International Telecommunication Union
Risk assessment for
services
Ahmed Zeddam
France Telecom R&D Division
ITU-T Workshop “Lightning Protection Technical Session“
12-16 December 2005, Geneva, Switzerland
Outline
ITU-T
1. Services considered by IEC 62305
2. Risk assessment for services
3. Comparison with ITU Rec. K46 and K47
4. Example
5. Open issues and future work
ITU-T SG 5 Technical Session “Lightning Protection“
12 December 2005, ITU Headquarters Geneva, Switzerland
dates
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Services in IEC 62305
ITU-T
o
The standard IEC62305 considers the
following services:
Telecommunication lines
2. Power lines
3. Pipelines
1.
 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 study
ITU-T SG 5 Technical Session “Lightning Protection“
12 December 2005, ITU Headquarters Geneva, Switzerland
dates
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Service to be considered :
The service to be considered is the 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.
ITU-T


The service to be considered includes the line equipment and the line
termination 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 the user’s equipment or any structure
connected at the ends of the service.
ITU-T SG 5 Technical Session “Lightning Protection“
12 December 2005, ITU Headquarters Geneva, Switzerland
dates
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IEC Risk assessment
ITU-T
IEC 62305-2 provides a method of calculating the
risk of loss for a structure/service due to lightning
strikes for the following sources :
S4: flashes
near a service
S3: flashes to a
service
S1: flashes to a
structure
S2: flashes near
a structure
Equipment
ITU-T SG 5 Technical Session “Lightning Protection“
12 December 2005, ITU Headquarters Geneva, Switzerland
dates
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IEC62305-2:Risk
assessment for a service
Risk components for a service
ITU-T
R’x=Nx·P’x·L’x
where :
•
Nx is the number of dangerous events
•
P’x is the probability of damage to a service
•
L’x is the consequent loss
 Type of loss which may be associated with a
service are only:
•
L’2: loss of service to the public
 Risk component R’2
•
L’4: loss of economic value (service and loss of activity)
 Risk component R’4
NOTE : Loss of human life associated with a service
is not considered in IEC62305-2 standard
ITU-T SG 5 Technical Session “Lightning Protection“
12 December 2005, ITU Headquarters Geneva, Switzerland
dates
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IEC62305-2:Risk
ITU-T
assessment for a service
Risk components for a service
Flash striking the Flash striking
service
near the
service
Source of
damage
S4
S3
Risk
component
Risk for each
type of loss
R`2 (public service)
R`4 (econom. value)
R`V
Physical
damage
*
*
R`W
Failure of
connected
equipment
*
*
S1
R`Z
R`B
R`C
Failure of
Connected
equipment
Physical
damage
Failure of
connected
equipment
*
*
*
*
*
*
ITU-T SG 5 Technical Session “Lightning Protection“
12 December 2005, ITU Headquarters Geneva, Switzerland
dates
Flash striking the
structure
7
IEC62305-2:Risk
assessment for a service
Partitioning of a service into sections SS:
ITU-T
 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.
ITU-T SG 5 Technical Session “Lightning Protection“
12 December 2005, ITU Headquarters Geneva, Switzerland
dates
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IEC62305-2:Risk
ITU-T
assessment for 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 comparison of
risk R’2 or R'4 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
ITU-T SG 5 Technical Session “Lightning Protection“
12 December 2005, ITU Headquarters Geneva, Switzerland
dates
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IEC62305-2:Risk
assessment for a service
Procedure to evaluate the need of
protection :
ITU-T
 identification of the tolerable risk RT
 comparison of the risk R with the tolerable


value RT
If R  RT lightning protection is not necessary
If R > RT protection measures shall be 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
Loss of human life or permanent injuries
10–5
Loss of service to the public
10–3
Loss of cultural heritage
10–3
ITU-T SG 5 Technical Session “Lightning Protection“
12 December 2005, ITU Headquarters Geneva, Switzerland
dates
RT(y-1)
10
IEC62305-2:Risk
ITU-T
assessment for a service
Risk components for a service
Source of damage
S3
S4
Lightning flash
to a service
Lightning flash near
a service
Type of damage
D2
R'V=NL·P'Vi·L'V
S1
Lightning
flash to a
structure
R'B=ND·P'Bi·L'B
RF =R`V+R`B
R'C=ND·P'Ci·L'C
RO=R`Z+R`W +R`C
Physical damage
D3
Failure of electrical and
electronic systems
R'W=NL·P'Wi·L'W
R'Z = (NI – NL ) P'Z L'Z
Resulting risk
according to the
type of damage
Resulting risk according
to the source of damage
RD =R`V+R`W
RI =R`Z+R`B+R`C
ITU-T SG 5 Technical Session “Lightning Protection“
12 December 2005, ITU Headquarters Geneva, Switzerland
dates
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Comparison with K46 and K47
 For telecommunication lines the risk component R'Z is
ITU-T
generally the most important component :
 Rec. 46 provides risk assessment for only the component
R'Z and gives the associated protective measures
•
S4 : Lightning flash near a service
 Rec. 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 62305-5
 Equipment along the line
 Shielding factor Ks
ITU-T SG 5 Technical Session “Lightning Protection“
12 December 2005, ITU Headquarters Geneva, Switzerland
dates
12
Comparison with K46 and K47
Shielding factor
ITU-T
The factor Ks 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
ITU-T SG 5 Technical Session “Lightning Protection“
12 December 2005, ITU Headquarters Geneva, Switzerland
dates
13
Comparison with K46 and K47
Probability P'Z of internal systems failure due to flashes
near the service
ITU-T •
NO SPDs: P'Z = PLI
• SPDs:
P'Z lower between PSPD and PLI
Uw
(kV)
Red
values
missed
in the
IEC
standard
1
1,5
2,5
4
6
No shield
Kse:
Shielding factor
related to the
earth
2
1
0,4
0,2
0,1
PLI
1
0,5
0,2
0,1
0,05
KSS: Shielding factor related to the
shield
5<RS20
(Ω/km)
1< RS 5
(Ω/km)
RS 1
(Ω/km)
0,3
0,15
0,06
0,03
0,02
0,08
0,04
0,02
0,008
0,004
0,04
0,02
0,008
0,004
0,002
Kse: shield not bonded to the same B.B. to which equipment is connected
Kss: shield bonded to the same B.B. to which equipment is connected
ITU-T SG 5 Technical Session “Lightning Protection“
12 December 2005, ITU Headquarters Geneva, Switzerland
dates
14
Comparison with K46 and K47
Shielding factor
ITU-T

Relation between Rs and Ks is given in Table B.5 of Annex B of IEC62305-2.
Type of internal wiring
KS3
Unshielded cable – no routing precaution in order to avoid loops 1)
Unshielded cable – routing precaution in order to avoid large loops
Unshielded cable – routing precaution in order to avoid loops
1
2)
3)
0,2
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 m 2).
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 m 2).
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 More precise evaluation of Ks for shielded and unshielded sections can be found in the
ITU Recommendation K.46.
K.46 gives shielding factors for external lines, while Table B.5/IEC62305-2
addresses internal wiring.
 Shielding factors for internal wiring have been treated in K.surge
ITU-T SG 5 Technical Session “Lightning Protection“
12 December 2005, ITU Headquarters Geneva, Switzerland
dates
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Comparison with K46 and K47
Shielding factor
ITU-T  Shielding 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
ITU-T SG 5 Technical Session “Lightning Protection“
12 December 2005, ITU Headquarters Geneva, Switzerland
dates
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Example
Tb
ITU-T
Hb
T1/2
3Hb
Ta
3Ha
a
b
section 1
Ha
section 2
structure b
(switching)
structure a
(user)
Structure
Dimensions (m)
(L · W · H)
Location factor
Cd
Number n of
services to
structure
“a”
25 · 20 ·15
2
3
“b”
20 · 30 · 10
0,5
10
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)
ITU-T SG 5 Technical Session “Lightning Protection“
12 December 2005, ITU Headquarters Geneva, Switzerland
dates
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Example
Section S1
ITU-T
Section S2
Comment
Symbol
Value
Comment
Symbol
Value
(m)

500
(m)

500
Length (m)
-
Lc
600
-
Lc
800
Height (m)
Buried
-
-
Aerial
Hc
6
Surrounded
Cd
0,5
Surrounded
Cd
0,5
Rural
Ce
1
Rural
Ce
1
-
R
0,5
Unshielded
-
-
Lead
-
-
Shield characteristics
No contact
with
soil
Kd
0,4
Type of line insulation
Paper
Uw (kV)
1,5
Plastic
Uw (kV)
5
Type of equipment in transition
point Tb
Electronic
Uw (kV)
1,5 (1)
Electronic
Uw (kV)
Type of equipment in transition
point T1/2
None
-
-
None
-
-
Protection measures
None
Kp
1
None
Kp
1
Parameter
Soil resistivity
Line location factor
Line environment factor
Line shielding resistance
(km)
Type of line shield
1,5 (1)
(1) Enhanced level of ITU-T Recommendation K.20
ITU-T SG 5 Technical Session “Lightning Protection“
12 December 2005, ITU Headquarters Geneva, Switzerland
dates
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Example
Risk R'2
for unprotected line
(values x 10-3)
ITU-T
Parameter
S1
S2
Line
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
1,845
R'Z(Tb) (6)
0,0119
1,5478
1,59
R'Z(T1/2) (7)
0,2967
1,5478
1,845
R'2(Ta)=R’+R'Z(Ta)
2,4311
R'2(Tb)=R’+R'Z(Tb)
2,1761
R'2(T1/2)=R’+R'Z(T1/2)
2,4311
 The value of the risk R'2 is greater than the tolerable value RT = 10–3,
therefore the line needs to be protected
ITU-T SG 5 Technical Session “Lightning Protection“
12 December 2005, ITU Headquarters Geneva, Switzerland
dates
19
Example
Risk R'2
ITU-T
for unprotected line
R'2(Ta)=R’+R'Z(Ta)
2,4311 x 10-3
R'2(Tb)=R’+R'Z(Tb)
2,1761 x 10-3
R'2(T1/2)=R’+R'Z(T1/2)
2,4311 x 10-3
 Due to the risk component R'Z in section S2, the risk R'2
overcame RT in transition points Ta, Tb and T1/2
 In order to reduce the risk R'2 below the tolerable value, it is
enough to select SPDs in accordance with LPL III, i.e. PSPD= 0,03
 The SPD installation at transition points Ta and T1/2:
 reduces the probabilities P'Z(Ta) and P'Z (T1/2) to the value PSPD;
 does not affect the probabilities P'V and P'W ;
 does not affect the probabilities P'B and P'C relevant to section S2
because it is aerial ;
 does not affect the probabilities P'B and P'C relevant to section S1
because they are lower than PSPD
see Annex D of IEC 62305-2
ITU-T SG 5 Technical Session “Lightning Protection“
12 December 2005, ITU Headquarters Geneva, Switzerland
dates
20
Example
ITU-T
Risk R'2
(values x 10-3)
for unprotected line
Parameter
S1
S2
Line
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
Risk R'2 with SPDs at T1/2
and Ta (PSPD = 0.03)
Parameter
S1
S2
Line
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) (5)
0,2967
1,5478
1,845
R'Z(Ta)
0,0178
0,0553
0,0731
R'Z(Tb) (6)
0,0119
1,5478
1,59
R'Z(Tb)
0,0119
-
0,0119
R'Z(T1/2) (7)
0,2967
1,5478
1,845
R'Z(T1/2)
0,0178
0,0553
0,0731
R’ = R'B(a)+ R'B(b)+ R'C(a)+ R'C(b)+ R'V+ R'W
R'2(Ta)=R’+R'Z(Ta)
2,4311
R'2(Ta) = R’+ R'Z(Tb)
0,6592
R'2(Tb)=R’+R'Z(Tb)
2,1761
R'2(Tb) = R’+ R'Z(Ta)
0,598
R'2(T1/2)=R’+R'Z(T1/2)
2,4311
R'2(T1/2)=R’+R'Z(T1/2)
0,6592
ITU-T SG 5 Technical Session “Lightning Protection“
12 December 2005, ITU Headquarters Geneva, Switzerland
dates
0,5861
21
Open issues and future work
 Amendment of K46, K47, K39


ITU-T

Align with IEC risk approach ?
Probability of a customer injury or death when using
telecommunications equipment
 see Phil's presentation
Amendment of IEC 62305
 Shielding factor (Kss, Kse) & Rules for the use of Table 7
(probability for shielded sections)
 see Celio's presentation


Probability of a customer injury or death when using
telecommunications equipment



Take into account the information of K.surge
Protection of powerlines and pipelines
Global approach of risk for Structure and Service ?
Evolution of the network architecture
 Risk assessment and protection of Customers near an RBS
 Risk assessment and protection of FTTC , FTTB, FFTH..
ITU-T SG 5 Technical Session “Lightning Protection“
12 December 2005, ITU Headquarters Geneva, Switzerland
dates
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