Let of a thyristor Vc1, Vc2, Vc3 are forward break over voltage for gate current Ig1, Ig2, Ig3 respectively. Then________________?

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. The capacitance of reversed bised junction J2 in a thyristor is CJ2 = 20 pF and can be assumed to be independant of the off state voltage. The limiting value of the charging current to turn on the thyristor is 16 mA. What is the critical value of dv/dt?

   A. 600 V/µs
   B. 800 V/µs
   C. 1200 V/µs
   D. 1000 V/µs

3. 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)

4. For an SCR gate – cathode characteristic is a straight line of 130. For triggered source volume of 15 V and allowable gate power dissipation of 0.5 W compute the gate source resistance_____?

   A. 111.9 Ω.
   B. 11.19 Ω.
   C. 108 Ω.
   D. 115 Ω

5. Gate circuit or triggering circuit of a thyristor is

   A. lower power circuit.
   B. high power circuit.
   C. magnetic circuit.
   D. may be low power or high power circuit

6. If holding current of a thyristor is 2 mA then latching current should be_____?

   A. 0.01 A.
   B. 0.002 A.
   C. 0.009 A.
   D. 0.004 A.

7. CB used for over current protection of thyristor operates when the fault current is__________?

   A. of long period
   B. of short duration
   C. both (A) and (B)
   D. neither (A) nor (B)

8. Leakage current flows through the thyristor in_________?

   A. forward blocking mode
   B. reverse blocking mode
   C. both forward and reverse blocking mode
   D. forward conduction mode

9. If the gate voltage of an SCR is removed, then the_______________?

   A. anode current decreases
   B. anode current does not decrease at all
   C. anode current increases
   D. cathode current increases

10. The ac output voltage waveform of VSI and AC output current waveform of CSI respectively is composed of___________?

    A. High dv / dt, low di / dt
    B. Low dv / dt, low di / dt
    C. Low dv / dt, high di / dt
    D. High dv / dt, high di / dt