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E. Bazelyan and Yu Raizer

EFFECT CORONA ON CONNECTING LEADER AND UPWARD LIGHTNING FROM HIGH STRUCTURES. E. Bazelyan and Yu Raizer. OUTLINE. Lightning activity Cause and conditions of an upward leader inception Corona over high structure: its influence on the upward leader

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E. Bazelyan and Yu Raizer

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  1. EFFECT CORONA ON CONNECTING LEADER AND UPWARD LIGHTNING FROM HIGH STRUCTURES E. Bazelyan and Yu Raizer

  2. OUTLINE • Lightning activity • Cause and conditions of an upward leader inception • Corona over high structure: its influence on the upward leader • Upward lightning and connecting leader: relation and difference • Attempts to improve a lightning rod

  3. LIGHTNING ACTIVITY • Europe: 3 – 5 strokes /km2 per year • Grounded structure of height h attracts lightning from 3h –radius • 30m structure experiences 1 stroke/10 years, 100 m – 1stroke/year • Very high structure ejects lightning itself • 540 m Ostankino Tower in Moscow undergoes 25-30 stokes/year, • 90% due to upward lightning • Downward lightning strikes object exciting • connecting leader and jointing with it • Lightning rod towers over defending object • and takes stroke on itself

  4. Conceivable ways to control lightning - • to eliminate lightning by acting on thundercloud • to influence on connecting and upward leaders • The 2nd task is “more realistic” what dictates interest to upward • leaders Cause of upward leader inception Rod’s top behaves as electrode with U = E0h = 1 MV for h = 100 m E0 =100 V/cm Field at the top Etop E0h/(2r0) Etop  30 kV/cm for these E0, h and r0 = 15 cm

  5. CONDITIONS FOR LEADER FORMATION • Streamer flash (at Etop > 30 – 50 kV/cm) • U =E0h > 400 kV and 400 kV falls on the length d  1 m • Leader vitality EL  E0 Leader velocity vL ~ (Utip )1/2

  6. Corona over high grounded structurehinders upward leader formationWhy? Glow corona is always stabilizing field at electrode top

  7. Effects of corona on leader Etop = Ecor < Eflash – prevents streamer flash Only very high dE/dt can counteract Smoothness of U(r) near the rod’s top results in: - obstacle for 400kV/1 m - obstacle for leader vitality

  8. NON-STATIONARY CORONAtheory and numerical simulation • Only stationary corona have been considered previously • Corona from grounded rod under thundercloud is • non-stationary: ion cloud expands “unrestrictedly” Model for numerical simulation U(t)=E0(t)h; U=0 at r  Spherical model for analytical theory

  9. Equations of spherical model • Ionization is happened in the thin layer nearby electrode top • - Field at electrode top is stabilized The main approximation , - quasi-stationary local current i(r,t) = 4r2E  i(t) – - results in R(t), i(t) for any U(t) - function

  10. Solution for U = At Strong dependence i upon dU/dt ! for U(t) = const Example: E0max = 100 V/cm  = 10 s h = 200 m Umax = 2 MV  = 1.5 cm2 (V s)-1 R = 32 m imax = 0.35 mA Q = 1.75 mC for t = 10 s

  11. Results of numerical simulation

  12. Critical current for corona-to-streamer transitions Critical current corresponds If i > icr ionization wave (“spherical streamer”) is incepted icr 6 mA for r0 = 1 cm (Ecor = 42.8 kV/cm) Condition i > i cr requires so high dE0/dt, E0max and h that thundercloud itself can never provoke streamer flash

  13. Empirical confirmation of corona influence Almost 100% probability, i.e. 1 trigger lightning for ~ 5 s 1 upward lightning for 40 thunderstorm hours 25-30 upward lightning for 40 thunderstorm hours

  14. Corona by combined action of thundercloud and approaching downward leader(numerical simulation) icr

  15. Ion density at joint action of thundercloud and approaching downward lightning

  16. Maximum horizontal displacement of downward lightning from rod for initiation of upward (connecting) leader D  4h, in reasonable agreement with empiric radius of lightning attraction, 3h

  17. Influence of corona on upward leader vitality Field by thundercloud, E0, necessary to sustain vitality of leader born from rod of height h

  18. COMMUNITY OF CONNECTING AND UPWARD LEADERS Connecting leader E0 due to cloud, Elid due to downward Leader Elid > E0 Upward lightning Elid << E0 dElid/dt >> dE0/dt -Upward lightning from high structure is provoked by far downward lightning, providing high dE0/dt -Upward lightning and connecting leader have the same origin: they both are incepted owing to downward lightning -Upward lightning heads for thundercloud Connecting leader heads for close downward one

  19. 1. To joint with downward lightning 2. To stop in some distance 3. To reach thundercloud and to convert into lightning LOT OF THE BORN UPWARD LEADER Numerical results Case 2

  20. Case 3. Upward leader from 540 m TV tower in Moscow went to cloud

  21. SOME ATTEMPTS TO IMPROVE LIGHTNING ROD Some authors and firms advertise lightning rod with very pointed top convincing that this facilitates inception of connecting leader NO, r0 < 1 cm is useless since leader is unviable

  22. MULTI-ELECTRODE LIGHTNING ROD - A lot (N ~ 5000) of needles l = 10 cm, r0 = 1 mm on surface r1 ~ 5 m - Corona ion cloud R >>r1 - Corona current i does not depend on N, r1, r0, l - Current from one needle i1= i/N << icr  No streamer flash  No connecting or upward leader  No lightning stroke Object placed under the system is protected, excepting case of the direct lightning hit

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