Frequency Dielectric Spectroscopy and Dissipation Factor Measurements during Thermal Cycles on Different Types of MV Cable Joints

Results of periodic measurements of Dissipation Factor (DF) and Frequency Dielectric Spectroscopy (FDS) on Medium Voltage (MV) cables during thermal cycles, are reported and discussed in this paper. Twelve cables equipped with different types of joints were connected together to form a ring in short-circuit. The ring was energized at rated voltage and current. Temperature cycles with a period of one day (11 hours of heating) were applied by controlling the current. Periodically, each cable was tested separately using both DF and FDS techniques to monitor the ageing progression. This paper focuses on the experimental results obtained testing six new cables provided by different types of new joints while the other six coming from the field, are not considered here. Results obtained testing the six new cables indicate that FDS evaluation is a reliable tool to distinguish the aging progression of the insulation from the seasonal and reversible changes while DF values recorded at different voltage levels show a non-regular behavior particularly in XLPE cables. These results clearly suggest that the systematic use of FDS in condition assessment of underground cables can provide more information on the ageing progression than the traditional DF measurements

DC Islands in AC Smart Grids

The advantages arising from dc distribution networks are related to the possibilities of achieving higher quality supply and easier reconfigurability of the system. This paper presents the concept of introducing some dc islands interconnected with the ac distribution network. This will make it easier to connect storage systems, electrical drives, power converters, and renewable sources (i.e., photovoltaic panels). In order to realize the aforementioned goals, a methodology for designing the control strategy of different power converters connected to a dc bus without a centralized system management control unit is proposed. In this way, a plug-and-play functionality for connecting new power converter interfaced elements in the dc network able to stabilize the voltage under different working conditions is realized. In order to prove the advantages obtainable with such a network, a 100-kW dc test facility has been realized at the laboratories of RSE. Different working conditions were tested by means both of numerical and experimental results, proving the effectiveness of the proposed strategy for voltage regulation, continuity of service, and the smart use of storage devices

Statistical Analysis of Broadband Underground Medium Voltage Channels for PLC Applications

This work presents a statistical analysis performed on a set of channels that were measured in real-life underground medium voltage power line communication (PLC) networks. The aim is to improve the knowledge of the medium from experimental basis, providing usable and closed-form expressions of the main metrics in order to foster the design of PLC technologies tailored to such challenging scenario. The work targets the 2-40 MHz band, and focuses on the average channel gain (ACG), the root-mean-square delay spread (RMS-DS) and the coherence bandwidth. Furthermore, the work presents the relation between the ACG, the RMS-DS and the network topology, and it infers the capacity as a function of the transmission bandwidth under power spectral density or total power constraints. Some results about the line impedance are also show

High Power Quality level DC distribution system for woodworking plants

Power quality is becoming more and more important for different kind of users. In particular, for industrial customers it represents a key factor for the productiveness and the efficiency. Also, the wide diffusion of electronic loads implies a spread use of power electronics. In this scenario, DC distribution networks are a suitable solution for solving problems of power quality both for the customer and for the supplier. In the paper, the opportunity of using a DC distribution network inside a woodworking plant is analyzed. A network configuration and a control strategy are proposed and verified by means of numerical simulations and experimental tests