AC circuit breaker with series connected switches

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AC circuit breaker with series connected switches

• George G Karady

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AC circuit breaker with series connected switches

• CBs protect power system
• Short circuit triggers the CB
• CB interrupts the inductive short circuit current
• After few cycle of arcing the current is
  interrupted at zero crossing

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AC circuit breaker with series connected switches

• Equivalent circuit
• Supply is represented by Thevenin equivalent
• Network open circuit voltage and short circuit
  impedance
• Zshort 1.8 ohm Vopen 7.2 kV
• Short circuit with zero fault impedance

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AC circuit breaker with series connected switches

• Equivalent circuit
• CB with switches connected in series.
• Snabber impedances are connected in parallel with
  each switch
• Typical values Capacitor 0.1microF, Resistance
  10kohm. Total impedance Zsnub 10k 26ki ohm

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AC circuit breaker with series connected switches

• The switches turn off in sequence
• The voltage across the switch that turns off
  first is the largest

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AC circuit breaker with series connected switches

• The equivalent circuit is

The voltage across the switch that turns off
first is
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AC circuit breaker with series connected switches

• Voltage across the switch turns off first is

• Voltage across the switch is close to the supply
  voltage

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Rectifier with thyristors connected in series
supplies a load
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Rectifier with thyristors connected in series
supplies a load

• Rectifier supplies a load

• Current path in the positive cycle
• Snubber is connected in parallel with each diode

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Rectifier with thrystors connected in series
supplies a load

• Each thrystor is protected by a snubber connected
  in parallel
• The current is determined by the load impedance
• The voltage across the diode that turns off first
  is

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Rectifier with thrystors connected in series
supplies a load
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AC circuit breaker with series connected switches
Switch 1
Switch 2

• Switching sequence
• A diode and a snubber circuit is connected in
  parallel with each switches
• In the positive cycle switch 1 turns off,
• The current is transferred to the diodes and
  interrupted at zero crossing
• Switch 2 turns off in the negative cycle to
  prevent conduction