LIGHTNING PHYSICS AND LIGHTNING PROTECTION:...

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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

01/10/2013LIGHTNING PHYSICS AND LIGHTNING PROTECTION – STATE OF ART 2013

DIFFERENT TYPES OF LIGHTNING

CLOUD TO CLOUD LIGHTNING – MIAMI

CLOUD TO GROUND LIGHTNING – NEBRASKA

CLOUD TO GROUND LIGHTNING - CN TOWER (CANADA)

Lightning in volcano eruptions – Island, May 2010

MULTIPLE CHANNEL TERMINATIONS ON GROUND

THE THUNDERCLOUD

Charge distribution in a thundercloud.

TYPES OF LIGHTNING

NEGATIVE CLOUD-TO-GROUND LIGHTNING FLASH

REFERENCE SPEED=LIGHT SPEED © RAI

LIGHTNING’S CURRENT WAVEFORMS

Positive flash

Negative flash

Berger et al., 1975

LEADER PROPAGATION MODELS

• 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)

BERGER’s Tower Measurements at Mont San Salvatore. Two instrumented towers: 1943-1972. 101 first strokes, 135 subsequent strokes.

LIGHTNING DETECTION: HISTORY

LIGHTNING DETECTION: GAISBERG TOWER

LIGHTNING DETECTION: 2011 - SÄNTIS TOWER

Triggered-Lightning Testing Area - University of Florida

ROCKET-TRIGGERED LIGHTNING VS. NATURAL LIGHTNING

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.

LIGHTNING’S LOCALISATION

1. Direction finding (DF)

2. Time of arrival (TOA)

3. Interferometry

4. Peak amplitude method

5. Field component methods

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

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.

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)

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.

EUCLID DATA ANALYSIS

Flash density over Europe (ALDIS)

Average amplitude over Europe (ALDIS)

SATELLITE BASED LIGHTNING LOCATION (OTD)

Global frequency and distribution of lightning (NASA, from 4 years Optical Transient Detector observation)

LIGHTNING LIVE MAPS

Lightning live maps are available for PC and mobile devices

http://www.blitzortung.org

Mapa burzowa i pogodowa - Mariusz Waśkowiec

LIGHTNING STRIKES TO TALL STRUCTURES

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.

LIGHTNING EFFECTS AND DAMAGES

Lightning damage to a house Exploded 110kV transformer, Neumarkt, 1983 (DER SPIEGEL: ‘Blitz im Atommeiler’ - 1983)

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

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

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)

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.

• 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

effects

Lightning

• Lightning data• Effects: damages and loss• Protection Measures

effects

CRITERIA OF PROTECTION

APPLICATION TO THE CIGRE DISTRIBUTION

PARAMETERS OF LIGHTNING CURRENT

10 % 10 %

IEC 2617/10

50 % I

IEC 2616/10

VALUES OF LIGHTNING PARAMETERS

LIGHTNING CURRENT PARAMETERS (CIGRE)

AMPLITUDE DENSITY OF THE LIGHTNING CURRENT

10–1

10–2

10–3

10–4

10–5

101 10

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

IEC 2627/10

LIGHTNING INFLUENCES SOURCES OF DAMAGE

Flash striking the structure

Flash striking near the structure

Flash striking the service

Flash striking near the service

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

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, opto-electronic decouplers)

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

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

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

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

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”

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

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

shock ofliving beings

RS= RA + RU

D2physical damage

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

RA + RB + RC

RI = RM + RU + RV + RW +RZ

TOLERABLE VALUE OF RISK RT

PROCEDURE FOR SELECTION OF PROTECTION MEASURES

SIMPLIFIED APPROACH FOR THE PROTECTION MEASURES SELECTION ACCORDING TO DOMINANT SOURCE OF DAMAGE

GRAZIE PER L’ATTENZIONE

DZIĘKUJĘ ZA UWAGĘ

LIGHTNING PHYSICS AND LIGHTNING PROTECTION:...

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