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Lightning and Power Transmission Lines

Lightning and Power Transmission Lines. EE --- Term Paper By ---. Outline of Presentation. The Thunderstorm The Lightning Discharge (Stages) Lightning Currents and Related Parameters Protection of Power-Transmission Effect of Lightning on Power Transmission systems. The Thunderstorm.

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Lightning and Power Transmission Lines

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  1. Lightning and Power Transmission Lines EE --- Term Paper By ---

  2. Outline of Presentation • The Thunderstorm • The Lightning Discharge (Stages) • Lightning Currents and Related Parameters • Protection of Power-Transmission • Effect of Lightning on Power Transmission systems

  3. The Thunderstorm • Global Distribution of Thunderstorms • The Thundercloud • Point-Discharge Currents • The Lightning Discharge

  4. Global Distribution of Thunderstorms

  5. The Thundercloud • Two main classes: heat storms and frontal storms • Heat storm in tropics and mountain areas • Frontal storms in temperate regions • Characterized by the electrical charge of water droplets.

  6. Point-Discharge Currents Electrostatic field distribution about vertical lightning conductor (could induce lightning discharge)

  7. The Thundercloud continued

  8. The Lightning Discharge (Stages) • Temporal Development of Flash to Ground • Mature Stage • The Leader Stroke • The Dart Leader

  9. The Lightning Discharge (Stages) continued

  10. Lightning Currents and Related Parameters • Lightning Currents • Average lightning current amplitude is 25 kA (lowest 2kA, highest recorded 270 kA) • Frequency of Lightning Discharges (flash density) • Varies from place to place • Measured in thunderstorm days and lightning flash density • Lightning flash density for Greece = 3.7 (most recent data)

  11. Protection of Power-Transmission Systems • Reasons for Protection • Avoid power disruptions • Lightning protection methods • The Air Terminal (overhead conductors) • Tower Impedance (ability of tower to resist lightning) • The Buried Earth System (underground grid of conductors) • Protective Leakage Paths-Pipe-Pipe Gaps (utilizes a gap between conductors) • Underground Cables (Utilizes insulation of the earth) • Lightning Arresters (acts as over-voltage release valves)

  12. Effect of Lightning on Power Transmission systems • Lightning Location • Prediction of Lightning Activities

  13. Lightning Location • Use of magnetic link locators, lightning counters location within country-wide networks • Recorded by Meteorological Services and Power distribution companies over time • Empirical formula for calculation of lightning flash density correlate well with actual flash density obtain from magnetic counters (most recent data obtained from Greece and Japan)

  14. Prediction of Lightning Activities • Prediction based on a variety of methods • Modeling of lightning parameters • Prediction based on neural networks • Prediction based on fuzzy neural networks • All based on data obtained from lightning location from meteorological and power services.

  15. Prediction based on Fuzzy Neural Networks • New technique used in Japan • Gave better prediction of lighting strike compared to neural networks • Limitations: only predicts lightning strike few hours before the strike.

  16. Conclusions • Thunderstorms occur at highest at the equatorial belt and decreases towards the poles. Local thunderstorm activity varies from year to year. • Lightning data is available from the meteorological services of countries in the form of flash maps showing isokeraunic lines, i.e. lines joining areas have the same number of thunderstorm days. • The mechanism of light formation and discharge involves electrical charging of water droplets within a cloud leading to a dipole. The electrical field thus produces causes a cloud to cloud lightning discharge or a cloud to earth discharge. • The average lightning current of about 25 kA.

  17. Conclusions continued • The earth flash density varies in different parts of the world with the earth flash density estimated at 1 to 2 flashes per 10 thunderstorm days. • A variety of protection mechanism exist for the lightning protection of transmission lines including ground conductors(air terminals), counterpoise , pipe-pipe gap, down-lead, grounding systems, underground cables and lightning arresters.

  18. Conclusions continued • Traditional methods of lightning monitoring include the use of magnetic link direction finders and lightning counters. • Correlation between lightning data obtained from meteorological lightning networks and those obtained using standard formula show good agreement. • More modern methods have focused on lighting prediction using neural network and fuzzy neural network techniques, but these only provide prediction a couple of hours before the lightning strike.

  19. End of Presentation Thank You

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