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______________________?

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. 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)

3. 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

4. 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

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. For series connected SCR’s dynamic equalising circuit consists of___________?

   A. R and C in series but with diode across C
   B. R and C in series but with diode across R
   C. Series R and diode with C across R
   D. Series R and diode with C across R

7. A thyristor equivalent of a thyratron tube is a _________?

   A. Diac
   B. Triac
   C. Silicon controlled-rectifier SCR
   D. None of above

8. Thyristor can be protected from over voltages by using____________?

   A. voltage clamping device.
   B. fuse.
   C. heat sink.
   D. snubber circuit.

9. 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

10. A thyristor can termed as__________?

    A. AC switch
    B. DC switch
    C. Both a and B
    D. Square wave switch