What is used to protect the SCR from over current ________________?

Related Mcqs:

1. 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

2. How can we protect SCR from thermal conditions _____________?

   A. Use of snubber circuit.
   B. Using heat sink.
   C. Using CB and fuse.
   D. Using equalizing circuit

3. Which of the following is used in SCR to protect from high dV / dt__________________?

   A. Snubber circuit
   B. Fuse
   C. Equalizing circuit
   D. Circuit breaker

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. 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

6. SCR will be turned off when anode current is_______________?

   A. < latching current but greater than holding current and gate signal is 0.
   B. less than holding current.
   C. < latching current but greater than holding current and gate signal is present.
   D. both (A) and (B).

7. Anode current in an SCR consists of____________?

   A. holes only
   B. electrons only
   C. either electron or holes
   D. Both electron and holes

8. With gate open, the maximum anode current at which SCR is turned off from ON condition is called____________?

   A. breakdown voltage
   B. peak reverse voltage
   C. holding current
   D. latching current

9. When a large surge current of very short duration flows through a thyristor then which one of the following device will operate to protect the thyristor ___________?

   A. CB
   B. Snubber circuit
   C. Voltage clamping device
   D. Fast acting current limiting device (FACL fuse)

10. An SCR is considered to be a semi controlled device because_______?

    A. it can be turned OFF but not ON with a gate pulse.
    B. it conducts only during one half cycle of an alternating current wave.
    C. it can be turned ON but not OFF with a gate pulse.
    D. it can be turned ON only during one half cycle of an AC.