Salah Belkhir, Moulai Hocine, Soukeur Fathallah, and Mohand Ouhrouche
[1] A. Domijan, Jr., R.K. Matavalam, A. Montenegro, W.S. Wilcox, Y.S. Joo, L. Delforn, J.R. Diaz, L. Davis, & J. D’Agostini, Effects of normal weather conditions on interruptions in distribution systems, International Journal of Power and Energy Systems, 25(1), 2005, 54–62. [2] M. Wu, S.S.P. Shen, & D.O. Koval, Modeling lightning caused transmission line outages in Alberta, Proceedings of the Fifth IASTED International Conference on Power and Energy Systems, Benalmadena, Spain, June 15–17, 2005, paper No. 468129, 106–111. [3] N. Baljepali, S.S. Venkata, C.W. Richter, Jr., R.D. Christie, & V.J. Longo, Distribution system reliability assessment due to lightning storms, IEEE Transactions on Power Delivery, 20(3), 2005, 2153–2159. [4] L. Thione, An overview of live line diagnostic techniques, CIGRE 2000, P1-02. [5] Guide for maintenance methods on energized power lines, IEEE Std 516, 2003. [6] L. Thione, An overview of live working and maintenance techniques, CIGRE 2000, P1-01. [7] Standard Techniques for High Voltage Testing, IEEE Std 4-1995. [8] Live Working – Minimum Approach Distances – Method of Calculation, IEC 61-472, 1998, 10–27. e [9] C. Atlani, Travaux sous tension,Techniques de l’Ing´nieur, D4 140, 1–9. [10] G. Gela, Live working and maintenance techniques, CIGRE 2000, P1-03. [11] P.L. Levin, A.J. Hansen, D. Beatovic, H. Gan, & J.H. Petrangelo, A unified boundary-element finite element package, IEEE Transactions on Electrical Insulation, 28(2), 1993, 161. [12] N.H. Malik, A review of the charge simulation method and its applications, IEEE Transactions on Electrical Insulations, 24(1), 1989, 3–20. [13] P. Sibillot & R. Coelho, Journal of Physics, 35, 1974, 141–148. [14] M. Aguet & M. Ianoz, Trait´ d’´lectricit´ – Haute tension, e e e Vol XXII (Lausanne, Switzerland: Publication des presses polytechniques et universitaires romandes, 2001) 391–392.Figure 9. MAD D versus curvature radius rp of the point, in rod–plane electrode system.4.2 Influence of the Radius of Curvature on the Minimum Approach Distance The strengthening of the electric field reigning around the edged tips submitted to high voltage stresses is a precursor element to the occurrence of arc discharges. Consequently, the radius of curvature of these edged parts plays a significant role in the dimensioning of the MAD. The methods of determination of the MAD commonly used consider tools or bodies of rounded shape of 12.5 mm diameter [7]. Since the electric field is dependent on the curvature radius of the used tools, we determine for each voltage level, a relationship between the MAD and the radius of curvature (Fig. 9). The obtained results show that the MAD must be accordingly more important than the radius of the tools is small. However, this importance becomes insignificant for radii greater than 20 mm. In the same figure are also reported the values of MAD corresponding to the considered voltages, obtained by interpolations in (17). A good agreement is found between these values, for the above described conditions, and the ones obtained accordingly to IEC 61-472 for an altitude of 200 m and a transient overvoltage factor T = 2.2. The more important deviation is 1.32% (corresponding to 3.1 cm) which is less than the difference between the generally considered values of the ergonomic distance for inadvertent movements (30 cm for IEEE-Std 516 and 50 cm for IEC 61-472). 5. Conclusion We have conducted a survey on electric field distribution in electrode arrangements commonly met while executing a live working on overhead lines using a simple software package based on charge simulating method. A close correlation between the influence of the curvature radius of the edged tools where high electric field intensities are concentrated, the electrode gap and the applied voltage is found. A method that consists in use of the numerical techniques is then developed to adapt the empirical methods 197
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