Peng Qian, Yao Xiao, Liu Ping, Liu Fan, Sichuan Electric Power Test & Research Institute, SiChuan, Chengdu, China, Su Jie, School of Electrical Engineering, Southwest Jiaotong University, SiChuan, Chengdu, China, "Analysis on Grounding Resistance affected by Heterogeneous Soil", Presented at the 2011 Third International Conference on Measuring Technology and Mechatronics Automation.
Abstract: In the most actual grounding project, we always come across a block or some blocks of soil whose resistivity is higher than that of soil surrounding them, that is heterogeneous soil. Effects on grounding resistance by heterogeneous soil under different conditions are different. On the basis of simulation by grounding analyzing engineering software CDEGS, this paper analyses effects on grounding resistance by heterogeneous soil under conditions of different surrounding soil resistivity, as well as different section area size, depth and thickness of heterogeneous soil, all of which provides evidence for building more accurate soil model in the grounding design under complex soil situation.
P.H. Pretorius,Trans-Africa Projects and K.R. Hubbard, Eskom Holdings Limited, "Assessment Of Electric Field Exposure In A 756 KV Open Air Substation - A Case Study", Presented at the Cigré 2009, 6th Southern Africa Regional Conference, Cape Town, South Africa.
Abstract: In view of Eskom’s current network expansion at 765 kV, it was necessary to address occupational exposure of substation workers to electric fields, particularly in 765 kV substations with busbar height of 12 m. This paper reports on the assessment of 50Hz electric field levels that substation workers may be exposed to in 765kV open air substation. It is shown that at 12 m busbar height, at 800 kV, the maximum calculated electric field, 21,9 kV/m, exceeds the ICNIRP Reference Level (20 kV/m) at 2 locations covering a small area (the larger about 11 m x 6 m) in the HV yard. Although the Reference Level is exceeded, it is shown that the ICNIRP Basic Restriction of 10 mA/m2 is met. This is important in view of possible future regulation of EMF exposure limits in South Africa. Electric field measurements close to primary equipment have been shown not to exceed the ICNIRP Reference Level. Protection against contact and discharge current is advisable.
P.H. Pretorius,A.A. Burger and C.Curtis, Trans-Africa Projects K.R. Hubbard, Eskom Holdings Limited, "On The Earthing Of Overhead Power Lines - A Case Study", Presented at the Cigré 2009, 6th Southern Africa Regional Conference, Cape Town, South Africa.
Abstract: Concern has been expressed about the overheating of current-carrying earth conductors, at two particular locations (Tower No 1 and Tower No 4) on a 400 kV overhead line. The overheating not only presents an associated fire and safety risk but can also lead to potential conductor damage. This paper covers the technical investigation into the case mentioned. The investigation included a site visit and steady state current measurements. In addition, a software model was developed to study current flow (under both steady state and fault conditions) in an attempt to confirm the cause of the problem and to make recommendations to correct the installation. The paper demonstrates the importance of a proper technical analysis in solving field problems and stresses the impact that a lack in technical skills may have on line construction and maintenance. In addition, the value of software modelling in studying various scenarios associated with the performance of large plant is highlighted.
P.H. Pretorius, D.Muftic, L. Peter and C. Van Der Merwe, Trans-Africa Projects, "On The Surge Impedance Of 756 KV Double Circuit Towers - Validation And Application", Presented at the Cigré 2009, 6th Southern Africa Regional Conference, Cape Town, South Africa.
Abstract: The surge impedance of a power line tower is an important design parameter employed in the lightning performance and insulation co-ordination of the line. Simplified numerical models are in many cases used to determine this parameter that is costly to determine by measurement. Where equations do not exist for specific towers, such as, cross rope suspension towers with guy wires, certain assumptions are made in determining the surge impedance for these towers. This paper addresses the application of an electromagnetic model to determine the surge impedance of new Eskom 765 kV double circuit towers presently under development. The tower top voltage and surge impedance obtained with the electromagnetic model are compared with the experimental findings from a Japanese UHV tower (Nishi –Gunma Line, Tower No 3) study. In addition, the model is applied to the new Eskom 765 kV double circuit self support and cross-rope towers presently being developed. Application of the model and the approach covered in this paper brings about a saving in cost (by excluding experimental work) and also supports improved design in using more advanced software models.
P.H. Pretorius, and A.A. Burger, Trans-Africa Projects, "Electromagnetic Coupling From Overhead Power Lines To Fences - Experimental Evaluation And Case Studies", Presented at the Cigré 2009, 6th Southern Africa Regional Conference, Cape Town, South Africa.
Abstract: Significant expansion of the electrical network in South Africa to meet the demand and growth in electricity usage includes the design and construction of new overhead transmission lines at voltages of 400kV and 765kV. The constraints introduced to the network expansion by availability of land present specific engineering challenges. In particular, the routing of power lines along and adjacent to the boundaries of farms, agricultural land and game reserves. These boundaries are in most cases delineated with a fence, be it a barbed wire fence, a game fence or an electrified fence. In such cases re-routing of the planned line is not always an option and co-existence of the line and fence has to be considered. In view of safety of humans (and animals), not only does electric and magnetic field coupling to the fence have to be considered but also transferred potentials under fault conditions. This paper highlights the parameters considered in the safety assessment in the context of power line coupling to fences. A specific experiment conducted to confirm the threat situation is covered. In addition, two case studies are covered, demonstrating the importance of assessment and means to ensure safety. The requirement of proper interfacing between landowner and the utility is also noted.
A A Burger, P H Pretorius , I Ferreira, N Mahatho, "On The Electric Field Performance Of An Overhead Conductor Real Time Monitoring System (RETMOS II)", Presented at the Proceedings of the 16th International Symposium on High Voltage Engineering, Cape Town, South Africa.
Abstract: A real time monitoring system (RETMOS) is currently being developed to monitor the operational parameters of high voltage overhead power line conductors. One particular parameter of interest is conductor sag based on certain load conditions. The monitoring system comprises a global positioning system (GPS) and radio transmitter to allow for data transfer to a central point. A radio receiver is then also installed on the tower closest to the location of installation of the monitoring system. During the development phase of the monitoring system, it was required to evaluate its performance in the high electric field environment presented by the high voltage conductor bundle. This paper covers the background and preliminary findings of the evaluation. Software modelling (COULOMB® and CDEGS®) was used in the assessment of the electric field performance of the system. Specific considerations from a field performance evaluation are presented. These will be incorporated in the final design.
P H Pretorius and C J Semmelink, "On The Tower Footing Resistance Of Micropile Anchors", Presented at the Proceedings of the 16th International Symposium on High Voltage Engineering, Cape Town, South Africa.
Abstract: The lightning performance of an overhead power line is one design aspect that needs to be addressed in the overall electrical reliability of the line. A family of new towers for high power transmission lines, constrained by servitude availability, is currently being developed in South Africa. High reliability requirements by the client demands specific attention and focus on lightning performance of the line. This paper addresses specific aspects considered in the application of new micropile technology applied as anchors for the towers. Although anchors demand mechanical considerations relating to the high voltage structure, its electrical characteristics and performance are also important design considerations in view of the lightning performance of the line. This paper addresses the electrical performance of the micropiles in various soil conditions by means of a software model and compared with measurements. Particular attention is given to the tower footing resistance presented by the micropiles considering the various soil conditions modeled.
Y. Ahmed, Graduate Student Member, IEEE, and S.M Rowland, Senior Member, IEEE, "Measurement and Prediction of Microshock Currents and Voltages in an HV Laboratory", Presented at the 8th International Power Engineering Conference – IPEC2007, 3-6 December 2007, Singapore, IEEE Catalogue Number: 07EX1686C, pp. 223-228.
Abstract: Microshocks are the low current, continuous discharges experienced by people capacitively coupled to high voltage equipment. The situations in which these discharges occur are complicated by the size and complexity of the high voltage equipment and the sensitivity of the person concerned. A simple model has been constructed in the commercial software package CDEGS. This has been used to model a geometrically simple object designed to represent a person adjacent to a high voltage tower. The predictions of the model are compared to experiments in a high voltage laboratory. The predictions are shown to be extremely accurate and suggest that CDEGS is capable of providing useful predictions in a more realistic scenario.
C. Charalambous, Member, IEEE, I. Cotton, Member, IEEE, P Aylott, "A simulation tool to predict the impact of soil topologies on coupling between a light rail system and buried third party infrastructure", Accepted to IEEE TRANSACTIONS ON VEHICULAR TECHNOLOGY.
Abstract: The production of stray currents by DC Light Rail Systems leads to the corrosion of the supporting and third party infrastructure in close proximity to the rail system. This work simulates two parallel tracks that are occupied by two trains; one on each track. This type of modeling constitutes a realistic case study that is utilized to investigate the effect of soil topologies on the corrosion performance of a floating DC Light Rail System focusing on the supporting and third party infrastructure. The modeling technique used involves the accurate computation of the shunt and series parameters for use in a resistive type model using a commercially available software package. The results demonstrate the importance that soil resistivity has on the corrosion risk to traction system and third party infrastructure. Such information could ultimately be used to vary the level of stray current protection across a light rail system to ensure an consistent lifetime across the whole system.
Konstantinos Kopsidas , Ian Cotton, Member IEEE, "Induced Voltages On Long Aerial And Buried Pipelines Due To Transmission Line Transients", Accepted to IEEE TRANSACTIONS ON POWER DELIVERY.
Abstract: In a previous paper, the voltage induced onto a 1km above ground pipeline by transmission line transients was shown to be significant in comparison to the induced voltage resulting from power system currents. This paper enhances the previous work in three distinct areas. Firstly, both aerial and buried pipelines are considered. Above ground pipelines are shown to be more at risk from transient induced voltages. Secondly, parallelisms of up to 10km are simulated. The results show that increasing parallelisms do not result in higher induced voltages once a critical distance has been reached. Thirdly, a backflashover from a tower in the vicinity to a pipeline is modeled. This allows conductive coupling to take place at the same time as inductive and capacitive coupling. Backflashovers are shown to be an important consideration in determining the maximum voltages observed on a nearby pipeline.
Simon M. Rowland , Member, IEEE, Konstantinos Kopsidas, and Ian Cotton , Member, IEEE, "Modeling of Currents on Long Span, Dielectric Cables on HV Overhead Lines", IEEE TRANSACTIONS ON POWER DELIVERY, VOL. 22, NO. 2, APRIL 2007.
Abstract: It is well established that all-dielectric self-supporting cables on high-voltage overhead power lines can suffer from damage through the mechanism of dry-band arcing. A number of heuristics have evolved over the past 20 years and these are used to determine whether such cables are capable of reliable performance. A key element to planning is modeling the installation conditions. In addition to the geometry of the high-voltage line, such a model needs to consider the climatic environment and potential pollutants on the cable. In this paper, a model is built based on the commercial software current distribution, electromagnetic fields, grounding and soil structure analysis which is widely used in the power industry. The model developed is shown to be consistent with a number of previously published models. It is demonstrated that the relative sags of all-dielectric self-supporting cable and conductors are key to the severity of the installed situation. It is also shown that the towers do not need to be modeled for the most severe cases of high pollution, but are required for accuracy in medium and low pollution cases.
Ian Cotton, Member, IEEE, Konstantinos Kopsidas and Yang Zhang, "Comparison Of Transient And Power Frequency Induced Voltages On A Pipeline Parallel To An Overhead Transmission Line", IEEE TRANSACTIONS ON POWER DELIVERY, VOL. 22, NO. 3, JULY 2007
Abstract: An analysis of the voltages induced on a 1km pipeline by a parallel overhead transmission line has been carried out when the transmission line is carrying power frequency (50Hz) current and when it is subject to the propagation of a lightning or switching transient. A frequency based circuit modeling technique coupled with forward and inverse Fourier transforms is used to carry out this analysis. The relative severity of the induced voltages from power frequency current or transient (lightning/switching) overvoltages is illustrated using the simulation results. The results demonstrate the high relative magnitude of induced pipeline voltages that result from the propagation of lightning transients down overhead lines. The need to model the full overhead line for such an analysis is investigated as is the variation of the level of transmission line / pipeline coupling as a function of the local soil resistivity. Analysis of the level of induced voltage as a function of length of parallelism is also carried out.
C. Charalambous and I. Cotton, "Influence of soil structures on corrosion performance of floating-DC transit systems", IET Electr. Power Appl., Vol. 1, No. 1, January 2007.
Abstract: The production of stray currents by DC-transit systems leads to the corrosion of nearby buried metallic structures, such as pipelines and cable sheaths. The paper details the corrosion performance of a DC transit system with a floating return rail, for a number of different soil resistivity structures: uniform, horizontal and vertical-layer models. This builds on previous work carried out in homogenous soils. It is shown that a variation in soil type along the route of a transit system can lead to high local leakage-current densities on buried metallic structures, increasing their vulnerability to corrosion damage.
Ian Cotton , Member, IEEE, Charalambos Charalambous, Pete Aylott, and Petra Ernst, "Stray Current Control in DC Mass Transit Systems", IEEE TRANSACTIONS ON VEHICULAR TECHNOLOGY, VOL. 54, NO. 2, MARCH 2005.
Abstract: Stray current control is essential in direct current (DC) mass transit systems where the rail insulation is not of sufficient quality to prevent a corrosion risk to the rails, supporting and third-party infrastructure. This paper details the principles behind the need for stray current control and examines the relationship between the stray current collection system design and its efficiency. The use of floating return rails is shown to provide a reduction in stray current level in comparison to a grounded system, significantly reducing the corrosion level of the traction system running rails. An increase in conductivity of the stray current collection system or a reduction in the soil resistivity surrounding the traction system is shown to decrease the corrosion risk to the supporting and third party infrastructure.