01․ The typical value of SCR for modern alternator is
Always the typical value of SCR for modern alternator is 0.5.
02․ An SCR has half cycle surge current rating of 3000 A for 50 Hz supply. One cycle surge current will be
03․ An SCR is considered to be a semi controlled device because
During positive half cycle SCR is in forward blocking mode. By applying gate pulse the SCR can be turned ON during forward blocking mode. But SCR can not be turned OFF by applying gate pulse. It automatically turns off when anode current is below the Holding current. That is why it is called semi controlled rectifier.
04․ A single phase one pulse controlled circuit has a resistance R and counter emf E load 400 sin(314 t) as the source voltage. For a load counter emf of 200 V, the range of firing angle control is
So, control range is θ to ( π- θ ) i.e. 30° to 150°.
05․ A single phase full bridge inverter can operated in load commutation mode in case load consist of
In this case reading current will flow in circuit and it will became zero so thyristor will be load commutated .
For step-up chopper, E0=Edc/(1-α), E0 = output voltage and Edc = output voltage,α = 1-(110/150) ⇒ 0.26 where α = duty cycle. recheck
07․ Which statement is true for latching current ?
Latching current is the minimum required anode current to turn on SCR.
08․ If holding current of a thyristor is 2 mA then latching current should be
Generally latching current is 2 or 3 times of holding current.
09․ In reverse blocking mode of a thyristor
In reverse blocking mode J1 and J2 is in reverse bias and J2 is in forward bias.
10․ In forward blocking mode of a thyristor
In forward blocking mode junction J2 acts in reverse bias whereas J1 and J3 act in forward bias.