lightning research at the university of florida · photograph by: dustin hill . 10 still-camera...

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

Introduction

Photograph by: Dustin Hill

What is

Lightning?

Lightning is the discharge of

atmospheric electricity

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)

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

Natural lightning at Camp Blanding Photograph by: Dustin Hill

10

Still-camera

image Streak-camera image

Channel-base current

(Adapted from Lightning Physics & Effects by V. A. Rakov & M. A. Uman)

Various Steps of Lightning Discharge Process over Time

11 (Adapted from Lightning by M. A. Uman)

12

M-component


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


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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)

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

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


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

Rocket Triggered Lightning at Camp Blanding

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Subsequent strokes in triggered lightning are

similar to those in natural lightning


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

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)

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.

Single-station expt. (Natural lightning around Gainesville)

Lightning Observatory in Gainesville

X-ray detector

dE/dt antenna

E-field antenna

Glass Cupola

Multi-station expt. (RTL at CB; far-field measurements at 45 km)

Lightning Observatory in Gainesville

Flash UF 09-25

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Near and far field measurement

Multi-station expt. (RTL at CB; far-field measurements at 3 km)

Single-station expt. (Natural lightning around Starke)

Starke Site

Study on distribution line done at Camp Blanding

Study on underground cable done at Camp Blanding

Fulgurite

Study on underground cable done at Camp Blanding

Study on residential house done at Camp Blanding

(Click on the photograph to start video)

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)

Test House

Lead

conductor

Test RunwayTest

3-Phase

Distribution

Line

IS1

600 V

Underground

Cable

Launch

Control

Tower

Launcher

Office

N

Experimental set-up

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.

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.

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.


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

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

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.


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


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

(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.


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)

(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.


(a)

(b)

0 20 40 60 80 100-10

-5

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

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

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)

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

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.

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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

• 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?

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

lightning research at the university of florida · photograph by: dustin hill . 10 still-camera...

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