Austin Energy Fusing and Fault Indicator Applications

1. Austin Energy Fusing and Fault Indicator Applications SWEDE - April 26th, 2011 - Bastrop Tommy Nylec

2. Overview • Introduction to Austin Energy • Purpose of Coordination Concern • Unique Situations • Engineering and Operational Solutions • Future Work and Conclusions

3. Austin Energy Statistics • >400,000 Customers • >2,800 MW Generation • ># mi Transmission • 56 Distribution Substations • > 10,000 miles of Distribution • >1,600 Employees • Serve 437 square miles including Austin city limits and neighboring areas • Started in 1887

4. Austin Energy Reliability • SAIFI = .63 • SAIDI = 43.97 • CAIDI = 69.86 • Challenge ourselves with high goals for reliability indices • Consistently in the top performance in the country

5. Coordination Scheme Revisited • Need to be simple to interpret for field personnel • Must allow for ease of use in design environment • Application must hold in > 80% cases • Point of coordination determined by maximum available fault current • 20% Separation between Total Clear and Minimum Melt curves of devices

6. Austin Energy Fault Current Levels • Item of Concern • Infinite Bus Calculations for Larger Transformers= 14.5 kA • Short Feeders • High density of substations • System is primarily 12.5 kV • Transmission Impedance on larger transformers creates approximately 10 kA • Majority of fuses are at > 2kA • Typical Unit Installation results in Fault Current < 8.5 kA at Bus

7. Warehouse Inventory • Limited space in warehouse and trucks • Minimize variety of fuses • Standardize applications • Reduction of inventory

8. Substation Coordination • Most relays set at 360 A Ground Pickup • Eases coordination with downstream devices • Provides adequate system protection • Considerations • Some substations do not have this setting • Conflicts with some fusing scenarios

9. Unique Scenarios • Slugging • Required due to presence of extra fuse • Fault Level Cheat Sheets • Rules of Thumb don’t apply • Skip fuse size between devices

10. Solution • Keep same fuse ampacity ratings • Limit number of fuses with same ampacity but different speeds • Allow duplicates in most common sizes • Austin Energy Rule of Thumb • Must skip 2 fuse sizes between devices

11. Feeder Coordination Studies • Studies performed on 5 year rotational basis • Creates opportunity to revisit coordination scheme • Allows adjustment of existing fuses to new scheme • Limited inventory restricts solutions to encountered problems

12. Fault Indicator Application • Fault must pass through equipment • Placed accordingly • Follow Cooper Application guide

13. Austin Energy Standard Traditional Placement: • Located at transformer Austin Energy Additional Requirements: • Additional F.I.’s located at risers and switchgears

14. Installation Methods • Concentric Neutral • Identified misapplication • Changes made to standard to correct • In accordance with industry standards

15. Fault Indicator Conclusions • Provide additional visual cues of fault locations • Decrease service restoration time • Reduce equipment exposure during restoration practices • Economic Impact

16. Questions?