Question 1-6 Are There Fundamental Performance Limits for Vacuum Breaking Technology?

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Question 1-6Are There Fundamental Performance
Limits for Vacuum Breaking Technology?

• R. Kirkland Smith, Ph.D.
• Eaton / Cutler-Hammer,
• Horseheads, NY, USA

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Key Vacuum Interrupter Functions

• Carry continuous current
• Carry peak momentary current
• Interrupt fault currents
• Withstand high voltages

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Carry continuous current

• Vacuum interrupters have one pair of contacts
• All heat must be conducted through the terminals
• 3150 Amps is typical convection cooled rating
• 4000 and maybe 5000 amps - forced cooled
• Cooling is a limit

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Carry peak momentary current

• Vacuum interrupters have one pair of contacts
• Added force must counter blow-off force
• at 25 kA - 200 kilograms force required
• at 100 kA - 1700 kilograms force required
• High mechanism force is a limit

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Interrupt fault currents

• VIs now available at
• 63 and 80 kA at 15 kV
• 40 kA at 38 kV
• Fault interruptions to 200 kA reported
• Experimental units work at 72.5 kV - 63 kA
• Interruption ratings meet most needs

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Withstand high voltages

• Breakdown voltage of vacuum gap levels off as gap
  increases
• 400 - 600 kV peak is practical limit
• 72.5 kV in a one VI looks like a limit

Withstand voltage is a definite limit
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Probable Future VI Ratings

• Low Voltage to 1.5 kV
• 100 to 200 kA 3150 to 4000 / 5000 A
• Medium Voltage to 52 kV
• 63 to 80 kA 3150 to 4000 / 5000 A
• High Voltage to 72.5 kV / 84 kV
• 40 to 80 kA up to 3150 A
• Two VIs in series will do 145 kV