1. AC circuit breaker with series connected switches George G Karady

2. AC circuit breaker with series connected switches CB’s 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

3. AC circuit breaker with series connected switches Equivalent circuit Supply is represented by Thevenin equivalent Network open circuit voltage and short circuit impedance Z short = 1.8 ohm V open = 7.2 kV Short circuit with zero fault impedance

4. 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 Z snub = 10k + 26ki ohm

5. 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

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

7. 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

8. Rectifier with thyristors connected in series supplies a load

9. Rectifier supplies a load Current path in the positive cycle Snubber is connected in parallel with each diode

10. 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:

11. Rectifier with thrystors connected in series supplies a load

12. AC circuit breaker with series connected switches 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 Switch 1Switch 2