International Telecommunication Union ITU-T Workshop Lightning Protection Technical Session 12-16...

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

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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

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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

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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.

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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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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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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)

*

*

*

*

*

*

*

*

*

*


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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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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

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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

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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

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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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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

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• 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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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.

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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

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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)

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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

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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

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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

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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)

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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..

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International Telecommunication Union ITU-T Workshop Lightning Protection Technical Session 12-16...

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