LIGHTNING PHYSICS AND LIGHTNING PROTECTION: STATE OF ART 2013 Prof. Carlo Mazzetti di Pietralata 1st October 2013, Warsaw WARSAW UNIVERSITY OF TECHNOLOGY
TOPICS 1. Physics 2. Modern research method 3. Lightning parameters 4. Lightning damages 5. Principle of lightning protection: International normalization Page 2
DIFFERENT TYPES OF LIGHTNING CLOUD TO CLOUD LIGHTNING MIAMI CLOUD TO GROUND LIGHTNING - CN TOWER (CANADA) CLOUD TO GROUND LIGHTNING NEBRASKA Page 3
DIFFERENT TYPES OF LIGHTNING Lightning in volcano eruptions Island, May 2010 Page 4
MULTIPLE CHANNEL TERMINATIONS ON GROUND Page 5
THE THUNDERCLOUD Charge distribution in a thundercloud. RAI Page 6
TYPES OF LIGHTNING RAI Page 7
NEGATIVE CLOUD-TO-GROUND LIGHTNING FLASH REFERENCE SPEED=LIGHT SPEED RAI Page 8
WAVEFORMS LIGHTNING S CURRENT WAVEFORMS Positive flash Negative flash Berger et al., 1975 RAI Page 9
LEADER PROPAGATION MODELS Page 9
LEADER PROPAGATION MODELS Dellera and Garbagnati (1990) 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 Page 9
LIGHTNING DETECTION: HISTORY BERGER s Tower Measurements at Mont San Salvatore. Two instrumented towers: 1943-1972. 101 first strokes, 135 subsequent strokes. Page 10
LIGHTNING DETECTION: GAISBERG TOWER Page 11
LIGHTNING DETECTION: GAISBERG TOWER Page 12
LIGHTNING DETECTION: 2011 - SÄNTIS TOWER Page 13
DIFFERENT TYPES OF LIGHTNING Triggered-Lightning Testing Area - University of Florida Page 14
ROCKET-TRIGGERED LIGHTNING VS. NATURAL LIGHTNING Page 15
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. Page 16
LIGHTNING S LOCALISATION 1. Direction finding (DF) 2. Time of arrival (TOA) 3. Interferometry 4. Peak amplitude method 5. Field component methods Page 17
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 Page 18
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 sensors. This method has been successfully applied by, e.g., more Krider and Uman (1973) Winn et al. (1973), Rakov et al. (1994) Idone et al. (1998) to determine the lightning location by triangulation. Page 19
COMPONENTS OF LIGHTNING ELECTROMAGNETIC PULSE (LEMP) Page 20
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) Page 21
EUCLID NETWORK EUCLID (European Cooperation for Lightning Detection) is a consortium of 16 European national lightning detecting networks. Presently, the complete network consists of 138 sensors contributing to the detection of lightning. Page 22
EUCLID DATA ANALYSIS Flash density over Europe (ALDIS) Average amplitude over Europe (ALDIS) Page 23
SATELLITE BASED LIGHTNING LOCATION (OTD) Global frequency and distribution of lightning (NASA, from 4 years Optical Transient Detector observation) Page 24
LIGHTNING LIVE MAPS Mapa burzowa i pogodowa - Mariusz Waśkowiec http://www.blitzortung.org Lightning live maps are available for PC and mobile devices Page 25
LIGHTNING STRIKES TO TALL STRUCTURES Page 26
LIGHTNING STRIKES TO TALL STRUCTURES Page 26
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. Page 29
LIGHTNING EFFECTS AND DAMAGES Lightning damage to a house Exploded 110kV transformer, Neumarkt, 1983 (DER SPIEGEL: Blitz im Atommeiler - 1983) Page 30
LIGHTNING STRIKES TO AN AIRCRAFT DIRECT EFFECTS INDIRECT EFFECTS 1.Thermal Effects 2.Sparking 3.Mechanical Effects 4.Puncture 5.Disruptive Forces 6.Shockwaves 1.Hidden Failures 2.Soft Failures 3.Visible or invisible 4.Hard Failures Page 31
LIGHTNING STRIKES TO AN AIRCRAFT Page 32
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 Page 33
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) Page 34
LIGHTNING EFFECTS AND DAMAGES Page 36
LIGHTNING EFFECTS AND DAMAGES Page 36
LIGHTNING EFFECTS AND DAMAGES Page 36
TRIGGERED-LIGHTNING TO STUDY THE EFFECTS ON GROUNDED STRUCTURES AND POWER SYSTEMS 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. 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 Page 35
CRITERIA OF PROTECTION Lightning data Effects: damages and loss Protection Measures effect s electrodynamic effects thermal effects effects on the human body PHYSICAL DAMAGES mechanical damages touch and step voltages fire dangerous sparking Lightning effect s electromagnetic effects (LEMP) overvoltages and overcurrents overvoltages electromagnetic interference A fire equipments failure B equipments malfunctioning C Page 37
APPLICATION TO THE CIGRE DISTRIBUTION Page 40
PARAMETERS OF LIGHTNING CURRENT 90 % ±i 50 % I 10 % O1 T1 t T2 IEC 2616/10 ±i QLONG 10 % 10 % t TLONG IEC 2617/10 Page 41
VALUES OF LIGHTNING PARAMETERS Page 42
LIGHTNING CURRENT PARAMETERS (CIGRE) Page 45
AMPLITUDE DENSITY OF THE LIGHTNING CURRENT Relevant frequency range for LEMP effects 3 10 First negative stroke 100 ka 1/200 µs 2 10 Amplitude density (A/Hz) 1 10 0 10 Subsequent negative stroke 50 ka 0,25/100 µs 1 1 f 10 2 10 1 2 3 10 f First positive stroke 200 ka 10/350 µs 4 10 5 10 1 10 2 10 3 10 4 5 10 10 6 10 7 10 Frequency f (Hz) IEC 2627/10 Page 46
LIGHTNING INFLUENCES SOURCES OF DAMAGE Flash striking the structure Flash striking near the structure Flash striking the service Flash striking near the service Page 47
DAMAGES AND LOSS 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 Page 48
PROTECTION MEASURES 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, optoelectronic decouplers) Page 49
RISK MANAGEMENT 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 Page 50
RISK DEFINITION AND EVALUATION 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 Page 51
NUMBER OF DANGEROUS EVENTS Affected by: lightning ground flash density dimensions of the structure and the characteristics of surroundings characteristics of services connected to the structure Page 52
PROBABILITY OF DAMAGE AND AMOUNT OF LOSS 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 Page 53
RISK ANALYSIS 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 R= RA+ RB + RC + RM + RU + RV + RW + RZ Each risk component RX = NX PX LX Page 54
RISK COMPONENTS FOR A STRUCTURE FOR DIFFERENT TYPES OF DAMAGE CAUSED BY DIFFERENT SOURCES Source of S1 damage Lightning flash Damage D1 shock of living beings to a structure S2 S3 S4 Lightning flash near a structure Lightning flash to a incoming service Lightning flash near a service RA RU Resulting risk according to type of damage R S= R A + R U D2 physical damage RB RV RF = R B + R V D3 failure of electrical and electronic systems RC Resulting risk according to the source of damage RD = RA + RB + RC RM RW RZ RO=RC + RM + RW + RZ RI = RM + RU + RV + RW +RZ Page 55
TOLERABLE VALUE OF RISK RT Page 56
PROCEDURE FOR SELECTION OF PROTECTION MEASURES Page 57
SIMPLIFIED APPROACH FOR THE PROTECTION MEASURES SELECTION ACCORDING TO DOMINANT SOURCE OF DAMAGE Page 58
GRAZIE PER L ATTENZIONE DZIĘKUJĘ ZA UWAGĘ