A voltage commutation circuit is shown in the figure given

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A voltage commutation circuit is shown in the figure given below. If the turn off time of the SCRs is 50 μ sec and a safety margin of 2 is considered, then what will be the approximate minimum value of capacitor required for proper commutation?

1. 2.88 μF
2. 1.44 μF
3. 0.91 μF
4. 0.72 μF

Correct Option: A

Firing of TH1 thyristor would commute TH2 and firing of TH2 would commute TH1 and in this way load will be transfered between TH1 and TH2 and vice-versa.
Circuit turn-off time for,
TH1, t₁ = R₁C ln 2
and turn-off time for
TH2, t₂ = R₂C ln 2
Safety margin = 2
Then, t₁ = t₂ = 2 × 50 × 10^{– 6} (given)
⇒ R₁ C ln2 = 2 × 50 × 10^{– 6}

⇒ C =	2 × 50 × 10^{– 6}	= 2.88 μF
	50 × ln 2