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History of SF6 High Voltage Circuit Breakers

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Presentation on theme: "History of SF6 High Voltage Circuit Breakers"— Presentation transcript:

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 ?


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