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1) If a shunt motor is started with its field winding open then? a. It will rotate at the same speed as that with its field winding closed b. It will rotate at less speed as that with its field winding closed c. It will rotate at dangerously high speed d. None of these
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2) A rectifier with an external low pass filter is an example of______________? a. Indirect switch matrix circuits b. Direct switch matrix circuits c. Embedded converters d. All of these
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3) The power demand can be estimated approximately by___________? a. Load survey method b. Mathematical method c. Statistical method d. Economic parameters
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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
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5) Unipolar modulation is generally used in____________? a. AC – AC converters b. AC – DC converters c. DC – AC converters d. DC – DC converters
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6) Dynamic equalizing circuit is used for________________? a. equal division of voltage across each thyristor b. equal division of current through each thyristor in parallel c. equal division of voltage across each thyristor in parallel d. equal division of current through each thyristor in series
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7) 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___________? a. 60 b. 70 c. 80 d. 90
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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 %
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9) Maximum di / dt in a SCR is________? a. Directly proportional to Vm of supply voltage b. Inversely proportional to Vm of supply voltage c. Inversely proportional to L in the circuit d. Both A and C
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10) 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
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11) 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
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12) By which one of the following we can measure the reliability of a string_____________? a. String efficient b. Reliability factor c. Factor of safety d. Derating factor
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13) Anode current in an SCR consists of____________? a. holes only b. electrons only c. either electron or holes d. Both electron and holes
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14) To meet high current demand we use SCRs in______________? a. series connection b. parallel connection c. anti parallel connection d. both B and C.
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15) Dynamic equalising circuit is useful____________? a. To limit di / dt of SCR b. To limit dV / dt of SCR c. For voltage equalisation d. Both B and C
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16) SCRs are used in series to meet_______________? a. high current demand b. low voltage demand c. low current demand d. high voltage demand
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17) Which following is a two terminal three layer device? a. BJT b. Power dioed c. MOSFET d. None of above
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18) ON state voltage drop across SCR lie between the range_____________? a. 0 – 0.5 V. b. 0.5 – 1 V. c. 1 – 1.5 V. d. 1.5 – 2 V.
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19) Which of following is not a power transistor? a. IGBTs b. COOLMOS c. TRIAC d. SITS
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20) Which statement is true ? a. Reverse recovery time ( trr ) > gate recovery time (tgr) b. Device turn OFF time ( tq ) > reverse recover time (trr) c. Circuit turn OFF time > device turn OFF time ( tq ) d. All of these
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