University of Rajshahi Department of Electrical & Electronic Engineering B.Sc. Engineering Part-IV Odd Semester Examination- 2017

Transcription

1 Course Code: EEE 4141 Course Title: Power System i. Answer to all parts (a), (b), (c) etc. of a question must be contiguous. ii. Use separate answer script for each Section (A/B). iii. Right margin indicates the full marks. 1 (a) Define per unit value of any electrical quantity with the advantages of per unit system. (b) What are the quantities whose base values are required to represent the power system by reactance diagram? (c) Draw the impedance diagram for the following system: 11 kv 0 MVA G j 0.15 T 1 T j 0.10 Δ - 1.5/13 kv (00 + j500) Ω Choose a base voltage of 13 kv for the transmission line and a base voltampere of 0 MVA. (a) What is subtransient, transient and steady state current of a synchronous machine? (b) Construct the bus from the following reactance diagram. Line j Δ 13/11 kv j 0.5 j 0.5 j MVA M j kv + j 0. j G 1 G (c) The bus impedance matrix of a two-bus network is given below. Find the fault current on bus-. Pre-fault voltage at bus- is 1.00 PU Z bus j (a) Prove that in absence of a path through the neutral of a three-phase system, the line currents contain 4 no zero sequence components. (b) Draw the zero-sequence network for the following power system. T 1 T 3 A Δ - - Δ B T T 4 Δ - - Δ 4 (a) Define load flow study. Why are load flow studies essential? (b) What are the difficulties of load flow problem?.75 (c) What is rotating VAR generator? Describe the method of controlling reactive power by rotating 4 VAR generator.

2 5 (a) What is meant by a fault? Write down the various types of faults those occur in transmission lines..75 (b) Draw the sequence networks for the system shown in the figure below. Determine the fault current 6 when (i) LLG and (ii) LL fault occurs at point F. T 1 Line 1 T G 1 G F Line The per unit reactances, all referred to the same base, are as follows: Xo X1 X G Both the generators G are generating Line 1 = Line PU voltage T T (a) State Fortescue s theorem. Why is it preferred in unsymmetrical fault calculation?.75 1 a (b) Prove that, a. a a (c) Derive an expression of the current for line to line fault in terms of symmetrical components. 4 7 (a) What is stability study? 1 (b) Define swing curve and derive an expression for the swing equation. 5 (c) A two pole 50 Hz, 60 MVA turbogenerator has a moment of inertia of kg-m. Calculate.75 (i) The kinetic energy in MJ at rated speed. (ii) The inertia constants M & H. 8 (a) Define critical clearing angle and find an expression for power angle. 3 (b) Explain in brief the method of improving power system stability. (c) Define critical clearing angle and critical clearing time (d) Explain equal area criterion of a given power system.

3 Course Code: EEE 4143 Course Title: Communication Engineering i. Answer to all parts (a), (b), (c) etc. of a question must be contiguous. ii. Use separate answer script for each Section (A/B). iii. Right margin indicates the full marks. 1 (a) What do you understand by continuous-time and discrete-time signals? Give some examples of 4 transformations of the independent variable. (b) Describe the Fourier transform for periodic signals. 3 (c) Draw a periodic impulse train and its Fourier transformed shape (a) How the energy and power content of a signal can be defined? (b) Define the autocorrelation function for the energy type and power type signals (c) Show that x(t) = Ae j(πf 0t+θ) is a power type signal and its power content is A. 3 3 (a) What do you mean by a linear system? Explain it in details with some mathematical expressions. 4.5 (b) What is random variable? List the most commonly used random variables in communications (c) Explain the basic concept of random processes in brief..5 4 (a) What are the most common noises encountered in electrical circuits? 0.75 (b) Describe the sources and characteristics of shot noise. 4 (c) Define noise figure for a linear two-port device. How it can be expressed?.5 (d) What is equivalent noise temperature? (a) What is pulse modulation? List the advantages and disadvantages of PAM, PWM and PPM methods. 4 (b) Describe a method for the generation of pulse position modulated wave (c) What would be the transmission bandwidth of a PPM signal? 1 6 (a) What do you mean by channel noise and quantization noise? (b) State and explain sampling theorem..75 (c) Draw the block diagram of a DM system and discuss the function of its constituent parts. 4 7 (a) Define the terms for telecommunication system: (i) simplex (ii) half-duplex, and (iii) full-duplex 3 (b) Draw and explain a simple telephone circuit (a) State and explain Kepler s laws with necessary figures that govern satellite motion. (b) Define the following terms: (i) Geostationary satellite (ii) Geosynchronous satellite(iii) Escape 3 velocity (c) Where inclined highly elliptical orbit is used? 1

4 Course Code: EEE 4145 Course Title: Project planning, Management and Engineering iv. Answer to all parts (a), (b), (c) etc. of a question must be contiguous. v. Use separate answer script for each Section (A/B). vi. Right margin indicates the full marks. 1 (a) Define a project from engineering point of view. (b) Identify and elaborate some key features of a project..75 (c) What are the functions of project management? 4 (a) What type of evaluation is feasibility study? Why and when is it done? (b) Give the short account of different feasibility studies normally conducted for engineering projects..75 (c) F. H. Enterprise is planning to undertake a commercial project. The project requires a total 4 investment of TK. 50,00,000/-. Probable cash flows from the project for five years are as follows: ear Cash inflow (TK) 1 11,05,000/- 11,10,000/- 3 1,15,000/- 4 1,35,000/- 5 1,0,000/- Is the project acceptable if the discount rate is 10%? 3 (a) What do you understand by project life cycle?.5 (b) Shortly elaborate the stages of project life cycle. 3.5 (c) What is project plan? At which stage of project life cycle planning is done?.75 4 (a) Why is project cost estimation necessary? (b) Describe different types of cost estimates. 4 (c) Mention the causes of variation of accuracy level of different cost estimates (a) What is project scheduling? How is it done? (b) Point out the stages of project scheduling. (c) The table below contains necessary scheduling information of construction project: Activity Immediate Time (in weeks) Predecessor Activity Optimistic Most Likely Pessimistic A None B None C None D A E B F C 5 8 G D, E 4 6 8

5 Required: (i) (ii) (iii) Draw a network diagram. What is the critical path? What is the probability of completing the project in 0 weeks? 6 (a) What is the meaning of project implementation to you?.75 (b) Discuss the stages of project implementation. 4 (c) Point out the factors that obstruct successful project implementation. 7 (a) Bring out the difference between PERT and CPM. In what ways these techniques are similar? 4 (b) Discuss the role of network techniques in project planning, scheduling and controlling. 8. Write short notes on: (a) Padma Bridge (b) ECNEC (c) IMED (d) Project Environment.75

6 Course Code: EEE 4149 Course Title: High Voltage Engineering i. Answer to all parts (a), (b), (c) etc. of a question must be contiguous. ii. Assume reasonable value for any missing data. iii. Right margin indicates the full marks. 1 (a) Briefly discuss different methods of generating ac high voltage in the laboratory. Justify which is the best. (b) A high voltage capacitor is to be tested at 500kV, 500 ma. The testing transformer available for this purpose has the following ratings: Voltage rating: 50 V/ 100kV, kva=100 kva, % Resistance =1%, % Reactance=5%. An external reactor having no resistance is used along with the transformer to generate the required high voltage. Calculate: (i) the inductance of the reactor. (ii) the transformer secondary voltage (iii) the primary voltage (iv) the primary current. 4 (a) Which are the factors affecting the breakdown of gases? 1 (b) Define Townsend s first and second ionization coefficients. Explain the Townsend s criterion for a spark. (c) State and explain Paschen s law. Explain Penning Effect when referred to gaseous discharges..75 (d) Derive expression for (pd)min and Vbmin if V b = Bpd, where symbols have their usual meaning. 3 lnapd/k Assume A = 1, B = 365, and γ = 0.0 for air. Determine (pd)min and Vbmin. 3 (a) What is corona? Explain why corona is disliked by power system engineers. 3 (b) Derive the criteria for formation of stable corona in an overhead high voltage transmission line (c) What is corona ring? 4 (a) What is meant by tracking in solid insulation materials? (b) Explain how internal discharge due to void leads to breakdown in solid dielectric (c) A solid insulating block of thickness 1.5 cm and having a dielectric constant of 4.5 is subjected to 50 Hz ac voltage. The specimen contains an air void of thickness 1mm. Considering the breakdown strength of air as 30 kv/cm (peak). Find the maximum voltage which can be applied across the specimen without any internal discharge. 5 (a) Define the terms (i) impulse flash over voltage (ii) impulse puncture voltage 1 (b) Draw a typical impulse current generator circuit and explain its operation and application. (c) Derive an expression for voltage efficiency of a single stage impulse generator..75 (d) An impulse current generator has total capacitance of 15µF, the charging voltage 15 kv, the cuircuit inductance mh and the dynamic resistance 1Ω. Determine the peak current and wave shape of the wave. 6 (a) What is meant by insulation co-ordination? Explain it (b) What are BILS? Explain their significance. (c) With a neat diagram describe the principle and operation of a valve type lightning arrester (a) With neat sketches explain the Cockroft-Walton voltage multiplier circuit. Explain its operation when the circuit is (i) unloaded and (ii) loaded. (b) A four-stage Cockroft-Walton type cascade circuit with capacitances all equal to 0.05 F is fed from 150 kv. If 1.7 ma current is to be supplied to the load by this circuit, determine (i) the ripple (ii) the voltage drop and (iii) regulation for supply frequency 50 Hz and 150 Hz. Calculate the same parameters for an eight-stage generator for a loaded current of 3.5 ma, the supply frequency being 150 Hz. 4 8 (a) What is the purpose of high voltage testing in the laboratory? Distinguish the difference between.75 destructive testing and non-destructive testing. (b) For a lossy dielectric prove that, tan = 1, where the symbols have their usual meaning. WC P R P 3 (c) Explain the necessity of sample preparation before H.V. tests. 3