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International Telecommunication Union ITU-T SG 5 Technical Session Lightning protection 12 December 2005, ITU Headquarters, Geneva Risk assessment for.

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Presentation on theme: "International Telecommunication Union ITU-T SG 5 Technical Session Lightning protection 12 December 2005, ITU Headquarters, Geneva Risk assessment for."— Presentation transcript:

1 International Telecommunication Union ITU-T SG 5 Technical Session Lightning protection 12 December 2005, ITU Headquarters, Geneva Risk assessment for structure Roberto Pomponi Telecom Italia, Italy

2 ITU-T ITU-T SG 5 Technical Session Lightning Protection 12 December 2005, ITU Headquarters Geneva 2 dates Contents o Lightning as source of damages: risks and risk components o Protection need: Tolerable Risk and risk component evaluation; Number of dangerous events; Probability and Loss values; o Coordinated SPDs protection Reference document: IEC Protection against lightning - Part 2: Risk management (doc. 81/263/FDIS)

3 ITU-T ITU-T SG 5 Technical Session Lightning Protection 12 December 2005, ITU Headquarters Geneva 3 dates Lightning as source of damages Direct to the structure Close to the structure Direct to the tlc line Close to the tlc line R A Injury to people R B Physical damage R C Equipment failure R U Injury to people R V Physical damage R W Equipment failure R M Equipment failure R Z Equipment failure R1: Risk of loss of human life = R A +R B +R U +R V +(R C +R W +R M +R Z ) R2: Risk of loss of service = R B +R C +R V +R W +R M +R Z R3: Risk of loss of cultural heritage = R B +R V R4: Risk of loss of economic value = R B +R C +R V +R W +R M +R Z Risk components Risks Question: R2 = MAX(R B +R C )+MAX(R V +R W )+R M +R Z ?

4 ITU-T ITU-T SG 5 Technical Session Lightning Protection 12 December 2005, ITU Headquarters Geneva 4 dates Lightning Protection Level, LPL A set of lightning current parameters values which defines lightning as source of damage Current parameters SymbolUnit LPL I (99%) II (98%) III (95%) IV (90%) First short stroke Peak currentIkA Short stroke charge Q short C Specific energyW/RkJ/W Time parametersT 1 / T 2 µ s/ µ s10 / 350 Subsequent strokes Peak currentIkA Average steepness di/dtkA/ µ s Time parametersT 1 / T 2 µ s/ µ s0,25 / 100

5 ITU-T ITU-T SG 5 Technical Session Lightning Protection 12 December 2005, ITU Headquarters Geneva 5 dates Protection need The protection is necessary when R > R T R T Tolerable risk R T = value suggested by the IEC standard

6 ITU-T ITU-T SG 5 Technical Session Lightning Protection 12 December 2005, ITU Headquarters Geneva 6 dates Risk components: Basic equations R x = N x × P x × L x N x Number of dangerous events P x Probability of damage L x Consequent loss of the damage N x = N g × A x N g Ground flash density [N/km 2 ×anno] A x Collection area A d for direct strokes A M for lightning close to the structure A L for direct lightning to the service A l for lightning near the service

7 ITU-T ITU-T SG 5 Technical Session Lightning Protection 12 December 2005, ITU Headquarters Geneva 7 dates Dangerous events

8 ITU-T ITU-T SG 5 Technical Session Lightning Protection 12 December 2005, ITU Headquarters Geneva 8 dates Dangerous events for direct flashes, N d N d = N g × A d A d collection area of the structure

9 ITU-T ITU-T SG 5 Technical Session Lightning Protection 12 December 2005, ITU Headquarters Geneva 9 dates Dangerous events due to direct flashes to the service, N L A l Collection area [m 2 ] C d Location factor C = 0.25 structure surrounded by higher structures or trees C = 0.5 structure surrounded by structures or trees of the same high or smaller C = 1 isolated structure: no other structure in the vicinity within a distance of 3H C = 2 isolated structure on a hilltop or a knoll

10 ITU-T ITU-T SG 5 Technical Session Lightning Protection 12 December 2005, ITU Headquarters Geneva 10 dates Collection area for direct flashes to a one section service L c Length of the line section H High of the line H a e H b High of the structures connected at the ends of the line section H 3H 1:3 Lightning stroke To earth Earth (top view) d Buried line: L Aerial line Buried line Simplified D equation respect to K.47

11 ITU-T ITU-T SG 5 Technical Session Lightning Protection 12 December 2005, ITU Headquarters Geneva 11 dates Dangerous events due to flashes near a structure, N M AdAd AMAM 250 m

12 ITU-T ITU-T SG 5 Technical Session Lightning Protection 12 December 2005, ITU Headquarters Geneva 12 dates Dangerous events due to flashes near a one section service, N l A i Collection area [m 2 ] C e Environmental factor C e = 1 for rural area C e = 0.5 suburban area (building with H < 10 m) C e = 0,1 urban area (building with 10 < H < 20 m) C e = 0 urban area (building with H > 20 m) C t for power line when there is a transformer Aerial line Buried line

13 ITU-T ITU-T SG 5 Technical Session Lightning Protection 12 December 2005, ITU Headquarters Geneva 13 dates Probability factors

14 ITU-T ITU-T SG 5 Technical Session Lightning Protection 12 December 2005, ITU Headquarters Geneva 14 dates Probability P A of injury to living beings due to a direct flash to a structure Protective measuresPAPA No protective measure 1 Electrical insulation of exposed down-conductor (e.g. at least 3 mm cross-linked polyethylene) Effective soil equipotenzialization Warning notices The probability values P A of injury to living beings due to step and touch voltage as function of the protective measures:

15 ITU-T ITU-T SG 5 Technical Session Lightning Protection 12 December 2005, ITU Headquarters Geneva 15 dates Probability P B of physical damage due to a direct flash to a structure The probability values P B of physical damage due to direct flashes to the structure as function of the LPS class: Characteristics of the structureClass of LPS P PSD Structure not protected with LPS No LPS1 Structure protected with a LPS IV0,2 III0,1 II0,05 I 0,02 PLS I air termination. Continuous metal down conductors 0,01 Continuous metal LPS system 0,001

16 ITU-T ITU-T SG 5 Technical Session Lightning Protection 12 December 2005, ITU Headquarters Geneva 16 dates Probability P C of internal systems failure due to a direct flash to a structure LPLP PSD Nessun SPD1 III – IV0.03 II0.02 I0,01 < I – 0,001 The IEC assumes that: An LPS or equivalent is installed SPDs are installed at the entrance of the line into the structure Coordinated SPD protection is adopted SPDs are designed as function of the selected LPL Higher current withstand capability

17 ITU-T ITU-T SG 5 Technical Session Lightning Protection 12 December 2005, ITU Headquarters Geneva 17 dates Probability P M of internal systems failure due to flashes near the structure K MS P MS 0,41 0,150,9 0,070,5 0,0350,1 0,021 0,01 0,016 0,005 0,014 0,001 0,013 0,0001 The probability values P M depend of the adopted lightning protection measure (LPM) according to a factor K MS : NO SPDs: P M = P MS SPDs: P M lower between P SPD and P MS K MS = K S1 × K S2 × K S3 ×K S4 K S1 LPS o other shields at LPZ0/LPZ1 boundary K S2 internal shields K S3 internal wiring: routing and shielding K S4 impulse withstand voltage (resistibility)

18 ITU-T ITU-T SG 5 Technical Session Lightning Protection 12 December 2005, ITU Headquarters Geneva 18 dates K.surge approach on K MS values Surge Protection Level (SPL): Peak values and waveform of the expected dangerous surge voltages or currents which could appear in different points of the telecommunication networks due to the lightning current as source of damage U SPL voltage corresponding the selected SPL, U R reference voltage (lower than U SPL ) that defines the minimum resistibility voltage level of the equipment connected to the line or of the line conductor insulation; N T (U) total number of strikes that will induce a voltage equal or greater than U. SPLV io(K.surge) [kV] K MS(K.surge) 0,052,230,7 0,023,50,43 0,014,90,3

19 ITU-T ITU-T SG 5 Technical Session Lightning Protection 12 December 2005, ITU Headquarters Geneva 19 dates Protection measures Unshielded line No routing precaution in order to avoid loops (large buildings A = 50 m 2 ) (a = d = 1 m) 1 Routing precautions in order to avoid large loops (A = 10 m 2 ) (d = 1 m; a = 0,15 m; same conduit) 0,2 Routing precaution in order to avoid loops (A = 0,5 m 2 ) (d = 1 m; a = 0,015 m; same cable) 0,02 Shielded line: shield resistance R [ /km] K s3 = 0,01 K s 5 < R 200,001 1 < R 50,0002 R 1 (R = 0,5)0,0001 Shield connected to B.B. at both ends and equipment connected to the same B.B. K S1 = K S2 = 0,12×w w = mesh dimension = transfer factor for cable trays and earth conductors and = shielding factor of CBN as defined by Rec. K.56

20 ITU-T ITU-T SG 5 Technical Session Lightning Protection 12 December 2005, ITU Headquarters Geneva 20 dates Probability P U of injury to living beings due to touch voltage by a flashes to the service The probability values P U depend on the service shield (R S ), the impulse withstand voltage, the typical protection measures and the SPDs at the entrance of the structure: NO SPDs: P U = P LD for unshielded service P LD = 1 SPDs: P U lower between P SPD and P LD Probability P LD U w kV 5

21 ITU-T ITU-T SG 5 Technical Session Lightning Protection 12 December 2005, ITU Headquarters Geneva 21 dates Probability P Z of internal systems failure due to flashes near the service The probability values P Z depend on the service shield (R S ), the impulse withstand voltage, the typical protection measures and the SPDs at the entrance of the structure: NO SPDs: P U = P LI SPDs: P U lower between P SPD and P LI U w (kV) No shield K se : Shielding factor related to the earth K SS : Shielding factor related to the shield 5

22 ITU-T ITU-T SG 5 Technical Session Lightning Protection 12 December 2005, ITU Headquarters Geneva 22 dates P X lower between P SPD and P LI ? I think that it is correct, but the following information is missed: When an SPD, which has been installed in a transition point of an unshielded line with a selected P SPD, is installed in the same point of a shielded line, its P SPD will be lower than the previous one SPD between conductor and shield Line shield SPD1 P SPD < P SPD K.surge: Direct flash to line P SPD = 0,05 Unshielded line Shielded line SPD between conductor and earth of an unshielded line P SPD = 0,002 Tlc or signal conductor Earth Equipment

23 ITU-T ITU-T SG 5 Technical Session Lightning Protection 12 December 2005, ITU Headquarters Geneva 23 dates Selection and installation of coordinated SPDs protection (Annex D of IEC standard)

24 ITU-T ITU-T SG 5 Technical Session Lightning Protection 12 December 2005, ITU Headquarters Geneva 24 dates Selection SPDs with regard to voltage protection level Equipment is protected when: U p(f) U w For voltage-limiting type SPD For voltage-switching type SPD: Greater value between U p(f) = U p Effective protection level, U p(f)

25 ITU-T ITU-T SG 5 Technical Session Lightning Protection 12 December 2005, ITU Headquarters Geneva 25 dates Coordinated SPDs: clause 7 of IEC o SPD shall be located at the line entrance of the structure at least o Additional SPD may be required when The distance between the location of the SPD and equipment to be protected is too long (greater than the protection distance ): Protection distance: maximum distance along the circuit from the equipment at which the SPD still protects the equipment U P(f) is greater than the impulse withstand voltage U W of the equipment to be protected o The selection and the installation of coordinated SPDs shall comply with: – IEC e IEC (for power systems)); – IEC e (for tlc and signalling systems). o Some basic information for the selection and installation of coordinated SPDs are given in the Annex D

26 ITU-T ITU-T SG 5 Technical Session Lightning Protection 12 December 2005, ITU Headquarters Geneva 26 dates Selection and installation of coordinated SPDs o At the line entrance into the structure (e.g. at the main distribution box, MB): SPD tested with impulse current I imp (waveform 10/350 s) SPD tested with nominal current I n when the risk of failure of SPDs due to direct flashes (S1 and S4) can be disregarded o Close to the equipment to be protected (e.g. at the secondary distribution box (SB) or at socket outlet, SA) SPD tested with the nominal current I n or combination waveform generation n o The value of I imp or I n depends on the selected LPL (Annex E of IEC IEC standard : Surges due to lightning at different installation points)

27 ITU-T ITU-T SG 5 Technical Session Lightning Protection 12 December 2005, ITU Headquarters Geneva 27 dates Oscillation protection distance, l po l po may be disregarded: U p(f) 0.5 U w d 10 m k = 25 V/m In the other cases:

28 ITU-T ITU-T SG 5 Technical Session Lightning Protection 12 December 2005, ITU Headquarters Geneva 28 dates Induction protection distance, l pi h = 300 × K S1 × K S2 × K S3 flashes near the structure h = × K S0 × K S2 × K S3 flashes to the structure (worst case) K S0 shielding of the structure, LPS or other shields on the structure: LPS: K s0 = K c K c = 1 (1 down conductor) K c = 0.3+1/2n (n down conductors) mesh: K s0 = 0.06×w 0.5 K S1 LPS o other shields at LPZ0/LPZ1 boundary K S2 internal shields K S3 internal wiring: routing and shielding

29 ITU-T ITU-T SG 5 Technical Session Lightning Protection 12 December 2005, ITU Headquarters Geneva 29 dates Induced loop missed in the IEC standard The voltage induced in the Loop A2 is not considered

30 ITU-T ITU-T SG 5 Technical Session Lightning Protection 12 December 2005, ITU Headquarters Geneva 30 dates Conclusions o IEC standard gives an exhaustive risk assessment for structures, its contents and connected services This standard should be used for protection need evaluation of the exchange or customers buildings and remote site o Critical points: Risk evaluation for loss of service Protection factor P M due to flashes near the structure o Necessary clarification and/or improvement: Protection factor values P Z due flashes near the service are missed for 1 kV equipment resistibility P SPD values for SPDs installed on shielded cables K s3 values and and factors of Recommendation K.56 Induction loop between two equipment inside the structure is missed


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