1) In a 3 phase VSI SPWM to use a single carrier signal and preserve the features of PWM technique, the normalized carrier frequency should be____________? a. Multiple of two b. Odd multiple of three c. Odd multiple of five d. Odd multiple of seven
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2) For commutation in three phase PAC, normally balanced three phase voltages VR, VY and VB are connected to the three legs of the converter via______________? a. Three inductances b. Three capacitances c. Three resistance d. Three transistors
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3) If all the SCR’s of 3 phase PAC is replaced by diodes, they would be triggered_____________? a. 120 degree after the zero crossing of the corresponding line voltages b. 60 degree after the zero crossing of the corresponding line voltages c. 120 degree before the zero crossing of the corresponding line voltages d. 60 degree before the zero crossing of the corresponding line voltages
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4) 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 as____________? a. Susceptibility b. Emission c. Interference d. Electromagnetic compatibility
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5) The opposite of susceptibility is___________? a. Immunity b. Emission c. Interference d. Electromagnetic compatibility
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6) The output current in PWM DC – DC converters is equal to___________? a. Average value of the output inductor current b. Product of an average inductor current and a function of duty ratio c. Either A. or B. d. None of these
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7) A step – down choppers can be used in___________? a. Electric traction b. Electric vehicles c. Machine tools d. All of these
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8) In a lossless inverter, the average power absorbed in one period by the load must be__________? a. Equal to the average power supplied by the dc source b. Greater than the average power supplied by the dc source c. Lesser than the average power supplied by the dc source d. Equal to the average power supplied by the ac source
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9) The ac voltage controller can be used for ___________? a. Lighting and heating control b. On – line transformer tap changing c. Soft starting d. All of these
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10) 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 that___________? a. Top switch of each leg is on at any instant b. Bottom switch of each leg is on at any instant c. Either A. or B. d. None of these
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11) The phase angle of gate signal in TRIAC can be shifted by using_____________? a. A capacitor b. A variable resistor c. An inductor d. Only (a) and (b)
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12) In the SPWM, the modulating signal is___________? a. Square b. Sinusoidal c. Triangular d. Saw – tooth
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13) A TRIAC can be turned on with______________? a. Positive voltage at the gate terminal b. Negative voltage at the gate terminal c. Either (a) or (b) d. None of these
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14) The transfer function of PWM is generally developed in______________? a. Time domain b. Frequency domain c. Either A. or B. d. None of these
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15) DIAC and TRIAC both are semiconductors devices and conduct in____________________? a. DIAC conducts in forward direction and TRIAC conducts in reverse direction b. Both conducts in forward direction c. Both conducts in reverse direction d. Both conducts in either direction
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16) The Graetz bridge makes excellent use of ______________? a. Current transformer b. Potential transformer c. Power transformer d. SCR
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17) In constant frequency PWM, at perturbation the amplitude of the sinusoidal component is a___________? a. Linear function b. Non linear function c. Constant function d. None of these
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18) If the firing angle becomes negative, then the rectifier begins to work as_______________? a. A rectifier b. An inverter c. A chopper d. A regulator
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19) In a 3 phase half wave rectifier, when firing angle is less than 90 degree, then the average dc output voltage becomes__________________? a. Positive b. Negative c. Zero d. None of these
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20) Transformer utilization factor is a measure of the merit of a rectifier circuit. It is the ratio of_______________? a. AC input power to the transformer volt – amp rating required by secondary b. AC input power to the transformer volt – amp rating required by primary c. DC output power to the transformer volt – amp rating required by secondary d. DC output power to the transformer volt – amp rating required by primary
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