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LIGHTNING PHYSICS AND LIGHTNING PROTECTION: STATE OF ART 2013Prof. Carlo Mazzetti di Pietralata
1st October 2013, Warsaw
WARSAW UNIVERSITYOF TECHNOLOGY
TOPICS
1. Physics
2. Modern research method
3. Lightning parameters
4. Lightning damages
5. Principle of lightning protection: International normalization
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DIFFERENT TYPES OF LIGHTNING
CLOUD TO CLOUD LIGHTNING – MIAMI
CLOUD TO GROUND LIGHTNING – NEBRASKA
CLOUD TO GROUND LIGHTNING - CN TOWER (CANADA)
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DIFFERENT TYPES OF LIGHTNING
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Lightning in volcano eruptions – Island, May 2010
MULTIPLE CHANNEL TERMINATIONS ON GROUND
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THE THUNDERCLOUD
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Charge distribution in a thundercloud.
© RAI
TYPES OF LIGHTNING
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© RAI
NEGATIVE CLOUD-TO-GROUND LIGHTNING FLASH
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REFERENCE SPEED=LIGHT SPEED © RAI
LIGHTNING’S CURRENT WAVEFORMS
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LIGHTNING’S CURRENT WAVEFORMS
© RAI
Positive flash
Negative flash
Berger et al., 1975
LEADER PROPAGATION MODELS
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LEADER PROPAGATION MODELS
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• Downward leader constant charge density
• Downward/upward leader propagating along electric field lines
• Critical radius concept
• Upward leader charge density 50μC/m
• Velocity ratio of 4 and 1
• Final jump condition
• Cloud represented by ring charges
Dellera and Garbagnati (1990)
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BERGER’s Tower Measurements at Mont San Salvatore. Two instrumented towers: 1943-1972. 101 first strokes, 135 subsequent strokes.
LIGHTNING DETECTION: HISTORY
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LIGHTNING DETECTION: GAISBERG TOWER
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LIGHTNING DETECTION: GAISBERG TOWER
LIGHTNING DETECTION: 2011 - SÄNTIS TOWER
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DIFFERENT TYPES OF LIGHTNING
Triggered-Lightning Testing Area - University of Florida
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ROCKET-TRIGGERED LIGHTNING VS. NATURAL LIGHTNING
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TRIGGERED-LIGHTNING PROPERTIES
1. Leader/return stroke sequences in rocket-triggered lightning are similar in most (if not all) respects to susequent leader/return stroke sequences in natural downward lightning and to all such sequences in object-initiated lightning.
2. Distributions of peak currents for triggered and natural (subsequent strokes only) lightning are similar. Median (or geometric mean) values are typically in the range of 10 to 15 kA.
3. The peak current is not much influenced by either strike-object geometry or level of man-made grounding.
4. The current risetime depends on the electrical properties of the strike object (1.2 µs for strikes to overhead conductors versus 0.4 µs for strikes to concentrated grounding system).
5. For triggered lightning, the current peak is essentially independent of current risetime.
6. Current wavefront parameters (in particular dI/dt peak) for triggered lightning are based on records acquired using better instrumentation than those for natural downward lightning.
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LIGHTNING’S LOCALISATION
1. Direction finding (DF)
2. Time of arrival (TOA)
3. Interferometry
4. Peak amplitude method
5. Field component methods
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TIME TO THUNDER
To work out how far away a thunderstorm is, count the time between when you see a lightning flash and when you hear the thunder. Thunder and lightning happen at the same time, but the light travels faster than sound, so the lightning flash reaches the eyes before the sound reaches the ears
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DIRECTION FINDING AND TIME OF ARRIVAL
The current associated with each stroke sends out electromagnetic waves that can be detected and mapped with lightning detection systems. There are two principle techniques of detecting lightning:
• Magnetic direction finding (MDF)
MDF detects the electromagnetic signature of a cloud to ground lightning flash. Detection by two or more antennae are used to triangulate on the lightning flash location.
• Time of arrival (TOA)
TOA technique uses the difference in the time when the electromagnetic signature of a lightning flash is detected by two or more sensors. This method has been successfully applied by, e.g.,
•Krider and Uman (1973)•Winn et al. (1973), Rakov et al. (1994)•Idone et al. (1998)
to determine the lightning location by triangulation.
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COMPONENTS OF LIGHTNING ELECTROMAGNETIC PULSE (LEMP)
PERFORMANCE MEASURES OF LLS
Stroke Detection Efficiency
Fraction (or percentage) of actual CG strokes that were detected by the network
Flash Detection Efficiency
Fraction (or percentage) of actual flashes that were detected by the network. A flash is detected if one or more strokes are detected.
Location Accuracy
The error in the position (lat/lon/altitude) provided by the network (expressed as a distance error: RMS or median)
Peak Current Estimation Error
Fraction (or percentage) error on the magnitude of the peak current estimate provided by the network
Type Classification Error
Fraction (or percentage) of the time that the network incorrectly identified the type of lightning discharge (CG or cloud discharge)
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EUCLID NETWORK
EUCLID (European Cooperation for Lightning Detection) is aconsortium of 16 European national lightning detecting networks. Presently, the complete network consists of 138 sensors contributing to the detection of lightning.
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EUCLID DATA ANALYSIS
Flash density over Europe (ALDIS)
Average amplitude over Europe (ALDIS)
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SATELLITE BASED LIGHTNING LOCATION (OTD)
Global frequency and distribution of lightning (NASA, from 4 years Optical Transient Detector observation)
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LIGHTNING LIVE MAPS
Lightning live maps are available for PC and mobile devices
http://www.blitzortung.org
Mapa burzowa i pogodowa - Mariusz Waśkowiec
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LIGHTNING STRIKES TO TALL STRUCTURES
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LIGHTNING STRIKES TO TALL STRUCTURES
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LIGHTNING PARAMETERS OF ENGINEERING INTEREST: SUMMARY
1. Ground lightning flash density (Ng) is the primary descriptor of lightning incidence. Multiple-station lightning locating systems (LLSs) are by far the best available tool for mapping Ng.
2. About 80% or more of cloud-to-ground lightning flashes are composed of two or more strokes. This percentage is appreciably higher than 55% previously estimated by Anderson and Eriksson (1980) based on less accurate records. The average number of strokes per flash is typically 3 to 5.
3. Roughly one-third to one-half of lightning flashes create two or more terminations on ground separated by up to several kilometers. When only one location per flash is recorded, the correction factor for measured values of Ng to account for multiple channel terminations on ground is about 1.5-1.7, which is considerably higher than 1.1 estimated by Anderson and Eriksson (1980).
4. From direct current measurements, the median return-stroke peak current is about 30 kA for first strokes in Switzerland, Italy, South Africa, and Japan, and typically 10-15 kA for subsequent strokes in Switzerland and for triggered and object-initiated lightning. Corresponding values from measurements in Brazil are 45 kA and 18 kA.
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LIGHTNING EFFECTS AND DAMAGES
Lightning damage to a house Exploded 110kV transformer, Neumarkt, 1983 (DER SPIEGEL: ‘Blitz im Atommeiler’ - 1983)
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LIGHTNING STRIKES TO AN AIRCRAFT
DIRECT EFFECTS
1.Thermal Effects
2.Sparking
3.Mechanical Effects
4.Puncture
5.Disruptive Forces
6.Shockwaves
INDIRECT EFFECTS
1.Hidden Failures
2.Soft Failures
3.Visible or invisible
4.Hard Failures
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LIGHTNING STRIKES TO AN AIRCRAFT
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LIGHTNING STRIKES TO AN AIRCRAFT
Lightning damage to a plane
The NASA Lockheed ER-2 has a larger payload capability than its predecessor the U-2. Both have provided direct observations of severe thunderstorms and other clouds using multi-sensor payloads including lasers, infrared, visible and microwave scanners, spectrometers, and electric field antennas
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DAMAGE TO ELECTRONIC DATA PROCESSING
The networked world, with its growing flow of information, is severely hindered by interference or damage to the essential power systems, transmission systems in the telephone and data networks
Partial lightning currents propagate on lines and mains(P. Hasse: Overvoltage protection of low voltage systems – 1998, IET)
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LIGHTNING EFFECTS AND DAMAGES
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LIGHTNING EFFECTS AND DAMAGES
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LIGHTNING EFFECTS AND DAMAGES
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TRIGGERED-LIGHTNING TO STUDY THE EFFECTS ON GROUNDED STRUCTURES AND POWER SYSTEMS
An overview of the ICLRT at Camp Blanding, Florida, 1999–2001.
A lightning strike at the center of a 70 × 70 m2 buried metallic grid
The ICLRT at Camp Blanding, Florida, was established by the Electric Power Research Institute (EPRI) and Power Technologies, Inc. (PTI) to study the effects of lightning on structures and on power lines.
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fire
• mechanical damages
• touch and step
voltages• fire
equipmentsfailure
equipmentsmalfunctioning
PHYSICAL DAMAGES
dangeroussparking
overvoltages
electromagneticinterference
overvoltages and overcurrents
electromagneticeffects (LEMP)
electrodynamic effects
thermal effects effects on the
human body
A
B
C
effects
Lightning
• Lightning data• Effects: damages and loss• Protection Measures
effects
CRITERIA OF PROTECTION
APPLICATION TO THE CIGRE DISTRIBUTION
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PARAMETERS OF LIGHTNING CURRENT
10 % 10 %
± i
QLONG
TLONG
t
IEC 2617/10
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O1
90 %
10 %
T1
T2
50 % I
± i
t
IEC 2616/10
VALUES OF LIGHTNING PARAMETERS
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LIGHTNING CURRENT PARAMETERS (CIGRE)
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AMPLITUDE DENSITY OF THE LIGHTNING CURRENT
Am
plit
ude
den
sity
(A
/Hz)
103
102
101
100
10–1
10–2
10–3
10–4
10–5
101 10
2 10
3 10
4 10
5 10
6 10
7
Frequency f (Hz)
First negative stroke 100 kA 1/200 µs
Relevant frequency range for LEMP effects
Subsequent negative stroke 50 kA 0,25/100 µs
First positive stroke 200 kA 10/350 µs
1 f
1
f2
IEC 2627/10
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LIGHTNING INFLUENCES SOURCES OF DAMAGE
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Flash striking the structure
Flash striking near the structure
Flash striking the service
Flash striking near the service
DAMAGES AND LOSS
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Possible damages
•Shock to living beings due to touch and step voltages
•Physical damages (fire,…)
•Failure or electrical and electronic systems due to overvoltages
Possible loss
•Human life
•Service to the public
•Cultural heritage
•Economic values
PROTECTION MEASURES
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The new IEC 62305 provides protection for:
•structures and contents
•electrical and electronic systems within a structure
A wide range of protection measures can be used:
•in IEC 62305-3 LPS type I to IV, upgraded LPS by integrating natural components of structure, protection against touch and step voltages
•in IEC 62305-4 spatial shielding, line routing and shielding, bonding network, bonding at each LPZ entry, SPD system, special devices (transformers and filters, opto-electronic decouplers)
RISK MANAGEMENT
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• to ascertain the need of protection
• to select optimal combination of protection measures,
• to check the residual risk after the installation of protection measures and
• to check the economical convenience of protection measures in the case of loss of economical values
RISK DEFINITION AND EVALUATION
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IEC 62305-2
Measure of probable annual loss (humans and goods) due to lightning, relative to the total value (humans and goods) of the object to be protected.
R = N·P·L
time of observation t= 1 year
N : number of potentially dangerous flashes
P : probability of damage by single flash
L : mean amount of loss due to single flash, usually expressed in relative way to the total loss of the object to be protected
NUMBER OF DANGEROUS EVENTS
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Affected by:
•lightning ground flash density
•dimensions of the structure and the characteristics of surroundings
•characteristics of services connected to the structure
PROBABILITY OF DAMAGE AND AMOUNT OF LOSS
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Affected by:
•content of structure
•characteristics of installation within the structure
•characteristics of connected services
•protection measures provided
Protection measures tend to limit:
•the values of stresses due to lightning and then the probability of damage
•the consequences of damage due to lightning and then the amount of loss
RISK ANALYSIS
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Risk: Probable loss (humans and goods) in one year due to lightning
Need of protection when:
R > RT
Assessment of risk as sum of “risk components”
+ RZ
Each risk component
RX = NX PX LX
R = + RU + RV + RW+ RMRA+ RB + RC
RISK COMPONENTS FOR A STRUCTURE FOR DIFFERENT TYPES OF DAMAGE CAUSED BY DIFFERENT SOURCES
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Source of damage
Damage
S1Lightning flash to a structure
S2Lightning flash near a structure
S3Lightning flashto a incoming
service
S4Lightning flash near a service
Resulting riskaccording
to type of damage
D1
shock ofliving beings
RA
RU
RS= RA + RU
D2physical damage
RB
RV
RF = RB + RV
D3failure of electrical
and electronic systems
RC RM RW RZ RO=RC + RM + RW + RZ
Resulting risk according to the
source of damage
RD =
RA + RB + RC
RI = RM + RU + RV + RW +RZ
TOLERABLE VALUE OF RISK RT
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PROCEDURE FOR SELECTION OF PROTECTION MEASURES
SIMPLIFIED APPROACH FOR THE PROTECTION MEASURES SELECTION ACCORDING TO DOMINANT SOURCE OF DAMAGE
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GRAZIE PER L’ATTENZIONE
DZIĘKUJĘ ZA UWAGĘ