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Risk assessment for services

Risk assessment for services. Ahmed Zeddam France Telecom R & D Division. Outline. 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. Services in IEC 62305.

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Risk assessment for services

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  1. Risk assessment for services Ahmed Zeddam France Telecom R&D Division

  2. Outline 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

  3. Services in IEC 62305 • The standard IEC62305 considers the following services: • Telecommunication lines • Power lines • 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 study

  4. 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. 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.

  5. IEC Risk assessment IEC 62305-2 provides a method of calculating the risk of loss for a structure/service due to lightning strikes for thefollowing sources : S1: flashes to a structure S2: flashes near a structure S3: flashes to a service S4: flashes near a service Equipment

  6. IEC62305-2:Risk assessment for a service Risk components for a service 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 consideredin IEC62305-2 standard

  7. IEC62305-2:Risk assessment for a service Risk components for a service

  8. IEC62305-2:Risk assessment for a service Partitioning of a service into sections SS: • 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.

  9. IEC62305-2:Risk 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

  10. IEC62305-2:Risk assessment for a service Procedure to evaluate the need of protection: • 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 > RTprotection 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

  11. IEC62305-2:Risk assessment for a service Risk components for a service

  12. Comparison with K46 and K47 • For telecommunication lines the risk component R'Z is 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 evaluationare given in IEC 62305-5 • Equipment along the line • Shielding factor Ks

  13. Comparison with K46 and K47 Shielding factor 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

  14. Comparison with K46 and K47 Probability P'Z of internal systems failure due to flashes near the service • NO SPDs: P'Z = PLI • SPDs: P'Z lower between PSPD and PLI Red values missed in the IEC standard PLI 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

  15. Comparison with K46 and K47 Shielding factor • Relation between Rs and Ks is given in Table B.5 of Annex B of IEC62305-2. • 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

  16. Comparison with K46 and K47 Shielding factor • Shielding factor related to earthKse • K46 givesa 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

  17. Example 3Hb 3Ha a Ha b Hb section 1 section 2 structure b (switching) structure a (user) Ta Tb T1/2 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)

  18. Example Section S1 Section S2

  19. Example Risk R'2for unprotected line (values x 10-3) • The value of the risk R'2 is greater than the tolerable value RT = 10–3, therefore the line needs to be protected

  20. Example Risk R'2for unprotected line • Due to the risk component R'Z in section S2, the risk R'2overcame RTin transition pointsTa, Tb andT1/2 • In order to reduce the risk R'2below 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 TaandT1/2: • 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 PSPDsee Annex D of IEC 62305-2

  21. Example Risk R'2for unprotected line Risk R'2with SPDs at T1/2 and Ta (PSPD = 0.03) (values x 10-3)

  22. Open issues and future work • Amendment of K46, K47, K39 • 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..

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