Questions 421–430 of 715. Imported answers require independent review unless marked reviewed.

Topic practice 715 questionsPage 43 of 72

Question 21

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A single-phase, 4 kVA, 200 V/100 V, 50 Hz transformer with laminated CRGO steel core has rated no-load loss of 450 W. When the high-voltage winding is excited with 160 V, 40 Hz sinusoidal ac supply, the no-load losses are found to be 320 W. When the high-voltage winding of the same transformer is supplied from a 100 V, 25 Hz sinusoidal ac source, the no-load losses will be ________ W (rounded off to 2 decimal places).

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Question 22

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A single-phase inverter is fed from a 100 V dc source and is controlled using a quasi-square wave modulation scheme to produce an output waveform,

, as shown. The angle

is adjusted to entirely eliminate the 3rd harmonic component from the output voltage. Under this condition, for

, the magnitude of the 5th harmonic component as a percentage of the magnitude of the fundamental component is ________ (rounded off to 2 decimal places).
Diagram for Electrical Engineering question 22


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Question 23

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A single 50 Hz synchronous generator on droop control was delivering 100 MW power to a system. Due to increase in load, generator power had to be increased by 10 MW, as a result of which, system frequency dropped to 49.5 Hz. Further increase in load in the system resulted in a frequency of 49.25 Hz. At this condition, the power in MW supplied by the generator is ________ (rounded off to 2 decimal places).

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Question 24

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Consider a negative unity feedback system with forward path transfer function

, where

are positive real numbers. For a Nyquist path enclosing the entire imaginary axis and right half of the

-plane in the clockwise direction, the Nyquist plot of

encircles the origin of

-plane once in the clockwise direction and never passes through this origin for a certain value of

. Then, the number of poles of

lying in the open right half of the

-plane is ________.

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Question 25

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The cross-section of a metal-oxide-semiconductor structure is shown schematically.
Diagram for Electrical Engineering question 25

Starting from an uncharged condition, a bias of +3 V is applied to the gate contact with respect to the body contact. The charge inside the silicon dioxide layer is then measured to be +Q. The total charge contained within the dashed box shown, upon application of bias, expressed as a multiple of Q (absolute value in Coulombs, rounded off to the nearest integer) is ________.

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Question 26

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EEMCQ2 marksNeeds review
For real numbers,

and

, with

, the maximum and minimum value of

for

are respectively, ________.
Your answerChoose one option.

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Question 27

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The vector function expressed by

represents a conservative field, where

are unit vectors along x, y and z directions, respectively. The values of constants

are given by:
Your answerChoose one option.

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Question 28

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A 250 V dc shunt motor has an armature resistance of 0.2

and a field resistance of 100

. When the motor is operated on no-load at rated voltage, it draws an armature current of 5 A and runs at 1200 rpm. When a load is coupled to the motor, it draws total line current of 50 A at rated voltage, with a 5 % reduction in the air-gap flux due to armature reaction. Voltage drop across the brushes can be taken as 1 V per brush under all operating conditions. The speed of the motor, in rpm, under this load condition, is closest to:
Your answerChoose one option.

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Question 29

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Two buses,

and

, are connected with a transmission line of admittance

, at the two ends of which there are ideal transformers with turns ratios as shown. Bus admittance matrix for the system is:
Diagram for Electrical Engineering question 29

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Question 30

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Consider the diode circuit shown below. The diode D obeys the current-voltage characteristic

, where

,

,

is the voltage across the diode and

is the current through it. The circuit is biased so that voltage,

and current,

. If you had to design this circuit to transfer maximum power from the current source (

) to a resistive load (not shown at the output), what values of

and

would you choose?
Diagram for Electrical Engineering question 30

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