1. History of SF6 High Voltage Circuit Breakers
Richard A. York
MEPPI

2. History of SF6 High Voltage Circuit Breakers
Why SF6?
SF6 Dielectric Properties
Interrupter Types and Design
Early SF6 Design
Industry Standards Development

3. The Early Days!
Bulk oil breakers dominated in the transmission industry from its inception

4. A ‘Successful’ Test!

5. Why SF6? Hazards of Oil – flammability
Size/weight of bulk oil breakers
Interrupter efficiency – multi-break per phase
Energy efficiency – high energy hydraulic & pneumatic drives

6. SF6 Development - Westinghouse
Alternatives to oil search began in late 40’s/early 50’s
SF6 previously recognized as good dielectric medium
Used in a variety of applications: X-ray equipment and transformers
Dielectric properties known
Interrupting capabilities determined to be superior due to the high electronegative characteristic

7. SF6 Development - Westinghouse
High Electronegative Characteristics are described by its capability to attach free electrons
Very short arc time constant (the ability to recover its dielectric strength following arc conduction) 100x better than air
SF6 arc time constant – approximately 1µsec
Air arc time constant – approximately 100µsec
Non-conductive arc by-products
High stability and no degradation over time

8. SF6 Breaker Design Challenges
Withstanding corrosive decomposition arc by- products
Special test chambers to generate the by-products
Original materials used were wood, paper and cloth phenolics with coatings
SF6 gas sealing
Silicone seals failed due to its high permeability
Neoprene, Ethylene Propylene selected

9. SF6 Breaker Design Challenges
Instrumentation
SF6 density monitor development (temperature compensated pressure switch) – SF6 performance based on density, not pressure alone
Interrupter enclosures as pressure vessels
ASME Pressure Vessel Code compliance
Graphite rupture disc selected for long life
SF6 gas handling & reclaiming
SF6 cost low
Environmental concerns unknown
Filling and reclaiming SF6 – new industry born!

10. Interrupter Design Various prototypes tested in early R&D phase
Liquid SF6 – similar to existing oil interrupter design
SF6 gas/liquid ‘hybrid’ – liquid SF6 injected into the arc
These early attempts suffered from the high pressure needed for the gas and high maintenance necessary for regular use

11. 1st SF6 Breaker Design Criteria
Considering the slow response to adapt in the utility and power industry, SF6 breaker design would mimic oil breakers as much as possible:
Dead Tank
Overlapping CT’s
Gang operated
Close by single pneumatic drive
Open by springs charged during closing (fail safe design)
No opening resistor
3-cycle interrupting time
CO-15 sec-CO and O-CO Duty Cycle capable
-30°C rated
Meet all existing ANSI/IEEE Standard requirements

12. Early SF6 Applications
First SF6 breaker 115 kV, 1,000 MVA interrupting rating (Standards specified only MVA ratings at this time)
Interrupter based on ‘self- pressure’ generating principle
Two sets of interrupters in series used at 115 kV
46 kV recloser using a single interrupter of this type installed in 1957 at Consumers Power

13. High Power Commercial Design
2-Pressure SF6 gas design selected
Puffer type interrupter considered viable, but new, higher mechanism design needed – time constraints prohibited development!

14. 2-Pressure SF6 Breaker 1960
Interrupter performance verified – 40 kA at 230 kV
High pressure SF6 blast valve controlled from pilot valve
Interrupter contacts, Teflon nozzle based on early puffer prototypes

15. SF6 Interrupter Evolution
Patent Disclosure Figures– 1959

16. Modern SF6 Interrupters
Single pressure puffer
Single pressure self-blast or arc-assist

17. IEEE Standards Evolution
AIEE – American Institute of Electrical Engineers
Electric Power Club (manufacturers association)
Association of Edison Illuminating Companies (AEIC)
National Electric Light Association

18. Electric Power Club 1919 Performance Standard
Breaker must be able to make two (2) Open operations within a two-minute interval
No limits on flame or oil ejection
If current interrupts – SUCCESS!

19. Performance Developments
Interrupting Times: 20 – 12 – 8 cycles; later reduced to 5 – 3 cycles
Operating Duty; 2 minutes; reduced to 15 seconds
Reclosing: 30 to 45 cycles; reduced to 20 cycles
Power frequency ‘hipot’ test originally only dielectric test
Lightning impulse, 2 and 3 µsec chop wave, switching impulse followed years later

20. First American Standard
Issued for ‘trial use’ in 1941
Published in 1945

21. 1st American Standard – ASA C37
C37 Series for Switchgear
C – Alternating-Current Power Circuit Breakers
C – Methods for Determining the Rms Value of a Sinusoidal Current Wave and Normal Frequency Recovery Voltage
C – Schedule of Preferred Ratings for Power Circuit Breakers
C – Operating Duty (Duty Cycle) for Standard Reclosing Service
C – Rated Control Voltages
C – Test Code for Power Circuit Breakers

22. Standards Evolution
1960’s – 70’s: Major changes to the basic rating structure
Original method of rating on MVA basis
New method based on symmetrical current basis
1990’s – 2000: Major changes to harmonize with IEC Standards
TRV definitions
Test procedures

23. Current Standards

24. Standards Development – Today
Major revisions to C37.04 and C37.09 in balloting process now:
C37.06 to be eliminated
Combined with C37.04 and C37.09 where appropriate
Further harmonization with IEC where possible

25. Special Thanks
Russ Yeckley worked with the original Westinghouse breaker team in the research, design and development of these 1st generation SF6 breakers. Thanks to Russ, I have been able to share some of the detailed knowledge acquired during this time.

26. Questions ?