Faculty of Electrical Engineering, University of Ljubljana

Lightning Protection

Distribution and industrial networks Seminar work

coordinator: Prof. Dr. Grega Bizjak author:

Agnieszka Litwiniuk

Table of Contents 1 Introduction ............................................................................................................................. 3 2 How the lightning begins to form ........................................................................................... 3 3 Types of lightning ................................................................................................................... 4 4 Polish directives about lightning protection ............................................................................ 8 5 Lightning protection of buildings ............................................................................................ 9 6 Types of grounding ............................................................................................................... 11 7 Lightning protection of objects situated on the buildings roofs ............................................ 13 8 Protection of electric distribution systems ............................................................................ 15 9 Solar systems protection........................................................................................................ 16 10 Air-termination systems for wind turbines ......................................................................... 17 11 Air-termination system for steeples and churches .............................................................. 18 12 Overvoltages ........................................................................................................................ 19 List of schemes ......................................................................................................................... 23 Questions and answers ............................................................................................................. 24 Homework ................................................................................................................................ 25 References ................................................................................................................................ 26

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1 Introduction Lightning is one of the most beautiful displays in nature. It is also one of the most deadly natural phenomena known to man. Today, lightning protection systems are in use on thousands of buildings, homes, factories, towers, and even the Space Shuttle's launch pad. It is worth to ask what exactly the lightning is and how is the origin of lightning.

2 How the lightning begins to form Lightning is an electrical discharge in the atmosphere, very similar to a spark, and usually produced by a thunderstorm. Lightning is usually associated with cumulonimbus clouds (thunderclouds) [1]. It can occur within or between clouds or between cloud and ground or cloud and air. In an electrical storm, the storm clouds are charged like giant capacitors in the sky. Electricity has two opposing components: positive and negative charges. When there is a charge separation in a cloud, there is also an electric field that is associated with the separation. Like the cloud, this field is negative in the lower region and positive in the upper region. The electric field causes the surrounding air to become separated into positive ions and electrons -- the air is ionized. After the ionization process, some kind of path between the cloud and the earth begins to form [5].

Scheme 1. Induced charges on transmission line [2].

Lightning occurs when these separated electric charges in the atmosphere build up such force that they literally rip apart the normally neutral charges in the air itself. When the 3

first strike occurs, current flows in an attempt to neutralize the charge separation. After the original stroke occurs, it is usually followed by a series of secondary strikes. These strikes follow only the path of the main strike. Each cloud-to-ground lightning involves an energy of roughly 109-1010 Joules. Most of the lightning energy is spent to produce thunder, hot air, light, and radio waves, so that only a small fraction of the total energy is available at the strike point. However, it is well known that this small fraction of the total lightning energy is sufficient to kill people and animals, start fires, and cause considerable mechanical damage to various structures. Lightning is also a major source of electrical disturbances.

3 Types of lightning Some lightning strikes take on particular characteristics. There is possibility to distinguish various types of lightning. Lightning discharges may occur between areas of cloud having different potentials without contacting the ground. This lightning can sometimes be observed at great distances at night as so-called "heat lightning". In such cases, the observer may see only a flash of light without thunder.. This type of strikes is called as cloudto-cloud lightning [6].

Scheme 2. Multi paths cloud-to-cloud lightning [8].

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Another type - dry lightning is a term which is used to refer to lightning strikes occurring without significant rainfall. This type of lightning is the most common natural cause of wildfires. Such thunderstorms are most common in the western part of the United States during the summer. They occur when the rain produced by thunderstorms falls through a substantial layer of very dry air which evaporates the rainfall before it reaches the ground [9]. Rocket lightning is a form of cloud discharge, generally horizontal and at cloud base, with a luminous channel appearing to advance through the air with visually resolvable speed, often intermittently. It is also one of the rarest of cloud discharges [6].

Scheme 3. Rocket lightning [10].

Cloud-to-ground lightning is a great lightning discharge between a cumulonimbus cloud and the ground initiated by the downward-moving leader stroke. This is the second most common type of lightning, and poses the greatest threat to life and property of all known types [6].

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Scheme 4. Cloud-to-ground lightning [11].

Bead lightning is a type of cloud-to-ground lightning which appears to break up into a string of short, bright sections, which last longer than the usual discharge channel. It is fairly rare. One of theories is the observer sees portions of the lightning channel end on, and that these portions appear especially bright. Immediately after a return stroke (first or secondary) discharges down the lightning channel, it begins a splitting stage in which the luminosity of the channel steadily decreases in intensity. In the latter part of this splitting stage, the luminous channel will break up into glowing 'beads' before dissipating altogether [12].

Scheme 5. Bead Lightning step by step [13].

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Ribbon lightning occurs in thunderstorms with high crosswinds and multiple return strokes. The wind will blow each successive return stroke slightly to one side of the previous return stroke, causing a ribbon effect[3]. Another type of lightning is the ground-to-cloud lightning - discharge between the ground and a cumulonimbus cloud from an upward- moving leader stroke [6].

Scheme 6. Ground-to-cloud lightning[4] .

Ball lightning is described as a floating, illuminated ball that occurs during thunderstorms. They can be fast moving, slow moving or nearly stationary. Some of them make hissing or crackling noises or no noise at all. Some have been known to pass through windows and even dissipate with a bang. Ball lightning has been described by witnesses but rarely recorded by meteorologists [6].

Scheme 7. Ball lighting[15].

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4 Polish directives about lightning protection In Poland exist a lot of regulations and directives connecting with lightning protection. Name of directive PN-86/E-05003/01

Description Lightning protection of buildings and structures. General requirements.

PN-IEC 61024-1:2001

Lightning protection of buildings and structures. General requirements.

PN-IEC 61024-1-1:2001

Lightning protection of buildings and structures. General requirements. Levels of protection for lightning rods.

PN-IEC 61024-1-2:2001

Lightning protection of buildings and structures. General requirements. Design, mounting and maintenance of lightning rods.

PN-IEC 61312-1

Protection for electromagnetic pulse coming from lightning

PN-IEC 61643-1

Overvoltage protection devices in low voltage grid. Technical requirements and researching methods.

PN-IEC 60364-4-443

Wiring in buildings. Overload protection.

Buildings and structures where a lightning protection system must always be protected [22][23]: 1. Assembly places and rooms which can accommodate more than 100 visitors. 2. Schools, museums and similar buildings. 3. Sales areas whose sales rooms have more than 2000 m2 of floor space. 4. Shopping centers with several sales areas which are connected to each other either directly or via escape routes, and whose sales rooms individually have less than 2000 m 2 of floor space but having a total floor space of more than 2000 m2. 5. Exhibition spaces whose exhibition rooms individually or together have more than 2000m 2 of floor space. 8

6. Restaurants with seating for more than 400 customers, or hotels with more than 60 beds for guests. 7. Hospitals and other buildings and structures having a similar purpose. 8. Medium-sized and large-scale garages. 9. High-risk buildings like buildings and structures with explosive materials, such as ammunition, factories, gas stations, towers.

5 Lightning protection of buildings The purpose of a lightning protection system is to protect buildings from direct lightning strikes and possible fire, or from the consequences of the load-independent active lightning current (non-igniting flash of lightning). If national regulations for building regulations, special regulations or special directives require lightning protection measures, they must be installed. The basic international standard of lightning protection for buildings is IEC 60364-5-548:1996.

Scheme 8. Lightning rod (simple rod or with triggering system) [18].

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Roof-mounted structures such as air-conditioning and cooling systems are used on the roofs of larger office blocks and industrial structures. According to the state of the art for lightning protection, such roof-mounted structures are protected against direct lightning strikes by means of separately mounted air-termination systems. This prevents partial lightning currents from entering the structure, where they would affect or even destroy the sensitive electrical installations.

Scheme 9. Example of air-termination systems with protective angle α [19].

Scheme 10. Relationship between protective angle and height for different levels of protection.

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6 Types of grounding When is necessity to lead the lightning potential to ground we can use a few types of grounding. First, horizontal grounding is made by laying a rod about 0.6m under the ground. the length of horizontal grounding according the polish standard PN-IEC 61024-1-2:2001 should be at least 5m.

Scheme 11. Scheme of horizontal grounding[26].

Vertical grounding is second of grounding method protecting from lightning. The standard says that the length of electrode should reach at least 2.5 m under the ground and the electrode have to be 1 m far away from protecting building. The pattern of the connection is show in scheme 11.

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Scheme 12. Pattern of vertical grounding[26].

Scheme 13. Rim grounding equipped with additional vertical rods [26].

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According to recommendation of valid standards to make an analysis of any type of grounding we should calculate the replacement radius (r) of grounding surface and compare with the minimal length of grounding rod (lr) which is equal 5m [26]. If: 1. r ≥ lr - the grounding system in enough. 2. r < lr - the grounding system should be fill up by additional vertical or horizontal grounding. Each of additional rods should have following length: 1. horizontal rod – lh+ = lr –r 2. vertical rod - lv+ = (lr - r)/2. The number of additional rods should be equal of number of down-conductors. This number cannot be smaller than 2.

7 Lightning protection of objects situated on the buildings roofs A lightning protection system is designed to protect a structure from damage due to lightning strikes by intercepting such strikes and safely passing their extremely high currents to ground. A lightning protection system includes a network of air terminals, bonding conductors, and ground electrodes designed to provide a low impedance path to ground for potential strikes [16]. Below graph shows the shape of lightning current. The quick growth of value is especially dangerous and can cause plenty of damages.

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Scheme 14. Definitions of lightning current parameters [15].

In a lightning protection system, a lightning rod is a single component of the system. The lightning rod requires a connection to earth to perform its protective function. Lightning rods come in many different forms, including hollow, solid, pointed or rounded. The main attribute common to all lightning rods is that they are all made of conductive materials, such as copper and aluminum. Copper and its alloys are the most common materials used in lightning protection [16]. Special problems may occur when roof-mounted structures, which are often installed at a later date, protrude from zones of protection. If, in addition, these roof-mounted structures contain electrical or electronic equipment, such as roof-mounted fans, antennas, measuring systems or TV cameras, additional protective measures are required. If such equipment is connected directly to the external lightning protection system, then, in the event of a lightning strike, partial currents are conducted into the structure. This could result in the destruction of surge sensitive equipment. Direct lightning strikes to such structures protruding above the roof can be prevented by having isolated air-termination systems [19]. If conductive parts are located on the surface of the roof, they can be used as a natural air-termination system if there is no conductive connection into the structure.

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Scheme 15. Lightning protection made by protection rod [17].

8 Protection of electric distribution systems In any lightning discharge, the charge on the down coming leader causes the conductors of the line to have a charge induced in them.

Scheme 16. Induced charge on Line [2].

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These charges are bound (held in that portion of the line nearest to the cloud) so long as the cloud remains near without discharging its electricity by a lightning stroke to an object. If however, the cloud is suddenly discharged, as it is when lightning strikes some object nearby, the induced charges are no longer bound, but travel with nearly the velocity of light, along the line to equalize the potential at all points of the line. This bound charge collapse leads to a voltage wave to be generated on the line in each direction. The value of this is given by the follow equation [2]: 𝑒𝑖 =

𝑞 𝐶

q- bound charge per unit length of line C- capacitance per unit length of line. This potential will vary along the line depending upon the distance of each element of line from the lightning stroke.

9 Solar systems protection Grounding is the most fundamental technique for protection against lightning damage. Anybody cannot stop a lightning surge, but it is possible to give it a direct path to ground that bypasses valuable equipment, and safely discharges the surge into the earth. An electrical path to ground will constantly discharge static electricity that accumulates in an aboveground structure. Often, this prevents the attraction of lightning in the first place. Lightning rods are static discharge devices that are placed above buildings and solarelectric arrays, and connected to ground. They prevent the buildup of static charge and eventual ionization of the surrounding atmosphere. They can help prevent a strike, and can provide a path for very high current to ground if a strike does occur. Modern devices are spike-shaped, often with multiple points.

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Scheme 17. Lightning rod above small solar plant.

10 Air-termination systems for wind turbines Wind turbine blades usually should be equipped with the safe receptor, which is fully compliant with IEC 61400-24, the latest international standard for lightning protection in blades. The lightning sensor provide the highest level of lightning protection and maximum protection from all natural lightning strikes and ensure that these strikes do not wreak havoc with annual energy production. The safe receptors work on the principle of capturing lightning as opposed to avoiding strikes. Effective good lightning protection in blades can protect against the worst effects of lightning on both blades and indirectly on other wind turbine components like nacelle and towers. A lightning strike has the potential to cause serious damage to the blade adversely affecting blade life and annual energy production. Strikes can cause energy surges of 200 kA with a temperature of 30,000°C, causing an explosive expansion of air within a blade, which in turn can result in severe damage to the blade surface and cracks on edges [20].

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Scheme 18. Wind turbine with integrated lightning sensor [19].

11 Air-termination system for steeples and churches According to the German standard DIN EN 62305-3, Supplement 2 meet the normal requirements for churches and steeples. In particular individual cases, for example in the case of culturally significant structures, a special risk analysis in accordance with IEC 62305-2 (EN 62305-2) must be carried out. The nave must have its own lightning protection system and, if a steeple is attached, this system must be connected by the shortest route with a down-conductor system of the steeple. In the transept, the air-termination conductor along the transverse ridge must be equipped with a down-conductor system at each end. If the down-conductor system of the steeple coincides with a down-conductor system of the nave, then a common down-conductor system can be used at this location. According to the German standard DIN EN 62305-3, Supplement 2, steeples above 20 m in height must be provided with at least two down

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conductors. At least one of these down-conductors must be connected with the external lightning protection system of the nave via the shortest route [19].

Scheme 19. Installing the down-conductor system at a steeple [19].

12 Overvoltages A transient overvoltage is a voltage peak with a maximum duration less than one millisecond. There are two possible causes of overvoltages on electrical networks: • natural causes (lightning), • other causes due to equipment or switching devices. Natural overvoltages on low voltage networks are caused by direct lightning strikes. The high level of energy contained in a direct lightning strike on a lightning conductor or an overhead low voltage line leads to considerable damage of the installation. The overvoltage can be over 20 times the nominal voltage. Operating or switching overvoltages linked to a network's equipment create overvoltages of a lower level (3 to 5 times the nominal voltage) but occur much more frequently, thus causing premature ageing of the equipment [24].

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We can distinguish three categories of overvoltage propagate on low voltage networks: • direct lightning strikes, • indirect effects of lightning strikes, • operating or switching overvoltages. For first option two cases should be consider. When lightning strikes a lightning conductor on the roof of a building which is grounding, the lightning current is dissipated into the ground. The impedance of the ground and the current flowing through create large difference of potential: this is the overvoltage. This overvoltage propagates throughout the building via the cables, damaging equipment along the way. In another case, when lightning strikes an overhead low voltage line, the latter conducts high currents which penetrate into the building creating large overvoltages. The damage caused by this type of overvoltage is usually spectacular (e.g. fire in the electrical switchboard causing the destruction of buildings and industrial equipment) and results in explosions [24].

Scheme 20. Direct lightning strike on a lightning conductor or the roof of a building and direct lightning strike on an overhead line [24].

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Scheme 21. Damages causing by overvoltage.

The basic standard for electrical installation IEC/EN 60364 includes the definition of overvoltage categories. According to the installation impedances, proximity to the origin of the installation and installed protective elements, it classifies four overvoltage categories. For each declared category/voltage the maximum size of transient voltages to be excepted during the measurement on electrical installation is defined. All equipment must at least fulfill the protective measures for the category they are installed in. Basic standard for safety of measuring equipment IEC/EN 61010-1 also considers overvoltages. The minimum protective measures for measuring equipment for all overvoltage categories are defined [25]. Overvoltage categories according with IEC/EN 60364 standard: 

Class IV – a transient can spread through the low impedance wiring at the origin of the installation to the distribution boards with low losses. Connected loads are high, outside wiring is susceptible to lightning. Therefore the risk of occurrence of dangerous transient voltages and surges is very high.



Class III – elements (like fuses, switches, etc.) and branches in the distribution boards damp the amplitude and energy of the transient/surges from both sides. The wiring impedance between the utility and the distribution board helps to damp the transient too. Distribution boards, machinery main switching devices close to the switchgears, industrial installations and high currents circuits ale classified to Class III.

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Class II – the transients are further damped in the wiring inside the building. All circuits are fused wth circiut fuses. Outlets, lightning swithes and connections in buildings at a distance more than 10 m from a Class III source are classified as Class II.



ClassI – on the electrical equipment side end the lowest transients are to be excepted. Electronics on secondary side of supply transformers, electrical equipment with supply voltage separation and low voltage outputs are classified as ClassI.

Scheme 22. Class I to Class IV according to IEC/EN 60364 standard [19].

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List of schemes Scheme 1. Induced charges on transmission line ...................................................................... 3 Scheme 2. Multi paths cloud-to-cloud lightning ....................................................................... 4 Scheme 3. Rocket lightning ........................................................................................................ 5 Scheme 4. Cloud-to-ground lightning ........................................................................................ 6 Scheme 5. Bead Lightning step by step ...................................................................................... 6 Scheme 6. Ground-to-cloud lightning ........................................................................................ 7 Scheme 7. Ball lighting............................................................................................................... 7 Scheme 8. Lightning rod (simple rod or with triggering system)............................................... 9 Scheme 9. Example of air-termination systems with protective angle α .................................. 10 Scheme 10. Scheme of horizontal grounding ........................................................................... 11 Scheme 11. Pattern of vertical grounding ................................................................................ 12 Scheme 12. Rim grounding equipped with additional vertical rods ........................................ 12 Scheme 13. Definitions of lightning current parameters ......................................................... 14 Scheme 14. Lightning protection made by protection rod ....................................................... 15 Scheme 15. Induced charge on Line......................................................................................... 15 Scheme 16. Lightning rod above small solar plant .................................................................. 17 Scheme 17. Wind turbine with integrated lightning sensor ..................................................... 18 Scheme 18. Installing the down-conductor system at a steeple ............................................... 19 Scheme 19. Direct lightning strike on a lightning conductor or the roof of a building and direct lightning strike on an overhead line .............................................................................. 20 Scheme 20. Damages causing by overvoltage. ........................................................................ 21 Scheme 21. Class I to Class IV according to IEC/EN 60364 standar ..................................... 22 Scheme 22. Dimensions of rim grounding for the structure .................................................... 25

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Questions and answers Question 1: What the lightning is? Answer: Lightning is an electrical discharge in the atmosphere, very similar to a spark, and usually produced by a thunderstorm. Question 2: What are the most common types of the lightning? Answer: The most common and popular types of lightning are cloud-to-cloud lightning and cloud to ground lightning. Another types occur less often. Question 3: What is the main reason of the thunderstorm? Answer: Thunderstorms can occur inside warm, moist air masses and at fronts. As the warm, moist air moves upward, it cools, condenses, and forms cumulonimbus clouds. Question 4: How we can protect buildings from lightning? Answer: The most fundamental technique for protection against lightning is grounding. The most safety is bringing the high potential to earth. In this case are using the lightning rods and air-termination systems. Question 5: Why lightning current is so dangerous? Answer: Because in very short time the value of the current drastically increase. The quick growth of value is especially dangerous and can cause plenty of damages. Question 6: What method is using to protect the wind turbines against the lightning? Answer: Wind turbine blades usually are equipped with the safe receptor, with provide protection from all natural lightning strikes. Question 7: From what materials the lightning rods are built? Answer: They are made of conductive materials, such as copper and aluminum. Copper and its alloys are the most common materials used in lightning protection. Question 8: List three categories of overvoltage propagate on low voltage networks. Answer: We can distinguish direct lightning strikes, indirect effects of lightning strikes and operating or switching overvoltages. Question 9: How many overvoltage class according with IEC/EN 60364 standard we can distinguish? Answer: According with IEC/EN 60364 exist four overvoltage class. Question 10: What kind of devices belong to Class I? Answer: Electronics on secondary side of supply transformers, electrical equipment with supply voltage separation and low voltage outputs are classified as Class I. In other words all sensitive electronic devices.

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Homework The structure has rim grounding as in the picture. Check if the grounding system is realize the requirements. If not, find number and length of additional elements.

Scheme 23. Dimensions of rim grounding for the structure.

Solution: 1. Calculating the surface which the rim grounding surround: 𝐴 = 12 ∗ 5 + 7 ∗ 7 = 109 𝑚2 2. Calculating the replacement radius (r): 𝑟=

𝐴 = 𝜋

109 = 5.89 𝑚 3.14

3. Compare with the minimal length of grounding rod: 5.89𝑚 > 5𝑚 So, this rim grounding is according with standard and realize the requirements.

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References [1] http://britannica.com/EBchecked/topic/340767/lightning [2] http://elect.mrt.ac.lk/HV_Chap3.pdf [3] http://stormhighway.com/videoghost.php [4] http://tonylebastard.deviantart.com/art/Ground-to-cloud-lightning-335022139 [5] http://science.howstuffworks.com/nature/natural-disasters/lightning1.htm [6] Staszewski Ł.: Lightning Phenomenon – Introduction and Basic Information to Understand the Power of Nature. Wrocław, Poland. [7] http://stormhighway.com/protection.php [8] https://flickr.com/photos/tigersharky80/411572749/ [9] http://en.wikipedia.org/wiki/Dry_lightning [10] https://.flickr.com/photos/lusr/4827322934/ [11]http://environment.nationalgeographic.com/wallpaper/environment/photos/lightninggeneral/cloud-ground-lightning13/ [12] http://stormhighway.com/videoghost.php [13]http://forum.weatherzone.com.au/ubbthreads.php/topics/1026350/Re_BEAD_LIGHTNIN G_Discussion_P [14] http://en.wikipedia.org/wiki/Ball_lightning [15]https://www.bicsi.org/uploadedfiles/bicsi_conferences/fall/2012/presentations/CONCSES _4C.pdf [16] http://en.wikipedia.org/wiki/Lightning_rod [17] Sowa A.: Ochrona odgromowa anten na dachach obiektów budowlanych. Białystok 2011. [18] http://electrical-installation.org/enwiki/Building_protection_system [19] https://dehn-international.com. [20] http://lmwindpower.com/Rotor-Blades/Products/Features/Add-Ons/Lightning-Protection [21] http://solarinsure.com/protect-your-solar-power-system-from-lightning [22] PN-86/E-05003/01, Ochrona odgromowa obiektów budowlanych. Wymagania ogólne. [23] PN-IEC 61024-1:2001, Ochrona odgromowa obiektów budowlanych. Zasady ogólne. [24] http://library.abb.com [25] IEC/EN 60364, Electrical Installations for Buildings. [26] Sowa. A.: Uziomy w ochronie odgromowej. Białystok 2011.

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