# Safety Grounding Update by rsr13049

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```									Safety Grounding Update
July 25, 2006
Phoenix, AZ
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
2006 PSSM Appendices
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
2006 PSSM Appendix K
Table 1 – pages 173 through 183
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
Table 1 Calculations
• Calculations use the maximum fault current
• Table 10.1 in 2006 PSSM – Cable Limits
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
Example 1 Calculation
Example 2 Calculation
2006 PSSM Appendix K
Table 2 – pages 184 through 190
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
Example 3 Calculation
Each Line Entered Twice
Example 4 Calculation
Example 4 Calculation
Table 3 2006 PSSM Appendix K
pages 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
Page 1 of Table 3
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
Page 2 of Table 3
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
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
Line Distance Grounds
• Calculated in 2% increments along Line

• Change conductors at distance listed for breakpoint

• Calculations based on 30 second clearing
Example 5 Calculation
Example 5
Example 5
Example 5
Example 6 Calculation
Example 6
Example 7 Calculation
Example 7
Example 8 Calculation
Example 8
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)
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
Questions?

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