Risk regarding safety

1. Risk regarding safety Phil Day Protection Specialist, Telstra Corp, Australia

2. Introduction • This presentation will introduce: • Missing risk components • Risk mechanisms • The magnitudes of voltages and currents relevant to electric shock; • Discussion on 62305-2 • Future work

3. Lightning as source of damages Close to the tlc line Direct to the tlc line Direct to the structure Close to the structure RU Injury to people RV Physical damage RW Equipment failure RA Injury to people RB Physical damage RC Equipment failure RM Equipment failure RZ Equipment 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+RZ R3: Risk of loss of cultural heritage = RB+RV R4: Risk of loss of economic value = RB+RC+RV+RW+RM+RZ

4. Missing Risk components • RA is the risk of electric shock component due to a strike to the structure • Does not calculate inside structure • Note in 620305 • Remote telecommunication earth is a particular risk and not calculated • Following figures show mechanisms

5. Missing Risk components • RU is the risk of eclectic shock component due to a strike to the services • Remote telecommunication earth is a particular risk and not calculated • Following figures show mechanisms

6. Risk mechanisms R A1 Figure 3 - Direct strike to structure (touch potential with respect to the ground outside the structure)

7. Risk mechanisms (cont) Figure 4 - Direct strike to structure (touch potential with respect to the floor of the structure)

8. Risk mechanisms (cont) Figure 5 - Direct strike to structure (touch potential; earthed object to a telecommunication line which is connected to a remote earth)

9. Risk mechanisms (cont) Figure 6 - Direct strike to structure (touch potential; floor to a telecommunication line which is connected to a remote earth)

10. Risk mechanisms (cont) R B1 Figure 7 - Direct strike to structure (flashover to internal wiring or plumbing)

11. Risk mechanisms (cont) Figure 8 - Direct strike to structure (flashover to telecommunication line due to EPR)

12. Risk mechanisms (cont) Figure 9 - Direct strike to structure (Damage to telecommunication equipment) (No SPDs)

13. Risk mechanisms (cont) Figure 10 - Direct strike to overhead power line (touch potential with respect to the floor of the structure)

14. Risk mechanisms (cont) Figure 11 - Direct strike to a power line (touch potential earthed object to the telecommunication line which is connected to a remote earth)

15. Risk mechanisms (cont) Figure 12 - Direct strike to a power line (touch potential floor to the telecommunication line which is connected to a remote earth)

16. Risk mechanisms (cont) Figure 13 - Direct strike to telecommunication line (touch potential with respect to the floor of the structure)

17. Risk mechanisms (cont) Figure 14 - Direct strike to telecommunication line (touch potential with respect to earthed object)

18. Risk mechanisms (cont) Figure 15 - Direct strike to power line (flashover to telecommunication line due to EPR)

19. Risk mechanisms (cont) Figure 16 - Direct strike to telecommunication line (flashover to structure)

20. Risk mechanisms (cont) Figure 17 - Direct strike to power line/cable (Damage to telecommunication equipment)

21. Risk mechanisms (cont) Figure 18 - Direct strike to telecommunication line/cable (Damage to telecommunication equipment)

22. Magnitudes Figure 1 - Resistance to ground at strike point

23. Magnitudes (cont) Figure 2 - EPR at strike point versus current

24. Cable type Limiting voltage Magnitudes (cont) Cellular (blown) CPFUT MB b/d voltage to screen 5 - 10 kV Solid PEIFLI MBHJ b/d voltage to screen up to 75 kV Unshielded PE cable b/d voltage to ground up to 150 kV Table 1 – Limiting voltage of different cable types Cable limits the voltage (MB = PE sheathed with Moisture Barrier screen; HJ = nylon jacket; PEIFLI = solid PE insulated conductors, grease filled lead-in cable; CPFUT = cellular insulated unit twin conductors;)

25. Type of soil or floor Contact resistance (kΩ)* ra and ru Magnitudes (cont) Agricultural, Concrete ≤ 1 10-2 Marble, Ceramic 1-10 10-3 Gravel, Moquette, Carpets 10-100 10-4 Asphalt, Linoleum, Wood ≥ 100 10-5 (*) Values measured between a 400 cm² electrode compressed with a force of 500 N and a point of infinity. Table 2 – Values of ra Low voltages only?

26. Discussion on 62305-2 • As described by Roberto the Risk of loss = NX * PX * LX • Nx for services uses Lc for the line length. Need to validate values for Lc • Maybe different for direct strikes versus induction • What determines the value of Lc • Need consistency for single section versus multiple sections

27. Discussion on 62305-2 (cont) • Px is the probability of damage. This includes: • Whether SPDs are installed • Shielding factors • Screen resistance • Some rationale has been provided by Roberto • IEC have assumed both an LPS and coordinated SPDs (software) • My approach is add one at a time. The most common protection is an MSPD and possibly a GDT on the telecommunication line

28. Discussion on 62305-2 (cont) • Lx is the consequence of loss. The factors include: • np, nt and tI have difficulty considering these as loss. They relate more to probability • In particular ra, ru, rp, rf and hz relate directly to probability of injury or damage • There is no loss factor for domestic equipment

29. Discussion on 62305-2 (cont) • Therefore I think SG 5 needs to review the use of loss versus probability • If loss is retained the values should be carefully selected and rationale provided • Loss factors for domestic equipment need to be developed

30. Future work • Consider • the use of 62305-2 • The factor Lc • The factor ra • Loss factors