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## Lightning interaction with medium-voltage overhead power distribution systems

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Lightning Interaction with Power Systems - Volume 2: Applications — Recommend this title to your library

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Distribution lines located in areas with high ground flash densities are prone to lightning-caused power interruptions. Lightning overvoltages can be produced on medium-voltage (MV) systems when lightning hits either the line conductors (direct strokes) or a point in the vicinity of the distribution network (indirect strokes). The evaluation of the lightning electromagnetic environment is essential to mitigate its effects and improve the power system quality. This chapter presents initially, using the concepts given in Chapter 5 of Volume 1, a procedure for the estimation of the mean annual number of direct lightning strikes to a given overhead distribution line. Then, the basic features of the lightning overvoltages are discussed. Although some typical characteristics can be identified, the analysis of the overvoltages depends on various parameters relevant to the adopted model of the lightning return stroke, soil and power network. The influences of the most important ones are discussed in this chapter, with examples of measured and calculated voltage waveshapes. Then, the main protective measures that can be applied to improve the lightning performance of MV distribution lines, namely the increase of the line insulation withstand capability, the use of periodically grounded shield wires and the installation of surge arresters along the line, are addressed. The analysis of the effectiveness of each measure as a function of the type of phenomenon (direct or indirect strikes) and of various parameters, such as the soil resistivity, ground resistance and grounding spacing, is performed. After that, the procedure presented in Chapter 1 of this volume for estimating the mean annual number of line flashovers that an overhead MV line can experience, is applied to the case of lines with different protective measures and the relevant performances are compared. The case of urban lines, whose performance is affected by the presence of buildings in their vicinity, is also dealt with, as well as the case of hybrid configurations, in which MV and high voltage (HV) lines share the same structures.

Chapter Contents:

• 4.1 Flash collection rate
• 4.2 Effects of various parameters on lightning overvoltages
• 4.2.1 Direct strokes
• 4.2.2 Indirect strokes
• 4.2.2.1 Lightning channel
• 4.2.2.2 Stroke current magnitude and waveform
• 4.2.2.3 Stroke current propagation velocity
• 4.2.2.4 Conductor height
• 4.2.2.5 Distance between the line and the stroke location and position of the observation point
• 4.2.2.6 Soil resistivity
• 4.2.2.7 Soil permittivity
• 4.2.2.8 Occurrence of an upward leader
• 4.2.2.9 Presence of nearby buildings
• 4.3 Lightning protection of MV systems
• 4.3.1 Increase of the line withstand capability
• 4.3.2 Use of shield wires
• 4.3.2.1 Ground resistance and soil resistivity
• 4.3.2.2 Distance between the line and the lightning strike point
• 4.3.2.3 Shield wire height
• 4.3.2.4 Grounding spacing
• 4.3.2.5 Relative position of the lightning channel and grounding points
• 4.3.2.6 Lightning current parameters
• 4.3.3 Application of surge arresters
• 4.3.3.1 Stroke current magnitude and waveshape
• 4.3.3.2 Ground resistance
• 4.3.3.3 Surge arrester spacing and relative position of the lightning strike point and arresters
• 4.4 Lightning performance of overhead distribution lines
• 4.4.1 Influence of the environment around the line
• 4.4.2 Lines located above open ground
• 4.4.2.1 Unprotected lines
• 4.4.2.2 Lines with a shield wire or neutral conductor
• 4.4.2.3 Lines with surge arresters
• 4.4.3 Lines surrounded by buildings
• 4.4.4 Hybrid configuration (MV and HV lines mounted on the same poles)
• 4.5 Concluding remarks
• References

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