Search results for "HV"

Predictability of PD inception in defects included in HVDC cables by conductivity models calibrated through experiments

2022

To date, there are several methods for calculating the electric field distribution within a dielectric layer subjected to HVDC voltage. However, experimental techniques for evaluating the accuracy of models for calculating the electric field, such as space charge measurement, are often not precise enough to be used for this purpose. At the same time, the knowledge of Partial Discharge (PD) phenomenon occurring under HVDC stress is also not as developed as that of PD under HVAC voltage. The main goal of this research is to study the effectiveness of dielectric conductivity models to forecast the inception condition for PD under load and HVDC voltage stress. This study has been carried out by…

Partial discharges characteristics during load transients in an HVDC model cable

2021

The occurrence of Partial Discharges (PD) in HVAC cables is widespread considered as one of the most important concerns for the stability of the insulation. To date, the role of PD in the ageing and definitive fault of HVDC cables has been poorly investigated. This is mainly due to some practical difficulties in the performing of the measurements. Compared to the PDs occurring under AC stress, the higher inception voltages and the lower repetition rates, obtainable under DC voltage, make the exclusion of the measurement noise more difficult. This paper is focused on the study of the characteristics of the PDs occurring in an artificial defect located in proximity of the outer dielectric' su…

Characteristics of partial discharges in an experimental setup reproducing HVDC cable insulation operating conditions

2021

The occurrence of Partial Discharge (PD) inside a cavity subjected to HVDC voltage can be considered as one of the most likely sources of insulation ageing and failure. In practical applications, the recognition of PD under HVDC is more difficult than under AC stress because of the lower repetition rates and the impossibility to obtain a PD pattern synchronized with the waveform of the applied voltage. In this paper, the relationship between conduction phenomena in dielectrics and the occurrence of PD is investigated by means of a novel experimental setup. A couple of dielectric cells connected in series is subjected to various HVDC stress levels. The applied voltage is divided between the …

Attività di Ricerca del Laboratorio LEPRE

2014

AN ACCURATE MODEL FOR STEADY-STATE AND DYNAMIC ANALYSIS OF THE SICILIAN NETWORK WITH HVDC INTERCONNECTIONS

2021

Sicily is one of the first Italian regions for installed power from renewable energy plants, especially photovoltaic and wind plants, and a crucial point for the Mediterranean energy hub. Its role as nexus between the European and the African Continents is becoming more and more significant due to the realization in a short time of the so called Tyrrhenian link and the High Voltage Direct Current (HVDC) connection with Tunisia. In this framework, the paper presents a model of the Sicily power generation and transmission system, including the Tyrrhenian link and two equivalent buses representing the Sardinian power network and the rest of the Continental Europe (CE) synchronous area, for both …

Transient behaviour of a “mixed” overhead-cable EHV line under lightning events

2009

Recently, in many countries have been undergone or are planning links with AC extra-high voltage (EHV) underground cables. Cable lines offer the possibility of a reduced environment impact and for this reason they are often the only alternative for the reinforcement or the expansion of power system accepted by public opinion. The coexistence of overhead and cable line in the so called ¿mixed¿ lines, however, raises several questions regarding their behaviour both in steady state and in transient. The purpose of this work is to investigate the transient behaviour of a mixed overhead-cable EHV line under lightning events, describing the effects of the following overvoltages on the system. The…

WIRELESS DETECTION OF PD PATTERNS: APPLICATIONS IN SMART GRIDS AND MODERN POWER SYSTEMS

In this thesis, different challenges for various applications of a wireless PD detection instrument are discussed and relevant solutions are proposed. The main purpose is to assess the applicability of such technology both in current HV and MV power systems as well as in future applications for smart grids. The main challenges for these types of diagnostic systems are the following: • voltage synchronization of Phase Resolved PD pattern; • PD recognition under non-sinusoidal voltage waveforms; • PD recognition under sinusoidal voltage superimposed harmonics; • PD recognition in laboratory and in real world situations under noise and other source of disturbance. Thanks to the collaboration w…

Programming distributed applications with symbolic reasoning on WSNs

2015

Programming Wireless Sensor Networks (WSNs) is a complex task for which existing approaches adopt rigid architectures that are only suitable for specific application fields. In previous papers we introduced a programming methodology and a lightweight middleware based on high-level programming and executable code exchange for distributed processing on WSNs. In this paper, we show how high-level programming can be effectively used on WSNs to implement symbolic reasoning. In order to prove the feasibility of our approach, we present a Fuzzy Logic system where the value updates and the rule evaluations are performed in a distributed way. Through the proposed methodology, we discuss the developm…

Shock formation in the dispersionless Kadomtsev-Petviashvili equation

2016

The dispersionless Kadomtsev-Petviashvili (dKP) equation $(u_t+uu_x)_x=u_{yy}$ is one of the simplest nonlinear wave equations describing two-dimensional shocks. To solve the dKP equation we use a coordinate transformation inspired by the method of characteristics for the one-dimensional Hopf equation $u_t+uu_x=0$. We show numerically that the solutions to the transformed equation do not develop shocks. This permits us to extend the dKP solution as the graph of a multivalued function beyond the critical time when the gradients blow up. This overturned solution is multivalued in a lip shape region in the $(x,y)$ plane, where the solution of the dKP equation exists in a weak sense only, and a…

Numerical study of the Kadomtsev–Petviashvili equation and dispersive shock waves

2018

A detailed numerical study of the long time behaviour of dispersive shock waves in solutions to the Kadomtsev-Petviashvili (KP) I equation is presented. It is shown that modulated lump solutions emerge from the dispersive shock waves. For the description of dispersive shock waves, Whitham modulation equations for KP are obtained. It is shown that the modulation equations near the soliton line are hyperbolic for the KPII equation while they are elliptic for the KPI equation leading to a focusing effect and the formation of lumps. Such a behaviour is similar to the appearance of breathers for the focusing nonlinear Schrodinger equation in the semiclassical limit.