A string of n parallel SCRs is operated at 72 KA, the rating of each SCR is 1 KA. If derating factor of the string is 0.1. value of n will be___________?

Related Mcqs:

1. A thyristor string is made of a no. of SCR connected in series and parallel. The string have volume and current of 11 KV and 4 KA. The voltage and current rating of available SCRs are 1800 V and 1000 A. For a string efficiency of 90 % let the number of SCRs in series and parallel are a and b respectively. Then the value of a and b will be_____________?

   A. 5, 7
   B. 4, 6
   C. 7, 5
   D. 6, 4

2. 4 thyristors rated 200 V in series. The operating voltage of the string is 600 V. Derating factor of the string is_____________________?

   A. 0.75
   B. 0.7
   C. 0.2
   D. 0.25

3. The turn-on time of an SCR with inductive load is 20 µs. The puls train frequency is 2.5 KHz with a mark/space ratio of 1/10, then SCR will___________?

   A. Turn on
   B. Not turn on
   C. Turn on if inductance is removed
   D. Turn on if pulse frequency us increased to two times

4. An SCR has half cycle surge current rating of 3000 A for 50 Hz supply. One cycle surge current will be_____?

   A. 1500 A.
   B. 6000 A.
   C. 2121.32 A.
   D. 4242.64 A.

5. Practical way of obtaining static voltage equalization in series connected SCRs is by the use of____________?

   A. One resistor across the string
   B. Resistors of the same value across each SCR
   C. Resistors of different values across each SCR
   D. One resistor in series with each SCR

6. SCRs are used in series to meet_______________?

   A. high current demand
   B. low voltage demand
   C. low current demand
   D. high voltage demand

7. To meet high current demand we use SCRs in______________?

   A. series connection.
   B. parallel connection.
   C. anti parallel connection.
   D. both B and C.

8. 60 thyrsistors are connected in series and parallel to form a 10 KV and 5.5 KA switch. Each thyristor is rated for 1.2 KV, 1 KA. The no. of parallel path are 6. The efficiency of the switch is______________________?

   A. 76.3 %
   B. 91.6 %
   C. 83.3 %
   D. 90.9 %

9. The typical value of SCR for modern alternator is____________?

   A. 1.5.
   B. 0.5.
   C. 1.0.
   D. 1.2.

10. A single phase full bridge inverter can operated in load commutation mode in case load consist of______?

    A. RL.
    B. RLC underdamped.
    C. RLC overdamped.
    D. RLC critically damped