researches, the feasibility of power line carrier applications will be demonstrated.

Resonance phenomena on line-to-ground fault current harmonics in MV networks

High levels of harmonic components measured on MV line fault currents have prompted a detailed investigation of the phenomena in order to develop models to accurately reproduce the observed harmonic currents and clarify the resonance characteristics of the system under line-to-ground fault conditions. A procedure which can predict the fault current wave-form of a whatsoever complex distribution system supplying a variety of loads, enabling identification of potentially harmonic resonance conditions, is presented. It may be applied, for instance, to verify the performance of networks adopting suppressing coil (which is normally tuned on the fundamental frequency) or zero-sequence protection relays. A parametric analysis on typical MV distribution systems shows how it is possible to identify critical fault locations which may give rise to very high harmonic currents.

Overall Cost Comparison Between Cable and Overhead Lines Including the Costs for Repair After Random Failures

This paper deals with the comparison between the overall whole-of-life costs of overhead lines (OHL) and those of underground insulated cables (UGC). Almost all the investigations published so far, when analyzing maintainability issues, take into account only the costs of planned/periodical maintenance; here, a method for assessing also the expenses sustained for repair after random failures is proposed. The number of random failure events for each kind of component over the entire service life of a transmission line can only be predicted on a probabilistic basis: its expected value is estimated by making use of the relevant mean failure rates from recent statistical surveys. The entire procedure is shown by carrying out a particular case study as an example; the break-even point between the OHL-UGC overall costs, corresponding to a typical rural land Italian market value wx = 26.9 Euros/m2, is identified. Nonetheless, the method may be widely applied to any type of OHL-UGC comparison.

Sequence impedances of insulated cables: Measurements versus computations

The computation of the sequence impedances is a very important topic for insulated cable systems chiefly in HV and EHV levels. This highlights the importance of using reliable procedures in order to compute these impedances since, up to now, their computations are based on simplified formulae. In this paper, results of some measurement campaigns have been compared with both simplified IEC formulae and advanced matrix procedures based on Multiconductor Cell Analysis (MCA) [1, 2, 3, 4]. MCA considers the cable system in its real asymmetry without simplified and approximated hypotheses. One of the advantages of the MCA is the possibility of supplying the cable system with three sequence voltage phasors and of computing the ratios between voltage and current phasors for each phase.