Rr222104-elctrical-and-electronics-engineering

Set No. 1

Code No: RR222104

II B.Tech II Semester Supplimentary Examinations, Aug/Sep 2008 ELCTRICAL AND ELECTRONICS ENGINEERING (Aeronautical Engineering) Time: 3 hours Max Marks: 80 Answer any FIVE Questions All Questions carry equal marks ⋆⋆⋆⋆⋆ 1. (a) Explain the current division in a parallel circuit. (b) A series circuit with a resistor of 100 ohm capacitor of 25 micro Farad and inductance of 0.15H is connected across 220V, 60Hz supply. Calculate i. current ii. power and iii. power factor in the circuit.

[6+10]

2. (a) How do you find critical field resistance of D.C. shunt generator? Explain. (b) A 20kW, 4-pole shunt generator has a terminal voltage of 250V when running at 400 rpm. The armature has a resistance of 0.16 Ω and consists of 652 conductors which are lap-wound. The diameter of the pole-shoe circle is 38cm. The poles are 20cm long and subtend an angle of 600 . Calculate the flux density in the air gap. Neglect shunt field current. [6+10] 3. (a) What are the various parts of transformer? Explain each part the function of. (b) A 3300 / 400V single phase transformer takes 1A at p.f. of 0.2 on no-load. Calculate the current drawn by the primary and its phase angle when the secondary supplies a current of 60A at 0.8 p.f. lag. Draw vector diagram. [6+10] 4. (a) A 3-phase, 16-pole alternator has a star connected winding with 144 slots and 10 conductors per slot. The flux per pole is 30mwb. The speed is 375 rpm. Find frequency, phase and line emf. (b) A three phase induction motor has an input of 100kW. The stator copper losses are 2.2kW. find i. the rotor copper loss per phase if the motor is running at slip of 4 percent and ii. the mechanical power developed by the motor. [8+8] 5. (a) Explain the following terms for P − N junction. i. Potential barrier ii. Depletion region (b) The resistivities of the two sides of a step graded silicon diode are 2 ohm − cm ( p - side ) and 1 ohm − cm ( n - side ). Calculate the height of Eo of the potential energy barrier. . If µn = 1300 cm2 / volt - sec , µ p = 500cm2 / volt − sec , ni = 1.5 × 1010 . Assume any necessary data. [8+8] 1 of 2

Set No. 1

Code No: RR222104

6. (a) Explain the current components of a PNP transistor with neat sketch. (b) For an NPN transistor if α = 0.98 and IE = 2mA find IC and IB .Neglect reverse saturation current. [10+6] 7. (a) Classify different types FET’s with symbols. (b) Draw and explain the V − I Characteristics of UJT.

[8+8]

8. (a) Derive electrostatic deflection sensitivity. (b) In a CRT the distance of the screen from centre of the magnetic field is 20 cm.The deflecting magnetic field of flux density 0.1 mWb / sq.m extends for a length of 2cm along the tube axis. The final anode voltage is 800V. Calculate the deflection of the spot. [12+4] ⋆⋆⋆⋆⋆

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Set No. 2

Code No: RR222104

II B.Tech II Semester Supplimentary Examinations, Aug/Sep 2008 ELCTRICAL AND ELECTRONICS ENGINEERING (Aeronautical Engineering) Time: 3 hours Max Marks: 80 Answer any FIVE Questions All Questions carry equal marks ⋆⋆⋆⋆⋆ 1. (a) Explain the current division in a parallel circuit. (b) A series circuit with a resistor of 100 ohm capacitor of 25 micro Farad and inductance of 0.15H is connected across 220V, 60Hz supply. Calculate i. current ii. power and iii. power factor in the circuit.

[6+10]

2. (a) Discuss the principle of operation of generator. (b) In a long-shunt compound generator, the terminal voltage is 230V when generator delivers 150 A. Determine i. induced e.m.f. ii. total power generated and iii. distribution of this power. Given that shunt field, series filed, divertor and armature resistances are 92Ω , 0.015Ω , 0.03Ω and 0.032Ω respectively. [6+10] 3. (a) Why is efficiency of transformer is generally high? (b) A 200kVA, single phase transformer has an efficiency of 98 percent at F.L. if the maximum efficiency occurs at 3/4 F.L. Calculate i. the iron loss, ii. the copper loss at F.L. iii. the efficiency at half − load. Assume a p.f. of 0.8 at all loads.

[6+10]

4. (a) The stator of a 3-phase, 8-pole synchronous generator driven at 750 rpm has 72 slots. The winding has been made with 36 coils having 10 turns per coil. Calculate the rms value of induced emf per phase if the flux per pole is 0.162 web, sinusoidally distributed. Assume that full pitch coils have been used. (b) The power input to the rotor of a 440V, 50Hz, 6-ple, 3-phase inductor motor is 80KW. The rotor electromotive force is observed to make 100 complete alternations per minute. Calculate i. ii. iii. iv.

Slip rotor speed rotor copper losses per phase mechanical power developed and 1 of 2

Set No. 2

Code No: RR222104

v. the rotor resistance per phase if the rotor current is 60A.

[8+8]

5. (a) Explain the variations of charge density , electric field and potential of open circuit P − N junction. (b) The resistivities of the two sides of a step graded germanium diode are 2 ohm − cm ( p - side ) and 1 ohm - cm ( n - side ). Calculate the height of Eo of the potential energy barrier. I f n = 3800 cm2 / volt - sec , µ p = 1800 cm2 / volt - sec , ni = 2.5 × 1013 . Assume any necessary data. [8+8] 6. Explain the procedure to obtain h − parameter values (all four ) of CB configuration. [16] 7. (a) Explain the zener and avalanche breakdown mechanisms. (b) Give the applications of Varactor diodes. 8. Sketch the block diagram of CRT, explain every part in it in detail. ⋆⋆⋆⋆⋆

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[10+6] [16]

Set No. 3

Code No: RR222104

II B.Tech II Semester Supplimentary Examinations, Aug/Sep 2008 ELCTRICAL AND ELECTRONICS ENGINEERING (Aeronautical Engineering) Time: 3 hours Max Marks: 80 Answer any FIVE Questions All Questions carry equal marks ⋆⋆⋆⋆⋆ 1. (a) Derive an expression for coefficient of coupling. (b) A flux meter is connected to a search-coil having 600 turns and mean area of 4cm2 . The search coil is placed at the centre of an air-cored solenoid 1 meter long and wound with 1000 turns. When a current of 4A is reversed, there is a deflection of 20 scale divisions on the flux meter. Calculate the calibration in Wb-turns per scale division. [6+10] 2. (a) What are the conditions to build up of generator voltage. (b) A four-pole generator, having wave-wound armature winding has 51 slots, each slot containing 20 conductors. What will be the voltage generated in the machine when driven at 1500rpm assuming the flux per pole to be 7.0 mWb? [6+10] 3. (a) What are the various losses in transformer? Explain. (b) A 10KVA 2000/400V single phase transformer has the following data R1 =4 ohms, X1 =8 ohms, R2 =015 ohms, X2 =0.5 ohms. Determine the secondary terminal voltage at full load 0.8 p.f. lagging when the primary supply voltage is 2000V. [6+10] 4. (a) Calculate the rms value of the induced emf per phase of a 10-pole, 3-phase, 50 Hz alternator with 2 slots per pole per phase and 4 conductors per slot. The coil span is 1500 , the flux per pole is 0.12 Wb. (b) A 3-phase, star-connected alternator has the following data : Voltage required to be generated on open circuit = 400V (at 50Hz) ; speed = 500 rpm ; stator slots / pole / phase = 3; conductors / slot = 12. Calculate i. Number of poles and ii. Useful flux pole.

[8+8]

5. (a) Explain the crystal structure of Intrinsic Semi Conductor with neat diagram. (b) Find the concentration of holes and electrons in N − type germanium at 3000 K if the receptivity is 10 ohm − cm. If µ n = 3800 cm2 / volt - sec , µ p = 1800 cm2 / volt - sec , ni = 2.5 × 1013 . Assume any necessary data. [8+8] 6. (a) Elaborate the consequences of Early effect. (b) For an circuit shown in figure 6b below , find all transistor currents.

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[8+8]

Set No. 3

Code No: RR222104

Figure 6b 7. (a) Can depletion MOSFET can be used as enhancement MOSFET ? If so explain how. (b) Derive the expression for time period of UJT relaxation Oscillator. 8. Sketch the block diagram of CRO, explain every part in it in detail. ⋆⋆⋆⋆⋆

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[8+8] [16]

Set No. 4

Code No: RR222104

II B.Tech II Semester Supplimentary Examinations, Aug/Sep 2008 ELCTRICAL AND ELECTRONICS ENGINEERING (Aeronautical Engineering) Time: 3 hours Max Marks: 80 Answer any FIVE Questions All Questions carry equal marks ⋆⋆⋆⋆⋆ 1. A mild steel ring of 30cm mean circumference has a cross sectional area of 6cm2 and has a winding of 500 turns on it. The ring is cut through at a point so as to provide an air-gap of 1mm in the magnetic circuit. It is found that a current of 4A in the winding, produces a flux density of 1T in the air gap. Find (a) the relative permeability of the mild steel and (b) inductance of the winding.

[16]

2. (a) Draw a neat diagram for various types of generators. (b) An 8-pole d.c. shunt generator with 778 wave-connected armature conductors and running at 500 rpm supplies a load of 12.5Ω resistance at terminal voltage of 250V. The armature resistance is 0.24 ohms and the field resistance is 250Ω . Find the armature current, the induced emf and the flux per pole. [6+10] 3. (a) How do you predetermine the efficiency of a transformer? Explain. (b) A 25kVA, 2200/220V, 50Hz, single phase transformer has the following resistance and leakage reactances. R1 =0.8 ohm, X1 =3.2 ohm, R2 =0.01ohm, X2 =0.03 ohm. Calculate the equivalent resistance and reactance referred to secondary side. [6+10] 4. (a) A 3-phase, 16-pole alternator has a star connected winding with 144 slots and 10 conductors per slot. The flux per pole is 30mwb. The speed is 375 rpm. Find frequency, phase and line emf. (b) A three phase induction motor has an input of 100kW. The stator copper losses are 2.2kW. find i. the rotor copper loss per phase if the motor is running at slip of 4 percent and ii. the mechanical power developed by the motor. [8+8] 5. (a) Explain the variations of charge density , electric field and potential of open circuit P − N junction. (b) The resistivities of the two sides of a step graded germanium diode are 2 ohm − cm ( p - side ) and 1 ohm - cm ( n - side ). Calculate the height of Eo of the potential energy barrier. I f n = 3800 cm2 / volt - sec , µ p = 1800 cm2 / volt - sec , ni = 2.5 × 1013 . Assume any necessary data. [8+8] 6. Compare the input characteristics of CB and CE configurations. What is the effect of base width modulation on these characteristics? [16] 1 of 2

Set No. 4

Code No: RR222104 7. (a) How Zener diode can be used as voltage regulator.

(b) Sketch the V − I characteristics of photo diode and explain.

[8+8]

8. (a) Compare the electrostatic and magnetic deflection systems. (b) Explain horizontal deflection system of CRO. ⋆⋆⋆⋆⋆

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[8+8]