# Presentation: 154733

## 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
- Distance and grounds start with home bus ground
- 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?