Roberto Turri

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.

Fast Analytical Computation of Power-Line Magnetic Fields by Complex Vector Method

The electromagnetic environment related to electric power installations is typically evaluated by numerical integration methods. Numerical techniques, although powerful, are not well suited for assessing the dependence of the field strength on electric and geometric parameters. In this paper, a fast procedure to analytically evaluate power-line magnetic fields, based on complex vectors, is proposed. The use of complex algebra greatly simplifies analytical calculations compared to other approaches proposed in literature, allowing also complex conductor arrangements to be taken into account. A general formula for the magnetic-field intensity of any multiphase single-circuit line configuration is obtained. An expression for practical three-phase line configurations is simply derived as a particular case of the general formula. The proposed approach is then extended successfully to double-circuit lines, taking the load differences between circuits into account. Approximate formulas are validated by comparing magnetic flux density values with those computed from the general expression.

An integral method for extremely low frequency magnetic shielding

A novel approach for analyzing conducting shields of extremely low frequency magnetic fields in linear media is presented. It consists of an integral formulation based on the cell method, expressed in terms of network-like loop currents and magnetic vector potential line integrals on the shield surface. This formulation leads to a considerable reduction of field problem variables, thus limiting the amount of allocated memory and speeding-up the numerical procedure compared to other differential and integral techniques. Eddy currents are computed first, then the magnetic vector potential and the magnetic flux density distributions are evaluated by applying the superimposition principle. A detailed comparison between this method and a three-dimensional finite element method code demonstrates the accuracy of the results and the advantages of the method.

Voltage management in unbalanced low voltage networks using a decoupled phase-tap-changer transformer

The paper studies a medium voltage-low voltage transformer with a decoupled on load tap changer capability on each phase. The overall objective is the evaluation of the potential benefits on a low voltage network of such possibility. A realistic Danish low voltage network is used for the analysis. The load profiles are characterized by using single phase measurement data on voltages, currents and active powers with a 10 minutes resolution. Different scenarios are considered: no tap action, three-phase coordinated tap action, single phase discrete step and single phase continuous tap action. The effectiveness of the tapping capability is evaluated by comparing the Voltage Unbalance Factor and the voltage levels on the neutral cable.

Analysis of the Italian distribution system evolution through reference networks

This paper presents initial results of a three-year research project entitled ATLANTIDE, which is aimed at developing a comprehensive digital archive of reference models of Italian distribution networks, including forecasted load and generation development evolving towards future smart grid scenarios. Such reference network models and evolutionary scenarios should provide a useful benchmark for testing and comparing different control methodologies, distribution schemes and operation strategies for dealing with the new challenges caused by the envisaged widespread diffusion and integration of distributed generation, renewable generation and distribution storage devices. The paper focuses on the criteria adopted for defining a set of evolutionary scenarios for the reference networks, accounting for current drives and future trends, valuable to a wide range of the stakeholders of the distribution business.

Coordinated voltage control in MV and LV distribution networks with inverter-interfaced users

In the last years there has been a progressive growing of distributed generators connected to the LV distribution networks, leading to possible depletion of power quality levels. For this reason, standards and grid codes are under revision and several studies have been conducted investigating the possibilities offered by grid connected inverter-interfaced generators to participate to network voltage regulation and unbalance correction. In this paper a control strategy is proposed applicable to a DMS coordinating the MV network regulation, applied through a novel adaptive regulation area criterion, with local LV network controllers which, in turn, coordinate the downstream inverter-interfaced generators. The aim is to demonstrate the benefits coming from a correct coordination of the distributed LV resources with the DMS located at the primary substation.

Accurate Calculation of the Right-of-Waywidth for Power Line Magnetic Field Impact Assessment

In this work, approximate formulas are presented for computing the magnetic fleld intensity near electric power transmission lines. Original expressions are given for single circuit lines of any type of arrangement and double circuit lines in both super-bundle and low-reactance conductor phasing. These expressions can be used for assessing directly the Right-of-Way width of power lines related to maximum magnetic fleld exposure levels which may be e-ciently used in environmental impact assessment. The accuracy of approximate formulas is demonstrated by comparison with exact formulas for computing the rms fleld distribution.

Analysis of load-induced unintentional islanding in Low Voltage grids with PV generators

The interest of unintentional islanding operation has recently grown in Low Voltage (LV) distribution grids because of the large penetration of Distributed Energy Resources (DERs), especially the ones based on the PhotoVoltaic (PV) energy source. The probability of unintentional islanding is increased also due to the newly introduced standards with extended frequency and voltage limits before the PV protection trips and due to the large number of PV generators, which can make ineffective the anti-islanding provisions each PV is equipped with. Moreover, interconnection standards of DERs require some additional grid support functions, such as active and reactive power regulation using P/f and Q/V droop characteristics, which can further increase the probability of unintentional islanding. In this paper, an analysis of this phenomena is provided using a simplified static and dynamic characterization of the generators and the loads. Simulation results based on Matlab and DIgSILENT tools on a simplified LV distribution network are reported together with preliminary experimental results on a lab-scale prototype.

Application of modal analysis for the enhancement of the performances of a UPFC controller in power oscillation damping

The aim of this work is to investigate and evaluate the performance of UPFC (unified power flow controller) devices operating in a transmission system in order to control inter-area power oscillations originated by small disturbances. Particular emphasis is given in using the participation factor matrix in order to identify the state variables which mostly affect the modes of inter-area oscillations and to intervene on those state variables directly related to the FACTS action. The efficiency of the method is subsequently assessed by means of detailed dynamic simulations.

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.