VACUUM INTERRUPTERS FOR GENERATOR CIRCUIT BREAKERS, THEY'RE NOT JUST FOR DISTRIBUTION CIRCUITS BREAK

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VACUUM INTERRUPTERS FOR GENERATOR CIRCUIT
BREAKERS, THEY'RE NOT JUST FOR DISTRIBUTION
CIRCUITS BREAKERS ANYMORE

• Presented by R. Kirkland Smith, Ph.D.
• Eaton / Cutler-Hammer, Horseheads, NY, USA
• Co-authors R. William Long Dale L. Burmingham

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A new, compact generator circuit breaker with TMF
Vacuum Interrupters

• Vacuum interruption
• compact breaker
• contained arc
• sealed for life interrupter
• long, low maintenance life
• Replaces old, large breakers
• Tested to new revised standard for Generator
  Circuit Breakers C37.013a

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Transverse Magnetic Field Contacts Great for
Generator Circuit Breakers

• Spreads arc energy over contact surfaces
• Tolerates long arcing times
• Produces significant arc voltage

Current Loop Drives the Arc
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TMF VIs Now Interrupt High Currents

• First VIs - 1966 for C-H
• low interrupt ratings for distribution circuits
• 15 kV - 12 kA
• Present VIs - 2003
• High interrupt ratings
• 15 kV - 63 kA
• Heading to 80 kA
• Long arcing time tolerance
• Fast TRV RRRV Ability

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Generator Circuit Fault Interruption

• Severe conditions for a circuit breaker
• High short circuit currents
• Long DC time constants and high DC components
• Fast Transient Recovery Voltages (TRVs)
• Delayed current zeroes
• Transverse Magnetic Field (TMF) Vacuum
  interrupters are now well suited for this duty

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A Typical Generator Circuit

• A - System-Source Fault B -
  Generator-Source Fault

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System-source faults

• Highest fault current magnitude
• Short, low resistance connections
• High ratio of L / R, inductance to resistance
• Asymmetrical current for fault interruption
• Long DC time constant
• High DC component at contact part
• Low added circuit capacitance plus high natural
  frequency of transformer
• Fast Transient Recovery Voltages

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System-source fault - High DC Component
Generator Circuit System-source Fault - DC
component of 75 or more Distribution Circuit
faults - DC component of 30 to 50
Contact Part
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System-source fault - Fast TRV
Fast Generator Breaker TRV
TRV for Generator Breaker about 10 times faster
than TRV for Distribution Breaker Fast TRV -
high transformer natural frequency - low added
capacitance from connected circuit
Slow Distribution Breaker TRV
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A Typical Generator Circuit

• A - System-Source Fault B -
  Generator-Source Fault

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Generator-source faults

• Lower fault current level
• 50 of System-Source Fault
• Fast Transient Recovery Voltages
• high generator natural frequency
• low added capacitance from connected circuit
• Extremely high DC component gt 100
• causing
• Delayed current zeros

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Delayed Current Zero

• High DC Component
• gt100
• Long DC Time Constant

Arcing time nearly 3 cycles
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Arc Voltage in a Transverse Magnetic Field (TMF)
Vacuum Interrupter

• VI Arc Voltage
• TMF VI
• 150 volts
• AMF VI
• 50 volts

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Arc Voltage Advances 1st Current Zero

• 150 Volts
• Doubles Circuit Resistance
• Cuts Time Constant in Half

Arcing time reduced to lt 2 cycles
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Tests on New, Compact Generator CB with TMF
Vacuum Interrupter

• 15 kV, 63 kA, 60 Hz, 3000 Amp, STC of 3s.
• System-source fault
• 63 kA 79 DC 3.7 kV / msec to 28 kV
• Generator-source fault
• 31.5 kA 135 DC 1.6 kV/ msec to 28 kV
• Out-of-Phase Switching
• 31.5 kA 3.7 kV / msec to 45 kV
• Robust performance for generator protection