lightning research at the university of florida · photograph by: dustin hill . 10 still-camera...
TRANSCRIPT
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Lightning Research at
the University of Florida
Shreeharsh Mallick
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The content of this presentation are for educational purpose. You are welcome to
use these materials as long as you acknowledge the source.
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The phenomenon of lightning occurs through a set of complex processes. In the subsequent slides, some of the details are abstracted in order to present the fundamental aspects of these processes in a simple way. To learn more about lightning, please refer to the books/papers in the reference slide (at the end) or contact • Dr. Vladimir A. Rakov (E-mail: [email protected]) • Dr. Martin A. Uman (Email: [email protected])
For information regarding UF Lightning Research Group, visit http://www.lightning.ece.ufl.edu
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Introduction
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Photograph by: Dustin Hill
What is
Lightning?
Lightning is the discharge of
atmospheric electricity
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Earth
Thundercloud
+ + + + + + + + + + + + + + + + _ _ _ _ + + + _ _ _ _ + + _ _ _ _ + Thundercloud
+ + + _ _ _ _ _ _ _ _ _
Cloud-to-ground flash
Cloud-to-air flash
Cloud-to-cloud flash
(intercloud)
Cloud-to-cloud flash
(intracloud)
TLE or Transient Luminous Events (sprites, elves)
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Downward
Negative
Downward
Positive
Upward
Negative
Upward
Positive
Depending on direction of propagation and polarity of charges (Adapted from Lightning Physics & Effects by V. A. Rakov & M. A. Uman)
Downward
Negative
(90% of
CG flash)
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Objects on
Ground
Thundercloud
+ + + + + + +
_ _ _ _ _ _ _
_ _ _ _ _ _
+
Charges in Cloud
+ + + + + + + + + +
+ + + + + + + +
Image Charges
on Ground
Streamer
Stepped
Leader
Striking
Distance Upward
Leaders
Attachment
1st Return Stroke
Current
Ionized Air
Dart/Dart-Stepped
Leader
2nd Return Stroke
3rd Return Stroke
Negative
downward
natural
lightning
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Natural lightning at Camp Blanding Photograph by: Dustin Hill
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Still-camera
image Streak-camera image
Channel-base current
(Adapted from Lightning Physics & Effects by V. A. Rakov & M. A. Uman)
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Various Steps of Lightning Discharge Process over Time
11 (Adapted from Lightning by M. A. Uman)
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M-component
(Adapted from Lightning Physics & Effects by V. A. Rakov & M. A. Uman)
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Negative Lightning for Cloud-to-Ground • Overall duration: 200-300 ms
• Peak current: 1st stroke = 30 kA
Sub. stroke = 10-15 kA
M-comp. = 100-200 A
• 10-90% current rise-time: 1st stroke = 5 µs
Sub. stroke = 0.3-0.6 µs
M-comp. = 300-500 µs
• Current duration to HPW-value on tail:
1st stroke = 70-80 µs
Sub. stroke = 30-40 µs
• Max. current rate of rise: 1st stroke = ≥10-20 kA/µs
Sub. stroke = 100 kA/µs
(Adapted from Lightning Physics & Effects by V. A. Rakov & M. A. Uman)
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Parameters Units Sample size
% exceeding tabulated values
95% 50% 5%
Peak current (min. 2 kA)
1st strokes kA
101 14 30 80
Sub. Strokes 135 4.6 12 30
Max. dI/dt 1st strokes
kA/µs 92 5.5 12 32
Sub. Strokes 122 12 40 120
Front duration (2 kA to peak)
1st strokes µs
89 1.8 5.5 18
Sub. Strokes 118 0.22 1.1 4.5
Stroke duration (2 kA to HPW-value on tail)
1st strokes µs
90 30 75 200
Sub. Strokes 115 6.5 32 140
Flash duration 1st strokes
ms 94 0.15 13 1100
Sub. Strokes 39 31 180 900
Time interval between strokes
ms 133 7 33 150
Parameters of downward negative lightning based on channel-based current.
Adapted from Berger et al. (1975)
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Ground-Based
Tall Object
Thundercloud
+ + + + + + +
_ _ _ _ _ _ _
_ _ _ _ _ _
+ Charges in Cloud
+ + + + + + + + + +
Image Charges
on Ground
Streamer
Upward
Positive
Leader
Initial
Continuous
Current
Subsequent
Return Stroke
Ionized Air Dart/Dart-Stepped
Leader
Upward
lightning
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Lightning striking Burj Khalifa in Dubai
(unknown source)
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Still-camera
image Streak-camera image
Channel-base current
Note initial continuous current in place of first return stroke
(Adapted from Lightning Physics & Effects by V. A. Rakov & M. A. Uman)
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Rocket
Launcher
Thundercloud _ _ _ _ _ _ _
_ _ _ _ _ _
+
Charges in Cloud
+ + + + + + + + + +
Image Charges
on Ground
Wire connected
to Ground
Streamer
Upward
Positive
Leader
Natural Channel
Exploded Wire
Initial
Continuous
Current Ionized Air
Dart/Dart-Stepped
Leader
Subsequent
Return Stroke
Triggered
lightning
using rocket-
and-wire
technique
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Rocket Triggered Lightning at Camp Blanding
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Subsequent strokes in triggered lightning are
similar to those in natural lightning
(Adapted from Lightning Physics & Effects by V. A. Rakov & M. A. Uman)
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Interceptor Rocket
Launcher
Thundercloud _ _ _ _ _ _ _
_ _ _ _ _ _
+
Charges in Cloud
+ + + + + + + + + +
Image Charges
on Ground
Wire not
connected to
ground
Streamers
Leaders
Current
Return Stroke
Altitude
triggered
lightning
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Lightning
strikes plane
while take off in
Japan
(unknown
source).
(classical
example of
altitude
triggered
lightning)
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UF Lightning Research
Group
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Facilities
• The Lightning Center for Lightning Research
and Testing (ICLRT) at Camp Blanding, FL
– Rocket-Triggered Lightning Experiments
• The Lightning Observatory in Gainesville, FL
(45 km from Camp Blanding)
• Starke Site (3 km from Camp Blanding)
• The Lightning Research Laboratory
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Activities
• Studying the various physical
processes in natural and rocket-
triggered lightning
– Current shunts/Pearson coil
– Electric and Magnetic field antennas
– X-Ray detectors
– HF and VHF systems
– Optical equipments
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ICLRT at Camp Blanding, Florida
26 (Adapted from Lightning Physics & Effects by V. A. Rakov & M. A. Uman)
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Rocket Triggered Lightning
(Click on the photograph to start video)
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Rocket Triggered Lightning
(Click on the photograph to start video)
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Rocket Triggered Lightning
(Click on the photograph to start video)
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LOG is located 45 km from CB. Starke site, which is located 3 km
from CB, is not shown on the map.
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Single-station expt. (Natural lightning around Gainesville)
Lightning Observatory in Gainesville
X-ray detector
dE/dt antenna
E-field antenna
Glass Cupola
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Multi-station expt. (RTL at CB; far-field measurements at 45 km)
Lightning Observatory in Gainesville
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Flash UF 09-25
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Near and far field measurement
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Multi-station expt. (RTL at CB; far-field measurements at 3 km)
Single-station expt. (Natural lightning around Starke)
Starke Site
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Study on distribution line done at Camp Blanding
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Study on underground cable done at Camp Blanding
Fulgurite
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Study on underground cable done at Camp Blanding
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Study on residential house done at Camp Blanding
(Click on the photograph to start video)
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Case Study
Triggered-Lightning Testing of Lightning Protective System
of a Residential Building
(Triggered-Lightning Testing of the Protective System of a Residential Building: 2004 and 2005 Results, B.A. DeCarlo, V.A. Rakov, J. Jerauld, G.H. Schnetzer, J. Schoene, M.A. Uman, K.J. Rambo, V. Kodali, D.M. Jordan, G. Maxwell, S. Humeniuk, and M. Morgan, ICLP 2006)
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Test House
Lead
conductor
Test RunwayTest
3-Phase
Distribution
Line
IS1
600 V
Underground
Cable
Launch
Control
Tower
Launcher
Office
N
Experimental set-up
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North Instrumentation boxNorth Instrumentation box
The test house at the ICLRT whose LPS was subjected to direct lightning strikes in 2004 and 2005. Approximate dimensions of the house are 10 x 7 x 6.5 m3. Photo from 2005.
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Experimental set-up (2004)
Ground
Level
Lightning current
injection point
To electrical
circuit neutral
Air
terminal
N
B
A
D
C
3.8 m
9.9 m
4.6 m
3.4 m 3 m 6.1 m
Diagram of the LPS of the test house in 2004. All conductors below the plane labeled “Ground Level” are buried (in direct contact with earth). Note: Return stroke current only was injected in 2004.
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Electrical diagram of test system configuration for 2004. Currents A, B, C, D, and K were measured at the test house, and current G was measured at IS1, 50-m away.
Experimental set-up (2004)
336 Ω 468 Ω 668 Ω 69 Ω
50 Ω50 Ω
600-V Cable
A B C
6 Ω
4 Ω
D
K
Buried
conductor
G
Watt-hour
meter
SPDs
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Injected
Point A
Point B
(a)
Return-stroke currents for stroke 0401-3, displayed on a 10 µs time scale. (a) injected current and currents at points A, B, C, D, and K; (b) currents for flash 0401-7.
Current division results (2004)
Point C Point D
Point K
(b)
336 Ω 468 Ω 668 Ω 69 Ω
50 Ω50 Ω
600-V Cable
A B C
6 Ω
4 Ω
D
K
Buried
conductor
G
Watt-hour
meter
SPDs
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Diagram of the LPS of the test house in 2005. All conductors below the plane labeled “Ground Level” are buried (in direct contact with earth). Note: Both initial-stage and return-stroke currents were injected in 2005.
Experimental set-up (2005)
3.8 m
9.9 m
4.6 m
6.8 m
3 m
3.4 m
Ground
Level
Lightning current
injection point
To electrical
circuit neutral
Air
terminal
N
B
B1
A1
A
D
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Experimental set-up (2005)
Electrical diagram of test system configuration for 2005. Currents A, A1, B, B1, and D were measured at the test house, and Current G was measured at IS1, 50 m away.
Buried loop conductor
442 Ω 488 Ω 518 Ω 524 Ω 636 Ω 69 Ω
50 Ω50 Ω
600-V Cable
A B1A1 B D G
Watt-hour
meter
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(a) Return stroke currents in four downleads (A, A1, B, and B1) , (b) The sum of the four downlead currents (A, A1, B, and B1) vs. the injected current
waveform displayed on a 110 µs time scale for stroke 0521-1.
Current division results (2005)
0 20 40 60 80 100-3
-2
-1
0
Time, s
Cu
rren
t, k
A0521-1
Downlead A
Downlead A1
Downlead B
Downlead B1
0 20 40 60 80 100-8
-6
-4
-2
0
Time, s
Cu
rren
t, k
A
0521-1
Injected Current
Sum of 4 Downleads
(a)
(b)
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(a) Injected current versus the difference between the sum of the four downlead currents and current D, labeled (Sum – D). The (Sum – D) waveform is scaled so that its peak is equal to that of the injected current and represents the current going to the grounding system (local) of the test house. (b) Current D versus current G.
Current division results (2005)
(a)
(b)
0 20 40 60 80 100-10
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0
Time, s
Cu
rren
t, k
A0521-1
Injected Current
(Sum - D), scaled
0 20 40 60 80 100-6
-4
-2
0
Time, s
Cu
rren
t, k
A
0521-1
Current D
Current G
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Current division results, 2004 vs. 2005
Peak value of current D (current to electrical circuit neutral) vs. injected peak current for return strokes in flashes triggered in 2004 and 2005.
Over 80% of the injected peak current was observed to enter the electrical circuit neutral in similar 1997 tests at the ICLRT (Rakov et al., 2002).
Characteristics Injected current,
kA
Current D, kA Current D relative
to Injected current,
%
2004 2005 2004 2005 2004 2005
Minimum 3.6 6.8 0.8 4.4 16 51
Maximum 17.8 34.4 3.4 8.5 28 72
Arithmetic Mean 9.4 14.4 2.1 6.6 22 59
Standard
Deviation
4.1 8.8 0.9 1.8 3.6 8.5
Geometric Mean 4.7 12.7 1.9 6.1 22 58
Sample Size 11 8 11 7 11 7
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Damage to the system
Damage to the insulation of the 600-V cable, (a) puncture of the insulation of one conductor of the 600-V cable, (b) damage to all three conductors of the cable.
y
4 mm Adjacent damage
(b) (a)
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Bar charts of peak current of injected (Inj.) current, currents in ground rod A, ground rod A1 (2005), ground rod B, ground rod B1 (2005), ground rod C (2004), and current D for events LSA-0401-1 and LSA-0521-1.
Current division results (2004 vs. 2005)
2005
0521-1
Inj. A A1 B B1 D
Peak C
urr
ent,
kA
0
2
4
6
8
Ground
Level
Lightning current
injection point
To
electrical
circuit
neutral
Air
terminal
N
B
B1
A1
A
D
2004
0401-1
Inj. A B C D
Pe
ak c
urr
en
t, k
A
0
2
4
6
8
10
12
14
16
Ground
Level
Lightning current
injection point
To electrical
circuit neutral
Air
terminal
N
B
A
D
C
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Current division results (2004 vs. 2005)
Bar charts of half-peak width of injected (Inj.) current, currents in ground rod A, ground rod A1 (2005), ground rod B, ground rod B1 (2005), ground rod C (2004), and current D for events 0401-1 and 0521-1.
3
Inj. A B C D
HPW
, µs
0
10
20
30
40
50
60
70
80
2004
0401-1
Ground
Level
Lightning current
injection point
To electrical
circuit neutral
Air
terminal
N
B
A
D
C
0521-1
Inj. A A1 B B1 D
HPW
, µ
s
0
5
10
15
20
25
30
35
2005 Ground
Level
Lightning current
injection point
To
electrical
circuit
neutral
Air
terminal
N
B
B1
A1
A
D
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• Current entering the electrical circuit neutral in percent of the
injected current:
1997 – >80%
2004 – 22%
2005 – 59% better grounding at the test house than in 1997
Summary • The primary objective was to examine current division between
local (at the test house) and remote grounding systems
• Overall, configuration tested in 2004 (RS only; SPDs installed)
performed better than the configuration tested in 2005 (IS + RS;
SPDs disconnected)
• In absence of SPDs in 2005, the watt-hour meter incurred damage,
similar to the no-SPD configuration tested in 1997 (Rakov et al.,
2002)
Roughly a factor of two to three larger current in 2005 than in 2004 was forced to search its way to remote ground
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For information regarding UF Lightning Research Group, visit
http://www.lightning.ece.ufl.edu
QUESTIONS?
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References • Lightning Physics and Effects, V. A. Rakov and M.
A. Uman, Cambridge University Press, 2003
• Lightning, M. A. Uman, Dover Publication, 1969
• Triggered-Lightning Testing of the Protective System of a Residential Building: 2004 and 2005 Results, B.A. DeCarlo, V.A. Rakov, J. Jerauld, G.H. Schnetzer, J. Schoene, M.A. Uman, K.J. Rambo, V. Kodali, D.M. Jordan, G. Maxwell, S. Humeniuk, and M. Morgan, ICLP 2006
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Photograph by: Dustin Hill