Lightning Protection Systems in Buildings
- 1. LIGHTNING PROTECTION SYSTEMS IN BUILDINGS Eng. D M W A Dassanayake C.Eng, MIE(SL) BSc. Eng.(Hons) University of Ruhuna CONDUCTED BY PART 01
- 2. What is Lightning? Lightning is a natural electrical discharge that occurs within a thunderstorm. It happens due to the buildup of electrical charges within the storm clouds and between the clouds and the ground. Typical Cloud to Ground Lightning between ground and negative charges Inter-cloud Strike (cloud to cloud) Discharge within cloud between negative base and positive top (intra-cloud) Typical Cloud to Ground Lightning between ground and negative charges
- 3. How Lightning Occurs? Charge Separation: Inside a thunderstorm, water droplets, ice crystals, and other particles collide and interact, causing the different materials to gain or lose electrons. This results in the separation of positive and negative charges within the cloud. Electric Fields: As the charges separate, an electric field forms between the positively and negatively charged regions within the cloud. This electric field intensifies as more charge separation occurs. Breakdown and Ionization: When the electric field becomes strong enough, it can ionize the air molecules along its path. This means that it strips electrons from some of the atoms, creating a conductive path through the air.
- 5. Lightning Discharge: Once the ionized path, known as a stepped leader, extends from the cloud toward the ground, it creates a channel of ionized air. Simultaneously, a positively charged region on the ground, called a streamer, reaches upward. When these two paths meet, a highly conductive channel is established, and a lightning bolt travels along this channel. This current flow is termed the return stroke and may carry currents as high as 200 kA, although the average current is about 20 kA. Lightning Bolt: The actual lightning bolt consists of a rapid series of electrical discharges that travel along the ionized path, creating a visible flash of light and releasing a tremendous amount of energy. The movement of the electrons generates intense heat and causes the air to expand rapidly, creating the characteristic thunderclap. How Lightning Occurs? (Cont.)
- 6. Return Stroke: The primary, initial discharge of the lightning bolt is called the "return stroke." It travels from the ground to the cloud and is what we see as a lightning flash. This return stroke happens extremely quickly, typically in a fraction of a second. Aftereffects: After the initial return stroke, subsequent strokes can follow the same path, creating a flickering effect that we perceive as lightning. The process can repeat multiple times along the same channel, creating a jagged appearance. How Lightning Occurs? (Cont.)
- 7. Necessity of a Lightning Protection System The purpose of a lightning protection system is to protect all living beings, buildings and structures from lightning strikes and possible fire, or from the consequences of the load independent active lightning current.
- 8. • The science of lightning protection is best attributed to Benjamin Franklin. • The first mention of the traditional lightning rod was published by Benjamin Franklin in 1750 in Gentleman’s Magazine and then later in his treatises on the subject published in 1751. • In this he recommends the use of lightning rods to “Secure houses, etc, from lightning” Introduction to Protection Methods and Risks
- 9. Damage Damage to structure •Including all incoming electrical overhead and buried lines connected to the structure Damage to a service Service in this instance being part of telecommunication, data, power, water, gas and fuel distribution networks. Damages: • Sources of damage (S) • Types of damage (D) Damage due to Lightning
- 10. Sources of Damage S1 – Lightning flash to the structure S2 – Lightning flash near the structure S3 – Lightning flash to the services S4 – Lightning flash near to the services
- 11. Types of Loss L1 – Loss of human life. L2 – Loss of essential service to the public. L3 – Loss of cultural heritage. L4 – Economic loss (structure and its contents, service and loss of activity).
- 12. Types of Damage D1 – Injury of living beings (humans and animals) due to touch and step potential. D2 – Physical damage (fire, explosion, mechanical destruction, chemical release). D3 – Failure of internal electrical/electronic systems due to lightning electromagnetic impulse.
- 13. The relationship between source of damage, type of damage and loss Point of Strike Source of damage Type of Damage Type of Loss Structure S1 D1 D2 D3 L1,L4a,L1 L2,L3,L4 L1b,L2,L4 Near a structure S2 D3 L1b,L2,l4 Line connected to the structure S3 D1 D2 D3 L1,L4a,L1 L2,L3,L4 L1b,L2,L4 Near a Line S4 D3 L1b,L2,l4
- 14. Types of Risks Associated with Losses Risk R: is the value of probable average annual loss (humans or goods) due to lightning, relative to the total value (humans or goods) of the structure to be protected.
- 15. Requirements for lightning protection • The need for the lightning protection of a structure to be protected in order to reduce the loss of social values L1, L2 and L3 shall be evaluated. • In order to evaluate whether or not lightning protection of a structure is needed, a risk assessment in accordance with the procedures contained in IEC 62305 shall be made. The following risks shall be taken into account, corresponding to the types of loss. • R1: risk of loss or permanent injury of human life • R2: risk of loss of services to the public • R3: risk of loss of cultural heritage • Protection against lightning is needed if the risk R (R1 to R3) is higher than the tolerable level RT R > RT • Risk R4: risk of loss of economic values, should be assessed whenever the economic justification of lightning protection is considered
- 16. International Standard The IEC 62305 standard covers the regulations required for the protection of equipment and structures from the effects of both direct and indirect lightning strikes Protection against lightning IEC 62305 Part 1 General principles Part 2 Risk management Part 3 Physical damage to structures and the hazard Part 4 Electrical and electronic systems within structures
- 17. Connection between the parts of IEC 62305 SPM - System Protection Measures LPS - Lightning Protection System
- 18. Protection measures • Protection is achieved by the lightning protection system (LPS) which includes the following features: • Air-termination system • Down-conductor system • Earth-termination system • Lightning equipotential bonding (EB) • Electrical insulation (and hence separation distance) against the external LPS • Possible System protection measures (SPM) to reduce failure of electrical and electronic systems include • Earthing and bonding measures • Magnetic shielding • Line routing • Isolating interfaces • Coordinated SPD system • These measures may be used alone or in combination.
- 19. Protection measures selection • Selection of the most suitable protection measures shall be made by the designer of the protection measures and the owner of the structure to be protected according to the type and the amount of each kind of damage, the technical and economic aspects of the different protection measures and the results of risk assessment. • The criteria for risk assessment and for selection of the most suitable protection measures are given in IEC 62305-2. • Protection measures, adopted to reduce damages and relevant consequential loss, shall be designed for the defined set of lightning current parameters against which protection is required (lightning protection level)
- 20. Lightning protection levels (LPL) • For the purposes of IEC 62305, four lightning protection levels (I to IV) are introduced. • For each LPL, a set of maximum and minimum lightning current parameters is fixed
- 21. Maximum values of lightning parameters according to LPL
- 22. Lightning protection zones (LPZ) • Lightning protection zone LPZ are used to define the lightning electromagnetic environment. The zone boundaries of an LPZ are not necessarily physical boundaries (e.g. walls, floor and ceiling). The zones are areas characterized according to threat of direct or indirect lightning flashes and full or partial electromagnetic field. Protection measures such as LPS, shielding wires, magnetic shields and SPD determine lightning protection zones (LPZ).
- 23. Lightning protection zones (LPZ)
- 24. Lightning protection zones (LPZ) With respect to the threat of lightning, the following LPZs are defined • LPZ 0A zone where the threat is due to the direct lightning flash and the full lightning electromagnetic field. The internal systems may be subjected to full or partial lightning surge current; • LPZ 0B zone protected against direct lightning flashes but where the threat is the full lightning electromagnetic field. The internal systems may be subjected to partial lightning surge currents; • LPZ 1 zone where the surge current is limited by current sharing and by isolating interfaces and/or SPDs at the boundary. Spatial shielding may attenuate the lightning electromagnetic field; • LPZ 2, ..., n zone where the surge current may be further limited by current sharing and by isolating interfaces and/or additional SPDs at the boundary. Additional spatial shielding may be used to further attenuate the lightning electromagnetic field.
- 25. Protection of structures The structure to be protected shall be inside an LPZ 0B or higher. This is achieved by means of a lightning protection system (LPS). An LPS consists of both external and internal lightning protection systems. The functions of the external LPS are • Air termination system - to intercept a lightning flash to the structure • Down conductor system - to conduct the lightning current safely to earth • Earth termination system - to disperse it into the earth
- 26. External LPS Design Considerations Air Termination Network Down Conductors Earth Termination
- 27. Air Termination System The three basic methods recommended for determining the position of the air termination systems: 1. The rolling sphere method 2. The protective angle method 3. The mesh method
- 28. Rolling Sphere Method • The Rolling Sphere method is a simple means of identifying areas that need protection, taking into account the possibility of side strikes to the structures. • Different radii of the rolling sphere correspond to relevant class of LPS.
- 29. Rolling Sphere Method • The distance of the last step is striking distance and determine by the amplitude of the lightning current. • This striking distance can be represent by a sphere with a radius equal to the striking distance. (Cont.)
- 30. Application of Rolling Sphere Method • It can be clearly seen that the corners are exposed to a quarter of the circular path of the sphere. • This means that if the last step falls within this part of the circular path it will terminate on the corner of the building. • Corners of structures are vulnerable to lightning strikes.
- 31. Protective angle method • Protective angle method is a mathematical simplification of rolling sphere method. • Only for simple shaped buildings.
- 32. Protective angle method • Protective angle – Angle created between the tip (A) of the vertical rod and a line projected down to the surface on which the rod sits.
- 33. Determination of Protective Angle
- 34. Determination of Protective Angle
- 35. Application of Protection using Angle Method
- 36. Application of Protection using Angle Method
- 37. Application of Protection using Angle Method (Catenary or suspended conductors)
- 38. Mesh Method • A “meshed” air-termination system can be used universally regardless of the height of the structure and shape of the roof. • This method is suitable where plain surfaces require protection if the following conditions are met: • Air termination conductors must be positioned at roof edges, on roof overhangs and on the ridges of roofs with a pitch in excess of 1 in 10 (5.7º) • No metal installation protrudes above the air termination system
- 39. Mesh Method • Different sizes of the mesh correspond to relevant class of LPS.
- 40. Air Termination System (Summary) • Air rods (or finials) • Free standing masts or linked with conductors to form a mesh on the roof. • Catenary (or suspended) conductors, • Supported by free standing masts or linked with conductors to form a mesh on the roof. • Meshed conductor network • Lie in direct contact with the roof or be suspended above it (in the event that it is of paramount importance that the roof is not exposed to a direct lightning discharge). Example for air rods (Finials) Example for Catenary air termination Example for mesh air termination
- 41. Types of External LPS Non isolated Isolated Air terminations Meshed conductors Only practical for specific circumstances Catenary Wires S- Separation distance requirement
- 42. LPS Design Values (Summary)
- 43. Positioning of Air Termination Systems
- 44. Down Conductor System • The lightning current is shared between the down conductors • The greater the number of down conductors, the lesser the current that flows down each • Typical values of the distance between down conductors
- 45. Down Conductor Installation • The down-conductors shall be installed so that, as far as practicable, they form a direct continuation of the air-termination conductors. • Test links use to separate down conductors from earth termination • Down-conductors shall be installed straight and vertical such that they provide the shortest and most direct path to earth. The formation of loops shall be avoided, but where this is not possible, the distance s, measured across the gap between two points on the conductor and the length, l, of the conductor between those points shall comply Electrical insulation between the air-termination or the down-conductor and the structural metal parts
- 46. Down Conductor Installation • It is encouraged to use of fortuitous metal parts on or within the structure, to be incorporated into the LPS • If the reinforcing bars are connected for equipotential bonding or EMC purposes then wire lashing is deemed to be suitable. • Internal reinforcing bars are required to be connected to external down conductors or earthing network • If the reinforcing bars (or structural steel frames) are to be used as down conductors then electrical continuity should be ascertained from the air termination system to the earthing system. (Cont.)
- 47. Recommended Materials For Air Termination Conductors, Down Conductors Material Configuration Cross - sectional area mm² Copper ,Tin plated copper Solid tape 50 Solid roundb 50 Strandedb 50 Solid round 176 Aluminium Solid tape 70 Solid round 50 Stranded 50 Aluminium alloy Solid tape 50 Solid round 50 Stranded 50 Solid round 176 Copper coated aluminium alloy Solid round 50 Hot dipped galvanized steel Solid tape 50 Solid round 50 Stranded 50 Solid round 176 Copper coated steel Solid round 50 Solid tape 50 Stainless steel Solid taped 50 Solid round 50 Stranded 70 Solid round 176
- 48. Earth Termination System • Effective Earthing System • Providing a low impedance network to dissipate the fast-rising lightning impulse • Minimization of touch and step potential hazards • Below 10 ohms • Three basic earth electrode arrangements are used. • Type A arrangement • Type B arrangement • Foundation earth
- 49. Type A arrangement • Horizontal or vertical earth electrodes, connected to each down conductor fixed on the outside of the structure. • Each down conductor has an earth electrode (rod) connected to it.
- 50. Type B arrangement • Fully connected ring earth electrode that is sited around the periphery of the structure.
- 51. Foundation earth • Comprises conductors that are installed in the concrete foundation of the structure
- 52. Earthing Connection • The connection of the earthing conductor to the earth electrode must be suitably protected from corrosion by applying grease or paint. • Material of earth electrode need to be good corrosion resistance.
- 53. Internal LPS • The function of the internal LPS is to prevent dangerous sparking within the structure, using Equipotential Bonding or a separation distance, s, (and hence electrical isolation) between the LPS components and other electrically conducting elements internal to the structure.
- 54. Recommended Materials For Earth Termination Material Configuration Dimensions Earth rod diameter mm Earth conductor mm 2 Earth plate mm Copper/Tin plated copper Stranded 50 Solid round 15 50 Solid tape 50 Pipe 20 Solid plate 500 X 500 Lattice plate 600 X 600 Hot dipped galvanized steel Solid round 14 78 Pipe 25 Solid tape 90 Solid plate 500 X 500 Lattice plate 600 X 600 Profile d Bare steel Stranded 70 Solid round 78 Solid tape 75 Copper coated steel Solid round 14 50 Solid tape 90 Stainless steel Solid round 15 78 Solid tape 100
- 55. Lightning Protection System Components Air Finial with Base Copper Mesh (2.5mm x 25mm) Test Joint Square Clamp DC Clamp / Saddle Earth rod Earth plate
- 56. Substation Lightning Protection • Lightning protection should be carried for open terminal substations to prevent the followings: • Damage to Substation Equipment • Loss of Power to Public • Equipment in a substation may be exposed to lightning in two ways. • By voltage and current waves travelling along the exposed lines leading to the station. • By direct lightning strokes to the station. • Outdoor substations and switchyards are shielded against direct lightning strokes by: • Earth Wires (Shield Wires) • Masts • Earth wires and Masts
- 58. Next Lecture : Lightning Protection Systems – Part 02 Thank you Stay Safe From Lightning!