System configuration, fault detection, location, isolation and restoration: a review on LVDC Microgrid protections

Low voltage direct current (LVDC) distribution has gained the significant interest of research due to the advancements in power conversion technologies. However, the use of converters has given rise to several technical issues regarding their protections and controls of such devices under faulty conditions. Post-fault behaviour of converter-fed LVDC system involves both active converter control and passive circuit transient of similar time scale, which makes the protection for LVDC distribution significantly different and more challenging than low voltage AC. These protection and operational issues have handicapped the practical applications of DC distribution. This paper presents state-of-the-art protection schemes developed for DC Microgrids. With a close look at practical limitations such as the dependency on modelling accuracy, requirement on communications and so forth, a comprehensive evaluation is carried out on those system approaches in terms of system configurations， fault detection, location, isolation and restoration

First-fault detection in DC distribution with IT grounding based on Sliding Discrete Fourier-Transform

Since dc distribution minimizes the number of power conversion stages, it lowers the overall cost, power losses, and weight of a power system. Critical systems use IT grounding because it is tolerant to the first-fault. Hence, this is an attractive option for hybrid electric aircraft (HEA), which combines gas engines with electric motors driven by power electronic converters. This letter proposes an accurate implementation for the procedure of first-fault detection with IT grounding. The ac component injection along with the sliding discrete Fourier transform (SDFT) is used to estimate the fault impedance. The procedure is very accurate due to the heavy filtering of the implicit moving average filter. Further computation savings are obtained by using the double look-up tables, and the Goertzel algorithm for the SDFT. Results are validated by simulations and experiments

Non-contact measurement and analysis of trapped charge decay rates for cable line switching transients

During reclosure of 275 kV cable circuits used for voltage control, excessive overvoltages were observed on the network. Such events cause onerous and costly failures. Transient simulations have shown that the normal voltage on its own cannot generate such excessive switching overvoltages. Initial investigations by the network operator pointed towards trapped charge on the unearthed as the cause of the failures. Measurement of these trapped charge voltages and their slow decay without interfering with the charge has, to the author’s knowledge, not been done before in an operational substation. This work introduces a technique to measure trapped charge at a 275 kV substation using the Electrostatic Field Mill. Since the electric field is a proxy measurement of surface voltage, field mills can also be used to measure voltage. In this paper, an on-site substation measurement setup using an electrostatic field mill has been developed for the non-contact measurement of trapped charge voltage on a 275 kV underground cable circuit following switching operations at a National Grid substation. Results of field measurements within the substation and laboratory experimentation are discussed. It is demonstrated that with adequate calibration, achieved by using the known pre-switching power frequency steady state voltage, the slowly decaying DC voltage caused by the cable trapped charge can be measured using this non-contact technique. The correlation between the instantaneous time constant and the relative humidity is also analysed

Selected Papers from 2020 IEEE International Conference on High Voltage Engineering (ICHVE 2020)

The 2020 IEEE International Conference on High Voltage Engineering (ICHVE 2020) was held on 6–10 September 2020 in Beijing, China. The conference was organized by the Tsinghua University, China, and endorsed by the IEEE Dielectrics and Electrical Insulation Society. This conference has attracted a great deal of attention from researchers around the world in the field of high voltage engineering. The forum offered the opportunity to present the latest developments and different emerging challenges in high voltage engineering, including the topics of ultra-high voltage, smart grids, and insulating materials

Using Virtual Reality Modelling to Enhance Electrical Safety and Design in the Built Environment.

This thesis presents a prototype desktop virtual reality model entitled ‘Virtual Electrical Services’, to enhance electrical safety and design in the built environment. The model presented has the potential to be used as an educational tool for third level students, a design tool for industry, or as a virtual electrical safety manual for the general public. A description of the development of the virtual reality model is presented along with the applications that were developed within the model. As part of the VR development process, this research investigates the cause and effects of electrical accidents in domestic properties. This highlights the high-risk activities, which lead to receiving an electric shock in a domestic property and identifies at-risk groups that could most benefit from electrical safety interventions. It also examines the theory of transfer touch voltage calculations and expands on it to show how to carry out a sensitivity analysis in relation to the design parameters that are being used by designers and installers. The use of Desktop Virtual Reality systems for enhancing electrical safety and engineering design is a novel prospect for both practicing and student electrical services engineers. This innovative approach, which can be readily accessed via the World Wide Web, constitutes a marked shift in conventional learning and design techniques to a more immersive, interactive and intuitive working and learning environment. A case study is carried out to evaluate the users’ attitudes toward VR learning environments and also the usability of the prototype model developed. From the completed case study, it appears that there is sufficient evidence to suggest that virtual reality could enhance electrical safety and design in the built environment and also advance training methods used to educate electrical services engineers and electricians. The thesis includes a discussion on the limitations of the system developed and the potential for future research and developmen

Earth Fault Protection of Compensated Rural Area Cabled Medium Voltage Networks

Recent storms in Nordic countries have damaged MV distribution networks and caused major outages. Furthermore, new quality requirements of electricity supply, and customers’ demands for more uninterruptable and better quality of supply have led to build weatherproof and reliable networks by replacing overhead lines by underground cables in rural areas. However, the rising level of cabling increases earth fault currents and produces dangerously high touch voltages in surrounding areas. Earth fault current through human body and related consequences depend on its magnitude and duration. In worst case even a low current can be fatal to victim. Because earth fault current consists of increased capacitive component and resistive part due to considered zero sequence series impedance with longer feeders, protection has to be implemented in different ways ensuring safety and selectivity during earth faults. Resistive part can not be compensated with Petersen coils, but it can be limited with decentralized compensation. Moreover, network structure and earthing method impact on the magnitude of earth fault current. Earth fault phenomenon with phase angle and admittance criteria was studied. Typical MV distribution network models using PSCAD simulation software were created. The aim was to find out how earth fault protection should be arranged with defined fault scenarios in different cases and what is the sensitivity that can be reached. The impacts of phase angle errors on protection were also studied in one situation. The results showed that admittance criterion is reliable and sensitive in radial networks, and protection even operates without the parallel resistor in some cases. However, it requires careful setting of certain admittance boundaries. When using phase angle criterion, parallel resistor should be connected or wider tolerance should be set in some cases. Phase angle criterion was not affected by errors, which was accounted for parallel resistor connection. In theory the admittance method was vulnerable to errors, but false operations can be avoided by placing the boundaries with sufficient margins. Consequently, threshold settings and accurate calculations of protection quantities should be done carefully.fi=Opinnäytetyö kokotekstinä PDF-muodossa.|en=Thesis fulltext in PDF format.|sv=Lärdomsprov tillgängligt som fulltext i PDF-format

DC Networks on the Distribution Level – New Trend or Vision?

"DC networks on Distribution Level – are they a new trend or a Vision?" That is the question that has focused the efforts of the Working Group the last two years, and whose consideration is summarized in this report. This report represents the first phase evaluation of this topic and is focused primarily on medium (MVDC) and low voltage (LVDC) level applications

Manual de riscos elétricos : introdução às redes de proteção

Tese de mestrado. Mestrado em Engenharia de Segurança e Higiene Ocupacionais. Faculdade de Engenharia. Universidade do Porto. 201

The use of an auxiliary spark gap placed across the surge arrester of a medium voltage transformer.

Thesis (M.Sc.Eng.)-University of KwaZulu-Natal, 2007.Thesis (M.Sc.)-University of KwaZulu-Natal, 2007.A possible lower cost alternative to medium voltage line arresters and parallel-connected surge arresters is the use of parallel-connected spark gaps across a metal oxide surge arrester. The function of the spark gap is to protect the transformer when the surge arrester fails. Clearly the breakdown voltage characteristics of such a gap need to be carefully co-ordinated with the transformer insulation and those of the arrester. Eskom (Electricity Supply Commission of South Africa) is the national electrical utility that provides the generation, transmission and distribution of electricity in South Africa. The majority of Eskom's electricity reticulation is done with either 11 kV or 22 kV electrical overhead networks. An unacceptable number of Eskom's pole mounted power transformers on these networks have failed over the past few years. The high failure rate of Distribution transformers in Eskom, South Africa has previously been highlighted and investigated in an MSc thesis, the most recent being the thesis completed at the University of KwaZulu-Natal by Chatterton [6]. The thesis proposed possible solutions to the problem but experienced high implementation costs and particular technical issues before widespread implementation could prove viable for the Distribution System. The average transformer failure rate for the Distribution Eastern Region for the twelve month period taken as a moving average was calculated to be 5.19 % per annum at the end of November 2005 and 3.84 % at the end of November 2006. (Eskom Eastern Region Plant report, November 2006). International norms seem to indicate that a transformer failure rate of between 0.5% and 1.0% per annum is acceptable, Chatterton [6]. The reason for the increased failure rates during 2005 was attributed to incorrect Ground Lead Disconnect (GLD) specifications by one of the major surge arrester manufacturers. The incorrect GLD specifications have resulted in premature and nuisance operations. These were triggered by low intensity lightning storms as a result of the lower threshold trigger values. These premature operations have left numerous transformers vulnerable for periods as long as six months and have resulted in the transformer failures increasing from 2.4% quoted by Chatterton [6] in 2002 to 5.19% in 2005 and a reduction to 3.84 % in November 2006 once the problem was identified and the GLDs corrected. See annexure A, Figure A1 of the Plant report for November 2006 for performance details. Hence, this manufacturing flaw and the GLD's sensitivity to specification necessitate further investigation into the spark gap as back-up protection. The spark gap therefore becomes more viable than line or double surge arresters due to its cost effectiveness and robustness. This thesis was based on an idea proposed by Eskom's (Industrial Association Resource Centre) IARC. The aim was to investigate the technical feasibility of using a spark gap to grade with a distribution class surge arrester whilst the surge arrester was operational. The purpose of the spark gap was to act as back-up protection when the arrester fails. Experimentation was undertaken via simulation using the FEMLAB software to model the most suitable gap and geometry for a given rod diameter. The breakdown characteristic of the rod was well understood and verified. Thus, the results obtained from the simulation were compared against the laboratory experiments for the same rod diameters and tip shapes used in the simulation. The results have been analyzed to determine whether the spark gap is a feasible solution for use with surge arresters to protect the transformer from induced strikes following arrester failure.A possible lower cost alternative to medium voltage line arresters and parallel-connecte

Estudio de la aparamenta, máquinas y demás equipos que componen una subestación eléctrica instalada para evacuar la energía generada en una central fotovoltaica = Study of the switchgear, machines and other equipment that make up an electrical substation installed in order to transfer power generated in a photovoltaic plant

[ES] El presente Trabajo de Fin de Grado consiste en un estudio de todos los sistemas que componen una subestación eléctrica destinada a la evacuación de energía fotovoltaica. Esto incluye el estudio de la aparamenta eléctrica de alta y media tensión y los sistemas de protección y control, así como el conjunto de servicios auxiliares y resto de equipos pertinentes. En primer lugar, se definen los conceptos más básicos acerca de las subestaciones para determinar los componentes con los que cuenta la instalación a estudiar, procediendo a realizar un análisis de cada uno de los elementos y equipos involucrados. Los equipos estudiados son clasificados según el sistema de la subestación en el que se encuentran. Existen, por lo tanto, sistema de 220 kV, transformador de potencia, sistema de 30 kV, sistema de protección y control y servicios auxiliares. Cada uno de los equipos es estudiado y analizado, explicando las funciones que cumple dentro de la subestación, los elementos que lo componen y las características técnicas con las que cuenta. A lo largo del trabajo se analizan productos de diferentes fabricantes, como son Arteche, ABB, Siemens, SEL, Ge Grid Solutions, A-EBERLE, Gedelsa, Genesal Energy o IMEFY. Finalmente, tras el estudio de todos los componentes que conforman el modelo de subestación, se realiza un ejemplo de configuración del conjunto de equipos estudiado, estableciendo así un modelo práctico de subestación. De esta manera, se pretende mostrar un ejemplo de aplicación de todos los equipos en conjunto, sirviendo dicho modelo como subestación tipo para la finalidad que posee, la de evacuar a red la energía procedente de parques fotovoltaicos