HV Power Cables Research Articles

Editorial

This issue is focused on underground cable diagnostics. Therefore, I thought it would be appropriate to review the latest changes occurring in the cable diagnostics business. Underground cables are an important part of electric power transmission and distribution systems. The global market of the HV power cables is estimated to grow to $14 billion during 2020–2024.

A new approach to partial discharge detection under DC voltage

The continuing development of HVDC power transmission systems presents many problems related to evaluation of the reliability of power system assets [1]-[5]. In this context the identification of insulation defects plays a key role in preventing unexpected failures of electrical components. Partial discharge (PD) measurement is a useful approach to assessing the condition of HV power apparatus and cables. Such measurements are also widely employed for HVAC systems. The inception mechanisms of PD in AC systems are well-known, and measurements are usually performed following the IEC 60270 standard [6]. PD measurements under DC voltage present complexities related to the nature of the phenomenon and the supply conditions [7]. In AC systems phase-resolved-partial-discharge (PRPD) patterns allow assessment of the insulation condition, and provide information on the types of defect present [8]. Such analysis cannot be performed under DC voltage, since each discharge event cannot be related to a phase value. The interpretation of the acquired data therefore requires a different approach.

Active cathodic protection for HV power cables in undersea application

This paper focuses on the performance analysis of the corrosion protection system of HV power cables for undersea applications. The aim of the work is to describe the relations between the main electrical parameters affecting the electric potential distribution in the cable layers and in the surrounding medium, when an active cathodic protection (CP) arrangement is used. In particular, the analysis focuses on the design of an active CP for reducing corrosion phenomena of the cable metallic shield. This study is based on a 2D analytical approach supported by a detailed 3D finite element analysis (FEM). It gives evidence to the relation between the electrical variables and the design criteria of the active cathodic protection system.

Editorial: Partial discharge measurement and interpretation

In the past two decades I have been honored by the Editor-in-Chief, Professor Reuben Hackam, to serve as Guest Editor of the IEEE Transactions on Dielectrics and Electrical Insulation on the subject of partial discharges for three times and more precisely in 1998 (Vol. 5, Issue N0.3), 2008 (Vol. 15, Issue No. 6) and for the present Issue of February 2017 (Vol. 24, No. 1). These commitments, with a separation time of ten years, gave me the opportunity to follow with continuity the progress of scientific knowledge on the issue of great interest of partial discharges. In this progress, an increasingly shared element is represented by the fact that partial discharge (PD) detection, measurement and classification constitute today an important tool for quality assessment of insulation systems utilized in HV power apparatus and cables. In fact, the patterns obtained with PD detectors may contain important characteristic features useful to identify the defects of the faults involved.

Geometrical Shapes Impact on the Performance of ABS-Based Coreless Inductive Sensors for PD Measurement in HV Power Cables

In this paper, a series of investigations on sensitivity and bandwidth for four types of Rogowski coil (RC) sensors was demonstrated. The proposed RC sensor design using acrylonitrile butadiene styrene material carries the advantages, such as lighter weight, robust, and higher temperature resistance. The prototype development first was carried out with the assistance of Solidwork 3D computer aided design software and MakerBot 2X 3D printer. Subsequently, the sensors were modeled and simulated using electromagnetic transient program-alternative transient program software environment based on the lumped parameter identification. A single-end measuring technique was used to locate the PD signal on the three-phase medium voltage underground cross-link polyethylene insulated power cable with a 240-mm2 nominal area copper conductor. In order to verify the results achieved from the simulation, an experiment was carried out. This experiment was repeated concurrently for each design of the RC sensors. In order to achieve the best PD detection, the precise selection for the best sensor is paramount. In this case, the results indicated that certain geometrical shape performed better with regard to the detection of the PD signal.

Increased operation reliability of HV apparatus through PD monitoring

In this article, the challenges with continuous partial discharge (PD) monitoring of HV power cables, transformers and rotating machines are presented. A versatile partial discharge monitoring system is described that is applicable to different high-voltage equipment and can be connected to a vast range of sensors. In the case of power cables, the paper deals with continuous monitoring of a 420 kV XLPE cable system in an underground tunnel. The method that can simultaneously detect and locate partial discharges at all accessories is described. In the case of transformers, partial discharges are measured at the bushing measuring taps and in the UHF range with an antenna installed within the transformer tank. The experience gathered from PD monitoring to assess the condition of turbo and hydro generator stator winding insulation is also presented in the paper. The advanced features for noise and PD defects separation based on synchronous multi-channel techniques are shown. Case studies are included, which indicate that critical defects can be detected early and their evolution can be monitored.

Reducing the impact of ELF electromagnetic fields of HV power cables on the environment by modeling the cable accessories

Purpose – Underground cables can produce higher electromagnetic fields directly above them than an overhead line. The majority of cable failures on distribution system are caused by defects in the cable accessories. Nowadays, significant research has been carried out worldwide into examining whether electricity, and in particular, the presence of electric and magnetic fields have an adverse impact on health, especially the occurrence of cancer and childhood leukemia. The purpose of this paper is to optimize the electric field distribution in underground cable accessories. This reduces the impact of the harmful effects of the fields on living beings and humans. Design/methodology/approach – Cable terminations and joints are designed to eliminate the stress concentration at the termination screen to avoid the breakdown of the cable and high values of electric field at these points. Any improvement in the cable termination and joints construction is of great interest. There are several methods for the solution of electric field distribution. These can be summarized as analytical, experimental, free-hand field mapping, analogue methods and numerical methods. In this paper cable accessories are modeled by using multilayer dielectric system and very thin deflector’s cones. Findings – This model includes specific insulators design and smart choice of electrodes position. Stress-grading nonlinear materials in form of tapes and tubes were used with much success. In order to optimize the cable joint parameters, two criteria were monitored – total electric field magnitude and magnitude of the tangential component. More than 30 percent is reduced impact of cables on the environment. Originality/value – In order to investigate the accuracy of the applied numerical model, various configurations of the cable accessories are studied. The first time is applied new Hybrid Boundary Elements Method on the protection of the environment.

On-site testing and diagnosis of transmission power cables up to 230 kV using damped AC voltages

Failures of the insulation of HV power cables can occur during operation at normal voltage or as a result of a transient voltage spike due to lightning or switching. Failures may occur if localized electrical stresses exceed the dielectric strength of the insulation or if the insulation is degraded to the point that it cannot withstand the applied voltage.

Application of K-Means method to pattern recognition in on-line cable partial discharge monitoring

On-line Partial Discharge (PD) monitoring is being increasingly adopted in an effort to improve asset management of the vast network of MV and HV power cables. This paper presents a novel method for autonomous recognition of PD patterns recorded under conditions in which a phase-reference voltage waveform from the HV conductors is not available, as is often the case in on-line PD based insulation condition monitoring. The paper begins with an analysis of two significant challenges for automatic PD pattern recognition. A methodology is then proposed for applying the K-Means method to the task of recognizing PD patterns without phase reference information. Results are presented to show that the proposed methodology is capable of recognising patterns of PD activity in on-line monitoring applications for both single-phase and three-phase cables and is also effective technique for rejecting interference signals.

Use of dissipation factor for life consumption assessment and future life modeling of oil-filled high-voltage power cables

Tan δ measurements can be used to assess the condition of OF insulation in HV power cables. Data showing the behavior of tan δ as a function of temperature at constant electrical stress, and as a function of electrical stress at constant temperature, at different stages of degradation (or aging) are essential. By combining on-site and laboratory measurements, the remaining service lifetime of a cable can be estimated for various future loading levels using a model incorporating ground temperature, the age of the cable, and its loading history.

Dedicated On-Site Condition Monitoring of High Voltage Power Cables up to 150kV

For advanced, non-destructive on-site condition monitoring of HV power cables up to 150kV by partial discharge detection and dielectric losses measurement it is necessary to energize the disconnected cable system. One of the methods available for this purpose is based on applying damped AC voltages up to 150kV. In this paper, the use of modern technological solutions in power electronics and signal processing as well as in technical design and production methods will be discussed on the basis of the ultra light system (300kg) which is able to test cables up to 20km lengths.

Influence of water and ion diffusion on generation and progress of bow‐tie tree

AbstractBow‐tie tree (BTT) generated from contaminant, such as metal, carbon, amber (overcured resin) or void is a deterioration factor of XLPE cable. In particular, BTT in contact with inner or outer semiconductive shield could significantly lower residual AC breakdown voltage of HV power cables. To evaluate the influence of water and ion diffusion on generation and progress of BTT, we investigated the relationship between water content of XLPE and the generation of BTT under various accelerated aging conditions. The number of BTT in XLPE samples with accelerated aging under the open condition, involving evaporation of water in which samples were immersed, was very large compared with the closed condition. Furthermore, when samples were intermittently immersed in water, the number of BTT in samples was large compared with samples immersed continuously. In these experiments the generation of BTT seemed to have nothing to do with changes in water content before and after accelerated aging. Therefore, it was suggested that diffusion of ions rather than water in XLPE played an important role in the generation of BTT. © 2007 Wiley Periodicals, Inc. Electr Eng Jpn, 162(3): 9–16, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.20413

Trends in partial discharge pattern classification: a survey

Partial discharge (PD) detection, measurement and classification constitute an important tool for quality assessment of insulation systems utilized in HV power apparatus and cables. The patterns obtained with PD detectors contain characteristic features of the source/class of the respective partial discharge process involved. The recognition of the source from the data represents the classification stage. Usually, this stage consists of a two-step procedure, i.e., extraction of feature vector from the data followed by classification/recognition of the corresponding source. The various techniques available for achieving the foregoing task are examined and analyzed; while limited success has been achieved in the identification of simple PD sources, recognition and classification of complex PD patterns associated with practical insulating systems continue to pose appreciable difficulty.

The fractal analysis of water trees: an estimate of the fractal dimension

Water trees result from ac electrical aging of the polymeric insulation of medium and HV power cables in a humid or wet environment. As suggested by their name, they arise from penetration of water in the polymer. Visual observation with the help of an optical microscope shows tree (bush) type structures. This suggests that water trees might be fractal objects. Calculation of the fractal dimension from experimental samples may confirm the fractal characteristics and also give information on the damage caused to the polymer. In this work images of water trees taken under the optical microscope, dyed by methylene blue and etched for scanning electron microscopy (SEM), were studied in order to estimate the fractal dimension using a box-counting algorithm. The photographs, made using an optical microscope (scale of 100 /spl mu/m), of the dyed samples were obtained from laboratory-aged low-density polyethylene (LDPE) specimens using accelerated techniques. Different field amplitude and frequency and also time of aging were used and the dimension values were compared. SEM images resulting from aged cross-linked polyethylene (XLPE) cables revealed a structure at a different scale (/spl sim/3 /spl mu/m). Each photograph was analyzed to compare regions with and without water trees.

Field testing of HV power cables: understanding VLF testing

DC testing of solid dielectric insulated cables has been shown to have limited usefulness. Currently, the two VLF test techniques, the author has found, seem to be the most promising alternatives for testing service-aged power cable systems with extruded dielectric insulation. >

Some Aspects of the Relationship between Water Treeing, Morphology, and Microstructure of Pplymers

Water treeing is one of the main causes of premature breakdown of the polymeric insulation of HV power cables. The work reported in this paper is the combined effort of three different laboratories to investigate water treeing behavior of several polymers by complementary techniques. These include determination of water tree growth kinetics by continuous optical monitoring, fatigue environmental stress cracking, tensile drawing behavior, and transmission electron microscopy. Two kinds of sample geometry have been used for the water electrodes so as to enlarge signi- ficance of results and experiments have been conducted at 20°C and 65°C. The structural and mechanical evidence presented shows that water tree growth can be modified by several mechanisms and points out the considerable influence of polymer morphology on the propagation of water trees.