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International Telecommunication Union
ITU-T Workshop “Lightning Protection Technical Session“12-16 December 2005, Geneva, Switzerland
Risk assessment for Risk assessment for servicesservices
Ahmed Zeddam France Telecom R&D Division
2dates
ITU-T
ITU-T SG 5 Technical Session “Lightning Protection“12 December 2005, ITU Headquarters Geneva, Switzerland
Outline
1. Services considered by IEC 623051. Services considered by IEC 62305 2. Risk assessment for services 2. Risk assessment for services 3. Comparison with ITU Rec. K46 and K473. Comparison with ITU Rec. K46 and K47 4. Example4. Example
5. Open issues and future work 5. Open issues and future work
3dates
ITU-T
ITU-T SG 5 Technical Session “Lightning Protection“12 December 2005, ITU Headquarters Geneva, Switzerland
Services in IEC 62305
o The standard IEC62305 considers the following services:
1. Telecommunication lines2. Power lines3. Pipelines
IEC 62305-2 deals with the risk assessment for structures and services
IEC 62305-5 deals with the protection of services Telecommunication lines Protection of power lines and pipelines under studyunder study
4dates
ITU-T
ITU-T SG 5 Technical Session “Lightning Protection“12 December 2005, ITU Headquarters Geneva, Switzerland
Service to be considered :The service to be considered is the physical connection physical connection between:
the switch telecommunication building and the user’s building or two switch telecommunication buildings or two users’ buildings, for the telecommunication (TLC) lines;
the switch telecommunication building or the user’s building and a distribution node, or between two distribution nodes for the telecommunication (TLC) lines;
the high voltage (HV) substation and the user’s building, for the power lines;
the main distribution station and the user’s building, for pipes.
The service to be considered includes the line equipmentline equipment and the line termination equipmenttermination equipment, such as:
multiplexer, power amplifier, optical network units, meters, line termination equipment, etc.;
circuit breakers, overcurrent systems, meters, etc.; control systems, safety systems, meters, etc.
Protection does not include does not include the user’s equipment or any structure connected at the ends of the service.
5dates
ITU-T
ITU-T SG 5 Technical Session “Lightning Protection“12 December 2005, ITU Headquarters Geneva, Switzerland
IEC Risk assessment
IEC 62305-2IEC 62305-2 provides a method of calculating the risk of loss for a structure/service due to lightning strikes for the following sources following sources : :
S1S1: flashes to a structure
S2S2: flashes near a
structure
S3S3: flashes to a service
S4S4: flashes near a service
EquipmenEquipmentt
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ITU-T
ITU-T SG 5 Technical Session “Lightning Protection“12 December 2005, ITU Headquarters Geneva, Switzerland
IEC62305-2:Risk assessment for a service
where :• Nx is the number of dangerous eventsnumber of dangerous events • P’x is the probability of damageprobability of damage to a service • L’x is the consequent lossconsequent loss
Type of loss which may be associated with a service are only:
• L’’2: loss of service to the publicservice to the public
Risk component RR’2’2
• L’’4: loss of economic valueeconomic value (service and loss of activity) Risk component RR’4’4
NOTE :NOTE : Loss of human lifeLoss of human life associated with a service is not consideredis not considered in IEC62305-2 standard
RR’x=’x=NNx·x·PP’x·’x·LL’x’x
Risk components for a service
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ITU-T
ITU-T SG 5 Technical Session “Lightning Protection“12 December 2005, ITU Headquarters Geneva, Switzerland
IEC62305-2:Risk assessment for a service
Source of Source of damagedamage
Flash striking the service
S3
Flash striking near the service
S4
Flash striking the structure
S1
Risk component
R`V
Physical
damage
R`W
Failure of connected equipmen
t
R`Z
Failure of Connected
equipment
R`B
Physical damage
R`C
Failure of
connected
equipment
Risk for each Risk for each type of losstype of loss
R`2 (public service)
R`4 (econom. value)
*
*
*
*
*
*
*
*
*
*
Risk components for a service
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ITU-T
ITU-T SG 5 Technical Session “Lightning Protection“12 December 2005, ITU Headquarters Geneva, Switzerland
IEC62305-2:Risk assessment for a service
Partitioning of a service into sections SPartitioning of a service into sections SSS:: To assess each risk component, the service could
be divided into sections SS. However a service may be, or may be assumed to be, a single section.
For all risk components (R'B, R'C, R'V, R'W, R'Z), sections SS are mainly defined by:
• type of service (aerial or buried) • factors affecting the collection area (Cd , Ce , Ct ) • characteristics of service ( type of cable insulation,
shield resistance).
Further sections may be defined according to:• type of connected apparatus;• protection measures existing or to be provided.
Partitioning of a service into sections should take into account the feasibility of implementation of the most suitable protection measures.
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ITU-T
ITU-T SG 5 Technical Session “Lightning Protection“12 December 2005, ITU Headquarters Geneva, Switzerland
IEC62305-2:Risk assessment for a service
Decision to protect a service :Decision to protect a service :
identification of the service to be protected and its characteristics
identification of all the types of loss in the service and the relevant corresponding risk R (R'2 & R'4)
evaluation of risk R for each type of loss (R'2 & R'4)
evaluation of need of protection, by comparisonby comparison of risk RR’’22 or R' or R'44 for a service with the tolerable risk RT
evaluation of cost effectiveness of protection by comparison of the costs of total loss with and without protection measures. In this case, the assessment of components of R’4 for a service is to be performed in order to evaluate such costs
10dates
ITU-T
ITU-T SG 5 Technical Session “Lightning Protection“12 December 2005, ITU Headquarters Geneva, Switzerland
IEC62305-2:Risk assessment for a serviceProcedure to evaluate the need of Procedure to evaluate the need of protectionprotection ::
identification of the tolerable risk RT
comparison of the risk R with the tolerable value RT
If RR RRTT lightning protection is is not not necessarynecessary
If RR > > RRTT protection measures shall be protection measures shall be adopted adopted in order to reduce R RT for all risks to which the service is subjected.
Typical values of tolerable risk RT
Types of loss RT(y-1)
Loss of human life or permanent injuries 10–5
Loss of service to the public 10–3
Loss of cultural heritage 10–3
11dates
ITU-T
ITU-T SG 5 Technical Session “Lightning Protection“12 December 2005, ITU Headquarters Geneva, Switzerland
IEC62305-2:Risk assessment for a service
Risk components for a service
Source of damage
Type of damage
S3Lightning flash
to a service
S4Lightning flash near
a service
S1Lightning flash to a structure
Resulting risk according to the type of damage
D2Physical damage
R'V=NL·P'Vi·L'V R'B=ND·P'Bi·L'B RRF F =R`V+R`B
D3Failure of electrical and
electronic systems
R'W=NL·P'Wi·L'W R'Z = (NI – NL ) P'Z L'Z R'C=ND·P'Ci·L'C RROO=R`Z+R`W +R`C
Resulting risk according to the source of damage
RRD D =R`V+R`WRRI =R`Z+R`B+R`C
12dates
ITU-T
ITU-T SG 5 Technical Session “Lightning Protection“12 December 2005, ITU Headquarters Geneva, Switzerland
Comparison with K46 and K47
For telecommunication lines the risk component R'Z is generally the most important component :most important component :
Rec. 46Rec. 46 provides risk assessment for only the component R'Z and gives the associated protective
measures
• S4 : Lightning flash near a service
Rec. 47Rec. 47 considers the other risk components (R'B,
R'C, R'V, R'W) and gives the associated protective
measures• S3 : Lightning flash to a service • S1 : Lightning flash to a structure
Additional information on risk component R’z evaluation are given in IEC 62305-5IEC 62305-5
Equipment along the line
Shielding factor KsKs
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ITU-T
ITU-T SG 5 Technical Session “Lightning Protection“12 December 2005, ITU Headquarters Geneva, Switzerland
Comparison with K46 and K47
The factor KKss play an important role in the determination of the probability PLI
Some values of this probability depending on the resistance RS of the cable screen and the impulse withstand voltage Uw of the equipment are given in Table B.7 of Annex B of IEC62305-2.
Probability P'Z of internal systems failure due to flashes near the service depends on the service shield (RS), the impulse withstand voltage, the typical protection measures and the SPDs at the entrance of the structure
Shielding factor
14dates
ITU-T
ITU-T SG 5 Technical Session “Lightning Protection“12 December 2005, ITU Headquarters Geneva, Switzerland
Comparison with K46 and K47
• NO SPDs: P'Z = PLI
• SPDs: P'Z 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
10,50,20,1
0,05
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
Probability P'Z of internal systems failure due to flashes near the service
PLI
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ITU-T
ITU-T SG 5 Technical Session “Lightning Protection“12 December 2005, ITU Headquarters Geneva, Switzerland
Comparison with K46 and K47
Relation between RsRs and KKss is given in Table B.5 of Annex B of IEC62305-2.
Shielding factor
K.46 gives shielding factors for external lines, while Table B.5/IEC62305-2 K.46 gives shielding factors for external lines, while Table B.5/IEC62305-2 addresses internal wiring. addresses internal wiring. Shielding factors for internal wiring have been treated in K.surgeShielding factors for internal wiring have been treated in K.surge
Type of internal wiring KS3
Unshielded cable – no routing precaution in order to avoid loops 1) 1
Unshielded cable – routing precaution in order to avoid large loops 2) 0,2
Unshielded cable – routing precaution in order to avoid loops 3) 0,02
Shielded cable with shield resistance 4) 5<RS 20 Ω / km 0,001
Shielded cable with shield resistance 4) 1 < RS 5 Ω / km 0,0002
Shielded cable with shield resistance 4) RS 1 Ω / km 0,0001
1) Loop conductors with different routing in large buildings (loop area in the order of 50 m2).2) Loop conductors routing in the same conduit or loop conductors with different routing in small buildings (loop area in the order of 10 m2).3) Loop conductors routing in the same cable (loop area in the order of 0,5 m2).4) Cable with shield of resistance RS (Ω / km) bonded to equipotential bonding bar at both ends and equipment connected to
the same bonding bar.
NOTE NOTE More precise evaluation of Ks for shielded and unshielded sections can be found in the
ITU Recommendation K.46.
16dates
ITU-T
ITU-T SG 5 Technical Session “Lightning Protection“12 December 2005, ITU Headquarters Geneva, Switzerland
Comparison with K46 and K47
Shielding factor related to earthShielding factor related to earth Kse
K46 gives a more precise evaluation of the shielding factor related to earth
Annex A of IEC 62305-5 gives some guidance :
" This situation is called “Shield not bonded to equipotential bonding bar to which equipment is connected” in Table B.7 of the IEC 62305-2 standard "
Need to use two standards for the risk assessment
!
Shielding factors for internal wiring are treated in K.surge
Shielding factor
17dates
ITU-T
ITU-T SG 5 Technical Session “Lightning Protection“12 December 2005, ITU Headquarters Geneva, Switzerland
Example
section 1
b
structure b(switching)
Hb
a Ha
3Ha
section 2
structure a(user)
3Hb
Structure Dimensions (m)(L · W · H)
Location factorCd
Number nn of services to structure
“a” 25 · 20 ·15 2 3
“b” 20 · 30 · 10 0,5 10
Tb T1/2Ta
Mean values of relative amount of loss per year relevant to risk R2 were assumed
Lf = 3·10-3 (loss due to physical damage)Lo =10-3 (loss due to failure of internal systems)
18dates
ITU-T
ITU-T SG 5 Technical Session “Lightning Protection“12 December 2005, ITU Headquarters Geneva, Switzerland
Example
Parameter Comment Symbol Value
Soil resistivity (m) 500
Length (m) - Lc 600
Height (m) Buried - -
Line location factor Surrounded Cd 0,5
Line environment factor Rural Ce 1
Line shielding resistance (km)
- R 0,5
Type of line shield Lead - -
Shield characteristics No contact with soil
Kd 0,4
Type of line insulation Paper Uw (kV) 1,51,5
Type of equipment in transition point Tb
Electronic Uw (kV) 1,5 (1)
Type of equipment in transition point T1/2
None - -
Protection measures None Kp 1
(1) Enhanced level of ITU-T Recommendation K.20
Comment Symbol Value
(m) 500
- Lc 800
Aerial Hc 6
Surrounded Cd 0,5
Rural Ce 1
Unshielded - -
Plastic Uw (kV) 55
Electronic Uw (kV) 1,5 (1)
None - -
None Kp 1
Section S1 Section S2
19dates
ITU-T
ITU-T SG 5 Technical Session “Lightning Protection“12 December 2005, ITU Headquarters Geneva, Switzerland
Example
ParameterParameter S1S1 S2S2 LineLine
R'B(a) (1) - 0,261 0,261
R'B(b) (1) 0 - 0
R'C(a) (2) - 0,0873 0,0873
R'C(b) (2) 0 - 0
R'V 0,0282 0,1566 0,1848
R'W 0,0008 0,0522 0,053
R’=R'B(a)+R'B(b)+R'C(a)+R'C(b)+R'V+R'W 0,5861
R'Z(Ta) (5) 0,2967 1,5478 1,8451,845
R'Z(Tb) (6) 0,0119 1,5478 1,591,59
R'Z(T1/2) (7) 0,2967 1,5478 1,8451,845
R'2(Ta)=R’+R'Z(Ta) 2,43112,4311
R'2(Tb)=R’+R'Z(Tb) 2,17612,1761
R'2(T1/2)=R’+R'Z(T1/2) 2,43112,4311
Risk R'2 for unprotected line (values x 10-3)
The value of the risk The value of the risk R'R'22 is greater than the tolerable value is greater than the tolerable value RRTT = 10 = 10–3–3, ,
therefore the line needs to be protected therefore the line needs to be protected
20dates
ITU-T
ITU-T SG 5 Technical Session “Lightning Protection“12 December 2005, ITU Headquarters Geneva, Switzerland
Example
Due to the risk component RR''ZZ in section S2, the risk RR''22 overcame RRTT in transition points TTa, a, TTb b andand TT1/21/2
In order to reduce the risk RR''22 below the tolerable value, it is
enough to select SPDs in accordance with LPL III, i.e. PPSPDSPD= 0,03= 0,03
The SPD installation at transition points TTaa and TT1/21/2:
reduces the probabilities P'reduces the probabilities P'ZZ(Ta) and P'(Ta) and P'ZZ (T1/2) to the value (T1/2) to the value PPSPDSPD;;
does not affect the probabilities does not affect the probabilities PP''VV and and PP''WW ; ;
does not affect the probabilities does not affect the probabilities PP''BB and and PP''CC relevant to section S2 relevant to section S2
because it is aerial ;because it is aerial ;
does not affect the probabilities does not affect the probabilities PP''BB and and PP''CC relevant to section S1 relevant to section S1
because they are lower than because they are lower than PPSPDSPD
see
Annex D of IEC 62305-2
Risk R'2 for unprotected line R'2(Ta)=R’+R'Z(Ta) 2,4311 2,4311 x 10-3
R'2(Tb)=R’+R'Z(Tb) 2,1761 2,1761 x 10-3
R'2(T1/2)=R’+R'Z(T1/2) 2,4311 2,4311 x 10-3
21dates
ITU-T
ITU-T SG 5 Technical Session “Lightning Protection“12 December 2005, ITU Headquarters Geneva, Switzerland
Example
ParameterParameter S1S1 S2S2 LineLine
R'B(a) (1) - 0,261 0,261
R'B(b) (1) 0 - 0
R'C(a) (2) - 0,0873 0,0873
R'C(b) (2) 0 - 0
R'V 0,0282 0,1566 0,1848
R'W 0,0008 0,0522 0,053
R’=R'B(a)+R'B(b)+R'C(a)+R'C(b)+R'V+R'W 0,5861
R'Z(Ta) (5) 0,2967 1,5478 1,8451,845
R'Z(Tb) (6) 0,0119 1,5478 1,591,59
R'Z(T1/2) (7) 0,2967 1,5478 1,8451,845
R'2(Ta)=R’+R'Z(Ta) 2,43112,4311
R'2(Tb)=R’+R'Z(Tb) 2,17612,1761
R'2(T1/2)=R’+R'Z(T1/2) 2,43112,4311
Risk R'2 for unprotected line
Risk R'2 with SPDs at T1/2 and Ta (PSPD = 0.03) ParameterParameter SS11 SS22 LineLine
R'B(a)- 0,261 0,261
R'B(b)0 - 0
R'C(a)- 0,0873 0,0873
R'C(b)0 - 0
R'V 0,0282 0,1566 0,1848
R'W 0,0008 0,0522 0,053
R’ = R'B(a)+ R'B(b)+ R'C(a)+ R'C(b)+ R'V+ R'W 0,5861
R'Z(Ta) 0,0178 0,0553 0,07310,0731
R'Z(Tb)0,0119 - 0,01190,0119
R'Z(T1/2)0,0178 0,0553 0,07310,0731
R'2(Ta) = R’+ R'Z(Tb) 0,65920,6592
R'2(Tb) = R’+ R'Z(Ta) 0,5980,598
R'2(T1/2)=R’+R'Z(T1/2) 0,65920,6592
(values x 10-3)
22dates
ITU-T
ITU-T SG 5 Technical Session “Lightning Protection“12 December 2005, ITU Headquarters Geneva, Switzerland
Open issues and future work Amendment of K46, K47, K39 Amendment of K46, K47, K39
Align with IEC risk approach ?Align with IEC risk approach ? Probability of a customer injury or death when using Probability of a customer injury or death when using
telecommunications equipment telecommunications equipment see Phil's presentation
Amendment of IEC 62305 Amendment of IEC 62305 Shielding factor (Kss, Kse) & Rules for the use of Table 7 Shielding factor (Kss, Kse) & Rules for the use of Table 7
(probability for shielded sections)(probability for shielded sections) see Celio's presentation
Probability of a customer injury or death when using Probability of a customer injury or death when using telecommunications equipment telecommunications equipment
Take into account the information of K.Take into account the information of K.surgesurge
Protection of powerlines and pipelinesProtection of powerlines and pipelines Global approach of risk for Structure and Service ?Global approach of risk for Structure and Service ?
Evolution of the network architectureEvolution of the network architecture Risk assessment and protection of Customers near an Risk assessment and protection of Customers near an
RBSRBS Risk assessment and protection of FTTC , FTTB, FFTH..Risk assessment and protection of FTTC , FTTB, FFTH..