Ricerc@Sapienza

The paper deals with the protective relaying of MV rings recently introduced by e-distribuzione, the largest Italian Distribution System Operator (DSO). The paper refers to an existing MV distribution system which includes a loop line. Attention is focused on Cross-Country Faults (CCFs), i.e. two Line-to-Ground Faults simultaneously occurring in two different phases at different locations. A large number of detailed ATP-EMTP simulations of CCFs are carried out, evidencing a few critical CCF combinations not detected by the presently adopted protective relays.

In high voltage transmission lines, the shield wires are often sectionalized for several reasons. This practice may have considerable effects on power line communications in multiconductor transmission lines. A careful simulation is performed in order to put in evidence the relevant channel features.

Large-scale ground-mounted PV plants, because of their large extend and localization, can be subject to lightning strikes. When a lightning strike falls into the area of the PV plant, the earthing system is affected by the current flowing in the lightning channel and potentially dangerous overvoltages may occur. Thus, the investigation on the performance of the grounding system is of paramount interest for the prediction of the potential threats either for people working in (or animals passing through) the solar farm area and for the installed electric and electronic equipments.

Electricity in small remote islands is generally supplied by diesel generators, leading to high energy cost and significant local pollution; the integration of renewable energy sources in such small networks is hindered by stability and reliability issues, as well as environmental constraints. The paper deals with the replacement of diesel generation in Giglio (a small island in the Tyrrhenian Sea), with an hybrid power plant which includes a photovoltaic power plant and a lithium battery energy storage system.

The lightning performance of an EHV overhead transmission line (OHL) largely depends on tower grounding behavior; when high ground flash density values are expected, a proper design of grounding arrangements, focused on their high frequency behavior instead of the conventional power frequency analysis, can significantly reduce the backflashover rate (BFR) of the OHL. A technical optimization is reported, aiming at improving the BFR of an EHV OHL in Brazil, which crosses a region with widely different soil resistivity values, resulting in a compact tower grounding system design.

The analysis of the thermal stress of underground MV power cable joints under different environmental conditions, both in normal operation and during faults, is crucial to assess any correlation between the occurrence of overheatings and the anomalous increase of failures (two to three times compared to previous years) which have been observed in the Italian distribution network during summer 2015 (the hottest year ever since 1880).

The latest updates in the European directive on energy performance of buildings have introduced the fundamental “nearly zero-energy building (NZEB)” concept. Thus, a special focus needs to be addressed to the thermal performance of building envelopes, especially concerning the role played by thermal inertia in the energy requirements for cooling applications. In fact, a high thermal inertia of the outer walls results in a mitigation of the daily heat wave, which reduces the cooling peak load and the related energy demand.

This paper deals with the mechanical solutions for installation of innovative direct-drives suited for steering gears onboard ships. The work is comprised in a research project commissioned by the Italian Navy. The research aims to realize a full-electric and oil-free drive for actuation of hydraulic loads in the perspective of more 'green ships'. The electrical drives proposed are based on a fractional slot permanent magnet linear motor sized and optimized for high force and low speed operation, as required by hydraulic loads onboard ships.

This paper deals with the electromagnetic, mechanical, and cooling solutions for an innovative direct-drive suited for steering gears on board ships. The work is comprised in a research project funded by the Italian Navy. The research aims to realize a full-electric and oil-free drive for actuation of hydraulic loads in the perspective of 'more green ships'. The electrical drive proposed is based on a fractional slot permanent magnet linear motor sized and optimized for high force and low speed operation, as required by hydraulic loads on board ships.

Torsional resonances may incur in induction drives due to large harmonic torques produced by the inverter. The torsion can affect the rotor-load system, but more sneaky resonances may arise in the rotor end-rings of fabricated-cage induction motors. Abnormal cage torsions may lead to bar breakage due to high-cycle fatigue. Since the high-frequency speed oscillations are difficult to detect, torsional resonances may go unnoticed and lead to drive fault on the long run.