Loose Fuse Tube Caps Impact Reliability How Improper Fuse Installation Causes Feeder Outages Other Issues

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

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

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

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

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!

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!