0000000000004840
AUTHOR
L. De Rai
Partial discharge detection and localization along medium voltage cables
In the last years different partial discharge (PD) measuring techniques have been developed because PD diagnostic is the most widely tool to evaluate the insulation condition of a power cable. Recently non-conventional methods and sensors have been used in order to reach improved results in PD measurements. The purpose of this work is to perform measurements that allow to study the variation of pulses when they travel along a MV cable and to locate the pulse source through the time arrival difference of the pulses obtained from two sensors installed separately.
Effect of Polarity Reversal on the Partial Discharge Phenomena
In the field of High Voltage Direct Current (HVDC) transmission, the space charge accumulation phenomenon and the Partial Discharges (PD) phenomena are considered the main causes of dielectric ageing. During the years, the degradation effect of both phenomena under constant DC stress has been widely studied by several researchers. In case of polarity reversal, typically carried out to control bi-directional power flow between interconnected High Voltage transmission systems, the space charge movement may not synchronously follow the electric field polarity. This could make the moment of reversing polarity a very critical one, where space charge injected during preceding polarity produces hi…
Different Measurement Setup Configurations for Space Charge test in Mini Cable Specimens with the PEA Method
Under DC stress, the space charge accumulation is believed one of the most responsible of dielectrics ageing. For this reason, due to the increase of the HVDC transmission, a recommendation has been proposed. The latter want to introduce the space charge measure, with the PEA method, in cable specimens during the prequalification or type tests. Considering the several issues related to this kind of measures the aim of the proposed work is find a measurement setup for mini cable specimens which is able to provide a clear and clean space charge profile. Therefore, different tests have been made in this work. In particular, the length of the cable specimen, the width of the pulse electrodes, a…
Different Space Charge Behavior of Materials Used in AC and DC Systems
The aim of the present work is to evaluate the behavior, from the space charge accumulation phenomenon point of view, of three different XLPE specimens used as insulation materials in high voltage systems. Considering that under DC stress the charge accumulation is more relevant as compared to the AC case, in the specimens for DC applications additives are typically added. In this work, three different specimens are analyzed. One is a free additive sample used conventionally under AC stress and two others include different additives that are used under DC stress. In order to measure the space charge accumulation, the Pulsed Electro Acoustic (PEA) method has been employed. For each sample, t…
Partial Discharges Diagnostics Along Medium Voltage Cables
In the last years different partial discharge (PD) measuring techniques have been developed because PD diagnostic is the most widely tool to evaluate the insulation condition of a power cable. Recently non-conventional methods and sensors have been used in order to reach improved results in PD measurements. New sensors based on wireless technology were developed in order to simplify PD measurement especially for on-line, on-site diagnosis. The purpose of this work is to perform measurements that allow to study the variation of pulses when they travel along a medium voltage cable and characterize a new smart PD source detector and locator, named Wings sensor. For these purposes, internal PD …
Partial discharge behavior under single phase half and full-bridge rectifier
The aim of the present work is to simulate partial discharges (PDs) phenomena under voltage stress close to the Direct Current (DC) waveform. The employed waveforms have been realized by using a full-wave and a half-wave rectifiers. After that, in order to generate a steadier voltage supply, a capacitive filter has been inserted in the output of the half-wave rectifier. Simulations have been carried out by modifying a previous software used in the case of Alternating Current (AC). Finally, experimental tests have been carried out in order to validate simulation results.
Interpretation of PEA Output Signal in a Multilayer Specimen
The aim of the present work is to evaluate the acoustic waves behavior within the Pulsed Electro-Acoustic (PEA) cell, in case of a multilayer specimen, in order to avoid misinterpretation of the output signal. Due to the reflection phenomenon of the acoustic waves travelling within the PEA cell, the output signal could be distorted. Because this aspect, for a given PEA cell with certain ground electrode and absorber thicknesses, depends on the sound velocity and thickness of the specimen under test, the latter must be carefully sized. For this aim, some useful relationships, that must be taken into account are given and described. In particular, a three layers sample simulating an air void …