Abstractos de Articulos Publicados por SES (Año 2004)

1. Effects of Current Unbalance and Transmission Line Configuration on the Interference Levels Induced on Nearby Pipelines

2. Application of Electromagnetic Field Theory to Measure Correct Grounding System Impedance: A Parametric Analysis

3. Database and Rule Based Automated Grounding System Design

4. Analysis of A Steel Grounding System: A Practical Case Study

5. Comparison of Computational Methods for the Design and Analysis of Power System Grounding: Parametric Analysis

6. A Parametric Analysis of Fault Current Division between Overhead Wires and Substation Grounding Systems

7. Computation Stability of Grounding Systems in Soils Containing Heterogeneous Volumes

8. Detailed Parametric Analysis of Grounding System Performance in Two-Layer Soil Structures

9. Steel Casing Overheating Analysis of Operating Power Pipe-Type Cables
   
   Para una lista completa de las publicaciones de SES porfavor referirse a Publicaciones Técnicas.

Y. Li,and F. P. Dawalibi

Corrosion/2004 NACE International Conference, New Orleans, March 28 to April 1, 2004

Abstract:  AC interference from high voltage power lines can be hazardous for the public and personnel while touching or standing near a pipeline when the pipeline shares the same right-of-way corridor with electric transmission lines. Furthermore, integrity of the pipeline coating and corrosion mitigation effectiveness may be compromised if the levels of steady-state or fault interference are high. Recent research work on magnetic field induction from nearby high voltage power lines to adjacent pipelines has uncovered several interesting and intriguing results under unbalanced load (steady-state) conditions of a horizontal three-phase transmission line. First, a minimum interference level was achieved for a specific unbalance load condition on the phase closest to the pipeline. Second, the interference levels exhibited an almost complete insensitivity to the soil resistivity variations for certain unbalance load conditions on a phase conductor. This paper focuses on a detailed study aimed at examining the effects of current unbalance on the interference levels for different power line configurations. To carry out the study, two typical horizontal three-phase transmission line configurations are examined. Various unbalanced currents on a phase conductor are studied to reveal the minimum interference level that can be achieved for a given right-of-way network configuration. This cancellation effect is caused by a particular combination of the transmission line geometrical unbalance with respect to the pipelines and the current unbalance introduced by a phase conductor. The investigation also shows that an unbalanced current condition on a different phase conductor can provide quite different results. The effects of the soil resistivity on AC interference levels have also been studied under different unbalanced current conditions. It is found that the interference levels decrease with a decrease of the soil resistivity for most unbalanced current conditions. However, significant variations of soil resistivity can have practically no impact on the interference levels during certain unbalanced conditions. The results obtained in this paper can be used to develop designs to manage optimally the AC interference level and AC corrosion mitigation on nearby pipelines.

R. D. Southey, and W. Ruan

The 15th Conference on Electric Power Supply Industry (CEPSI) Shanghai, China, October 18-22, 2004.

Abstract: Measurement of the grounding system impedance of a substation or power plant is often required immediately after construction, in order to verify that the design calculations correctly predict the performance of the system. Years later, new measurements are sometimes required to check that the performance of the grounding system has not deteriorated. This type of measurement, however, which is typically carried out using the fall-of-potential method, is plagued by a number of potential problems: conductive coupling between the grid under test and the remote current return electrode, especially for soil structures with low resistivity over high; inductive coupling between current and voltage test leads; inductive coupling between test leads and grounding grid conductors; inductive coupling between test leads and power line static or neutral wires; additional grounding provided by power line static and neutral wires, which lowers the apparent impedance of the grounding grid. This paper presents a methodology for measuring ground impedances that minimizes the effects of inductive coupling, conductive coupling, and power line grounding. A parametric analysis is carried out to illustrate how measurement error changes as a function of grid dimensions, soil structure, test electrode locations, test lead separation distance, locations of test lead connections to the grounding grid, and test signal frequency used. It is found that accurate ground impedances can be obtained by interpreting the test data using electromagnetic field models that determine the expected error as a function of test signal frequency.

J. Liu, and F. P. Dawalibi

The 15th Conference on Electric Power Supply Industry (CEPSI) Shanghai, China, October 18-22, 2004.

Abstract: The design of grounding systems is often based on rough guidelines, derived from engineering experience. It is frequently a trial and error procedure and can be quite time consuming, since it is too difficult to account for the large number of variables (geometrical proportions of the grid, its depth, the nature of the soil and of the grid’s conductors, whether or not grounding rods are attached to the grid, etc…) that can affect the grid’s performance. This paper presents a database and rule based automated grounding system design method to meet design requirements (such as ground potential rise, touch voltage, step voltage, and ground resistance limits), given the soil structure, dimensions of the grid area, characteristics of conductors, configuration of the grid, and fault current discharged by the grid.

A three-step approach is used for the automated grounding system design. First, a grounding system which consists of a large number of horizontal conductors forming a very dense grid is modeled. It is almost equivalent to a buried metallic plate. This gives the minimum achievable ground impedance for a grid of the specified size, and verifies whether the desired ground impedance and safety limits can be achieved at all. Second, an appropriate preliminary grid design is retrieved from a database of predefined grids, based on the input data provided. Next, this initial design is refined recursively using rule-based techniques and algorithms to improve its performance and meet the safety constraints, while reducing the overall cost of the grid.

The grid database is, optionally, the starting point of any automated design and will cover most grids that are encountered in practice. Extensive collections of predefined grids have been analyzed, constructed and can be easily updated by the user. A strategy has been devised to quickly find an appropriate grid, while at the same time minimizing the size of the database.

The techniques presented in this paper can help electrical engineers design safe grounding installations quickly and efficiently. The time devoted to design a safe and cost-effective grounding grid is minimized by the use of the database and rule based automated grounding system design method and technology.

Y. Li, F. P. Dawalibi, J. Ma, and Y. Yang

The 15th Conference on Electric Power Supply Industry (CEPSI) Shanghai, China, October 18-22, 2004.

Abstract: This paper presents a thorough analysis of the performance of a large grounding system made of steel instead of copper conductors. The grounding system is located in a relatively low resistivity soil and is interconnected to an extensive network of overhead transmission lines, in low soil resistivity. The extent of the grounding combined with its steel conductors and the low resistivity soil invalidates the equipotential assumption that is usually made when analyzing grounding systems. The presence of a large circulating fault current in the grounding system aggravates this problem further. Obviously, classical grounding analysis methods are no longer applicable and more advanced techniques must be used. This paper presents a detailed study of such problems. The measured soil resistivities and the grounding system impedance are compared to the computed values. Fault current distribution between the grounding system and the other metallic paths are computed to determine the portion of fault current discharged in the grounding system. The performance of the grounding system, including its GPR (ground potential rise), GPDs (grounding potential differences) between the ground conductors and the touch and step voltages have been evaluated accurately, taking into account the impedance of the steel ground conductors and their mutual inductive components. Numerical results are presented and compared to those obtained based on a conventional approach. The paper also examines briefly the electromagnetic coupling between the control cables and the ground conductors to illustrate a typical analysis of the integrity of the electronic equipment connected to the control cables.

S. Fortin, W. Ruan, and F. P. Dawalibi

Proceedings of the Seventh IASTED International Conference on Power and Energy Systems, Clearwater Beach, FL, USA, November 28 - December 1, 2004.

Abstract:  This paper examines three approaches used in grounding analysis and illustrates the advantages, limitations, and the applicability of each approach. The comparisons are carried out using grounding grids of sizes varying from 50 m to 500 m, in uniform and two-layer horizontally layered soil structures. Soil resistivities vary from 1 Ohm-m to 10,000 Ohm-m. The errors in GPR (Ground Potential Rise) and touch voltages, as well as computation time, are compared between the three approaches. The discussions and conclusions given in this paper can be used as a reference when deciding which approach should be used to carry out an accurate and efficient grounding analysis. >

C. Li, X. Wei, Y. Li, and F. P. Dawalibi

Proceedings of the Seventh IASTED International Conference on Power and Energy Systems, Clearwater Beach, FL, USA, November 28 - December 1, 2004.

Abstract: This paper presents a parametric analysis of the fault current distribution between a substation grounding system and its overhead ground wires and their effects on the grounding systems performance. The influence of the following variables are studied: the resistance of the substation grounding system, the characteristics of the shield wires, the number and the length of the transmission lines connected to the substation, the terminal types (i.e., power source and non-power source terminals), soil resistivity, and power line configurations. It is concluded that the fault current division factor is dramatically affected by the substation grounding resistance, the shield wires conductor characteristics, and the number of transmission lines while it is less influenced by the soil resistivity along the transmission lines and tower resistances. It is difficult to estimate the current division factor for a practical case. The only way to compute accurately the current division factor is to analyze individual cases based on the existing conditions with proper software tools.

F. P. Dawalibi, N. Mitskevitch, and S. Fortin

Proceedings of the Seventh IASTED International Conference on Power and Energy Systems, Clearwater Beach, FL, USA, November 28 - December 1, 2004.

Abstract: This paper studies the performance of grounding systems in soil structures containing heterogeneous soil volumes. This type of soil is crucial for the investigation of a range of practical problems that cannot be approximated by a layered soil structure. This type of problems involves grounding systems that are either close to, partially or totally immersed in one or several finite volumes of soil materials that have resistivity values quite different from that of the bulk volume of surrounding soil (native soil). This paper focuses on the stability of the algorithm used to compute the response of grounding grids for different scenarios. It also describes and discusses the computed results that pertain to a number of typical grounding scenarios, comparing them to some known limiting case solutions.

J. Liu and F. P. Dawalibi

Proceedings of the Seventh IASTED International Conference on Power and Energy Systems, Clearwater Beach, FL, USA, November 28 - December 1, 2004.

Abstract: An extensive parametric analysis of rectangular grounding grids in two-layer soils has been carried out to determine their overall performance. A large number of variables that can affect the grid’s performance (such as the geometrical proportions of the grid, the characteristics of the soil including the reflection coefficient and top layer thickness, and the density of conductors) have been analyzed in details. Ground resistances, touch voltages, and step voltages of grounding systems have been computed and compared for various scenarios. The ultimate objective of this parametric study is to provide detailed evaluations of the grounding system performance. The computed results are summarized in charts; these results will be useful for quick estimates of the expected performance of practical grounding designs.

F. P. Dawalibi, J. Liu, S. Fortin, S. Tee, and Y. Yang

Proceedings of the Seventh IASTED International Conference on Power and Energy Systems, Clearwater Beach, FL, USA, November 28 - December 1, 2004.

Abstract: This paper discusses the analysis of an overheating problem which has been observed within a 140’ (43 m) long steel pipe casing containing 115 kV three-phase electric power cables. A steel casing electromagnetic field model has been built to determine the induced current (eddy currents) distribution along the radial, transverse, and longitudinal directions of the casing caused by the energized cables under different operating conditions. This model takes the combined effects of the inductive, conductive, and capacitive interference into account. This study involved a circuit model to determine the voltage and current distributions in the conductors of the buried power cables. Furthermore, a detailed analytical model of the cylindrical steel casing (assuming an infinitely long casing) was conducted to determine the actual paths of eddy current flow and their density throughout the cross section from the inner surface to the outer surface of the steel casing. The computation results show that induced currents in the steel casing can cause significant heat losses and that the exact distribution of the induced current density within the steel casing plays a crucial role in the heat losses generated by such currents.