Year 2024

Week # 4 Quiz 1

Q1. A bulb in a staircase has two switches, one switch being at the ground floor and the other one at the first floor. The bulb can be turned ON and also can be turned OFF by any one of the switches irrespective of the state of the other switch. The logic of switching of the bulb resembles

Q2. A boost converter operating at duty cycle of 0.5 with input voltage of 100 V dc suppling a resistive load of 100 \(\Omega\). The input current of the buck converter will be,

Q3. A dc voltage source of is supplying R-L load through an SCR with pulse width of \(100 \mu s\). Latching current of SCR is 100 mA in case load consists of R = 20 \(\Omega\) in series with L = 0.5 H.

Q4. A step up chopper is used to feed a load at 400 V DC from a 250 V DC source. The inductor current is continuous. If the ‘OFF’ time of the switch is 20 \(\mu s\), the switching frequency of the chopper in kHz is                

Q5. A 300 A thyristor is to be operated in parallel with a 400 A thyristor. The ON state voltage drops are 1.6 V and 1.4 Volts. What is the value of resistance R to be connected in series with each thyristor, so that current through the combination is 700 A and each of them is fully loaded ?

Q6. A voltage commutated chopper feeds power to a battery-powered electric car. The battery voltage is 74 V. Starting current is 67 A and the SCR turn-off time is 20 μs. Calculate the value of inductance (L) required for the commutating circuit.

Q7. When two identical SCRs are placed back to back in series, with a load and if each is fired at 90°, a DC voltmeter across the load read

Q8. What is the average value of the output voltage \(V_{av}\) of resistive load chopper when the supply voltage is \(V\) and \(T_{on}\) & \(T_{off}\) are the periods of conduction and blocking of thyristor?

Q9. A string of n parallel SCRs is operated at 68 KA, the rating of each SCR is 1.2 KA. If derating factor of the string is 0.1. Then calculate the value of n

Q10. In current source inverter (CSI), if the frequency of voltage input to CSI is 'f' Hz, then the frequency of the output voltage is_____________Hz.