Lightning Protection System Design and Installation ... · Lightning Protection System (LPS) design...

Hong Kong Polytechnic Universityg g y yDepartment of Building Services Engineering

Lightning Protection System Design and Installation Reviewand Installation Review

Organised by Prof YP Du

Dr Tony Sung BSc(Hon) MSc PhD FIET FCIBSE MIEE SenMIEEEAdj t P fAdjunct Professor

Chairman of CIBSE Electrical Services Grouphttp://www.cibse-electricalservicesgroup.co.uk

Dec 2012 Slide no: 1Adjunct Prof Tony Sung

Outline of LectureOutline of Lecture

Fundamental of Lightning PhenomenaPhenomenaStandards and Design GuidesImportant TermsQuantifying RisksQuantifying RisksControl MeasuresTh R l W ldThe Real WorldConclusion


Theory of LightningTheory of Lightning (ref: Furse Guide to BS EN 62305)


Separation of ChargesSeparation of Charges

How 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 lightning.

As 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.

(we can visualise it by analogy with HV overhead lines)


)

Lightning DischargeLightning Discharge






St d d Li ht iStandards Lightning Protection SystemsProtection Systems

IEC 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 Protectiong gCIBSE Guide K (updated by CIBSE Electrical Services Group)p)


BS EN 62305:2006 Lightning Protection Systems


Types of DamageTypes of Damage


Issues to be considered• Rise of Earth Potential. 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 induction Very 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.

• 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.


Issues to be considered• Electric induction. Electric fields of up to 500kV/m can occur p

before 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.

• Lightning Electromagnetic Pulse (LEMP). This 'far-field' effect can be caused by cloud-to-cloud lightning as well as by distant y g g ycloud-to-ground strokes.

• Thermal and mechanical effects due to the intense energies i t d ith li ht i M tl ff t t t ' f b i dassociated 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 strike This isMultiplicity and duration of strokes in a single strike. This is

important for error-correction and system software recovery.


Lightning StrokesLightning StrokesA t i l li ht i Lightning Stroke ShapeA typical lightning

'stroke' can last for over one second

g g p

over 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).


200kA). Another standard waveform is 20/80s normally consideredafter zone 0.

Lightning Protection System (LPS) design

Comprising:• A risk assessment based on actual lightning exposure • Design of the air termination network and down-

conductors D i f th th t i ti t 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 EXPLOSION


Lightning RisksLightning RisksRi k t i b d li ht i t ik d it• 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.


Hong Kong isokeraunic mapg g p


source: HK Observatory

Components of an LPSComponents of an LPS (ref: Dehn (UK))


External and Internal Parts of a LPS '( f D h (UK))

External part of a LPS

(ref: Dehn (UK))

A typical level 3 or 4 LPSInternal part of a LPSDec 2012 Slide no: 18Adjunct Prof Tony Sung

A typical level 3 or 4 LPSInternal part of a LPS

Air Termination SystemsAir Termination Systems


Rolling Sphere method


Down Conductors

Minimum number of down conductors to beMinimum number of down conductors to be based on typical separation distance.


Rolling Sphere methodRolling Sphere method


Protection Level andLevel and

Probabilities


Probabilities of a Lightning Strike(Risk of Lightning)


Protection angle


Rise of Earth Potential St V lt- Step Voltage


External and Internal Parts of a LPS '( f D h (UK))

External part of a LPS

(ref: Dehn (UK))

A typical level 3 or 4 LPSInternal part of a LPSDec 2012 Slide no: 27Adjunct Prof Tony Sung

A typical level 3 or 4 LPSInternal part of a LPS

Damage, g ,Loss and

Risk


Source,Source, Damage and Loss


Lightning Protection ZonesLightning Protection Zones


Lightning Electromagnetic Protection


A iAssessing RisksRisks

(LPS design is by riskby risk

assessments)


RiskRiskCalcusing RiskRisk Com-

ponents


Factors of RiskRisk

Components


Risk ComponentsRisk Components


IdentificationIdentification of Tolerable Ri k RRisk RT


BS7671 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 buildings


BS7671 Surge protection Requirements

• Section 443 – Protection against Overvoltages of atmospheric Origin or due to switching within the installationinstallation

• Table 44.3 gives the required minimum impulse withstand voltage of apparatus within an installationwithstand voltage of apparatus within an installation


Examples of Various Impulse Category Equipment


Estimation of lightning 2flash density in flashes /km2


SPD Selection Design ProceduresSPD Selection Design Procedures

Remember Kirchhoff’s Current Law?


Expected Surge

currentcurrent example


Limit SPD conductor lengthsLimit SPD conductor lengths

InducedInduced Voltage:


Induced VoltagesInduced Voltages


Di tDistance betweenbetween SPD and Victims


SPD Selection

Flow ChartFlow Chart


Final selections 1Final selections - 1


Final selections 2Final selections - 2


Remember surge inputs can be direct or indirectcan be direct or indirect

S1 S3S1 S3

BuildingstructureS2 S4

Meterbox

S4Groundlevel


A Typical Risk Assessment ReportA Typical Risk Assessment Report


Report Contents


Report Contents


Report Contents


Report Contents


Report Contents


ConclusionsConclusions• Risk assessments should be carried out – either

to BE EN/IEC 62305 or to comply with HK COP_E (or other country’s WRs)

• Designers and Installers must incorporate SPDs to control/minimise risks to an electrical i t ll ti finstallation for:– Power circuits (motor controls/dampers etc)

Data Circuits (network equipment/routers etc)– Data Circuits (network equipment/routers etc)– Life safety circuits (fire alarm/security/medical

equipment etc)equipment etc)• Maintenance of SPD (i.e., replacement access)

must be allowed for the life of the building.Dec 2012 Slide no: 56Adjunct Prof Tony Sung

must be allowed for the life of the building.

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