MCQOPTIONS
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MCQOPTIONS
This section includes 257 Mcqs, each offering curated multiple-choice questions to sharpen your Power Electronics knowledge and support exam preparation. Choose a topic below to get started.
| 101. |
In given fig. PIV required for the diode is: |
| A. | 300 V |
| B. | 100 V |
| C. | 200 V |
| D. | 400 V |
| Answer» E. | |
| 102. |
A single-phase voltage controller feeds power to a resistance of 10 . The source voltage is 200 V rms. For a firing angle of 90 , the rms value of thyristor current in amperes is |
| A. | 20 |
| B. | 15 |
| C. | 10 |
| D. | 5 |
| Answer» D. 5 | |
| 103. |
In a single-phase voltage controller with RL load, ac output power can be controlled if |
| A. | firing angle > (load phase angle) and conduction angle = |
| B. | > and < |
| C. | < and = |
| D. | < and > |
| Answer» C. < and = | |
| 104. |
The SCR ratings, di/dt in A/ sec and dv/dt in V/ sec, may vary, respectively, between |
| A. | 20 to 500, 10 to 100 |
| B. | both 20 to 500 |
| C. | both 10 to 100 |
| D. | 50 to 300, 20 to 500 |
| Answer» C. both 10 to 100 | |
| 105. |
For an SCR with turn-on time of 5 microseconds, an ideal trigger pulse should have |
| A. | short rise time with pulse width = 3 sec |
| B. | long rise time with pulse width = 6 sec |
| C. | short rise time with pulse width = 6 sec |
| D. | long rise time with pulse width = 3 sec |
| Answer» D. long rise time with pulse width = 3 sec | |
| 106. |
On-state voltage drop across a thyristor used in a 250 V supply system is of the order of |
| A. | 100 110 V |
| B. | 240 250 V |
| C. | 1 to 1 5 V |
| D. | 0 5 to 1 V |
| Answer» D. 0 5 to 1 V | |
| 107. |
A single-phase voltage controller feeds an induction motor (A) and a heater (B) |
| A. | In both the loads, fundamental and harmonics are useful |
| B. | In A only fundamental and in B only harmonics are useful |
| C. | In A only fundamental and in B harmonics as well as fundamental are useful |
| D. | In A only harmonics and in B only fundamental are useful |
| Answer» D. In A only harmonics and in B only fundamental are useful | |
| 108. |
Thermal resistance in SCRs has the units of (W/ C, or ohms or C/W) and heat sinks are made from (copper/steel/aluminium) |
| A. | C/W, Aluminium |
| B. | C/W, Copper |
| C. | W/ C, Aluminium |
| D. | W/ C, Copper |
| Answer» B. C/W, Copper | |
| 109. |
The di/dt rating of on SCR is specified for its |
| A. | decaying anode current |
| B. | decaying gate current |
| C. | rising gate current |
| D. | rising anode current |
| Answer» E. | |
| 110. |
The object of connecting resistance and capacitance across gate circuit is to protect the SCR gate against |
| A. | over-voltages |
| B. | dv/dt |
| C. | noise signals |
| D. | over-currents |
| Answer» D. over-currents | |
| 111. |
Once SCR starts conducting a forward current, its gate loses control over |
| A. | anode circuit voltage only |
| B. | anode circuit current only |
| C. | anode circuit voltage and current |
| D. | anode circuit voltage, current and time |
| Answer» D. anode circuit voltage, current and time | |
| 112. |
In a thyristor, the magnitude of anode current will |
| A. | increase if gate current is increased |
| B. | decrease if gate current is decreased |
| C. | increase if gate current is decreased |
| D. | not change with any variation in gate current |
| Answer» E. | |
| 113. |
Turn-on time for an SCR is 10 sec. If an inductance is inserted in the anode circuit, then the turn-on time will be |
| A. | 10 sec |
| B. | less than 10 sec |
| C. | more than 10 sec |
| D. | about 10 sec |
| Answer» D. about 10 sec | |
| 114. |
Turn-off time of an SCR is measured from the instant |
| A. | anode current becomes zero |
| B. | anode voltage becomes zero |
| C. | anode voltage and anode current become zero at the same time |
| D. | gate current becomes zero |
| Answer» B. anode voltage becomes zero | |
| 115. |
The average on-state current for an SCR is 20 A for a conduction angle of 120 . Its average on-state current for 60 conduction angle would be |
| A. | 20 A |
| B. | 10 A |
| C. | less than 20 A |
| D. | 40 A |
| Answer» D. 40 A | |
| 116. |
Surge current rating of an SCR specifies the maximum |
| A. | repetitive current with sine wave |
| B. | non-repetitive current with rectangular wave |
| C. | non-repetive current with sine wave |
| D. | repetititive current with rectangular wave |
| Answer» D. repetititive current with rectangular wave | |
| 117. |
For an SCR with turn-on time of 5 microsecond, an ideal trigger pulse should have |
| A. | short rise time with pulse width = 3 sec |
| B. | long rise time with pulse width = 6 sec |
| C. | short rise time with pulse width = 6 sec |
| D. | long rise time with pulse width = 3 sec |
| Answer» C. short rise time with pulse width = 6 sec | |
| 118. |
Specification sheet for an SCR gives its maximum rms on-state current as 35 A. This rms rating for a conduction angle of 120 would be |
| A. | more than 35 A |
| B. | less than 35 A |
| C. | 35 A |
| D. | 52 5 A |
| Answer» D. 52 5 A | |
| 119. |
The average on-state current an SCR is 20 A for a resistive load. If an inductance of 5 mH is included in the load, then average on-state current would be |
| A. | more than 20 A |
| B. | less than 20 A |
| C. | 15 A |
| D. | 20 A |
| Answer» B. less than 20 A | |
| 120. |
The function of snubber circuit connected across an SCR is to |
| A. | suppress dv/dt (b) |
| B. | increase dv/dt |
| C. | decrease dv/dt (d) |
| D. | keep transient overvoltage at a constant value |
| Answer» B. increase dv/dt | |
| 121. |
For an SCR, dv/dt protection is achieved through the use of |
| A. | RL in series with SCR |
| B. | RC across SCR |
| C. | L in series with SCR |
| D. | RC in series with SCR |
| Answer» C. L in series with SCR | |
| 122. |
An UJT exhibits negative resistance region |
| A. | before the peak point |
| B. | between peak and valley points |
| C. | after the valley point |
| D. | both (a) and (c) |
| Answer» C. after the valley point | |
| 123. |
The circuit symbol for a GTO is |
| A. | a |
| B. | b |
| C. | c |
| D. | d |
| Answer» C. c | |
| 124. |
For dynamic equalizing circuit used for series connected SCRs, the choice of C is based on |
| A. | reverse recovery characteristic |
| B. | turn-on characteristics |
| C. | turn-off characteristics |
| D. | rise-time characteristics |
| Answer» B. turn-on characteristics | |
| 125. |
In a single-phase full converter, for discontinuous load current and extinction angle > , each SCR conducts for |
| A. | |
| B. | |
| C. | |
| D. | + |
| Answer» C. | |
| 126. |
For a pulse transformer, the material used for its core and the possible turn-ratio from primary to secondary are, respectively |
| A. | ferrite; 20: 1 |
| B. | laminated iron; 1: 1 |
| C. | ferrite; 1: 1 |
| D. | powdered iron; 1: 1 |
| Answer» D. powdered iron; 1: 1 | |
| 127. |
The functions of connecting a resistor in series with gatecathode circuit and a zener-diode across gate-cathode circuit are, respectively, to protect the gate circuit from |
| A. | overvoltages, overcurrents |
| B. | overcurrents, overvoltages |
| C. | overcurrents, noise signals |
| D. | noise signals, overvoltages |
| Answer» C. overcurrents, noise signals | |
| 128. |
For an UJT employed for the triggering of an SCR, standoff ratio = 0 64 and dc source voltage V |
| A. | 12 8 V |
| B. | 13 1 V |
| C. | 10 V |
| D. | 5 V |
| Answer» C. 10 V | |
| 129. |
In controlled rectifiers, the nature of load current, i.e. whether load current is continuous or discontinuous |
| A. | does not depend on type of load and firing angle delay |
| B. | depends both on the type of load and firing angle delay |
| C. | depends only on the type of load |
| D. | depends only on the firing angle delay |
| Answer» C. depends only on the type of load | |
| 130. |
In a 3-phase semiconverter, the three SCRs are triggered at an interval of |
| A. | 60 |
| B. | 90 |
| C. | 120 |
| D. | 180 |
| Answer» D. 180 | |
| 131. |
In a single-phase full converter, if load current is I and ripple free, than average thyristor current is |
| A. | <table><tr><td style="border-bottom:1px solid #000000;vertical-align:bottom;padding-bottom:2px;"><center>1</center></td><td rowspan="2">l</td></tr><td align="center">2</td></table> |
| B. | <table><tr><td style="border-bottom:1px solid #000000;vertical-align:bottom;padding-bottom:2px;"><center>1</center></td><td rowspan="2">l</td></tr><td align="center">3</td></table> |
| C. | <table><tr><td style="border-bottom:1px solid #000000;vertical-align:bottom;padding-bottom:2px;"><center>1</center></td><td rowspan="2">l</td></tr><td align="center">4</td></table> |
| D. | l |
| Answer» B. <table><tr><td style="border-bottom:1px solid #000000;vertical-align:bottom;padding-bottom:2px;"><center>1</center></td><td rowspan="2">l</td></tr><td align="center">3</td></table> | |
| 132. |
In a 3-phase full converter, if load current is I and ripple free, than average thyristor current is |
| A. | <table><tr><td style="border-bottom:1px solid #000000;vertical-align:bottom;padding-bottom:2px;"><center>1</center></td><td rowspan="2">l</td></tr><td align="center">2</td></table> |
| B. | <table><tr><td style="border-bottom:1px solid #000000;vertical-align:bottom;padding-bottom:2px;"><center>1</center></td><td rowspan="2">l</td></tr><td align="center">3</td></table> |
| C. | <table><tr><td style="border-bottom:1px solid #000000;vertical-align:bottom;padding-bottom:2px;"><center>1</center></td><td rowspan="2">l</td></tr><td align="center">4</td></table> |
| D. | l |
| Answer» C. <table><tr><td style="border-bottom:1px solid #000000;vertical-align:bottom;padding-bottom:2px;"><center>1</center></td><td rowspan="2">l</td></tr><td align="center">4</td></table> | |
| 133. |
A 3-phase semiconverter can work as |
| A. | converter for = 0 to 180 |
| B. | converter for = 0 to 90 |
| C. | inverter for = 90 to 180 |
| D. | inverter for = 0 to 90 |
| Answer» B. converter for = 0 to 90 | |
| 134. |
In a 3-phase semiconverter, for firing angle equal to 120 and extinction angle equal to 100 , none of the bridge elements conduct for |
| A. | 10 |
| B. | 20 |
| C. | 30 |
| D. | 60 |
| Answer» C. 30 | |
| 135. |
In a 3-phase semiconverter, for firing angle equal to 120 and extinction angle equal to 110 , freewheeling diode conducts for |
| A. | 10 |
| B. | 30 |
| C. | 50 |
| D. | 110 |
| Answer» D. 110 | |
| 136. |
A single-phase full bridge VSI has inductor L as the load. For a constant source voltage, the current through the inductor is |
| A. | square wave |
| B. | triangular wave |
| C. | sine wave |
| D. | pulsed wave |
| Answer» C. sine wave | |
| 137. |
In a single-phase semiconverter, for discontinuous conduction and extinction angle > , each SCR conducts for |
| A. | |
| B. | |
| C. | |
| D. | |
| Answer» B. | |
| 138. |
In a single-phase semiconverter, for discontinuous conduction and extinction angle < , each SCR conducts for |
| A. | |
| B. | |
| C. | |
| D. | |
| Answer» C. | |
| 139. |
In a single-phase semi converter, with discontinuous conduction and extinction angle > , free wheeling diode conducts for |
| A. | |
| B. | |
| C. | + |
| D. | |
| Answer» C. + | |
| 140. |
In a single-phase semi converter, with discontinuous conduction freewheeling diode conducts for |
| A. | |
| B. | |
| C. | |
| D. | + |
| Answer» B. | |
| 141. |
In a single-phase semi-converter, for continuous conduction, each SCR conducts for |
| A. | |
| B. | |
| C. | + |
| D. | |
| Answer» E. | |
| 142. |
In a 3-phase semiconverter, for a firing angle equal to 90 and for continuous conduction, each SCR and diode conduct, respectively, for |
| A. | 30 60 |
| B. | 60 30 |
| C. | 60 60 |
| D. | 30 30 |
| Answer» D. 30 30 | |
| 143. |
In a single-phase full converter, for continuous conduction, each pair of SCRs conduct for |
| A. | |
| B. | |
| C. | |
| D. | + |
| Answer» C. | |
| 144. |
In a single-phase semi converter, the average output voltage is given by |
| A. | (a) |
| B. | (b) |
| C. | (c) |
| D. | (d) |
| Answer» D. (d) | |
| 145. |
In a single-phase full converter bridge, the average output voltage is given by |
| A. | (a) |
| B. | (b) |
| C. | (c) |
| D. | (d) |
| Answer» D. (d) | |
| 146. |
A single-phase full-wave mid-point thyristor converter uses a 230/200 V transformer with center tap on the secondary side. The P.I.V. per thyristor is |
| A. | 100 V |
| B. | 141 4 V |
| C. | 200 V |
| D. | 282 8 V |
| Answer» E. | |
| 147. |
In a single-phase full converter with resistive load and for a firing angle , the load current is zero and non-zero, respectively, for |
| A. | , |
| B. | , |
| C. | , + |
| D. | , |
| Answer» B. , | |
| 148. |
The frequency of the ripple in the output voltage of a 3- phase semiconverter depends upon |
| A. | firing angle and load resistance |
| B. | firing angle and load inductance |
| C. | the load circuit parameters |
| D. | firing angle and the supply frequency |
| Answer» E. | |
| 149. |
In a 3-phase full converter, three SCRs pertaining to one group are fired at an interval of |
| A. | 30 |
| B. | 60 |
| C. | 90 |
| D. | 120 |
| Answer» E. | |
| 150. |
In a single-phase semi converter with resistive load and for a firing angle , each SCR and freewheeling diode conduct, respectively, for |
| A. | , 0 |
| B. | , |
| C. | + |
| D. | , 0 |
| Answer» E. | |