Charlie Williams Power System Services S&C Electric Co.

1. Loose Fuse Tube Caps Impact ReliabilityHow Improper Fuse Installation Causes Feeder Outages & Other Issues Charlie Williams Power System Services S&C Electric Co.

2. Fuse Installation • Fuses are installed in cutout tubes • The fuse is a current carrying device • Proper installation requires a TIGHT cap on the fuse tube and a TIGHT button on the fuse (if a button is used) • Typically 20 Ft-LBS torque required on fuse door cap

3. Capacitor Currents • 100% Load Factor When Energized • Typically energized 12 – 24 Hrs/Day • Steady load current • Magnifies heating of poor connections compared to cyclic loads

4. Current Path for a Fuse Cutout • Should be metal to metal • Threaded joints are poor connections

5. Capacitor Construction

6. Capacitor Pack Failures • Packs fail by shorting • Usual cause is overvoltage or manufacturing defect • When a pack fails it increases voltage on remaining packs • This results in shorter life for remaining packs • The rsult is that pack failures cascade over time

7. Capacitor Failures Increase Currents

8. Typical Failure – One fuse door open

9. Loose Fuse Door Cap and Fuse Button

10. All Cutouts in Series Equal current in each fuse cutout Wrench Tight Loose Cap Loose Button & Cap

11. Result of Excess Cutout Heating • Cutout doors were examined after 2 weeks • All fuse sheaths were totally incinerated • White ash residue found in cutout door

12. Fuse Sheath Incinerated

13. Increased Temperature of Cutout Door Connection • Can cause annealing of springs in the head of the cutout • Results in poor connection • Consequence is arcing and burning and possible dropout of door without melting fuse • Arc is not interrupted and results in fault • Result is Feeder Outage

14. Heating andArcing cause Cutout Failure

15. Cutout Current Interruption Issues • Difficult at current extremes • Very High current • Very Low current • Low Current Interrupt is accomplished by use of tube on fuse link • Compresses fuse gasses to provide sufficient pressure to expulse • Assures Arc interruption in Cutout Door • Failure results in external arc • Arc can then flow and cause external fault on pole

16. Current Interruption Failure • Results in Arc external to cutout • Most capacitors are on mainline feeder • Arc flows up on pole causing feeder fault • Result is Feeder Outage

17. Cure for Cutout Heating • Insure Fuse Buttons are Tight • Insure Cutout Door Caps are Wrench Tight • Not Hand Tight • Annual Infrared Inspections of Capacitor Banks

18. B/L Fuse Upstream of Test 395 Deg F !!

19. Other Connection Issues Failure can result in arcing and Fuse blowing

20. Branch Line Reliability • Loose Fuses result in increased heating of branch line fuses • Low load factor on branch lines would lead to the belief that this is a non-issue? • However, fault currents coupled with loose fuses results in accelerated heating!

21. Branch Line Reliability • The result is a failure of “fuse save” protection schemes and unnecessary outages to branch lines • When it occurs it appears as a temporary fault that no cause could be found. • Accelerated fuse heating acts like a large pre-load on the fuse and reduces the fuse blow time. • Result is a branch line outage that should only have been a momentary interruption!

22. Fuse clears Current Breaker Trips Voltage

23. Proper fuse installation procedure • Tighten buttons well by hand • Tighten fuse caps with a wrench to 20 ft-lbs! • Result • Proper fuse operation • Fuse save schemes that work! • No feeder outages from capacitor banks! • Improved Reliability!