Abstractos de Artículos Publicados por SES (Año 2007)
Recent Advances in the Modeling and Mitigation of AC Interference in Pipelines |
W. Ruan, R. Southey, S. Tee, and F. P. Dawalibi
Corrosion/2007 NACE International Conference & Expo, Nashville, Tennessee, March 11 -15, 2007.
Abstract: The design of mitigation to reduce AC interference levels in a pipeline is a relatively straightforward matter when the mitigation can be installed with the pipeline, at the bottom of the trench. On the other hand, retrofitting introduces design challenges, which are discussed in this paper. For one thing, the depth of burial of gradient control wires running parallel to the pipeline is often limited by practical considerations: as a result, the effectiveness of these wires is reduced by soil freezing in northern climes. A second problem is the frequent need to interrupt the gradient control wires at road crossings, water bodies, wetlands, and other such obstacles. The level of protection is obviously compromised to some degree at such locations. It is found that consideration of the exponentially decreasing nature of soil resistivity with depth, during frozen conditions, can result in a dramatically improved assessment of mitigation performance. It is also found that, depending upon the soil structure, gaps of tens of meters in otherwise continuous gradient control wires may yield acceptable performance.
| Effects of Distribution System and Metallic Infrastructure on the Electromagnetic Field Level Surrounding Power Lines |
Y. Li and F. P. Dawalibi
The International Conference on Electrical Engineering 2007 (ICEE), Hong Kong, July 8 - 12, 2007.
Abstract: High voltage AC transmission lines produce magnetic and electric fields in the surrounding air and soil. Neighboring metallic utilities such as gas and oil pipelines, railways and communication lines are therefore subjected to electromagnetic interference, and the interference level can be high enough to damage the system integrity as well as to raise safety concerns. The calculation of voltages induced in the utilities following power line corridors is a complicated procedure. Until recently, some tools that were used to predict interference levels were typically based on simplified methods that are based on simple topologies and assumptions that often looked reasonable accuracy. This situation was responsible for costly overdesign or harmful underdesign, in particular when the right-of-way included buried infrastructure components that exhibit significant inductive and conductive coupling. This paper illustrates this point based on a parametric analysis and practical case studies that show how a complete model, including all major infrastructures and distribution systems, can result in a more accurate assessment of interference levels and therefore more suitable mitigation.
| Electromagnetic Environmental Evaluation of HVDC Transmission Lines |
H. Zhao, S. Fortin, J. Ma and F. P. Dawalibi
The International Conference on Electrical Engineering 2007 (ICEE), Hong Kong, July 8 - 12, 2007.
Abstract : This paper presents an analysis of the corona electric field strength around HVDC transmission lines for typical line configurations. A new iterative method is introduced to solve Poisson’s equation for HVDC transmission line systems, accounting for the presence of space charge. With this method, the electric field strength can be calculated in the space around the HVDC transmission lines or on the ground. The system can be in homopolar mode, bipolar mode or hybrid mode, and include sky wires or non-corona
conductors. The conductors in the bundles are treated individually. The method accounts for the different
corona onset gradient of positive and negative energized conductors and for ion recombination in bipolar zones. Also, the positive and negative ions can possess different mobilities.
| Equipment Protection Against Ground Potential Rise Due to Faults At Substations: A Case Study |
W. Ruan, S. Tee and F.P. Dawalibi
The International Conference on Electrical Engineering 2007 (ICEE), Hong Kong, July 8 - 12, 2007.
Abstract: This paper describes an incident where a fault on a 110 kV system at a substation of a power company resulted in significant damages to its communications equipment about 3.5 km away. Computer simulations have been carried out to investigate the cause of the damage, and to provide possible mitigation measures. The study shows that the currents flowing in the cable sheath reach about 1600 A during the fault. These currents are primarily caused by the magnetic induction due to its parallelism with the transmission line. Various mitigation measures, which include opening the cable messenger wire at both ends, installing a shield wire, installing a neutral wire on the underbuild distribution circuit, improving transmission line pole groundings and isolating the cable from the substation, have been used to reduce the stress voltage between the signal wire and sheath. None of them was found to be very effective. It is found that the most effective way to mitigate the stress voltages is to install adequate surge arresters at both ends of the 5.3 km cable and one or two arresters near the middle of the cable. The study shows that the surge arresters in this case should be rated for a minimum fault discharge current of 2500 A.
| Frequency Behavior of Impedance of Large Grounding Systems in Horizontal Multilayer Soils |
S. Fortin, Y. Yang and F. P. Dawalibi
The International Conference on Electrical Engineering 2007 (ICEE), Hong Kong, July 8 - 12, 2007.
Abstract: This paper studies the frequency behaviors of large grounding systems of energized conductors in horizontal multilayer soils. The method of full-wave solution of Maxwell’s equation is used in the study. The results show that the nature of the soil can affect the frequency response of the ground impedance; In particular, the impedance can decrease in some cases as the frequency increases. Generally speaking, the phenomenon of impedance decrease can happen whenever the resistivity of any soil layer deeper than the layer containing the conductor is higher than the soil resistivity where the conductor is located. Analytical calculations are provided to illustrate the mechanism behind this behavior. It is shown to be consistent with the analytical explanations.
| Effects of Ground Plates Used in Power System Grounding |
J. Ma and F. P. Dawalibi
The International Conference on Electrical Engineering 2007 (ICEE), Hong Kong, July 8 - 12, 2007.
Abstract: This paper examines the performance of the grounding plates used in power system grounding. The analysis is based on the theory of grounding grids in multilayer soils using the method of images published previously by the authors. Numerical results are presented for grounding plates in various soil models and are compared with those for grounding grids. The solution for a grounding plate is valuable because a plate represents the limiting case of an extremely dense grounding grid which cannot be accurately modeled. At the design stage, the plate model provides the best ground resistance and touch voltages that can be achieved by a grid in a given soil. The plate model can also be used to represent steel rebars in concrete which cannot be accurately modeled due to their great density.
| Equivalent Inductive and Conductive Models of Rail Ballast Resistance in Electromagnetic Interference Studies |
F. P. Dawalibi, J. Ma and J. Liu
The International Conference on Electrical Engineering 2007 (ICEE), Hong Kong, July 8 - 12, 2007.
Abstract: Electromagnetic interference caused by electric power lines sharing a common corridor with railways can compromise the safe operation of the signal and protection systems of the railways under both load and fault conditions. Excessive induced voltages along rails can result in electrical shock hazards for people touching or standing nearby the rail track. This paper is specifically concerned with the accurate modeling of the rail ballast leakage resistance. A computerized analysis has been conducted for a typical example, examining the effects of rail ballast resistance on electromagnetic interference in circuit and electromagnetic field models. Several typical scenarios have been studied to illustrate the overall results and effects of various soil structures, some of which were unexpected.
Electromagnetic Interference of Transmission Lines on Nearby Railways Accounting for the Rail Track Arresters |
J. Liu, F. P. Dawalibi and J. Ma
The International Conference on Electrical Engineering 2007 (ICEE), Hong Kong, July 8 - 12, 2007.
Abstract: A typical study of electromagnetic interference on railways caused by electrical transmission lines under steady state and fault conditions with a particular emphasis on the modeling of rail track arresters is presented. In this paper, the firing of the track arresters in a cascade throughout the common corridor during a single phase-to-ground fault on the transmission line near the railways has been carried out in detail. This study involves an electromagnetic interference analysis that accounts simultaneously for the transmission lines, railroad tracks, track arresters, equivalent signaling circuits along the railways, railroad equipment houses and their grounds, system energizations, rail ballast resistances, and soil structures along the railways. The values of the rail-to-remote soil potentials and the rail touch voltages are computed and examined. Furthermore, mitigative measures have been designed to effectively reduce electromagnetic interference to acceptable levels.
| A New Efficient Measurement Technique Based on the Wenner Four Electrode Method |
R. Southey, S. Tee, W. Ruan and F. P. Dawalibi
The International Conference on Electrical Engineering 2007 (ICEE), Hong Kong, July 8 - 12, 2007.
Abstract: Soil resistivity measurements are of fundamental importance in performing accurate grounding analyses. This paper presents the soil resistivity measurements carried out based on a modified standard Wenner 4-pin method, which the authors have named “the Unipolar Wenner” method and compares its
performance with the standard Wenner method. The Unipolar method has a logistical advantage, since it requires the displacement of only one electrode. Based on computer simulations of soil resistivity measurements, it is shown that the Unipolar Wenner method appears to be less susceptible to error arising from lateral variations in surficial soil resistivities. On the other hand, the Unipolar Wenner method appears to be less sensitive than the standard Wenner method to local variations in soil resistivity as a function of depth. For the design of power system grounds or large electrodes or for a general characterization of an area, the Unipolar Wenner method would appear to be the preferred test method.
| Zone of Influence around Electrical Installations Subjected to Ground Faults |
J. Liu and F. P. Dawalibi
The International Conference on Electrical Engineering 2007 (ICEE), Hong Kong, July 8 - 12, 2007.
Abstract: The zone of influence (ZOI), resulting from the ground potential rise (GPR) in the event of phase-to-ground faults in power substations is difficult to determine accurately since it is not easy to account for the large number of variables such as complex soil structures and grounding systems. The shape of equipotential lines is also determined by a number of factors such as variations in soil resistivity, proximity effects of buried metallic structures, etc. Simple formulas have been recommended by IEEE STD 367-1996 and are used in the determination of the ZOI. However, by ignoring some variables, it may lead to inaccurate grounding system designs. The objective of this paper is to demonstrate how to avoid inaccurate determination of the ZOI. Many computer simulations have been carried out using powerful and accurate computerized techniques in order to produce complete and accurate results.
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