Electromagnetic Transient Modelling of Grounding Structures

Grounding is traditionally modelled as a pure resistance. This is a good approximation at low frequencies, but as the frequency gets higher, inductance starts to play an important role. To acquire accurate transient response of the system it is desirable to consider this fact. Special computer programs like CDEGS are required to analyze grounding structures, but this is not directly compatible with other programs for analysis of over-voltages and transients. The main objective of this project is to create a database containing frequency response for some common electrode types with different parameter combinations. This frequency response can be further used to create an equivalent time - domain grounding impedance that can be exported to EMTP programs.Three types of ground electrodes were analyzed in this project; earthing rod, counterpoise grounding with four radials, and horizontal ring electrode. A uniform soil model with variable values of resistivity and relative permittivity was used in all simulations. Geometrical dimensions of the electrodes were varied as well. All conductors were modelled as bare copper conductors. Parameters were determined based on the results of simulations in CDEGS and general recommendations for grounding of transmission towers given by Statnett.Unit current at different frequencies was injected into ground electrodes through a 0.1 meter long copper conductor. Ground potential rise of this conductor, which is equal to impedance to earth of the ground electrode, was extracted from HIFREQ in text format. Frequency resolution in the simulations is 10 points per decade between 0 and 0.1 MHz, 40 points between 0.1 and 1 MHz, and 80 points between 1 and 10 MHz. As a result of the project a database containing impedance and admittance as function of frequency for three types of electrodes has been created. Total number of responses stored in the database is 2268.Vector Fitting is used to convert frequency domain responses to time domain state - space models or RLC - networks. Vector fitting is a method to approximate measured or calculated frequency domain responses with a sum of rational functions. A Matlab routine interfit.m was developed to extract response of an electrode with given parameters. For parameters between the points in the database, linear interpolation is used. As a second step the function calls vector fitting that creates a time ? domain model from the frequency response of the defined ground electrode. Order of approximation in vector fitting should be adjusted for each case, starting with a low value and gradually increasing it till a sufficient approximation after passivity enforcement is achieved. Time ? domain simulations in CDEGS and ATPDraw gave similar results when order of approximation in vector fitting was chosen correctly. Negligible deviation was observed between the responses in time range between 0 and 5 µs in some cases. The results indicate that frequency - dependent models created by this method can be used in EMTP programs

Lightning Modeling and Its Effects on Electric Infrastructures

When it comes to dealing with high voltages or issues of high electric currents, infrastructure security and people’s safety are of paramount importance. These kinds of phenomena have dangerous consequences, therefore studies concerning the effects of lightning are crucial. The normal operation of transmission and distribution systems is greatly affected by lightning, which is one of the major causes of power interruptions: direct or nearby indirect strikes can cause flashovers in overhead transmission and distribution lines, resulting in over voltages on the line conductors. Contributions to this Special Issue have mainly focused on modelling lightning activity, investigating physical causes, and discussing and testing mathematical models for the electromagnetic fields associated with lighting phenomena. In this framework, two main topics have emerged: 1) the interaction between lightning phenomena and electrical infrastructures, such as wind turbines and overhead lines; and 2) the computation of lightning electromagnetic fields in the case of particular configuration, considering a negatively charged artificial thunderstorm or considering a complex terrain with arbitrary topograph

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

Characterisation of earthing systems and materials under DC, variable frequency and impulse conditions

This thesis is primarily concerned with experimental tests and computer simulations to evaluate the performance and behaviour of earth electrode systems subjected to DC, AC variable frequency and impulse currents. The performance of the earth electrode systems at the power frequency is now well understood. However, the response of the system under high frequency and transient conditions still need more clarification. Therefore, simulations and experimental investigations in both laboratory and full-scale field site have been performed and reported in this thesis. The results contribute to better understanding of complex earthing systems under high frequency and transient conditions. The response of the earthing system of different configurations (vertical and horizontal electrode) was conducted for soil resistivity ranged from 10Ωm to 10kΩm using numerical computational model. The effect of soil resistivity, permittivity, and the electrode length on the performance of the earthing system was investigated. Particular emphasis applied to study the effect of segmentation on the evaluation of earthing electrode response. The investigations result in some recommendations contribute to the better evaluation of the performance and the behaviour of simulated earth electrodes. New earthing system facilities were prepared. The first stage was soil resistivity survey, which resulted in 2D soil models construction showed both horizontal and vertical soil resistivity variation. In addition, step voltages and touch voltages were computed to ensure the safety of the workers. Then, high frequency and impulse characteristics of vertical test rod and horizontal electrode buried in non-uniform soil at Llanrumney were tested. DC, AC and impulse tests results show that the measured earth impedance is constant over a low-frequency range, while higher impedance values are observed in the high-frequency range due to the inductive effects. To validate the analytical approaches and computational models, a new earthing system facility was prepared at Dinorwig substation at North Wales, UK. High frequency and impulse characteristics of 5m × 5m earth grid electrodes immersed in fresh water (close to uniform medium) were tested. DC, AC and impulse test results show that the resistive behaviour dominates the performance of the earthing grid. In addition, the measured impulse resistance exhibits constant values with the increase of the injected currents. Experiments were carried out at new high voltage laboratory to investigate the frequency dependence of electrical soil parameters. The soil was prepared and mixed with a different percentage of water contents according to weight. The results showed that both the resistivity and the permittivity decreased with increasing water contents. In addition, the results compared with the developed models available in literature and exhibited close agreements with them. Moreover, experimental investigations carried out at the laboratory on high resistivity material (gravel and concrete) which are used to increase the contact resistance between the earth and workers. The resistance showed a decrease in its value with increasing the water contents

Estimation of the lightning performance of transmission lines with focus on mitigation of flashovers

The growth of transmission networks into remote areas due to renewable generation features new challenges with regard to the lightning protection of transmission systems. Up to now, standard transmission line designs kept outages resulting from lightning strokes to reasonable limits with minor impacts on the power grid stability. However, due to emerging problematic earthing conditions at towers, topographically exposed transmission towers and varying lightning activity, such as encountered at the 400 kV Beauly-Denny transmission line in Scotland, the assessment of the lightning performance of transmission lines in operation and in planning emerges as an important aspect in system planning and operations. Therefore, a fresh approach is taken to the assessment of the lightning performance of transmission lines in planning and construction, as well as possible lightning performance improvements in more detail, based on the current UK/Scottish and Southern Energy 400 kV tower design and overhead line arrangements. The approach employs electromagnetic transient simulations where a novel mathematical description for positive, negative and negative subsequent lightning strokes, which are all scalable with stroke current, is applied. Furtermore, a novel tower foot earthing system model which combines soil ionisation and soil frequency-dependent effect is used. Novel lightning stroke distribution data for Scotland as well as novel cap-and-pin insulators with arcing horn flashover data derived from laboratory experiments are applied. For overhead lines, transmission towers, and flashover mitigation methods describing their physical behaviour in lightning stroke conditions state-of-the-art models are utilised. The investigation features a variety of tower and overhead line arrangements, soil conditions and earthing designs, as well as the evaluation of various measures to improve the performance. Results show that the lightning performance of a transmission line is less dependent on the tower earthing conditions, but more dependent on the degree of lightning activity and stroke amplitude distribution. The assessment of flashover mitigation methods shows that cost-effective and maintenance free solutions, such as underbuilt wires can effectively replace a costly improvement of the tower earthing system. However, in locations where challenging earthing conditions prevail, tower line arresters or counterpoise are the only options to maintain an effective lightning protection

Recent Topics in Electromagnetic Compatibility

Recent Topics in Electromagnetic Compatability discusses several topics in electromagnetic compatibility (EMC) and electromagnetic interference (EMI), including measurements, shielding, emission, interference, biomedical devices, and numerical modeling. Over five sections, chapters address the electromagnetic spectrum of corona discharge, life cycle assessment of flexible electromagnetic shields, EMC requirements for implantable medical devices, analysis and design of absorbers for EMC applications, artificial surfaces, and media for EMC and EMI shielding, and much more

Outdoor Insulation and Gas Insulated Switchgears

This book focuses on theoretical and practical developments in the performance of high-voltage transmission line against atmospheric pollution and icing. Modifications using suitable fillers are also pinpointed to improve silicone rubber insulation materials. Very fast transient overvoltage (VFTO) mitigation techniques, along with some suggestions for reliable partial discharge measurements under DC voltage stresses inside gas-insulated switchgears, are addressed. The application of an inductor-based filter for the protective performance of surge arresters against indirect lightning strikes is also discussed

MARE-WINT: New Materials and Reliability in Offshore Wind Turbine Technology

renewable; green; energy; environment; law; polic