risk assessment for structure
DESCRIPTION
Risk assessment for structure. Roberto Pomponi Telecom Italia, Italy. Contents. Lightning as source of damages: risks and risk components Protection need: Tolerable Risk and risk component evaluation; Number of dangerous events; Probability and Loss values; Coordinated SPDs protection. - PowerPoint PPT PresentationTRANSCRIPT
International Telecommunication Union
ITU-T SG 5 Technical Session “Lightning protection”12 December 2005, ITU Headquarters, Geneva
Risk assessment for Risk assessment for structurestructure
Roberto Pomponi Telecom Italia, Italy
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ITU-T
ITU-T SG 5 Technical Session “Lightning Protection“12 December 2005, ITU Headquarters Geneva
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 protectionReference document: IEC 62305-2 “Protection against lightning - Part 2: Risk management” (doc. 81/263/FDIS)
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ITU-T
ITU-T SG 5 Technical Session “Lightning Protection“12 December 2005, ITU Headquarters Geneva
Lightning as source of damages
Direct to the
structure
Close to the structure
Direct to the tlc line
Close to the tlc line
RA Injury to people
RB Physical damage
RC Equipment failure
RU Injury to people
RV Physical damage
RW Equipment failure
RMEquipment failure
RZEquipment failure
R1: Risk of loss of human life = RA+RB+RU+RV+(RC+RW+RM+RZ)R2: Risk of loss of service = RB+RC+RV+RW+RM+RZR3: Risk of loss of cultural heritage = RB+RVR4: Risk of loss of economic value = RB+RC+RV+RW+RM+RZ
Risk
co
mpo
nen
ts
Risks
Question: R2 = MAX(RB+RC)+MAX(RV+RW)+RM+RZ?
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ITU-T
ITU-T SG 5 Technical Session “Lightning Protection“12 December 2005, ITU Headquarters Geneva
Lightning Protection Level, LPL
A set of lightning current parameters values which defines lightning as source of damage
Current parameters Symbol Unit
LPLI
(99%)
II(98%
)
III(95
%)
IV(90%
)
First short stroke
Peak current I kA 200 150 100Short stroke
chargeQshort C 100 75 50
Specific energy W/R kJ/W 104 5.625
2.500
Time parameters
T1 / T2 µs/µs 10 / 350
Subsequent
strokes
Peak current I kA 50 37.5 25Average
steepnessdi/dt kA/µs 200 150 100
Time parameters
T1 / T2 µs/µs 0,25 / 100
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ITU-T
ITU-T SG 5 Technical Session “Lightning Protection“12 December 2005, ITU Headquarters Geneva
Protection need
The protection is necessary when
R > RT
•RT Tolerable risk
•RT = 10-3 value suggested by the IEC 62305-2 standard
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ITU-T
ITU-T SG 5 Technical Session “Lightning Protection“12 December 2005, ITU Headquarters Geneva
Risk components: Basic equations
Rx = Nx × Px × LxNx Number of dangerous events
Px Probability of damageLx Consequent loss of the damage
Nx = Ng × Ax
Ng Ground flash density [N/km2×anno] Ax Collection area
Ad for direct strokesAM for lightning close to the structureAL for direct lightning to the serviceAl for lightning near the service
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ITU-T
ITU-T SG 5 Technical Session “Lightning Protection“12 December 2005, ITU Headquarters Geneva
Dangerous events
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ITU-T SG 5 Technical Session “Lightning Protection“12 December 2005, ITU Headquarters Geneva
Dangerous events for direct flashes, Nd
Nd = Ng × Ad
Ad collection area of the structure
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ITU-T
ITU-T SG 5 Technical Session “Lightning Protection“12 December 2005, ITU Headquarters Geneva
Dangerous events due to direct flashes to the service, NL
6dlgL 10CANN
Al Collection area [m2]Cd 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
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ITU-T
ITU-T SG 5 Technical Session “Lightning Protection“12 December 2005, ITU Headquarters Geneva
Collection area for direct flashes to a one section service
)]H(H3[LH6A bacl
)]H(H3[LD2A bacl
Lc Length of the line sectionH High of the line Ha e Hb High of the structures connected at the ends of
the line section
H 3H3H1:3
Lightning strokeTo earthEarth
(top view)d
Buried line: L
Aerial line
Buried line
Simplified D equation respect to K.47
ρ0,5D
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ITU-T
ITU-T SG 5 Technical Session “Lightning Protection“12 December 2005, ITU Headquarters Geneva
Dangerous events due to flashes near a structure, NM
Ad
AM
250 m
6ddMgM 10)CAA(NN
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ITU-T
ITU-T SG 5 Technical Session “Lightning Protection“12 December 2005, ITU Headquarters Geneva
Dangerous events due to flashes near a one section service, Nl
6teigl 10CCANN
Ai Collection area [m2]Ce Environmental factor
Ce = 1 for rural areaCe = 0.5 suburban area (building with H < 10 m)
Ce = 0,1 urban area (building with 10 < H < 20 m) Ce = 0 urban area (building with H > 20 m)
Ct for power line when there is a transformer
ci L1000A
Aerial lineci L25A
Buried line
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ITU-T
ITU-T SG 5 Technical Session “Lightning Protection“12 December 2005, ITU Headquarters Geneva
Probability factors
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ITU-T SG 5 Technical Session “Lightning Protection“12 December 2005, ITU Headquarters Geneva
Probability PA of injury to living beings due to a direct flash to a structure
Protective measures PANo protective measure 1 Electrical insulation of exposed down-conductor (e.g. at least 3 mm cross-linked polyethylene)
10-1
Effective soil equipotenzialization
10-2
Warning notices 10-1
The probability values PA of injury to living beings due to step and touch voltage as function of the protective measures:
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ITU-T
ITU-T SG 5 Technical Session “Lightning Protection“12 December 2005, ITU Headquarters Geneva
Probability PB of physical damage due to a direct flash to a structure
The probability values PB of physical damage due to direct flashes to the structure as function of the LPS class:
Characteristics of the structure Class of LPS
PPSD
Structure not protected with LPS No LPS 1Structure protected with a LPS IV 0,2
III 0,1II 0,05I 0,02
PLS I air termination. Continuous metal down conductors
0,01Continuous metal LPS system 0,001
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ITU-T
ITU-T SG 5 Technical Session “Lightning Protection“12 December 2005, ITU Headquarters Geneva
Probability PC of internal systems failure due to a direct flash to a structure
LPL PPSDNessun SPD 1
III – IV 0.03II 0.02I 0,01
< I 0.005 – 0,001
f(LPL)PP SPDC
The IEC 62305-2 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
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ITU-T
ITU-T SG 5 Technical Session “Lightning Protection“12 December 2005, ITU Headquarters Geneva
Probability PM of internal systems failure due to flashes near the structure
KMS PMS
≥ 0,4 10,15 0,90,07 0,50,035 0,10,021 0,010,016 0,0050,014 0,001
≤ 0,013 0,0001
The probability values PM depend of the adopted lightning protection measure (LPM) according to a factor KMS:
• NO SPDs: PM = PMS• SPDs: PM lower between PSPD and PMSKMS = KS1× KS2× KS3×KS4KS1 LPS o other shields at
LPZ0/LPZ1 boundaryKS2 internal shieldsKS3 internal wiring:
routing and shieldingKS4 impulse withstand
voltage (resistibility)
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ITU-T
ITU-T SG 5 Technical Session “Lightning Protection“12 December 2005, ITU Headquarters Geneva
K.surge approach on KMS 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
RT
SPLT
UNUN
SPL • USPL voltage corresponding the selected
SPL, • UR reference voltage (lower than USPL) that
defines the minimum resistibility voltage level of the equipment connected to the line or of the line conductor insulation;
• NT(U) total number of strikes that will induce a voltage equal or greater than U.
SPL Vio(K.surge) [kV]
KMS(K.surge)
0,05 2,23 0,70,02 3,5 0,430,01 4,9 0,3
R o I
gT dxxddiipNN ...cos...42
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ITU-T
ITU-T SG 5 Technical Session “Lightning Protection“12 December 2005, ITU Headquarters Geneva
Protection measuresw
4S U1.5K
?βKs3
Unshielded lineNo routing precaution in order to avoid loops (large buildings A = 50 m2) (a = d = 1 m)
1
Routing precautions in order to avoid large loops (A = 10 m2) (d = 1 m; a = 0,15 m; same conduit)
0,2
Routing precaution in order to avoid loops (A = 0,5 m2) (d = 1 m; a = 0,015 m; same cable)
0,02
Shielded line: shield resistance R [ /km]
K’s3 = 0,01Ks
5 < R ≤ 20 0,001 1 < R ≤ 5 0,0002 R ≤ 1 (R = 0,5) 0,0001Shield connected to B.B. at both ends and equipment connected to the same B .B.
KS1= KS2 = 0,12×w w = mesh dimension
ddaln
0,691or
50AKS3
= transfer factor for cable trays and earth conductors and = shielding factor of CBN as defined by Rec. K.56
?Ks1
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ITU-T
ITU-T SG 5 Technical Session “Lightning Protection“12 December 2005, ITU Headquarters Geneva
Probability PU of injury to living beings due to touch voltage by a flashes to the service
The probability values PU depend on the service shield (RS), the impulse withstand voltage, the typical protection measures and the SPDs at the entrance of the structure:
• NO SPDs: PU = PLD for unshielded service PLD = 1• SPDs: PU lower between PSPD and PLDProbability PLD
Uw
kV5<RS20(Ω/km)
1<RS 5 (Ω/km)
RS1(Ω/km)
1,52,546
10,950,90,8
0,80,60,30,1
0,40,2
0,04 0,02
This is also valid for the probability values PV and PW.
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ITU-T SG 5 Technical Session “Lightning Protection“12 December 2005, ITU Headquarters Geneva
Probability PZ of internal systems failure due to flashes near the serviceThe probability values PZ depend on the service shield (RS), the impulse withstand voltage, the typical protection measures and the SPDs at the entrance of the structure:• NO SPDs: PU = PLI• SPDs: PU lower between PSPD and PLI
Uw(kV)
No shield
Kse: Shielding
factor related to the earth
KSS: Shielding factor related to the shield
5<RS20
(Ω/km)
1< RS 5
(Ω/km)
RS 1(Ω/km)
11,52,546
21
0,40,20,1
10,50,20,10,05
0,30,150,060,030,02
0,080,040,02
0,0080,004
0,040,02
0,0080,0040,002
Red values missed in the IEC standard
Kse: shield not bonded to the same B.B. to which equipment is connectedKss: shield bonded to the same B.B. to which equipment is connected
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ITU-T SG 5 Technical Session “Lightning Protection“12 December 2005, ITU Headquarters Geneva
PX lower between PSPD and PLI?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 PSPD, 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 SPD1
P’SPD < PSPD
K.surge:Direct flash to line
kA5,437225,0
)135220(125,1R0,25
)RR(mnIIs
csfp
kA25,120110025,0
mnI520,
If
p PSPD = 0,05Unshielded lineShielded line
SPD between conductor and earth of an unshielded line
P’SPD = 0,002
Tlc or signal conductor
Earth
Equipment
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ITU-T
ITU-T SG 5 Technical Session “Lightning Protection“12 December 2005, ITU Headquarters Geneva
Selection and installation of coordinated SPDs
protection
(Annex D of IEC 62305-4 standard)
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ITU-T
ITU-T SG 5 Technical Session “Lightning Protection“12 December 2005, ITU Headquarters Geneva
Selection SPDs with regard to voltage protection level
Equipment is protected when: Up(f) ≤ Uw
For voltage-limiting type SPD
EBB
L1
SPD
L1’
U1
U1’
Up Up(f)
'11pp(f) UUUU
For voltage-switching type SPD:Greater value between
Up(f) = Up
'11p(f) UUU
Effective protection level, Up(f)
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ITU-T
ITU-T SG 5 Technical Session “Lightning Protection“12 December 2005, ITU Headquarters Geneva
Coordinated SPDs: clause 7 of IEC 62305-4
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
• UP(f) is greater than the impulse withstand voltage UW of the equipment to be protected
o The selection and the installation of coordinated SPDs shall comply with:
– IEC 61643-12 e IEC 60364-5-53 (for power systems));– IEC 61643-21 e 61643-22 (for tlc and signalling systems).
o Some basic information for the selection and installation of coordinated SPDs are given in the Annex D
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ITU-T
ITU-T SG 5 Technical Session “Lightning Protection“12 December 2005, ITU Headquarters Geneva
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 Iimp (waveform
10/350 s)• SPD tested with nominal current In 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 In or
combination waveform generationo The value of Iimp or Inn depends on the selected LPL
(Annex E of IEC IEC 62305-1 standard : Surges due to lightning at different installation points)
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ITU-T
ITU-T SG 5 Technical Session “Lightning Protection“12 December 2005, ITU Headquarters Geneva
Oscillation protection distance, lpo
kUU
l p(f)wpo
B.B.
L1
SPD Eq. U
lpo
L
C L1
’
U1
U1’
Up Up(f)
In Iimp
lpo may be disregarded:• Up(f) 0.5 Uw • d 10 m
k = 25 V/m
In the other cases:
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ITU-T
ITU-T SG 5 Technical Session “Lightning Protection“12 December 2005, ITU Headquarters Geneva
Induction protection distance, lpi
hUU
l p(f)wpi
h = 300×KS1× KS2× KS3 flashes near the structureh = 30000×KS0× KS2× KS3 flashes to the structure (worst case)KS0 shielding of the structure, LPS or other shields on the
structure:LPS: Ks0 = Kc Kc = 1 (1 down conductor) Kc = 0.3+1/2n (n down conductors)mesh: Ks0 = 0.06×w0.5
KS1 LPS o other shields at LPZ0/LPZ1 boundaryKS2 internal shieldsKS3 internal wiring: routing and shielding
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ITU-T
ITU-T SG 5 Technical Session “Lightning Protection“12 December 2005, ITU Headquarters Geneva
Induced loop missed in the IEC standard
S2
MET
S A
A1
LPS
S1
Customer’s building
A2
I
The voltage induced in the Loop A2 is not considered
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ITU-T
ITU-T SG 5 Technical Session “Lightning Protection“12 December 2005, ITU Headquarters Geneva
Conclusions
o IEC 62305-2 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 customer’s buildings and remote site
o Critical points:• Risk evaluation for loss of service• Protection factor PM due to flashes near the structure
o Necessary clarification and/or improvement:• Protection factor values PZ due flashes near the service
are missed for 1 kV equipment resistibility • PSPD values for SPDs installed on shielded cables• Ks3 values and and factors of Recommendation K.56• Induction loop between two equipment inside the
structure is missed