Safety Grounding Update

1. Safety Grounding Update July 25, 2006 Phoenix, AZ

2. Power System Safety Manual (PSSM) • 2005 PSSM did not have Grounding Tables for Regions • 2006 PSSM has new Grounding Tables for Regions • Appendix K for DSW Grounding Tables

3. 2006 PSSM Appendices

4. 3 Tables for DSW Data • Table 1 – Substation Grounds for both the lines and substation equipment • Table 2 – Line Grounds for entire line • Table 3 – Line Grounds with specific section breaks

5. 2006 PSSM Appendix KTable 1 – pages 173 through 183

6. Table 1 Explanation • Faults placed on all buses in cases with DSW and connected systems • 3 Phase and SLG faults – maximum of both • 3 Grounding conductor sizes • SBS for substation • LNS for lines

7. Table 1 Calculations • Calculations use the maximum fault current • Table 10.1 in 2006 PSSM – Cable Limits

8. Substation and Line Calculations • 15 Second time used for Substation Bus grounding cables • 30 Second time used for Line grounding cables • 90% derating is used for 2 or more cables

9. Example 1 Calculation

10. Example 2 Calculation

11. 2006 PSSM Appendix KTable 2 – pages 184 through 190

12. Table 2 Explanation • Same calculations as Table 1 for each substation line • Home Bus and Home Bus kV • Remote Bus • Maximum for entire line • 2/0 cables used • 30 second time

13. Example 3 Calculation

14. Each Line Entered Twice

15. Example 4 Calculation

16. Example 4 Calculation

17. Table 3 2006 PSSM Appendix Kpages 192 through 193 • 2 Pages • Spreadsheet with data is 2 pages wide • Match pages for the full line entry • Most lines have 2 entries with home bus at each end • Not all lines in Table 3 • Use Table 2 for max grounding if line not in Table 3

18. Page 1 of Table 3

19. Page 1 of Table 3 • Contains the data for the substations • Home and Remote Buses • Home Bus Grounding for substation – • 15 Second Clearing for Buswork • 27,000 Amps / 2/0 ground cable • 90% used for multiple ground threshold • Three phase and SLG fault current at home bus • Maximum fault current at home bus used

20. Page 2 of Table 3

21. Page 2 of Table 3 • Contains the data for the lines • Home bus line grounding given • Length of line given • 4 distances from home bus for ground changes

22. Home Bus Line Grounds • 30 Second Clearing for Lines • 20,000 Amps / 2/0 ground cable • 90% used for multiple ground threshold • Three phase and SLG fault current at home bus (Page 1 of Table 3) • Maximum fault current at home bus used

23. Line Distance Grounds • Calculated in 2% increments along Line • Change conductors at distance listed for breakpoint • Distance and grounds start with home bus ground • Calculations based on 30 second clearing

24. Example 5 Calculation

25. Example 5

26. Example 5

27. Example 5

28. Example 6 Calculation

29. Example 6

30. Example 7 Calculation

31. Example 7

32. Example 8 Calculation

33. Example 8

34. Example 8 • 2 % increments are 4.8 miles • Higher conductor number to lower conductor change uses end of 2% increment (conservative) • Lower conductor number to higher conductor change uses beginning of 2% increment (conservative)

35. Future Work • Put lines in Table 3 for all lines with 1 or more break points on grounding cable number • Update values for lines from previous study • Remove buses in Table 1 that are not WAPA buses • Remove PTI bus numbers in Tables

36. Questions?