PCB-Based Planar Inductive Loops for Partial Discharges Detection in Power Cables

Partial discharge (PD) diagnosis tests, including detecting, locating, and identifying, are used to trace defects or faults and assess the degree of aging in order to monitor the insulation condition of medium- and high-voltage power cables. In this context, an experimental evaluation of three different printed circuit board (PCB)-based inductive sensor topologies, with spiral, non-spiral, and meander shapes, is performed. The aim is to assess their capabilities for PD detection along a transmission power cable. First, simulation and experimental characterization are carried out to determine the equivalent electrical circuit and the quality factor of the three sensors. PD activity was studi…

Different scenarios of electric mobility: Current situation and possible future developments of fuel cell vehicles in Italy

The diffusion of electric vehicles in Italy has started but some complications weight its spread. At present, hybrid technology is the most followed by users, due particularly to socioeconomic factors such as cost of investment and range anxiety. After a deep discussion of the Italian scenario, the aim of the paper is to recognize whether fuel cell technology may be an enabling solution to overcome pollution problems and respect for the environment. The opportunity to use fuel cells to store electric energy is quite fascinating&mdash

The effect of the axial heat transfer on space charge accumulation phenomena in HVDC cables

To date, it has been widespread accepted that the presence of space charge within the dielectric of high voltage direct current (HVDC) cables is one of the most relevant issues that limits the growing diffusion of this technology and its use at higher voltages. One of the reasons that leads to the establishment of space charge within the insulation of cables is the temperature dependence of its conductivity. Many researchers have demonstrated that high temperature drop over the insulation layer can lead to the reversal of the electric field profile. In certain conditions, this can over-stress the insulation during polarity reversal (PR) and transient over voltages (TOV) events accelerating …

A New Approach to Partial Discharge Detection Under DC Voltage: Application to Different Materials

Usability of a new Direct Current Periodic waveform for partial discharge qualification in HVDC systems is exemplified by tests performed on different materials.

Modelling, simulation and characterization of Li-Ion battery cell

The decarbonizing process of the transportation system and the spread of unplanned renewables energy source, such as photovoltaic and wind energies, brought the constant need of ever more efficient energy storage technologies. Among these technologies, batteries, particularly the li-ion chemistry, are widely used in automotive and energy storage applications. For an optimized management of the cell it is advisable to have models that can accurately describe cell behaviour. In this paper a battery model for performance simulation in automotive application is identified. The main shapes of battery cells with their own advantages and disadvantages are shown, and a roundup of the best available…

Time Evolution of Partial Discharges in a Dielectric Subjected to the DC Periodic Voltage

Partial discharge (PD) detection can be considered one of the most useful tools for assessing the insulation conditions of the power apparatus in high-voltage systems. Under AC conditions, this analysis is widely employed in online and offline tests, such as type tests or commissioning, and can be carried out by applying the phase-resolved PD (PRPD) method, since the patterns can give information about the defect classification. Under DC voltages, the classic pattern recognition method cannot be performed, and the measurements show complexities related to the nature of the phenomena. For this reason, to date, a standard for PD measurements under DC does not exist. In previous papers, a new …

The Industrial Applicability of PEA Space Charge Measurements, for Performance Optimization of HVDC Power Cables

Cable manufacturing industries are constantly trying to improve the electrical performance of power cables. During the years, it was found that one of the most relevant degradation factors influencing the cable lifetime is the presence of space charge in the insulation layer. To detect the accumulated charge, the pulsed electro-acoustic (PEA) method is the most used technique. Despite the wide use of the PEA cell, several issues are still present. In particular, the PEA output signal is strongly disturbed by the acoustic waves reflections within the PEA cell. This causes the distortion of the output signal and therefore the misinterpretation of the charge profiles. This, in turn, may result…

Partial Discharges in HVDC Cables - The Effect of the Temperature Gradient During Load Transients

The paper investigates the role of the space charge accumulation phenomena in the inception of Partial Discharges (PD) in a defect within the bulk of the dielectrics of a High Voltage Direct Current (HVDC) cable. It is widespread accepted that the number of PD occurring in an HVDC cable during its lifetime is largely less than that under AC voltage stress. This is essentially due to higher values of the voltage between the conductor and the screen needed to trigger PD under a steady DC voltage than the same value under AC stress. Nevertheless, due to the dependency of the electrical conductivity of the insulation on the electric field and temperature, PD in HVDC cables is strongly influence…

The Effect of the Harmonic Content Generated by AC/DC Modular Multilevel Converters on HVDC Cable Systems

With the increasing penetration of renewable and decentralized energy sources into the power grid, an extended use of DC voltages is expected on both distribution and transmission levels. Generation of DC voltages by means of voltage source converters is associated with a wide spectrum of harmonic distortions at converter terminals, both on the ac and on the dc sides. This can lead to partial discharges in power cables, which deteriorate insulation material thus weakening its performance and reducing cable life-time. In the previously published paper, the effect of harmonic distortion on appearance of partial discharges in cable insulation was evaluated. Here, the study related to the PD be…

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…

Modelling of Pulsed Electro Acoustic Method for Space Charge Detection on Single and Multilayer Dielectrics

Experimental Investigation on the Performances of Innovative PV Vertical Structures

The sustainable development of our planet is considerably related to a relevant reduction of CO2 global emissions, with building consumption contributing more than 40%. In this scenario, new technological conceptions, such as building-integrated photovoltaic technology, emerged in order to satisfy the requirements of sustainability imposed by the European Union. Therefore, the aim of this work is to provide a technical and economical comparison of the performances of different vertical-mounted innovative photovoltaic systems, potentially integrated on a building instead of on traditional windows or glass walls. The proposed investigation was carried out by means of experimental tests on thr…

Effect of Heat Exchange Transient Conditions with Moving Water-Air Interface on Space Charge Accumulation in Undersea HVdc Cables

The accumulation of space charge inside the dielectric layer of an HVdc cable is one of the most important issue to be considered in the design stage and during the operating conditions. The separation of space charge is due to several factors including the dependence on temperature of the electrical conductivity of the insulation and the establishment of a thermal gradient under load conditions. This article is focused on the investigation of the effect of an axial heat transmission on the space charge and electric field distributions in an HVdc cable. In order to assess the impact of this phenomenon, a case study involving a cable immersed partly in water and partly in air has been simula…

Polarity reversal in HVDC joints - The effect of the axial thermal conduction

It has been shown that the establishment of a thermal gradient over the radius of HVDC cables involves the accumulation of space charge within the dielectric layer. High thermal gradients over the insulation thickness of loaded cables can lead to the inversion of the radial electric field pattern. In this scenarios, transient overvoltages and polarity reversal can lead to local and transitory peaks of electric field. Since the temperature distribution plays an important role in reaching critical values of the electric field, it has been considered interesting to have a more in-depth view of the thermal behavior of HVDC systems close the discontinuities of the geometry along the cable axis. …

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…

Acoustic Wave Behavior in a Specimen Containing an Air Void Defect

The PEA method is the most used technique for the space charge measurements. As is well known, this method uses pressure waves to detect the charges accumulated in solid dielectrics. Based on its working principle, the generated acoustic waves travel within PEA cell and the specimen under test in order to be finally detected by the piezoelectric sensor. For a multilayer specimen and, in particular, in case of different materials that make up the specimen, the acoustic wave reflection is inevitable. Considering that, in several cases, the reflected waves could be detected by the piezoelectric sensor before than the main signals, the PEA cell output profile could results distorted. Based on t…

Investigation on partial discharges in HVDC cables after polarity reversal events

Due to the accumulation of space charge inside the insulating layer of HVDC cables, the electric field under load conditions may be altered compared to what is established in HVAC cables. For example, a high thermal gradient leads to the inversion of the electric field pattern until the maximum value is reached in proximity of the dielectric-semicon interfaces. These maximum values can be further increased due to transient overvoltages and polarity reversal events until reaching electric field values higher than the rated ones. The main goal of this research is to investigate the possibility that, during these transient phenomena, conditions are created that favor the occurrence of partial …

Design of Soft Ferrite filters for EMI reduction in Power Conversion Systems

The use of a discrete passive filter is the most attractive solution for EMI reduction in power conversion systems. This is due to its simplicity of concept and efficiency in the frequency range up to tens of megahertz and over. The common mode and differential mode sections of the EMI filter contain capacitors and soft magnetic chokes and, when they are used in the transportation context, their design has to satisfy further constraints in terms of low weight, low volume, low losses and low cost in adjoint to filtering efficiency. In this framework the authors, by using an EMI filter design procedure already setup by themselves, investigate, also with an experimental setup, the possibility …

Use of Time-Frequency map combined with DBSCAN algorithm for separation of partial discharge pulses under DC voltage

The Phase-Resolved-Partial-Discharge pattern (PRPD) is a conventional technique used for the evaluation of partial discharges (PD) phenomena in High-Voltage-Alternating-Current (HVAC) systems. This map is constructed by plotting the peak of each detected pulses as a function of the phase angle of the supply voltage. Therefore it is obvious that this technique cannot be used for the analysis of data from PD mesaurement under different supply voltage condition (DC). The aim of this paper is to evaluate the application of the Time-Frequency map (TF map) for the analysis of a dataset obtained from PD measurement under DC voltage. A density-based clustering algorithm was also used to gain more i…

Space charge accumulation in undersea HVDC cables as function of heat exchange conditions at the boundaries – water-air interface

Transmission lines with undersea HVDC cables are an interesting technological solution for the supply of electrical energy to islands. The accumulation of space charge inside the dielectric layer of a HVDC cable is one of the most important element to consider in its design and during operation. The formation of space charge is due to various factors including the high dependence on the temperature of the electrical conductivity of the insulation and the establishment of a thermal gradient under load conditions. This research is focused on the space charge accumulation phenomenon around a section of a HVDC cable half dipped in water and half in air. Due to the high difference in thermal con…

Performances of a PCB-based Loop Antenna Inductive Sensor for Partial Discharges Detection

This paper presents the test results of an electrically small loop antenna sensor towards detecting the radiated magnetic field due to partial discharge (PD) activities. The loop antenna prototype was printed on an FR-4 substrate with a thickness of 1.6 mm, featuring a compact size of 20 mm times20 mm times1.7 mm. The proposed sensor, initially simulated with Ansys HFSS software, has a resonant frequency of about 100 MHz. Its detection capability for three types of partial discharges (i.e., corona, surface and internal PDs) has been evaluated. Laboratory experiments showed that the evaluated loop spiral antenna is appropriate for the detection of the three types of PDs. Indeed, the results …

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

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…

Investigation of PCB-based Inductive Sensors Orientation for Corona Partial Discharge Detection

This paper presents an experimental investigation of two different printed circuit board (PCB) inductive sensors, with meander and non-spiral shapes, to assess their capabilities and best orientation for corona partial discharge (PD) detection. First, simulations with the Ansys HFSS software are performed in order to evaluate the equivalent electrical circuit of the two sensors and their 2d radiation patterns. The meander sensors presented a resonant frequency of 600 MHz, while it was around 1.1 GHz for the non-spiral. The 2d radiation pattern showed that better sensitivity is achieved when the inductive sensor is oriented 90 degrees with respect to the PD source. Experimental tests showed …

Electromagnetic Full-Wave Simulation of Partial Discharge Detection in High Voltage AC Cables

Partial discharge (PD) activity in the insulation system of an electrical equipment can determine the failure of the whole apparatus. PD sensors are widely used in high-voltage electrical systems as the main elements of a detecting system oriented to real time monitoring. Recently, non-invasive sensors have been proposed in industrial applications for cable and other sensitive electrical parts: they are based both on capacitive and on the electromagnetic radiating coupling. In order to assess the real performance of a new sensor produced by a high voltage AC cables manufacturer, the paper proposes electromagnetic fullwave simulation results.

The Role of Right Interpretation of Space Charge Distribution for Optimized Design of HVDC Cables

In the field of high-voltage transmission systems, different degradation phenomena affect the reliability of the employed components. In particular, under dc stress, the space charge accumulation phenomenon is believed to be the most responsible of the dielectrics lifetime reduction. To measure the accumulated space charges in flat specimens, the pulsed electro-acoustic (PEA) method is one of the most used techniques. The working principle of the PEA cell is based on the acoustic waves propagation and detection. As is well known, the acoustic waves propagating in different means are partially transmitted and partially reflected. Therefore, the piezoelectric sensor of the PEA cell is subject…

Radiometric Partial Discharge Detection: A Review

One of the most common failures or breakdowns that can occur in high-voltage (HV) equipment is due to partial discharges (PDs). This occurs as a result of inadequate insulation, aging, harsh environmental effects, or manufacturing flaws. PD detection and recognition methods have gained growing attention and have seen great progress in the past decades. Radiometric methods are one of the most investigated detection approaches due to their immunity to electromagnetic interference (EMI) and their capabilities to detect and locate PD activities in different applications such as transformers, cables, etc. Several review articles have been published to classify and categorize these works. Nonethe…

Reliability of PEA Measurement in Presence of an Air Void Defect

This paper deals with the reliability of the Pulsed Electro-Acoustic (PEA) technique in the case of a specimen containing an air layer. The first approach to this study has been proposed by the authors in previously published works. In these papers, the mathematical description, the PEA cell simulation model, and some experimental tests have been reported. In this work, a more accurate description of the acoustic wave behavior within the PEA cell and specimen with and without an air layer is given. Moreover, the comparison between simulation and experimental tests for both cases (specimen with and without air layer) allowed the validation of the previously developed PEA cell simulation mode…

Review of the PEA Method for Space Charge Measurements on HVDC Cables and Mini-Cables

This review takes into account articles and standards published in recent years concerning the application of the Pulsed Electro Acoustic (PEA) method for space charge measurement on High Voltage Direct Current (HVDC) cables and mini-cables. Since the 80s, the PEA method has been implemented for space charge measurements on flat specimens in order to investigate space charge phenomena and to evaluate the ageing of dielectrics. In recent years, this technique has been adapted to cylindrical geometry. Several studies and experiments have been carried out on the use of the PEA method for full size cables and HVDC cable models. The experiments have been conducted using different arrangements of…

The effect of Transient over Voltages on the Partial Discharges activity in HVDC joints

Rapid growth of HVDC cable line installations is expected in the coming years. Several research groups have investigated dielectric phenomena that occur in the insulation of HVDC cables and accessories that accelerate aging and reduce the reliability of this technology over time. Unlike in HVAC cables, under HVDC stress, the distribution of the electric field inside the insulation layer depends not only on the applied voltage but also on the temperature distribution and on other factors related to manufacturing such as the presence of impurities. Reaching local and transient electric field peaks can enhance the onset of Partial Discharges (PDs) which can lead to premature aging of the insul…