Lightning Protection System Design and Installation ...

1 Hong Kong Polytechnic UniversityggyyDepartment of Building Services EngineeringLightning Protection System Design and Installation Reviewand Installation ReviewOrganised by Prof YP DuDr Tony Sung BSc(Hon) MSc PhD FIET FCIBSE MIEE SenMIEEEAdjt P fAdjunct ProfessorChairman of CIBSE Electrical Services 2012 Slide no: 1 Adjunct Prof Tony SungOutline of LectureOutline of Lecture Fundamental of Lightning PhenomenaPhenomena Standards and Design Guides Important Terms Quantifying Risks Quantifying Risks Control Measures Th R l W ld The Real World ConclusionDec 2012 Slide no: 2 Adjunct Prof Tony SungTheory of LightningTheory of Lightning (ref: Furse Guide to BS EN 62305)Dec 2012 Slide no: 3 Adjunct Prof Tony SungSeparation of ChargesSeparation of ChargesHow charges build up in the cloud is not well understood but the separation of charges in thethe separation of charges in the cloud is the source of the build up and separation continues until the voltage difference between the cloud and the ground exceeds the air ginsulation strength, it resulted in a Lightning discharge as the air resistance is overcomeresistance is overcome.

2 (we can visualise it by analogy with HV overhead lines)Dec 2012 Slide no: 4 Adjunct Prof Tony Sung) Lightning DischargeLightning DischargeDec 2012 Slide no: 5 Adjunct Prof Tony SungLightning DischargeLightning DischargeDec 2012 Slide no: 6 Adjunct Prof Tony SungLightning DischargeLightning DischargeDec 2012 Slide no: 7 Adjunct Prof Tony SungStd d Li ht iStandards Lightning Protection SystemsProtection SystemsIEC EN 62305:2006 (due to be revised in 2013)BS EN 62305:2006 (due to be revised in 2013)() Lightning Protection Standard (NFPA 780)IEEE Guide for Residential Lightning ProtectionggCIBSE Guide K (updated by CIBSE Electrical Services Group)p)Dec 2012 Slide no: 8 Adjunct Prof Tony SungBS EN 62305:2006 Lightning Protection SystemsDec 2012 Slide no: 9 Adjunct Prof Tony SungTypes of DamageTypes of DamageDec 2012 Slide no: 10 Adjunct Prof Tony SungIssues to be considered Rise of Earth Potential.

3 Soil has significant resistance, so Lightning strokes can cause large potential differences betweenlightning strokes can cause large potential differences between areas nominally at the same 'earth' potential. [8] shows that the 'traditional' practices (which are not recommended in this series) of star earthing and bonding cable screens at only one end makes this sort of damage more likely. Magnetic inductionVery high surge voltages can be induced Magnetic induction. Very high surge voltages can be induced into any conductors by magnetic coupling from Lightning strikes up to 100 metres away.

4 Surge Current injection. Direct strikes to external equipment or cables often results in damage to the internal equipment they are connected to and can damage unrelated equipment due to sideconnected to, and can damage unrelated equipment due to side-flashes in shared cable routes or terminal cabinets. Dec 2012 Slide no: 11 Adjunct Prof Tony SungIssues to be considered electric induction. electric fields of up to 500kV/m can occur pbefore a Lightning strike , over an area of up to 100m from the eventual strike point. These can induce damaging currents into conductors and devicesconductors and devices.

5 Lightning Electromagnetic Pulse (LEMP). This 'far-field' effect can be caused by cloud-to-cloud Lightning as well as by distant yggycloud-to-ground strokes. Thermal and mechanical effectsdue to the intense energies i t d ith li ht iM tlff ttt' f b idassociated with Lightning . Mostly affects a structure's fabric and its Lightning conductors. Fire is one of the deadly results. Multiplicity and duration of strokes in a single strikeThis isMultiplicity and duration of strokes in a single strike . This is important for error-correction and System software recovery. Dec 2012 Slide no: 12 Adjunct Prof Tony SungLightning StrokesLightning Strokes At i lli ht iLightning Stroke Shape A typical Lightning 'stroke' can last for over one secondggpover one second and consist of many 'strokes' (discharges)(discharges), sometimes over ten, each with an'arc-each with an arcchannel' current of between 2kA and 200kA (1% of200kA (1% of strokes exceed 200kA).)

6 Dec 2012 Slide no: 13 Adjunct Prof Tony Sung200kA). Another standard waveform is 20/80 s normally consideredafter zone Protection System (LPS) designComprising: A risk assessment based on actual Lightning exposure Design of the air termination network and down-conductors Di fththt itit k d th Design of the earth termination network and earth electrodes Bonding of the metalwork within a structure and of the Bonding of the metalwork within a structure, and of the metallic services entering a structure, to the LPS It helps reduce the risk of FIRE and EXPLOSION It helps reduce the risk of FIRE and EXPLOSIONDec 2012 Slide no.

7 14 Adjunct Prof Tony SungLightning RisksLightning RisksRi kt i bdli ht it ik dit Risk assessment is based on Lightning strike density maps called isokeraunic (or isoceraunic)maps, plus: The structure's'effective collection area'forThe structure s effective collection area for Lightning strikes. Its use. Its type of construction. Its contents. The consequential effects of any damage. The degree of its isolation from other structures. The type of terrain. Dec 2012 Slide no: 15 Adjunct Prof Tony SungHong Kong isokeraunic mapggpDec 2012 Slide no: 16 Adjunct Prof Tony Sungsource: HK ObservatoryComponents of an LPSC omponents of an LPS (ref: Dehn (UK))Dec 2012 Slide no: 17 Adjunct Prof Tony SungExternal and Internal Parts of a LPS '( f D h (UK))External part of a LPS(ref: Dehn (UK))A typical level 3 or 4 LPSI nternal part of a LPSDec 2012 Slide no: 18 Adjunct Prof Tony SungA typical level 3 or 4 LPSI nternal part of a LPSAir Termination SystemsAir Termination SystemsDec 2012 Slide no.

8 19 Adjunct Prof Tony SungRolling Sphere methodDec 2012 Slide no: 20 Adjunct Prof Tony SungDown ConductorsMinimum number of down conductors to beMinimum number of down conductors to be based on typical separation 2012 Slide no: 21 Adjunct Prof Tony SungRolling Sphere methodRolling Sphere methodDec 2012 Slide no: 22 Adjunct Prof Tony SungProtection Level andLevel and ProbabilitiesDec 2012 Slide no: 23 Adjunct Prof Tony SungProbabilities of a Lightning strike (Risk of Lightning )Dec 2012 Slide no: 24 Adjunct Prof Tony SungProtection angleDec 2012 Slide no: 25 Adjunct Prof Tony SungRise of Earth Potential StV lt-Step VoltageDec 2012 Slide no: 26 Adjunct Prof Tony SungExternal and Internal Parts of a LPS '( f D h (UK))External part of a LPS(ref: Dehn (UK))A typical level 3 or 4 LPSI nternal part of a LPSDec 2012 Slide no: 27 Adjunct Prof Tony SungA typical level 3 or 4 LPSI nternal part of a LPSD amage, g,Loss and RiskDec 2012 Slide no: 28 Adjunct Prof Tony SungSource,Source, Damage and LossDec 2012 Slide no: 29 Adjunct Prof Tony SungLightning Protection ZonesLightning Protection ZonesDec 2012 Slide no.

9 30 Adjunct Prof Tony SungLightning Electromagnetic ProtectionDec 2012 Slide no: 31 Adjunct Prof Tony SungAiAssessing RisksRisks(LPS Design is by riskby risk assessments)Dec 2012 Slide no: 32 Adjunct Prof Tony SungRiskRiskCalcusing RiskRisk Com-ponentsDec 2012 Slide no: 33 Adjunct Prof Tony SungFactors of RiskRisk ComponentsDec 2012 Slide no: 34 Adjunct Prof Tony SungRisk ComponentsRisk ComponentsDec 2012 Slide no: 35 Adjunct Prof Tony SungIdentificationIdentification of Tolerable Ri kRRisk RTDec 2012 Slide no: 36 Adjunct Prof Tony SungBS7671 Lightning Protection Requirements BS7671 does not prescribe rules for Protection against Lightningprotection against Lightning -Exclusion BS7671 refers Designers and BS7671 refers Designers and Installers to use BS EN 62305 to Design and install LPS to protectdesign and install LPS to protect buildingsDec 2012 Slide no.

10 37 Adjunct Prof Tony SungBS7671 Surge Protection Requirements Section 443 Protection against Overvoltages of atmospheric Origin or due to switching within the installationinstallation Table gives the required minimum impulse withstand voltage of apparatus within an installationwithstand voltage of apparatus within an installationDec 2012 Slide no: 38 Adjunct Prof Tony SungExamples of Various Impulse Category EquipmentDec 2012 Slide no: 39 Adjunct Prof Tony SungEstimation of Lightning 2flash density in flashes /km2 Dec 2012 Slide no: 40 Adjunct Prof Tony SungSPD Selection DesignProceduresSPD Selection Design ProceduresRemember Kirchhoff s Current Law?