Effect of water on electrical properties of Refined, Bleached, and Deodorized Palm Oil (RBDPO) as electrical insulating material

This paper describes the properties of refined, bleached, deodorized palm oil (RBDPO) as having the potential to be used as insulating liquid. There are several important properties such as electrical breakdown, dielectric dissipation factor, specific gravity, flash point, viscosity and pour point of RBDPO that was measured and compared to commercial mineral oil which is largely in current use as insulating liquid in power transformers. Experimental results of the electrical properties revealed that the average breakdown voltage of the RBDPO sample, without the addition of water at room temperature, is 13.368 kV. The result also revealed that due to effect of water, the breakdown voltage is lower than that of commercial mineral oil (Hyrax). However, the flash point and the pour point of RBDPO is very high compared to mineral oil thus giving it advantageous possibility to be used safely as insulating liquid. The results showed that RBDPO is greatly influenced by water, causing the breakdown voltage to decrease and the dissipation factor to increase; this is attributable to the high amounts of dissolved water

How to protect a wind turbine from lightning

Techniques for reducing the chances of lightning damage to wind turbines are discussed. The methods of providing a ground for a lightning strike are discussed. Then details are given on ways to protect electronic systems, generating and power equipment, blades, and mechanical components from direct and nearby lightning strikes

Simulation and Analysis of High Voltage Engineering in Power Systems

This book address important issues regarding the modelling and simulation tools and techniques that are applied in high-voltage engineering in modern power systems. The presented conceptual, constructive, empirical, experimental, and theoretical results are obtained in the area of high-voltage engineering. Special attention is given to protection methods against direct lightning strikes, partial discharge tests, discharges’ influence on different structures, cable screening, and induced voltages, among others

Experimental Investigations of the Multiple Impulse Energy Handling Capability of Metal-Oxide Varistors for Applications in Electrical Power Engineering Translation of: Experimentelle Untersuchungen zur Mehrfachimpulsbelastbarkeit von Metalloxidvaristoren für Anwendungen in der elektrischen Energietechnik

In this thesis, the results of the research on multiple impulse energy handling capability of metal-oxide varistors (MOVs) are described. The focus here is on repetitive impulse stresses with a high energy density where the specimens cool down to ambient temperature after each energy injection. The repetitive energy injection handling capability of MOVs is compared to their single impulse energy handling capability. It is widely known that the single impulse energy handling capability of MOVs increases with the current density of the impulse stress. This is due to the homogeneous current distribution within MOVs when applying higher current densities. The findings described in this thesis suggest that the temperature dependence of electrical resistance causes a further homogenization of the current distribution within the material of the MOVs at higher current densities. However, the impact of this seems to be small as its influence on the single impulse energy handling capability of the MOVs is not measurable. Furthermore, the results of experiments conducted for this thesis show that short interruptions of longduration current impulse stresses up to the range of seconds do not increase the impulse energy handling capability of MOVs. Additionally, the research results illustrate that the repetitive impulse energy handling capability of MOVs does not correlate with their single impulse energy handling capability. Concerning repetitive energy injections at lower current densities, the stress handling capability is very close to the single impulse energy handling capability. However, repetitive impulse stresses with higher current densities cause a reduced stress handling capability compared to the single impulse energy handling capability. Nonetheless, the energy handling capability when applying repetitive energy injections does not drop below the characteristic volume-related nominal energy handling capability of standard surge arresters. With regard to these findings, it is also shown that a change in reference voltage due to prior repetitive stressing of the MOV is not a sure sign for a pre-damage that leads to a decrease in single impulse energy handling capability. The results gained from this research are discussed with regard to routine tests of MOVs, the usage of surge arresters within electric power systems and the international standardization of surge arresters

Effect of compaction parameters and sintering configurations on the performance of ZnO varistor

Zinc oxide varistors are electronic ceramic devices processed through conventional ceramic technique. Its primary function is to protect an electrical circuit by limiting transient surges repeatedly without failing thereby enhancing the system reliability. There are various critical parameters of varistors, defined to evaluate the performance characteristics. Investigating the influence o f the compaction and other processing variables and their optimization in terms of the performance characteristics were the primary objectives of this project. Enhanced energy absorption capability of the varistor is highly beneficial either in increasing the reliability of the device and of the system or in reducing its volume providing the same level of protection. Varistor discs capable of absorbing more energy will aid in reducing the cost or be suitable for more demanding applications. Evaluation of the effect of compaction parameters was carried out by varying the pressing load and speed. The influence of holding times in pressing cycle was also studied. In addition to the energy absorption capability, some other important properties of the varistor were also investigated. Statistical approaches such as the response surface methodology and factorial design of experiments were adopted to develop necessary mathematical models on the basis of the experimental data. The reliability of the models were also verified. A correlation of the physical property and the electrical performance of the ZnO varistor with the sintering orientation was established. The analysis by extensive measurement of the microhardness revealed a relationship between the hardness and grindability of varistor. The tensile strength measured on the disc shaped sections of the arrester block was also found to differ significantly. The density gradient of the sintered disc shows a remarkable influence of the sintering orientation of the disc. By microstructural analysis the observed difference was confirmed. A few alternative methods have been suggested to overcome the adverse effects arising from the sintering orientation. In this regard horizontal sintering on Veegroove support was found to be advantageous. Influence of the surface to volume ratio was evaluated by converting the cylindrical discs into hexagonal shape by grinding. A new design with a hexagonal shape has been proposed. The fracture mechanism of the varistor in a high amplitude short duration (HASD) test was studied and a significant role of the stress wave was observed. The celerity measured by a laser beam based technique through the varistor material was found to be in good agreement with the theoretical prediction. An experimental study also revealed the effect of the stress wave. This understanding will lead to a new approach in combating the fracture from the high current pulse

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

Relationship between lighting impulse current injection and the degree of electrical degradation of the MOV

A dissertation submitted to the Faculty of Engineering and the Built Environment, University of the Witwatersrand, Johannesburg, in fulfilment of the requirements for the degree of Master of Science in Engineering, 2017Surge Protective Devices (SPDs) are used to protect electrical and electronic equipment against damages and operational malfunctions caused by surges. The commonly employed SPDs are composed of Metal Oxide Varistors (MOVs). MOVs are typically known for being inexpensive and for withstanding reasonable high values of current transients; they degrade over time depending on the severity and frequency of the surges they are subjected to. When MOVs are not properly monitored, the equipment they are meant to protect may remain unprotected and susceptible to surges. Reference voltage and leakage current of the MOV are commonly measured to deduce the operational status of the MOV. However, measuring the reference voltage only provides a pass or fail status of the MOV and not the degree of degradation, and measuring the leakage current and other dielectric parameters of the MOV (such as return voltage, decay voltage, etc.) is not always practical depending on the manner in which the MOVs are connected, especially the low voltage MOVs. This results in limited preventative maintenance techniques since the degree of degradation of the MOV is not known and other parameters of the MOV cannot always be measured. Therefore, the preventative maintenance mechanisms are sought. Extensive studies have been done to investigate the electrical and microstructural degradation of MOVs. However, the relationship between the current impulse injected and the degree of electrical degradation of the MOV have not been clearly defined. Therefore, defining this relationship can help to achieve preventative maintenance on lightning protection composed of MOVs by characterising and quantifying the degree of degradation of the MOV caused by a lightning impulse current without physically measuring dielectric parameters of the MOV. Thus, the study done in this dissertation answers the research question entitled: What is the relationship between an 8/20 µs lightning impulse current applied and the degree of degradation of the MOV? This question is answered through proposing a mathematical model that characterises the percentage of degradation of the MOV caused by a lightning impulse current. The mathematical model is specifically for MOVs with sizes ranging from 5 mm to 40 mm. The proposed model is tested against experimental test results and is found to match them by at least 75%. The discrepancy in matching is due to the assumption used in the matching process that all the MOVs exhibit the same response when subjected to the same impulse current. Nonetheless, the proposed model provides a minimum possible degradation level caused by a particular impulse current. The proposed model is thus deemed suitable to describe the relationship between the lightning impulse current injected and the degradation of the MOV. This dissertation is dedicated to Hlengiwe Mnisi Thank you for your love, support and encouragement. Most of it all, thank you for believing in meXL201

Grounding Performance under Lightning Surges in High Voltage Substations

Postponed access: the file will be accessible after 2019-05-31To achieve electromagnetic compatibility (EMC) and sufficient protection against lighting transients in the power transmission system, understanding of the grounding system transient behavior becomes crucial when deviating from international design standards and recommendations. To consider design deviations the present work is focused towards developing a method of integrating simplified grounding system models in transmission systems and perform lightning transient analysis on both parts to evaluate a particular design case. Firstly, the grounding system models for substation grounding grids, with a variety of configurations and sizes, is implemented. The characteristic transient response of the grounding system is visualized through simulations to study the sensitivity of configurations and modified soil parameters during current injections. The method of implementation allows for a detailed view and pre-processing of large data-sets from simulations. The advantages of this method is used to extract overall measured values to create a tool for EMC analysis and in addition processing different parameters and functions of the grounding system. Secondly, the grounding system model is integrated into transmission systems using a newly released interfacing application. The application allows for co-simulation between the development software of the grounding system and a specialized tool for the transmission system. The innovation of this modeling approach is given as a contribution to an international conference by submitting a paper. Finally, the integrated grounding models and transmission system are studied with two substation design cases; a short and long cable between surge arrester and transformer. The short cable case follows well-known design standards where the long cable case is a design deviation which is common in larger domestic hydropower plants. Even though the long cable case is deviating from design recommendations, the results show a less negative impact on the grounding system compared to the short cable case.Masteroppgave i energiMAMN-ENERGENERGI39

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