InterviewSolution
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InterviewSolution
This section includes InterviewSolutions, each offering curated multiple-choice questions to sharpen your knowledge and support exam preparation. Choose a topic below to get started.
| 101. |
A single phase half wave controlled rectifier circuit has a free wheeling diode. The load is a combination of R and L. The firing angle is . The period of conduction of SCR and free wheeling diode respectively are |
| Answer» SCR conducts from a to p and free wheeling diode from p to (2p + a). | |
| 102. |
In a circuit using a full wave converter (M - 2 connection) the PIV of each thyristor is 400 V. For the same output voltage and fully controlled bridge converter, PIV will be |
| Answer» In bridge connection PIV is half of that in M-2 connection. | |
| 103. |
A dc separately excited motor has constant field current. The armature is fed from a single phase supply through a full converter. When = 0, speed is 500 rpm. If = 45°, the speed is likely to be |
| Answer» Average output voltage ∝ cos a and therefore reduced to 0.707 of the value for a = 0. Speed is nearly proportional to voltage. | |
| 104. |
A two winding transformer is feeding a single phase half wave rectifier circuit. The load is purely resistive. The rms value of transformer secondary current is I and rms value of load current in I. Then |
| Answer» . | |
| 105. |
A chopper |
| Answer» A chopper is a dc-ac converter. It converts a fixed dc voltage into a variable dc voltage. | |
| 106. |
In a single phase full wave regulator, the firing angles in the positive and negative half cycles are generally |
| Answer» Firing angles are kept equal to get symmetrical output voltage. | |
| 107. |
An electric heater is controlled by thyristors through on-off control. If = 0.4, the heating is |
| Answer» Vl = V a. Therefore Vl2 - V2 (a). Heating is proportional to a. | |
| 108. |
The terminals of a power BJT are called |
| Answer» In a BJT terminals are emitter, base and collector irrespective of rating. | |
| 109. |
In single phase half wave regulator, the average current over one full cycle |
| Answer» The input current during positive half cycle is less than that during negative half cycle. | |
| 110. |
The dynamic equalising circuit consists of a series combination of capacitor C and resistor R across each thyristor. This resistance R (along with parallel connected diode) |
| Answer» Discharge current flows through Re . | |
| 111. |
The value of capacitor C for dynamic equalising circuit of series connected thyristors is determined by |
| Answer» Value of C is proportional to maximum difference between reverse charge of SCRs in series. | |
| 112. |
A single phase semiconverter is feeding a highly inductive load and has freewheeling diode across the load. The waveshapes of output voltage and output current |
| Answer» When freewheeling diode conducts output current exists but output voltage is zero. | |
| 113. |
A 3 kV circuit uses SCR of 800 V rating. If derating is 25%, the number of SCRs in series is |
| Answer» . | |
| 114. |
Current derating may be necessary when thyristors are operating in |
| Answer» Since current does not divide equally, current derating is necessary. | |
| 115. |
If duty cycle is and the load is a resistance R, the rms value of output voltage is |
| Answer» RMS output voltage VL = a V. | |
| 116. |
For a BJT = 0.98, then β = |
| Answer» | |
| 117. |
In a multiphase chopper, all choppers operate together. |
| Answer» They operate in a sequence. | |
| 118. |
The terminals of a power MOSFET are called |
| Answer» In a MOSFET terminals are source, gate, drain irrespective of rating. | |
| 119. |
In a thyristor the gate current is increased, then |
| Answer» Gate current does not affect the magnitude of anode current. | |
| 120. |
Thyristors are not suitable for logic circuits. |
| Answer» Thyristors can be used for logic circuits. | |
| 121. |
A single phase half wave rectifier is feeding a resistive load. Input voltage = V sin ω. The output dc voltage is V and output rms voltage is V . If firing angle is 180°, V and V respectively are |
| Answer» Put a = 180° in Eqs Otherwise also a = 180° means no conduction. Hence zero output voltage. | |
| 122. |
A thyristor has a turn on time of 6 μs. If the anode circuit is inductive, the turn on time will be |
| Answer» Inductive load increases the turn on time. | |
| 123. |
The total number of leads in reverse conducting thyristor is |
| Answer» | |
| 124. |
A single phase half wave rectifier is feeding a resistive load. When = 0, dc output voltage is 127 V. When = 30°, the dc output voltage will be about |
| Answer» Using Eq = 0.933. Hence Vdc for 30° firing angle = 0.933 x 127 = ≈ 120 V. | |
| 125. |
If V is the dc output voltage in half wave controlled rectifier circuit feeding resistive load and V is the dc output voltage in full wave controlled rectifier circuit (M - 2 connection) feeding resistive load, then |
| Answer» and Vdc = (1 + cos a). | |
| 126. |
A semi converter operates in two quadrants. |
| Answer» It operates only in quadrant. | |
| 127. |
Figure shows a chopper feeding RLE load, The free wheeling diode conducts when |
| Answer» FD is forward biased only when thyristor is off. | |