l. A 10 kW, 400 50 Hz, 4-pole delta-connected squirrel-cage induction motor is excited by 90 V with blocked rotor. The machine consumes 1350 watts and draws 35 A from a.c. mains. The d.c. resistance of stator winding per phase is O· 6 ohms. Assuming effective a.c. resistance per phase to be 1·2 times the d.c. value, compute the starting torque for direct on line starting. Assume X2
The per phase parameters of 50 Hz, 1OOkm long, 3-phase transmission line are R 10 ohms, L 111·7 mH, C =O·9954 µF. The transmission line delivers 20 MW at a power factor of 0·8 lagging and 66 kV to a balanced load. Calculate
the sending end voltage, efficiency and regulation using nominal-T representation.
Determine the ripple factor, form factor and utilization factor for a single-phase diode bridge rectifier supplying a purely resistive load.

The unit step response of a unity feedback system is 1 Determine
the type and order of the system;
the static error constants of the system;
the open-loop poles of the system.


Find the gain Vo/V¡ for the ideal OP-AMP shown in the figure below

src='./qimages/7962-1e.jpg'>

2. A single-phase transformer. having 1000 and 800 number of turns (weighing 80 kg of copper) in primary and secondary windings, is wound over hot-rolled steel core (µr 6000) of uniform cross-sectional area of 80 cm^2 weighing 100 kg. What will be the maximum primary voltage at 50 Hz that can be applied to primary winding which does not force the flux in core to exceed 1·2 T What is the corresponding exciting current? If the core of this transformer is replaced by CRGO with maximum flux density capability of 1·6 T find the saving in core and wire material assuming volume density of both core materials to be approximately same and they same core flux. Assume mean magnetic path length of 160 cm and µo x 10^-7.


The open-loop transfer function of a unity feedback system is given as

src='./qimages/7962-2b.jpg'>

Draw the root locus of the system when a varies from 0 to


A set of 10 readings whose individual values are less than (127)10 is stored in memory location starting at XX80 H.Write an assembly language program- to check each reading to determine whether it is +ve or

to reject all negative readings;

to add all +ve readings;

to output this sum to PORT at any time when the sum exceeds eight bits to indicate overflow, otherwise display the sum to PORT 2




3. The self and mutual inductances of two coupled coils of an electromagnetic relay are given by

src='./qimages/7962-3a.jpg'>
over a certain displacement x in meters. Obtain the expression tor force on armature as a function of time, if i1 Im1 sin ω1t and i2 Im2 sin ω2 t. Find the magnitude of average force in case ω1 not equal to ω2 and ω1 ω2

Determine the currents supplied to ring mains shown in the figure below from A to

src='./qimages/7962-3b.jpg'>

A three-phase, three-pulse, half-wave controlled rectifier is supplying an R-L load, where L A freewheeling diode is also connected across this load. Determine the fundamental displacement factor and distortion factor for this converter as a function of firing angle a and hence determine the power factor of the converter.

4. A shunt motor is connected to a constant d.c. voltage source and it drives a constant load torque. Determine the effect of back e.m.f. Ea on speed as a
function of flux,
src='./qimages/7962-4a.jpg'>

A d.c. link has a loop resistance of 40 .Q and is connected to transformers giving secondary voltage of 120 kV at each end. The bridge-connected converters operate as follows

Rectifier α 15º, 15 ohms
Inverter ß 25º, X 15 ohms

Calculate the direct current delivered, if the inverter operates on constant ignition angle ß control.

Write down the trigonometric Fourier series representation of the following signal

src='./qimages/7962-4c.jpg'>


5. An 11000/440 50 Hz, 800 kVAtransformer draws 7 · 5 kW when excited at normal voltage and frequency with secondary circuit open. At reduced voltage with full-load current, the transformer requires 1·42 kW input, when the secondary is short-circuited. Calculate the all-day efficiency, if the duty cycle of the transformer is as follows

src='./qimages/7962-5a.jpg'>



A single-phase a.c. voltage regulator is made of anti-parallel combination of a thyristor and a diode. This controller is connected to a resistive load of 2 ohms from a 220 50 Hz supply. Determine the average and r.m.s. values of thyristor and diode currents for α 60°.


Find the phase margin and gain margin of a feedback system with

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Is the feedback system stable?


Convert a D flip-flop into a J-K flip-flop. Use additional logic gates. Draw the implementation.
Determine the Laplace transform and the ROC of the signal
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6. Develop an expression for torque of a 3-phase induction motor from first principles and show that

src='./qimages/7962-6a.jpg'>

where ß R2 X2, Tdm and Tfl are breakdown and full-load torque respectively, Sfl is the value of slip at full-load torque.

An angle-modulated signal has a carrier

src='./qimages/7962-6b-1.jpg'>

that produces a frequency deviation of 75 kHz due to information signal and a single interfering signal

src='./qimages/7962-6b-2.jpg'>

Determine the-
frequency of the demodulated interfering signal;
peak phase and frequency deviations due to interfering signal;
improvement in the voltage signal-to-noise ratio at the output of the demodulator compared to signal-to-noise ratio at the input.

Two sequences are defined as
src='./qimages/7962-6c.jpg'>


where a is +ve. Find


7. A feedback system is shown in the figure below. Using Nyquist stability criterion, determine-
the number of closed-loop poles of the system in the right half s-plane;
the closed-loop stability of the system.


src='./qimages/7962-7a.jpg'>


A synchronous generator, capable of developing 500 MW of power, operates at a power angle of 8º. By how much can the input shaft power be increased suddenly without loss of stability?

A buck-boost regulator has an input voltage of 6 V. This produces an output voltage of 15 V while supplying an average load current of O· 5 A. The converter is operated at a frequency of 20 kHz. If the inductance and capacitance of the converter are 250 µHand 440 µF, then determine the duty cycle, ripple current of inductor and ripple voltage of filter capacitor. Draw the waveforms and derive the relationship used for computing ripple in voltage and current.



8. Design a state feedback controller for the linear system described by the following equations

src='./qimages/7962-8a.jpg'>


x1 and x2 are state variables and u is the input. Design specifications are 20% overshoot and settling time of 5 sec for a step input. Settling time is given for tolerance band.


For a simple four-bus system, the line admittances are given below

src='./qimages/7962-8b.jpg'>



Assuming a flat voltage start, determine the voltage at the end of first iteration using Gauss-Seidel method. Take α 1 · 6 is acceleration factor).


A single-phase full-bridge bipolar PWM inverter employs selective harmonic elimination method. The output voltage waveform of the inverter is shown in the figure below. For α1 23·62º and α2 33·30°, find the amplitude of
7th, 9th and 11th harmonics

src='./qimages/7962-8cjpg'>