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25 previous year questions for Electrical Engineering from 3 years. Practice with year-wise breakdown.
25
Questions
3
Years
2
Papers
Answer the following sub-parts (a) to (e):
(a) The block diagram of a system is as shown below. Evaluate the overall transfer function Y(s)/R(s) using block-diagram reduction technique. [10M]
(b) Explain the operation performed by 8085 microprocessor when the following instructions are executed: (i) JMP unconditionally (ii) POP (iii) PUSH (iv) RET (v) STC [10M]
(c) For the circuit shown in the figure below, give an expression for the overall uncertainty in the value of the combined resistance R. Further, evaluate the overall uncertainty in R when R1 = 50 ± 0.1 Ω, R2 = 100 ± 0.2 Ω, R3 = 100 ± 0.2 Ω. [10M]
(d) A factory has a fixed load of 860 kW and is operating at 0.85 power factor. The electric utility company offers to supply energy at the following two alternate rates: (i) LV supply at ₹30/kVA max demand/annum + 12 paise/kWh (ii) HV supply at ₹25/kVA max demand/annum + 10 paise/kWh The HV switchgear costs ₹50/kVA and switchgear losses at full load amount to 4 %. Interest and depreciation charges for switchgear are 10 % of the capital cost. If the factory is to work 48 hours per week, determine the more economical tariff option. [10M]
(e) If the generator polynomial is (x⁴ + x + 1) and the message bits are 1101101, obtain the CRC code. [10M]
Consider the circuit of an operational amplifier given here in which Zener diodes Z1 and Z2 are having reverse breakdown voltage = 7.4 V and forward voltage drop = 0.6 V. (i) Draw the output voltage waveform showing voltage value with time and calculate frequency of output waveform. (ii) Modify the circuit for duty cycle factor D = 0.25 by replacing R1 from combination of suitable resistances and diodes, so that output frequency is not changed.
(i) Draw the output voltage waveform showing voltage value with time and calculate frequency of output waveform.
(ii) Modify the circuit for duty cycle factor D = 0.25 by replacing R1 from combination of suitable resistances and diodes, so that output frequency is not changed.
Answer the following sub-parts (a) to (c):
(a) An LTI system with the following state-space representation is given: ẋ = [0 1; 0 –0.5] x + [0; k] u, y = [1 0] x. Design a phase-lead compensator so that the system achieves a settling time of 2 s for a 2 % tolerance band and has a damped natural frequency of 2 rad/s. Also realise the designed compensator using passive components. [20M]
(b) For 8085 microprocessor, write the instructions to perform the following: (i) Set the zero flag when a register pair is used as a down counter. (ii) Load the accumulator with the contents of location 2050H, if memory location 2050H contains byte F8H. (iii) Load 3AH in memory location 2050H, if registers H and L contain 20H and 50H. (iv) Subtract 25H with borrow from accumulator, if the accumulator contains 37H and the borrow flag is set. (v) Complement the accumulator that contains data byte 89H. [20M]
(c) A moving-coil instrument with a resistance of 10 Ω gives full-scale deflection for a current of 1 mA. A manganin shunt is used to extend its range to 1 A. Calculate the error caused by a 5 °C fall in temperature when— (i) the manganin shunt is directly connected across the moving coil; and (ii) a 90 Ω manganin resistance is used in series with the moving coil before applying the manganin shunt. Assume the temperature coefficient of copper as 0.004/°C and that of manganin as 0.00015/°C. [10M]
Consider the Boolean function : F(A, B, C, D) = Σ m (1, 3, 4, 11, 12, 13, 14, 15) Implement it with a 4-to-1 multiplexer and external gates. Connect inputs A and B to the selection lines. Input to the four data lines is a function of the variables C and D which are obtained by expressing F as a function of C and D for each of the four cases when AB = 00, 01, 10 and 11. Functions are to be implemented with external gates.
Answer the following sub-parts:
(a(i)) Sketch the approximate root-locus plot for a time-delay system approximated by the transfer function G(s) = K(1 – s/2) / [s(s + 1)(1 + s/2)]. Also compute the largest value of K for which the system is stable under unity feedback and verify this value from the root-locus plot. [10M]
(a(ii)) The signal-flow graph of a system is as shown below. Determine the overall transmission R(s)/Y(s) and evaluate the sensitivity of the output to variations in K1 at s = 10. What would be the value of sensitivity obtained under DC condition, i.e. s = 0? [10M]
Answer the following sub-parts:
(a) For the Schottky transistor circuit shown below, determine IB, ID, IC and VCE. Next, remove the Schottky diode and determine IB, ID, IC and VCE assuming additional values of VBE(sat.) = 0.8 V and VCE(sat.) = 0.1 V. Assume parameter values of β = 50, VBE(on) = 0.7 V and Vf = 0.3 V for the Schottky diode. [20M]
(b) Find the Fourier transform of the following signals and specify the properties used: (i) x(t) = [ 2 sin (3πt) ⁄ πt ] · [ sin (2πt) ⁄ πt ] (ii) x(t) = ∫_{−∞}^{t} [ sin (2πτ) ⁄ πτ ] dτ [20M]
(c) In the circuit shown below, Vs is the a.c. voltage source given by Vs = Vo cos ωt, with Vo = 14.14 V and ω = 300 rad s⁻¹. Calculate the value of load resistance RL for maximum power transfer and also find the maximum power transferred to the load. (Turns ratio: k = 1, n = 0.2). [10M]
Answer all parts:
(a) As shown in the figure, just inside the surface of a dielectric slab, the electric field E1 is 15 V m⁻¹ and it makes an angle of 30° with the surface. The electric field E2 makes an angle of 65.5° with the surface just above the slab. Determine the magnitude of E2 and the dielectric constant of the slab. [10M]
(b) Show, with the help of suitable derivations, that the voltage regulation of a transformer varies with the power factor of the load. For what power factor will the voltage regulation be (i) zero, and (ii) maximum? [10M]
(c) A single-phase Thyristor converter circuit, as shown in the figure, feeds a constant-current load of 10 A. The supply is 230 V, 50 Hz with source inductance 2 mH. Assuming ideal Thyristors and a triggering angle α = 30°, calculate (i) the overlap angle u, and (ii) the drop in output voltage. [10M]
(d) Show that for a binomial random variable the mean is np and the variance is np (1 − p), where n is the number of trials and p is the probability of success. [10M]
Answer the following:
(a) (i) What is meant by armature reaction in d.c. machines? Using a developed view of armature conductors and poles, show that the effect of armature m.m.f. on the main field is entirely cross-magnetising. (ii) A 10 kW, 220 V d.c. shunt motor draws a line current of 5 A while running at a no-load speed of 1200 r.p.m. The armature resistance is 0.2 Ω and the field resistance is 200 Ω. Determine the efficiency of the motor when it delivers rated load. [20M]
(b) A converter circuit, as shown in the figure, is being used to charge a 24 V battery. The average charging current is Idc = 6 A and the supply voltage is Vs = 60 V, 50 Hz. Determine (i) the value of the limiting resistor R, and (ii) the input power factor. [20M]
(c) The transmitted power spectral density of a DSB-SC amplitude-modulated signal is shown in figure (a). The signal is corrupted by additive white Gaussian noise of two-sided power spectral density N0⁄2 in the pass-band. The received signal is demodulated and passed through a low-pass filter as shown in figure (b). Determine the output signal-to-noise ratio (SNR) at the filter output. [BW = bandwidth] [20M]
(a) What are the limitations of (i) Proportional (P), (ii) Integral (I), (iii) Derivative (D), and (iv) PID Controllers? What is the application of positive feedback control system? (b) Explain the operation performed by 8085 microprocessor when the following arithmetic instructions are executed: (i) ADD M (ii) ADC M (iii) DAD rp (iv) SBI d8 (v) DCR reg (c) The ohmmeter circuit has VB = 1.5 V, R1 = 15 kΩ, Rm = 50 Ω, R2 = 50 Ω and meter FSD = 50 μA. Determine the ohmmeter scale reading at 0.5 FSD. (d) Calculate the power loss in a cable insulation having capacitance 9 μF, loss angle 0.05 degree and operating at 11 kV, 50 Hz. Draw the phasor diagram and equivalent circuit also. (e) Explain the concept of a constellation diagram. Draw the PSK signal constellations for the value of M = 2, 4 and 8, if all have same transmitted signal energy Es.
(a) Limitations of P, I, D and PID controllers and application of positive feedback control system. [10M]
(b) Operation performed by 8085 micro-processor for the instructions ADD M, ADC M, DAD rp, SBI d8 and DCR reg. [10M]
(c) Determine the ohmmeter scale reading at 0.5 FSD for the given circuit (VB = 1.5 V, R1 = 15 kΩ, Rm = 50 Ω, R2 = 50 Ω, FSD = 50 μA). [10M]
(d) Calculate power loss in a 9 μF cable insulation (loss angle 0.05°) at 11 kV, 50 Hz and draw the phasor diagram and equivalent circuit. [10M]
(e) Explain constellation diagram and draw PSK constellations for M = 2, 4 and 8 with equal signal energy Es. [10M]
(a) The open-loop transfer function of a feedback control system incorporating a dead-time element is given by G(s) = K e^{–Ts} / [ s (s + 1) ] where K > 0 and T > 0 are variable scalar parameters. For a given value of T, show that the closed-loop system will be stable for all values K < K0 where K0 = ω0 cosec (ω0 T), and ω0 is the smallest value of ω satisfying ω = cot (ω T). (b) (i) Compare I/O-mapped I/O and memory-mapped I/O interfacing techniques used in 8085 micro-processor. (ii) What are the operating modes of Port-A of 8255? Explain hand-shake operation in I/O ports. (c) In a parallel circuit, in one branch the current I1 = (100 ± 2) A and in the other branch the current I2 = (200 ± 5) A. Determine the total current considering the following errors: (i) Limiting error (ii) Probable error Comment upon the results as well.
(a) Show stability limit K < K0 for the dead-time feedback system G(s) = K e^{–Ts}/[s(s+1)]. [20M]
(b) Compare I/O-mapped and memory-mapped I/O techniques in 8085 and explain operating modes of Port-A of 8255 with hand-shake operation. [20M]
(c) Find total current and associated limiting and probable errors for I1 = (100 ± 2) A and I2 = (200 ± 5) A in a parallel circuit; comment on the results. [10M]
(c) Find the logic equations for the outputs in the concise form and write the corresponding truth table for the circuit given below :
(a) An under-damped second-order system having the transfer function M(s) = K ωn² / ( s² + 2 ξ ωn s + ωn² ) has a frequency-response plot as shown in the figure. Compute the system gain K and the damping factor ξ. (b) A CRT has an anode voltage of 3 kV and its parallel deflecting plates are 2.5 cm long and 5 mm apart. The screen is 30 cm from the centre of the plates. Assuming the amplifier gain applied to the plates is 100, calculate: (i) Beam speed (ii) Deflection sensitivity of the CRT (iii) Deflection factor of the CRT (iv) Input voltage required to deflect the beam through 5 cm (c) Write an assembly-language program to add two numbers of 8-bit data stored in memory locations 4200H and 4201H and store the result in 4202H and 4203H.
(a) From the given frequency plot of M(jω), compute K and damping factor ξ for M(s) = K ωn² /(s² + 2 ξ ωn s + ωn²). [20M]
(b) For a CRT with Va = 3 kV, plate length 2.5 cm, spacing 5 mm, screen distance 30 cm and amplifier gain 100, find (i) beam speed, (ii) deflection sensitivity, (iii) deflection factor, (iv) input voltage for 5 cm deflection. [20M]
(c) Assembly program to add 8-bit numbers at 4200H and 4201H and store the sum at 4202H and 4203H. [10M]
a) In the circuit diagram given here, load resistance R_L is to be set for maximum power transfer. Draw Thevenin equivalent circuit across ab and calculate the value of R_L for maximum power transfer. Also calculate the power loss in resistance R_3, when the circuit is delivering maximum power to load R_L. b) (i) Define input bias current and input offset voltage for an OPAMP. Using an OPAMP, draw an inverting amplifier circuit with gain = –4 in such a way that the effect of bias current is minimized. (ii) In the linear regulated power-supply circuit shown here, calculate the output-voltage adjustment range and maximum power dissipation in transistor T₁ in the worst case. c) A circuit using three 2-input multiplexers is shown below. Determine the function performed by this circuit :
(a) Load resistance R_L for maximum power transfer; draw Thevenin equivalent across ab; compute R_L and power loss in R_3. [20M]
(b(i)) Define input bias current and input offset voltage of an OPAMP; draw an inverting amplifier of gain –4 with minimized bias-current effect. [10M]
(b(ii)) For the given linear regulated power-supply circuit, find the output-voltage adjustment range and the maximum power dissipation in T₁ (worst case). [10M]
(c) Determine the function performed by the circuit that uses three 2-input multiplexers. [10M]
(a) A piezoelectric (low-voltage) transducer has capacitance 2000 pF and charge sensitivity 30 × 10^–3 C/m. Assume a 1 MΩ feedback resistor with 100 pF shunt capacitance for the charge amplifier and a connecting cable of capacitance 150 pF. Calculate: (i) Sensitivity of the cable–transducer combination (ii) High-frequency sensitivity of the complete system (iii) Maximum frequency measurable by the system with ±5 % amplitude error (iv) Value of feedback resistance that can be increased by 5 % error allowance up to 20 kHz
(a) Calculate sensitivities, bandwidth and allowable feedback resistance for the specified piezoelectric transducer system. [20M]
a) A uniform plane wave travels in vacuum along +y direction. The electric field of the wave at some instant is given as \vec{E} = 4\hat{x} + 3\hat{z}. Find the vector magnetic field \vec{H}. (Given, μ₀ = 4π×10⁻⁷ H/m, ε₀ = 1/(36π)×10⁻⁹ F/m) b) The maximum efficiency of a 200 kVA, 3300/600 V, 50 Hz, single-phase transformer is 98% and occurs at 75% full load and unity power factor. If the leakage impedance is 10%, find the voltage regulation at full load and power factor 0·8 lagging. c) A diode circuit with an L–C load is shown in the figure, with the capacitor having an initial voltage V_C(t = 0) = 120 V, capacitance C = 12 µF and inductance L = 48 µH. If switch S is closed at t = 0 s, then find : (i) Peak value of current i, and (ii) Conduction time of the diode. d) How can linear pre-emphasis and de-emphasis filters be employed to improve the performance of an FM system? Is the improvement in output S/N ratio dependent on both the frequency responses of the pre-emphasis filter and the de-emphasis filter? e) A transmission line is 25 m long. Its characteristic impedance is Z₀ = 40 Ω and it operates at 2 MHz. The line is terminated with a load of Z_L = (50 + j30) Ω. If the wave velocity is u = 0·8c (with c = 3×10⁸ m/s) on the line, determine (i) the reflection coefficient and (ii) the input impedance.
(a) Determine the magnetic-field vector H for a uniform plane wave in vacuum given E = 4x̂ + 3ẑ V/m. [10M]
(b) For the given 200 kVA transformer, find the voltage regulation at full load and 0·8 pf lagging. [10M]
(c) For the diode L-C load circuit, find (i) peak current and (ii) diode conduction time when S is closed at t = 0 s. [10M]
(d) Explain use of linear pre-emphasis and de-emphasis filters in FM; discuss dependency of S/N improvement on their responses. [10M]
(e) For a 25 m, 2 MHz transmission line with Z₀ = 40 Ω and Z_L = 50 + j30 Ω, find (i) reflection coefficient and (ii) input impedance (u = 0·8c). [10M]
Answer any or all of the following sub-parts (a) to (e).
(a) The block diagram of a position-control system is shown in the figure. Determine the sensitivity of the closed-loop transfer function T(s) with respect to G(s) and H(s) for 1 rad / s. [10M]
(b) The disc in a single-phase energy meter rotates 1320 times when monitoring a 110 V, 3 A load at unity power factor over a period of 8 hours. Calculate the meter constant. If the meter makes 750 revolutions when measuring the energy supplied to a 110 V, 5 A load for 3 hours, determine the load power factor. [10M]
(c) Write the bus admittance matrix for the network shown in the figure. [10M]
(d) A single-core cable without grading operates at 14 kV. The conductor radius is 1·12 cm and the insulation radius is 2·75 cm. If the cable employs inter-sheath grading at a suitable radius, calculate the maximum operating voltage of the cable. [10M]
(e) How does information get passed from one layer to the next in the Internet model? How do the layers of the Internet model correlate to the layers of the OSI model? [10M]
a) (i) An AM signal s(t) = A_c[1 + k_a m(t)] cos(2π f_c t) is applied to the system shown. Show that the message signal m(t) can be obtained from the square-rooter output v₃(t). Assume |k_a m(t)| < 1 for all t, that m(t) is limited to –ω_s ≤ f ≤ ω_s and that the carrier frequency f_c > 2ω_s. (ii) A narrow-band FM signal is approximately given as s(t) = A_c cos(2π f_c t) – βA_c sin(2π f_c t) sin(2π f_m t). Determine the envelope of this modulated signal. Also determine the ratio of the maximum to the minimum value of this envelope. Plot this ratio versus β for 0 ≤ β ≤ 0·4. Also determine the average power of the narrow-band FM signal as a percentage of the average power of the unmodulated carrier. b) (i) Explain why PWM inverters are preferred over square-wave inverters. Further, draw the harmonic spectrum to highlight differences between unipolar and bipolar PWM techniques. (ii) A single-phase, full-bridge inverter has a DC-link voltage V_DC = 400 V and fundamental frequency 50 Hz. Find the r.m.s. value of the voltages of the fundamental and the next two prominent harmonics for : (1) square-wave mode, and (2) voltage-cancellation mode with α = 20°.
(a(i)) Show extraction of m(t) from square-rooter output for the given AM signal and assumptions. [10M]
(a(ii)) For the narrow-band FM signal, find the envelope, ratio of max/min envelope, plot versus β (0–0·4), and compute average power percentage. [10M]
(b(i)) Explain preference for PWM inverters over square-wave; draw harmonic spectrum for unipolar and bipolar PWM. [10M]
(b(ii)) For a single-phase full-bridge inverter (V_DC = 400 V, 50 Hz), find r.m.s. fundamental and next two harmonic voltages for (1) square-wave mode, (2) cancellation mode with α = 20°. [10M]
Answer the following sub-parts (a) and (b).
(a) Calculate the power loss in the transmission system shown in the figure. The numerical values of the transmission system are: I₁ = 0·75 ∠0° p.u., I₂ = 0·8 ∠0° p.u. V₃ = 1·2 ∠0° p.u. Z₁ = (0·07 + j0·15) p.u. Z₂ = (0·06 + j0·20) p.u. Z₃ = (0·05 + j0·06) p.u. [20M]
(b) The fuel input equations of two power-plant units are: F₁ = 0·3 P₁² + 35 P₁ + 125, ₹/h F₂ = 0·2 P₂² + 30 P₂ + 140, ₹/h If the maximum and minimum loading on each unit are 90 MW and 20 MW respectively and the total demand is 200 MW, calculate: (i) The economical operating schedule and the corresponding cost of generation. (ii) The savings in production cost if the load is equally shared by both units compared with (i), assuming equal incremental cost loading. Neglect transmission losses. [20M]
(a) (i) Draw the neat and properly labelled output voltage waveform of a three-phase, phase-controlled rectifier having firing angle α. Also derive the relationship for average output voltage in terms of line voltage V_LL and firing angle α. (ii) A three-phase full-wave controlled rectifier is being operated from a star-connected, 415 V, 50 Hz supply. This rectifier is feeding a constant load current of 15 kW. It is required to obtain an average output voltage of 80% of maximum possible output voltage. Find the firing angle, r.m.s. value of line current and input power factor. Assume devices are ideal. (b) (i) Show that the maximum power that a synchronous generator can supply when connected to constant voltage, constant frequency busbars increases with the excitation. (ii) An 11 kV, 3-phase, star-connected turbo-alternator delivers 250 A at unity power factor when running on constant voltage and frequency busbars. If the excitation is increased so that the delivered current rises to 300 A, find the power factor at which the machine now operates and the percentage increase in the induced e.m.f., assuming a constant steam supply and unchanged efficiency. The armature resistance is 0·5 Ω per phase and the synchronous reactance is 10 Ω per phase. (c) A medium has infinite conductivity for z ≤ 0, ε_r = 7 and μ_r = 18, and σ = 0 for z > 0. The electric field for z > 0 is given as E̅ = 10 cos(3×10^8 t − 15x) ẑ. Determine the surface charge density and surface current density at location (3, 4, 0) at t = 0·8 ns. Given, μ_0 = 4π×10^−7 H/m, ε_0 = 1/(36π)×10^−9 F/m.
(a) (i) Draw the output voltage waveform of a three-phase, phase-controlled rectifier with firing angle α and derive the expression for average output voltage in terms of V_LL and α. (ii) For a 415 V, 50 Hz three-phase full-wave controlled rectifier feeding a 15 kW constant load, obtain the firing angle, rms line current and input power factor when average output voltage is 80 % of the maximum possible. [20M]
(b) (i) Prove that the maximum power of a synchronous generator connected to constant-voltage, constant-frequency busbars increases with excitation. (ii) An 11 kV, 3-phase, star-connected turbo-alternator initially supplies 250 A at unity power factor. When excitation is raised so that current becomes 300 A, determine the new power factor and percentage rise in induced e.m.f. (R_a = 0.5 Ω/phase, X_s = 10 Ω/phase). [20M]
(c) For a medium with infinite conductivity for z ≤ 0 (ε_r = 7, μ_r = 18) and σ = 0 for z > 0, the electric field for z > 0 is E̅ = 10 cos(3×10^8 t − 15x) ẑ. Find the surface charge density and surface current density at (3, 4, 0) when t = 0.8 ns. Given μ_0 = 4π×10^−7 H/m, ε_0 = 1/(36π)×10^−9 F/m. [10M]
(a) In the figure shown, the plane y + z = 1 divides space into region 1 (containing the origin) with μ_r1 = 5 and region 2 with μ_r2 = 7. Given B̅_1 = 3.0 a_x + 1.0 a_y (T), determine B̅_2 and H̅_2. Take μ_0 = 4π×10^-7 H/m. (b) The message signal m(t) has a bandwidth of 20 kHz, a power of 20 W and a maximum amplitude of 8. It is to be transmitted to a destination through a channel having 80 dB attenuation and additive white noise with power spectral density S_n(f) = N_0/2 = 0.5×10^-12 W/Hz. An SNR of at least 50 dB is required at the modulator output. Determine the required transmitter power and channel bandwidth for each of the following schemes: (i) DSB-SC AM (ii) SSB AM (iii) Conventional DSB AM with modulation index 0.6 (c) An ideal DC–DC converter (shown) has V_s = 20 V, duty ratio D = 0.25 and switching frequency 20 kHz. With L = 150 µH, C = 240 µF and average diode current 1.2 A, calculate: (i) Peak-to-peak inductor ripple current (ii) Peak current through switch S
(a) Plane y + z = 1 separates regions with μ_r1 = 5 (origin side) and μ_r2 = 7. Given B̅_1 = 3 a_x + 1 a_y (T), find B̅_2 and H̅_2 (μ_0 = 4π×10^-7 H/m). [20M]
(b) For m(t) (BW = 20 kHz, P = 20 W, max amplitude = 8) sent through a channel with 80 dB attenuation and noise PSD 0.5×10^-12 W/Hz, find required transmitter power and channel bandwidth to obtain ≥50 dB SNR at the modulator output for: (i) DSB-SC AM (ii) SSB AM (iii) DSB AM (m = 0.6) [20M]
(c) For the ideal DC–DC converter (V_s = 20 V, D = 0.25, f_s = 20 kHz, L = 150 µH, C = 240 µF, I_D(avg) = 1.2 A), determine: (i) Inductor peak–peak ripple current (ii) Peak current through switch S [10M]
The figure shows a unity feedback system. The steady-state value of the unit step response c(t) is 0.8. Determine the maximum overshoot in the response c(t). A circuit breaker is rated as 2500 A, 1500 MVA, 33 kV, 3 sec, 3-phase, oil circuit breaker. Determine its rated normal current, breaking current, making current and short-time rating (current). An audio signal, whose bandwidth is 15 kHz, is to be digitized using PCM. Uniform quantization with 1024 levels and binary encoding are assumed. Determine the minimum sampling rate. If the actual sampling rate is 20 % in excess of the minimum rate, determine the minimum permissible bit rate. Briefly explain the following logical instructions of 8085 microprocessor: (i) ANA M (ii) XRA M (iii) CMC (iv) STC (v) RRC In a three-phase 400 km long transmission line, the conductors are spaced at the corners of an equilateral triangle of side 5 m. The diameter of each conductor is 3 cm. Calculate the capacitance per phase of the 400 km long conductor.
(a) Determine the maximum overshoot in the unit-step response of the unity feedback system shown in the figure. [10M]
(b) Determine rated normal current, breaking current, making current and short-time rating (current) for the 2500 A, 1500 MVA, 33 kV, 3-sec, 3-phase oil circuit breaker. [10M]
(c) For a 15 kHz audio signal digitised with PCM (1024 quantisation levels, binary encoding) find the minimum sampling rate. If the actual rate is 20 % higher, find the minimum permissible bit-rate. [10M]
(d) Briefly explain logical instructions of 8085: ANA M, XRA M, CMC, STC, RRC. [10M]
(e) Calculate the capacitance per phase of a 400 km, three-phase line whose conductors form an equilateral triangle of side 5 m and have 3 cm diameter. [10M]
The block diagram of a feedback system is shown in the figure. (i) Sketch the complete root locus of the system. (ii) What is the value of K at s = 0 ? (iii) Find the range of K for closed-loop stability. Draw the connection diagram of a Schering bridge to measure the capacitance and dissipation factor. Write the balance equations and derive the formulae for finding the capacitance and dissipation factor. A linear delta modulator is designed to transmit speech signal band-limited to 4 kHz. The specifications are: sampling rate = 10 × Nyquist rate step size = 100 mV The system is tested with a 1 kHz sinusoidal signal. Determine the maximum amplitude of the test signal so that slope overload does not occur. Calculate the maximum power that can be transmitted without slope overload.
(a) Root-locus analysis of the feedback system; value of K at s = 0; range of K for stability. [20M]
(b) Schering bridge: connection diagram, balance equations, formulae for capacitance and dissipation factor. [20M]
(c) Delta modulator: maximum permissible input amplitude to avoid slope overload and corresponding maximum transmitted power. [10M]
Write the state and output equations for the system shown in the figure. Choose state variables x₁ and x₂ as shown. Check the controllability and observability of the system. Differentiate between full decoding and partial decoding techniques used by 8085 microprocessor to decode an address. Give advantages and disadvantages of each technique. Discuss with example how BCD number addition is performed using DAA instruction of 8085 microprocessor. A 6600 V, 50 Hz, single-core, lead-sheathed cable has the following data: Conductor diameter = 1·6 cm Length = 5 km Internal diameter of sheath = 3·2 cm Resistivity of insulation = 1·5 × 10¹² Ω-m Relative permittivity of insulation = 3·8 Calculate the insulation resistance, capacitance and the maximum electric stress in the insulation.
(a) State-space model; determine controllability and observability. [20M]
(b(i)) Full decoding vs partial decoding in 8085; advantages and disadvantages. [10M]
(b(ii)) BCD addition using DAA instruction of 8085, with example. [10M]
(c) For the given 6600 V cable, compute insulation resistance, capacitance and maximum electric stress. [10M]
Consider a systematic linear block code with binary elements whose parity-check equations are p₁ = m₁ + m₂ + m₃, p₂ = m₂ + m₃ + m₄, p₃ = m₁ + m₃ + m₄, p₄ = m₁ + m₂ + m₄, where mᵢ are message digits and pᵢ are parity check digits. (i) Find the generator matrix and parity-check matrix for the code. (ii) How many errors can this code detect? How many errors can be corrected? (iii) If 10100100 is the received code word, find the corresponding transmitted code word assuming that single-bit error has been made during transmission. A transmission line has the following parameters: A = D = 1∠25°, B = 88 ∠75° (i) Determine the sending-end voltage and the voltage regulation if the line supplies a load of 40 MW at 0.8 p.f. lagging with receiving-end voltage 132 kV. (ii) Find the power and power factor of the load if the voltages at the two ends are 132 kV and with a phase difference of 30°. Explain four instructions which are used to control interrupt structure of 8085 microprocessor.
(a) Generator and parity-check matrices; error-detecting and correcting capabilities; decoding of received word 10100100. [20M]
(b) Transmission-line performance using given ABCD parameters: (i) sending-end voltage and regulation for specified load; (ii) power and p.f. for given end voltages and phase angle. [20M]
(c) Explain four instructions that control the interrupt structure of 8085 microprocessor. [10M]
A bank of three identical single-phase transformers having 11000 V / 231 V voltage ratio are connected in delta-star combination with the delta side connected to 11 kV, 3-phase balanced supply. The star side is supplying a balanced load of 120 kVA at 0.8 pf lag. A single-phase load of 40 kW, upf is now connected between one line and neutral of the secondary side. Calculate the input line currents at the delta side under this condition. (Neglect any magnetising currents of the transformers)
We have 25 UPSC Mains Electrical Engineering optional subject questions spanning 3 years (2023–2025).
Electrical Engineering has 2 papers in UPSC Mains: Electrical Engineering-II, Electrical Engineering-I. Each paper carries 250 marks.