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Power Electronics & Applications1)???A rectifier with an external low pass filter is an example ofa.?Indirect switch matrix circuitsb.?Direct switch matrix circuitsc.?Embedded convertersd.?All of theseANSWER: Direct switch matrix circuits2) In ac – dc conversion, when the switch is closed then the sum of voltages around the loop isa. Zero b. Non zeroc. Equal to the sum of voltage when switch is opend. Twice of the voltage when switch is openANSWER: Non zero3) An ideal switch isa. Losslessb. Carry current in any direction when it is onc. Does not carry any current in any direction when it is offd. All of theseANSWER: All of these4) IGBT stands fora. Insulated gate bipolar transistorb. Insulated gate bidirectional transistorc. Inductive gate bipolar transistord. Inductive gate bidirectional transistorANSWER: Insulated gate bipolar transistor5) Number of PN junction in an SCR isa. Twob. Threec. Fourd. FiveANSWER: Three6) In a silicon controlled rectifier, the load is connecteda. Across anodeb. In series with anodec. Across cathoded. In series with cathodeANSWER: In series with anode7) Anode of an operational SCR is a. Always positive w.r.t cathodeb. Always negative w.r.t anodec. Always positive w.r.t anoded. Always negative w.r.t cathodeANSWER: Always positive w.r.t cathode8) If the gate voltage of an SCR is removed, then thea. anode current decreasesb. anode current does not decrease at allc. anode current increasesd. cathode current increasesANSWER: anode current does not decrease at all9) A single phase ac – dc converter is also known asa. rectifierb. inverterc. chopperd. regulatorANSWER: rectifier10) In a single phase full wave rectifier, during blocking state the peak inverse voltage of diode isa. V mb. 2 V mc. V m / 2d. 4 V mANSWER: 2 V m11) In a full wave rectifier, the rectification ratio is approximately equal toa. 61%b. 71%c. 81%d. 91%ANSWER: 81%12) For power output higher than 15 kW, the suitable rectifier isa. Single phaseb. 3 phasec. Poly phased. Only (b) and (c)ANSWER: Only (b) and (c)13) The sum of all phase current in a star connected primary winding with no neutral connection is equal toa. Phase currentb. Three times the phase currentc. Three times the line currentd. Zero at all timesANSWER: Zero at all times14) In a 3 phase bridge rectifier the ripple frequency is a. Equal to the input frequencyb. Twice the input frequencyc. Three times the input frequencyd. Six times the input frequencyANSWER: Six times the input frequency15) DIAC are specifically designed to triggera. TRIACb. SCRc. GTOd. Only (a) and (b)ANSWER: Only (a) and (b)16) As the breakdown voltage reached, the DIAC exhibitsa. Negative resistance characteristicsb. Goes into avalanche conditionc. Voltage drop snaps backd. All of theseANSWER: All of these17) In BJT, the forward biased base emitter junction inject holes from base to emitter, the holesa. Do not contribute to the collector currentb. Result in net current flow component into the basec. Contribute to the collector currentd. Only (a) and (b)e. Only (b) and (c)ANSWER: Only (a) and (b)18) In BJT, switching losses occursa. Only at turn – onb. Only at turn – offc. Both at turn on and offd. None of theseANSWER: Both at turn on and off19) Choppers is aa. AC – DC convertersb. AC – AC convertersc. DC – AC convertersd. DC – DC convertersANSWER: DC – DC converters20) The average value of the output voltage in a step – down dc chopper is given bya. V 0 = V sb. V 0 = D V sc. V 0 = V s / Dd. V 0 = V s / ( 1 – D )ANSWER: V 0 = D V s21) The control method used for PWM dc – dc converter isa. Voltage mode controlb. Current mode controlc. Hysteric controld. All of theseANSWER: All of these22) The main objective of static power converters is toa. Obtain an dc output waveform from a dc power supplyb. Obtain an ac output waveform from a dc power supplyc. Obtain an dc output waveform from a dc power supplyd. Obtain an ac output waveform from a ac power supplyANSWER: Obtain an ac output waveform from a dc power supply23) A capacitive load in voltage source inverters generates a. Small current spikes and can be reduced by using an inductive filterb. Large current spikes and can be increased by using an inductive filterc. Small current spikes and can be increased by using an inductive filterd. Large current spikes and can be reduced by using an inductive filterANSWER: Large current spikes and can be reduced by using an inductive filter24) The carrier which are commonly used in constant – frequency PWM isa. Sawtooth carrierb. Inverted sawtooth carrierc. Triangle carrierd. All of theseANSWER: All of these25) Double edge modulation eliminates certain harmonics when the reference is aa. Sine waveb. Square wavec. Triangular waved. Trapezoidal waveANSWER: Sine wave26) In a three phase voltage source invertersa. Only amplitude of voltage is controllableb. Only phase is controllablec. Both amplitude and phase is controllabled. Amplitude, phase and frequency of voltages should always be controllableANSWER: Amplitude, phase and frequency of voltages should always be controllable27) In a 3 phaseVSI out of eight valid states, the number of valid states that produce zero ac line voltages is/area. One b. twoc. Threed. FourANSWER: two28) In the operation and control of both naturally commutated and forced commutatedSCR base converter, commutation plays an important role. The converters is / area. AC – DCb. DC – DCc. DC – ACd. All of theseANSWER: All of these29) In commutation PAC stands fora. Permanent angle converterb. Phase angle converterc. Phase angle commutationd. Phase and commutationANSWER: Phase angle converter30) Any electrical signal present in a circuit other than the desired signal is known asa. Noiseb. Distortionc. Interferenced. All of theseANSWER: Noise31) The man made noise sources is / area. Motorsb. Switches, radio interferencesc. Computers, digital electronicsd. All of theseANSWER: All of these32) Due to non sinusoidal waveform of the input current, the power factor of the rectifier isa. Negatively affected by firing angleb. Negatively affected by distortion of the input currentc. Positively affected by both firing angle and distortion of the input currentd. Both (a) and (b)ANSWER :1) An ideal diode isa. Unidirectionalb. Bidirectionalc. Fixed voltage polarityd. Only (a) and (c)ANSWER: Only (a) and (c)2) Bidirectional semiconductor device isa. Diodeb. BJTc. SCRd. TRIACANSWER: TRIAC3) With gate open, the maximum anode current at which SCR is turned off from ON condition is calleda. breakdown voltageb. peak reverse voltagec. holding currentd. latching currentANSWER: holding current4) The curve between V and I of SCR when anode is positive w.r.t cathode and when anode is negative w.r.t cathode are known asa. both as forward characteristicsb. both as reverse characteristicsc. former as forward characteristics and later as reverse characteristicsd. former as reverse characteristics and later as forward characteristicsANSWER: former as forward characteristics and later as reverse characteristics5) Form factor of a rectifier is the ratio of a. Root mean square value of voltage and current to its peak valueb. Root mean square value of voltage and current to its average valuec. Average value of current and voltage to its root mean square valued. Peak value of current and voltage to its root mean square valueANSWER: Root mean square value of voltage and current to its average value6) Ripple factor is the ratio ofa. Rms value of the ac component of load voltage to the dc voltageb. Average value of the ac component of load voltage to the peak value of voltagec. Average value of the dc component of load voltage to the ac voltaged. Peak value of the dc component of load voltage to the ac voltageANSWER: Rms value of the ac component of load voltage to the dc voltage7) Transformer utilization factor is a measure of the merit of a rectifier circuit. It is the ratio ofa. AC input power to the transformer volt – amp rating required by secondaryb. AC input power to the transformer volt – amp rating required by primaryc. DC output power to the transformer volt – amp rating required by secondaryd. DC output power to the transformer volt – amp rating required by primaryANSWER: DC output power to the transformer volt – amp rating required by secondary8) In a 3 phase half wave rectifier, when firing angle is less than 90 degree, then the average dc output voltage becomesa. Positiveb. Negativec. Zerod. None of theseANSWER: Positive9) If the firing angle becomes negative, then the rectifier begins to work asa. A rectifierb. An inverterc. A chopperd. A regulatorANSWER: An inverter10) The Graetz bridge makes excellent use of a. Current transformerb. Potential transformerc. Power transformerd. SCRANSWER: Power transformer11) DIAC and TRIAC both are semiconductors devices and conduct ina. DIAC conducts in forward direction and TRIAC conducts in reverse directionb. Both conducts in forward directionc. Both conducts in reverse directiond. Both conducts in either directionANSWER: Both conducts in either direction12) A TRIAC can be turned on with a. Positive voltage at the gate terminalb. Negative voltage at the gate terminalc. Either (a) or (b)d. None of theseANSWER: Either (a) or (b)13) The phase angle of gate signal in TRIAC can be shifted by using a. A capacitorb. A variable resistorc. An inductord. Only (a) and (b)ANSWER: Only (a) and (b)14) The ac voltage controller can be used for a. Lighting and heating controlb. On – line transformer tap changingc. Soft startingd. All of theseANSWER: All of these15) An RC snubber network used in BJTa. Divert the collector current during turn – offb. Improves the reverse bias safe operating areac. Dissipates a fair amount of switching powerd. All of theseANSWER: All of these16) A MOSFET, for its conduction usesa. Only minority carriersb. Only majority carriersc. Both minority and majority carriersd. None of theseANSWER: Only majority carriers17) MOSFET stands fora. Metal – oxide semiconductor field effect transistor b. Molybdenum – oxide semiconductor field effect transistor c. Metal – oxide silicon field effect transistor d. Metal – oxide semiconductor field effect transmitterANSWER: Metal – oxide semiconductor field effect transistor18) In a push – pull converter, the filter capacitor can be obtained asa. Cmin = V / ( Vr L f2 )b. Cmin= ( 1 – D ) V / ( Vr L f2 )c. Cmin= ( 1 – 2 D ) V / 32 ( Vr L f2 )d. Cmin= ( 1 – 2 D ) V / 42 ( Vr L f2 )ANSWER: Cmin= ( 1 – 2 D ) V / 32 ( Vr L f2 )19) In a flyback converter, the inductor of the buck-boost converter has been replaced by aa. Flyback capacitorb. Flyback resistorc. Flyback transformerd. Flyback transistorANSWER: Flyback transformer20) Advantages of Cuk converter is / area. Large number of reactive componentb. Low stress on switchc. Low stress on capacitord. None of theseANSWER: None of these21) The ac output voltage waveform of VSI and AC output current waveform of CSI respectively is composed ofa. High dv / dt, low di / dtb. Low dv / dt, low di / dtc. Low dv / dt, high di / dtd. High dv / dt, high di / dtANSWER: High dv / dt, high di / dt22) If energy is taken from the AC side of the inverter and sends it back into the DC side, then it is known asa. Motoring mode operationb. Braking mode operationc. Regenerative mode operationd. None of theseANSWER: Regenerative mode operation23) A combination of synchronized leading edge and trailing edge modulation has also been used to control aa. Boost single – phase power factor converterb. A buck dc – dc converter to reduce ripple in the intermediate dc bus capacitorc. Both (a) and (b)d. None f theseANSWER: Both (a) and (b)24) Regulator sampling PWM is usually used ina. High power invertersb. Rectifiersc. Low power invertersd. Only (a) and (b)ANSWER: Only (a) and (b)25) In a 3 phase VSI SPWM to use a single carrier signal and preserve the features of PWM technique, the normalized carrier frequency should bea. Multiple of twob. Odd multiple of threec. Odd multiple of fived. Odd multiple of sevenANSWER: Odd multiple of three26) In square wave operation mode of 3 phase VSI, the VSIa. Can control the load voltageb. Cannot control the load voltagec. Cannot control the load voltage except by means of dc link voltaged. Cannot control the load voltage except by means of dc link currentANSWER: Cannot control the load voltage except by means of dc link voltage27) For commutation in three phase PAC, normally balanced three phase voltages VR, VY and VB are connected to the three legs of the converter viaa. Three inductancesb. Three capacitancesc. Three resistanced. Three transistorsANSWER: Three inductances28) If all the SCR’s of 3 phase PAC is replaced by diodes, they would be triggereda. 120 degree after the zero crossing of the corresponding line voltagesb. 60 degree after the zero crossing of the corresponding line voltages c. 120 degree before the zero crossing of the corresponding line voltagesd. 60 degree before the zero crossing of the corresponding line voltagesANSWER: 60 degree after the zero crossing of the corresponding line voltages29) The ability of an electronic system to function properly in its intended electromagnetic environment and should not be a source of pollution to that electromagnetic environment is known asa. Susceptibilityb. Emissionc. Interferenced. Electromagnetic compatibilityANSWER: Electromagnetic compatibility30) The opposite of susceptibility isa. Immunityb. Emissionc. Interferenced. Electromagnetic compatibilityANSWER: Immunity31) The output current in PWM DC – DC converters is equal toa. Average value of the output inductor currentb. Product of an average inductor current and a function of duty ratioc. Either (a) or (b)d. None of theseANSWER: Either (a) or (b)32) A step – down choppers can be used ina. Electric tractionb. Electric vehiclesc. Machine toolsd. All of theseANSWER: All of these33) In a lossless inverter, the average power absorbed in one period by the load must bea. Equal to the average power supplied by the dc sourceb. Greater than the average power supplied by the dc sourcec. Lesser than the average power supplied by the dc sourced. Equal to the average power supplied by the ac sourceANSWER: Equal to the average power supplied by the dc source34) In a full bridge VSI, in order to avoid the short circuit across the DC bus and the undefined AC output voltage condition, the modulating technique should ensure thata. Top switch of each leg is on at any instantb. Bottom switch of each leg is on at any instantc. Either (a) or (b)d. None of theseANSWER: Either (a) or (b)35) In the SPWM, the modulating signal is a. Squareb. Sinusoidalc. Triangulard. Saw – toothANSWER: Sinusoidal36) The transfer function of PWM is generally developed ina. Time domainb. Frequency domainc. Either (a) or (b)d. None of theseANSWER: Either (a) or (b)37) In constant frequency PWM, at perturbation the amplitude of the sinusoidal component is a a. Linear functionb. Non linear functionc. Constant functiond. None of theseANSWER: None of these38) In variable frequency, PWM gain a. Phase lead helps to increase the phase margin of the control loopb. Phase lag helps to increase the phase margin of the control loopc. Phase lead helps to decrease the phase margin of the control loopd. Phase lag helps to decrease the phase margin of the control loopANSWER: Phase lead helps to increase the phase margin of the control loop1) Silicon controlled rectifier can be turned ona. By applying a gate pulse and turned off only when current becomes zerob. And turned off by applying gate pulsec. By applying a gate pulse and turned off by removing the gate pulsed. By making current non zero and turned off by making current zeroANSWER: By applying a gate pulse and turned off only when current becomes zero2) TRIAC is a semiconductor power electronic device which contains a. Two SCR’s connected in reverse parallelb. Two SCR’s connected in parallelc. Two SCR’s connected in seriesd. Two BJT’s connected in seriesANSWER: Two SCR’s connected in reverse parallel3) An SCR can be used a. as static conductorb. for power controlc. for speed control of dc shunt motord. all of theseANSWER: all of these4) A crowbar is a circuit which is used to protect aa. voltage sensitive load from excessive dc power supply output voltagesb. current sensitive load from excessive dc power supply output voltagesc. voltage sensitive load from excessive ac power supply output voltagesd. current sensitive load from excessive ac power supply output voltagesANSWER: voltage sensitive load from excessive dc power supply output voltages5) A full wave rectifier with resistive load producesa. Second harmonicb. Third harmonicc. Fifth harmonicd. Do not produce harmonicsANSWER: Do not produce harmonics6) The input current waveform of a bridge controlled rectifier when the load is perfectly filtered isa. Sine waveb. Square wavec. Saw – tooth waved. Trapezoidal waveANSWER: Square wave7) The advantage of using free – wheeling diode in half controlled bridge converter is thata. There is always a path for the dc current independent of the ac lineb. There is always a path for the ac current independent of the ac linec. There is always a path for the dc current dependent of the ac lined. There is always a path for the ac current independent of the ac lineANSWER: There is always a path for the dc current independent of the ac line8) Harmonics in 3 phase inverters can be reduced by usinga. Passive filterb. Active filterc. Both passive and active filtersd. None of theseANSWER: Both passive and active filters9) The most suited gate pulses given to the AC regulator with R – L load can be in the form ofa. Continuous signalb. Large isolating pulse transformerc. A train of pulsesd. None of theseANSWER: A train of pulses10) With increase in firing angle,a. Both harmonic distortion and quality of input current increasesb. Harmonic distortion increases and quality of input current decreases c. Harmonic distortion decreases and quality of input current increases d. Both harmonic distortion and quality of input current decreasesANSWER: Harmonic distortion increases and quality of input current decreases11) The power MOSFET device is aa. Current controlled unipolar deviceb. Voltage controlled unipolar devicec. Current controlled bipolar deviced. Voltage controlled bipolar deviceANSWER: Voltage controlled unipolar device12) The conduction losses in IGBT isa. More than that of MOSFETb. Lower than that of MOSFETc. Equal to that of MOSFETd. Equal to that of BJTANSWER: Lower than that of MOSFET13) For a buck converter to reduce the conduction losses in diodea. A high on – resistance switch can be added in parallelb. A low on – resistance switch can be added in parallelc. A high on – resistance switch can be added in seriesd. A low on – resistance switch can be added in seriesANSWER: A low on – resistance switch can be added in parallel14) For bidirectional operation of convertersa. A parallel combination of controllable switch and a diode is usedb. A parallel combination of controllable switch and capacitor is usedc. A series combination of controllable switch and a diode is usedd. A series combination of controllable switch and a capacitor is usedANSWER: A parallel combination of controllable switch and a diode is used15) Single phase VSI are mainly used in a. Power suppliesb. Upsc. Multilevel configurationd. All of theseANSWER: All of these16) Very large values of modulation index (greater than 3.24) lead toa. Square AC output voltageb. Sine AC output voltagec. Triangular AC output voltaged. Trapezoidal AC output voltageANSWER: Square AC output voltage17) In single phase VSI, the harmonic which is not present isa. 2ndb. 3rdc. 5thd. 7thANSWER: 2nd18) Double fourier series analysis of PWM is a. Two dimensional functionsb. Three dimensional functionsc. One dimensional functionsd. All of theseANSWER: Two dimensional functions19) In bipolar modulation, the carrier is symmetric about zero with amplitude equal to Cm, the PWM output a. Zerob. Switches between – 1 / 2 and + 1 / 2c. Switches between – 1 and + 1d. Switches between 0 and + 1ANSWER: Switches between – 1 / 2 and + 1 / 220) Unipolar modulation is generally used ina. AC – AC convertersb. AC – DC convertersc. DC – AC convertersd. DC – DC convertersANSWER: DC – DC converters21) The square wave operation of 3 phase VSI lines contains the harmonics. The amplitudes area. Directly proportional to their harmonic orderb. Inversely proportional to their harmonic orderc. Not related to their harmonic orderd. None of theseANSWER: Inversely proportional to their harmonic order22) Under harmonic free load voltages, the 3 phase VSI a. Does not contains second harmonicb. Does not contains third harmonicc. Does not contains fifth harmonicd. Does not contains seventh harmonicANSWER: Does not contains second harmonic23) For similar carrier and modulating signals, the line current used in CSI isa. Identical to line voltage in a VSIb. Identical to line current in VSIc. Identical to phase voltage in VSId. Identical to phase voltage in CSIANSWER: Identical to line voltage in a VSI24) In a 3 phase CSI, if the required line output voltages are balanced and 120 degree out of phase, then the chopping angles are used to eliminate only the harmonics at frequenciesa. 5b. 7c. 11d. All of theseANSWER: All of these25) In a three phase converter, the number of notches per cycle isa. Oneb. Threec. Sixd. NineANSWER: Six26) During the commutation period in 3 phase converter, overlap time isa. Dependent on the load currentb. Dependent on the voltagec. Dependent on both the load current and load voltage behind the short circuit current d. Independent on both the load current and load voltageANSWER: Dependent on both the load current and load voltage behind the short circuit current27) Between the incoming and outgoing devices in voltage commutationa. Large overlapping takes placeb. Small overlapping operationc. No overlapping operationd. None of theseANSWER: No overlapping operation28) The effects of EMI can be reduced by a. Suppressing emissionsb. Reducing the efficiency of the coupling pathc. Reducing the susceptibility of the receptord. All of theseANSWER: All of these29) In radiative coupling, the emitter radiation fielda. Decays as 1 / R, where R is the separation distance between the emitter and the receptorb. Decays as R, where R is the separation distance between the emitter and the receptorc. Decays as 1 / 2 R, where R is the separation distance between the emitter and the receptord. Decays as 2R, where R is the separation distance between the emitter and the receptorANSWER: Decays as 1 / R, where R is the separation distance between the emitter and the receptor30) In EMCsignal, the source delivers maximum power to the input of transmission line when the transmission line input impedancea. Is equal to the source resistanceb. Greater than the source resistancec. Smaller than the source resistanced. None of theseANSWER: Is equal to the source resistance31) For swept frequency measurements, the input impedance of the mismatched transmission line would vary with frequency as the electrical length of the transmission line woulda. Decrease with frequencyb. Remains same with change in frequencyc. Increase with frequencyd. Either (a) or (b)ANSWER: Increase with frequency32) Voltage commutation circuit can be converted into a current commutation by interchanging the positions ofa. Diode and capacitorb. Capacitor and SCRc. Inductor and capacitord. Capacitor and loadANSWER: Diode and capacitor33) In a load commutated DC – DC chopper, the capacitor has aa. Symmetric triangular voltage across itselfb. Symmetric rectangular voltage across itselfc. Symmetric trapezoidal voltage across itselfd. Symmetric sinusoidal voltage across itselfANSWER: Symmetric trapezoidal voltage across itself34) In current commutated DC-DC choppers, the voltage spike appears across the load whena. Voltage across the commutating inductances collapsesb. The capacitance voltage adds to the supply voltagec. Both (a) and (b)d. None of theseANSWER: Both (a) and (b)35) LISN is a device used to measure conducted emissions. LISN stands fora. Line integrated stabilization networkb. Line impedance stabilization networkc. Line integrated stored networkd. Laser integrated stabilization networkingANSWER: Line impedance stabilization network36) The output power of the cascaded amplifier / attenuator system can be determined using a. Actual gain of amplifierb. Actual gain of amplifier and attenuatorc. Gain in dB of amplifier and attenuatord. Actual gain of attenuatorANSWER: Actual gain of amplifier and attenuator37) An SCR is made up of silicon becausea. silicon has large leakage current than germaniumb. silicon has small leakage current than germaniumc. silicon has small leakage voltage than germaniumd. silicon has large leakage voltage than germaniumANSWER: silicon has small leakage current than germanium38) AC power in a load can be controlled by usinga. two SCR’s in parallel oppositionb. two SCR’s in seriesc. three SCR’s in seriesd. four SCR’s in seriesANSWER: two SCR’s in parallel opposition39) The switching function of semiconductor devices can be characterized witha. Duty ratio onlyb. Frequency onlyc. Duty ratio and frequency d. Duty ratio, frequency and time delayANSWER: Duty ratio, frequency and time delay ................
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