A Roadmap for Evaluation of Lightning Elimination Technologies

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Ronald Brooks
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1 Non-Conventional Lightning Mitigation: Fact or Fiction? A Roadmap for Evaluation of Lightning Elimination Technologies IEEE PES 2003 General Meeting July 16, 2003

2 Purpose of Talk Review methods that have been used to observe performance: Small or large-scale high-voltage tests using electrostatic or switching-impulse excitation Anecdotes and Lack of Damage Visual Inspection for Damage Visual Observations during Storms Measurements of DC or impulse current Remote measurements from lightning location systems

3 Introduction Lightning control or mitigation has been proposed with a wide range of treatments: The Franklin Rod, a conductive electrode that provides a preferred path for lightning. Multiple shells of conductive material, providing increased protection to the interior

4 Conventional Protection IEC Dehn & Söhne, 1995 Zone 0 Zone 1 Zone 2

5 Introduction Lightning control or mitigation has been proposed with a wide range of treatments: Small conductive electrodes that modify the electric field, making them more attractive to lightning than a conventional lightning rod. -Concept of critical radius in switching surge testing - Rocket triggered lightning Large conductive electrodes that modify the electric field to make a structure less attractive to lightning. - Rod-plane versus sphere-plane gap flashover

6 Introduction Lightning control or mitigation has been proposed with a wide range of treatments: Semiconductive electrodes intended to limit peak current and rate of current rise. Semiconductive electrode extensions such as laser plasma, liquid jets, glow discharge or streamers, ionizing radiation

7 Laboratory Studies High-voltage facilities and resources for adequate study of leader development are not widely available. Unfortunately, extrapolation of reduced-scale corona and nonlinear field effects from small to larger physical scales has usually been problematic. streamer formation process dominates the impulse flashover of 0.1-m gaps flashover of 1-m gaps is dominated by leader formation, with streamer formation contributing a minor time delay.

8 Laboratory Studies Small Scale 570 kv/m 300 kv/m 200 kv/m

9 Typical Laboratory Study - Grounding 800 kv, 2us impulse,

10 Typical Field Observations

11 Laboratory Studies Physics of switching-surge flashover at 3-15 m scale has been extrapolated to the final jump of the lightning, a process that occurs over a 30 to 200-m gap. Positive switching-surge leaders have speeds of 10 4 m/s, currents of 0.4 A, and linear charge of about 40 C/m. Corresponding values for natural lighting are 10 5 m/s, 100A and 1000 C/m. Even so, the resulting models [Rizk, Dellera-Garbagnati adapted by Tarchini] describe many of the same features as the Electrogeometric model (EGM) that relates the observed reach of the final jump to the current in the resulting flash.

12 Laboratory Studies Laboratory tests of spherical tips or enhanced air terminals in large rod-to-plane gaps have been used to address questions of the optimal size and shape of treatments, whether intended to increase or decrease stroke incidence. Comparison tests of treated and untreated rods are sensitive to height: An advantage of less than 0.03 m was noted in tests comparing a 72- Curie radioactive source treatment to a rod. There is increased leader inception and switchingsurge flashover voltage in a 7-m gap for a critical electrode radius of greater than 0.4 m.

to ground - Commercial airplanes typically struck once

13 Typical Field Observations Lightning triggered by airplane - Upward branching to sky - Downward branching to ground - Commercial airplanes typically struck once a year - Most flashes triggered by the presence of the airplane

14 Electric Field Mapping LAUNCH PAD LIGHTNING WARNING SYSTEM (LPLWS)

15 Electric Field Mapping LAUNCH PAD LIGHTNING WARNING SYSTEM (LPLWS) Total of 36 flashes in 100 km 2

16 Anecdotal Interpretation There was lightning all around. The flash-to-bang time was less than 15 seconds. My 220-m (720 ) tower, recently treated, was not struck. The treatment works.

17 Models for Flash Incidence to Towers Upward Flashes 1600kV E gc h -7.3 kv/m Downward Flashes N d N 10 g (25.9h ) N g h 0.96

18 Quantitative Interpretation There was a storm flash density of 0.36/km 2. The expected number of downward flashes to a 220-m tower on flat ground would be 0.13, based on the storm flash density. The expected number of upward flashes from a 220-m tower on flat ground would be 0.033, based on the observed ground-level field strength values.

19 Quantitative Interpretation To see a conclusive (2- ) difference in treatment, one would need to observe for a period that would have produced n flashes, where 0 n 2 n 2 n This means that: n 4/0.13 = 31 similar storms need to be observed to comment on the treatment for downward flashes storms would need analysis for upward flashes based on this distribution of ground-level electric fields.

20 Quantitative Interpretation Year-to-year variations in storm exposure can be large: N g at Bruce NGS

21 Example of Adequate Comparison Study N. Kuwabara, T. Tominaga, M. Kanazawa, and S. Kuramoto, Probability Occurrence of Estimated Lightning Surge Current at Lightning Rod before and after Installing Dissipation Array System (DAS), 1999 IEEE Intl EMC Symposium Paper 00476, Seattle WA, ISBN Before Treatment: 26 surges recorded in three years. After Treatment*: 16 surges recorded in one year. After Correction for Storm Exposure: No difference, treated / untreated. * The treatment was penetrated by a 2-m lightning rod, which would have been enveloped by any corona envelope greater than 2 m.

22 Example of Adequate Comparison Study N. Kuwabara, T. Tominaga, M. Kanazawa, and S. Kuramoto, Probability Occurrence of Estimated Lightning Surge Current at Lightning Rod before and after Installing Dissipation Array System (DAS), 1999 IEEE Intl EMC Symposium Paper 00476, Seattle WA, ISBN

23 Lightning Location Systems In continental USA/Canada, a sophisticated and accurate network of receivers has provided lightning location and amplitude data since the mid 1990s. The technology is based on GPS time of arrival and direction finding based on the strong radiation from a vertical lightning channel.

24 Lightning Location Technology 30 ka

25 Lightning Location Technology

26 Lightning Location Technology

27 Lightning Location Technology

28 Lightning Location Technology T=92.3 µs T=539.7 µs T=632.0 µs

29 Lightning Location Technology Hyperbola with T=92 µs (28 km) D D+28 km

30 Lightning Location System Performance Location accuracy of measured data from ALDIS (GAI) lightning detection network for correlated strokes to a 100-m tower in Gaisburg, Austria. The tower is centered at the origin. G. Diendorfer, W. Hadrian, F. Hofbauer, M. Mair, W. Schultz, Evaluation of Lightning Location Data Employing Measurements of Direct Strikes to a Radio Tower, CIGRE Session 2002, paper

31 LLS Observation of Treated Area FEDEX installation in Memphis, TN

32 LLS Observation of Treated Area FEDEX installation in Memphis, TN

33 LLS Observation of Treated Area FEDEX installation in Memphis, TN

34 LLS Observation of Treated Area FEDEX installation in Memphis, TN Correct Size of Dots, Based on 400-m Uncertainty

35 Conclusions Anecdotal data: There was lightning all around but the treatment was not struck is inconclusive for typical structure heights and typical reporting periods. Quantitative data: The ground-level electric field Ez >(1600/h), the treatment reacted and was/was not struck, instead a nearby structure/ground was struck.

36 Conclusions Transfer functions are needed between: Excitation (local static or dynamic vertical electric fields) and Treatment effects (visible, UV corona or related currents)

37 Conclusions Lightning location system data are essential: For validating time-tagged records of structure currents For normalizing observations of performance However, holes in the data before and after treatment need to be larger than 400-m observation error and should have enough samples to be convincing. Locally, n 2 n n 2 n after after before before While globally, n after = n before

38 Conclusions Direct rather than indirect measurements are needed to assess treatments. Before and after treatment, with a minimum of four responses in one group and no responses, for the same lightning exposure, in the other group, is convincing. Damage to equipment is a poorly-calibrated measure of response, since replacement equipment often has different (and higher) surge absorption capability.

Proposed revisions to IEEE Standard 998 (1996) Guide for Direct Lightning Stroke Shielding of Substations

Rationale Proposed revisions to IEEE Standard 998 (1996) Guide for Direct Lightning Stroke Shielding of Substations Franco D Alessandro, PhD, MIEEE, WGD5 Participant Martin Havelka, MIEEE, WGD5 Member