Basic Electrical Engineering B.Tech Question Bank : tits.ac.in

Name of the College : Turbomachinery Institute of Technology &Sciences (TITS)
University : JNTU Hyderabad
Department : Department of Computer Science & Engineering
Subject Name : Basic Electrical Engineering
Degree : B.Tech
Year/Sem : II/I
Website : tits.ac.in
Document Type : Question Bank

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Basic Electrical Engineering Question Paper

Unit – I

1. a) State and explain Kirchoff’s laws.
b) In the circuit given below Figure , find the current through 5 O resistor. [7+8] May 2011 , Set 1
2. By means of node voltage analysis obtain the current through 15 O resistor in the following circuit (Figure ).

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3. (a) A transmission line cable consists of 19 strands of identical copper conductors each 1.5 mm in diameter. The length of the cable is 2 km but because of the twist of the stands, the actual length of each conductor is increased by 5 percent. What is resistance of the cable? Take the resistivity of the copper 1.78*10 -8 ohm-m.
(b)Explain KVL and KCL and ohm’s Law. [10+5] Dec 2011, Set 1
4. a)Explain ohm’s Law and discuss the different Factors on which the resistance is dependent?
(b) Calculate the resistance of copper conductor having a length of 2 km and a cross-section of 22 mm 2. Assume the resistivity is 18*10 -9 ohm-m. [7+8] May 2011, Set 2
5. Find the voltage VAB in the circuit shown in below figure and drop across each branch. May 2011, Set 4

Unit – II

1. Define the following:
i)Alternating quantity ii)RMS value iii) Average value iv) Form factor .[8M] Nov-09,Set-2,Sept-07 Set- 1&2,May-07 Set 1,2,3
2. In an R-C series circuit, Voltage across the combination is given by 40 sin (2000t+45), R=10O. The current leads the voltage by p/3 rad. Find the value of C. Also find the expression for current. .[8M] Jan -10, Set-1

3. A coil A having a resistance of 10 ohms and inductance of 0.2 Henry is connected in series with another coil B having a resistance of 30 ohms and inductance 0.1 H. The two coils in series are fed from 200 V, 50 Hz supply. Determine the voltage across each coil, power dissipated in each coil, and the power factor of the combined series circuit: Draw the phasor (vector) diagram. [16] June 2010, Set 1

4. A coil A having a resistance of 10 ohms and inductance of 0.2 Henry is connected in series with another coil B having a resistance of 30 ohms and inductance 0.1 H. The two coils in series are fed from 200 V, 50 Hz supply. Determine the voltage across each coil, power dissipated in each coil, and the power factor of the combined series circuit: Draw the phasor (vector) diagram. [16] June 2010, Set 2

5. (a) A current of 10A in a series circuit consisting of R = 10 ; L = 0.1H and C = 100 µF. Find the power, and impedance, if the frequency of the supply is 50Hz.
(b) A 50 Hz sinusoidal voltage; V=141 sin wt is supplied to a series R-L circuit comprising of R=3O , and L=0.01272 Henry. Compute :i. the effective value of the steady state current as well as the relative phase angle;
ii. the instantaneous current ( time equation);
iii. effective magnitude, the phase angle of the voltage drops appearing across each circuit element ? [7+8] May 2011, Set 2

6. Find the active and reactive components of the current taken by a series circuit consisting of a coil of inductance 0.1 H and resistance 8 and a capacitor of 120µF connected to a 240 V, 50 Hz supply? [15] MAY 2011, Set 2

7. (a) An alternative voltage of (160 +j120)V is applied to a circuit and the current in the circuit is given by 6+j8  A. Find : i. the values of elements of the circuit; ii. the power factor of the circuit; iii. power consumed?
(b) A choking coil of negligible resistance takes a current of 3.2A, when connected to 200V, 50Hz supply, Calculate i. inductance, and ii. the current taken by the coil, if the frequency is reduced to 20Hz? [8+7] May 2011, Set 3

8. (a) A circuit consists of resistance R, and capacitive reactance of 60 connected in series. Determine the value of R for which p.f. of the circuit is 0.8 and also draw its phasor diagram.
(b) A circuit consisting of a variable resistor in series with a capacitance of 80µF is connected across a 120V, 50Hz supply. Calculate the value of resistance so that the power absorbed is 100W. [8+7] Dec 2011, Set 2

9. (a) The voltage applied to a circuit is V = 100 sin(wt+30 0), and the current owing in the circuit is i = 15(wt+60 0). Determine the impedance, resistance, reactance, power and the power factor.
(b) A 230V, 50 Hz voltage is applied to a coil of L = 0.5 H and R = 200 in series with a capacitor C. What value must C have in order that the total voltage across the coil shall be 250V? Dec 2011, Set 4

10. (a) The voltage applied to a circuit is: v = 100 sin(wt+300), and the current owing in the circuit is i = 15(wt+600). Determine the impedance, resistance, reactance, power and the power factor of the circuit.
(b) A circuit consists of resistance R, and capacitive reactance of 30O connected in series. Determine the value of R for which p.f. of the circuit is 0.8 and also draw the phasor diagram. [8+7] Dec 2011, Set 1

11. An a.c. circuit consists of a resistance of 5 ohms, an inductance of 0.1 H, and a capacitance of 100 µF, all in series. Determine for this circuit: (a) total reactance; (b) impedance; (c) admittance; (d) susceptance, and (e) conductance. The supply frequency is 60 Hz. [15] Dec 2011, Set 3

Unit – III

1. Explain the construction of a single phase transformer. .[8M] June-10 Set-1, 2,3, 4.June-09, Set-1
2. Discuss in detail the difference between the core type and shell type transformer. .[8M] June-10 Set-1, 2,3,4. June-09 Set-1.

3. a) Derive an emf equation of a single phase transformer.
b) The maximum flux density in the core of 250/3000 Volts 50 Hz single phase transformer is 1.2 webers per square meter. If the emf per turn is 8 volts determine primary and secondary turns and area of the core. [8+8] June 2010, Set 1,2,3,4

4. A 1- f phase transformer takes 10A on no-load at a power factor of 0.1. The turns ratio 4:1. If a load is supplied by the secondary at 200 A, and a power factor of 0.8, find the primary current, and the power factor. Neglect the internal voltage drops in a transformer and also draw the phasor diagram. [15] May 2011, Set 2

5. (a) The design requirement of a 11,000 / 415 V, 50 Hz, single phase, core-typ transformer are approximate emf/ turn is 15 V, maximum flux density 1.5 T. Find a suitable number of primary, and secondary turns and the net cross sectional area of the core.
(b) Explain different losses in case of transformer. [8+7] May 2011, Set 1

6. A 220/440 V, 10 KVA , 50 Hz single-phase transformer has at full-load, a copper loss of 120 W. If it has an efficiency of 98% at full-load and unity p.f determine the iron losses. What would be the efficiency at half fullload, and 0.8 p.f lagging?[15] May 2011, Set 3

7. (a) Explain in detail O.C and S.C tests to be conducted on a transformer for calculation of regulation.
(b) The open-circuit test readings on a 400/200 V, single phase transformer conducted from L.V side are : voltage = 200 V; current = 0.7 A ; power = 95 W. Calculate the no-load circuit parameters referred to H. V side. [9+6] Dec 2011, Set 2

8. (a) Draw the phasor diagram of Transformer under no load.
(b) A 1,000/200 V transformer takes 0.3 A at p.f of 0.2 on open circuit. Find the magnetizing, and iron loss component of no-load primary current. [7+8]Dec 2011, Set 4

9. (a) Describe in detail constructional features of a single – phase, 50 Hz, core-type transformer has a square cores of 20 cm side. Permissible maximum flux- density is 1 wb/m2. Calculate the number of turns per limb on the High and low-voltage sides for a 3000/220 V ratio.
(b) Derive the induced e.m.f equation of transformer. [8+7]Dec 2011, Set 1

10. (a) Derive the induced e.m.f equation of transformer.
(b) A single-phase, 25 Hz transformer has 50 primary turns and 600 secondary turns. The cross sectional area of the core is 400 sq.cm. If the primary of the transformer is connected to 230 V supply. Find
i. the secondary induced emf
ii. the flux density (peak) in the core. [7+8] Dec 2011, Set 3

Unit – IV

1. Draw a detailed sketch of a dc machine and identify the different parts. Briefly explain the function of each major part. [16] June 2010, Set 1,2,3,4, May 2011, Set 2,4, Dec 2011, Set 2
2. (a) Discuss the classification of d.c generators with suitable diagrams.
(b) A 10KW shunt generator supplies load at a terminal voltage of 200 volts. The shunt field resistance is 100 ohms and armature resistance is 0.1 ohm.
3. Calculate the e.m.f induced in the generator. [7+8] MAY 2011, Set 2
4. (a) Name the main parts of a D.C. Machine and state the materials of which each part is made.
(b) A shunt generator delivers 450 A at 230V and the resistances of the shunt field and armature is 50 and 0.03 respectively. Calculate the generated e.m.f. [15] May 2011, Set 1

5. a) Explain the compound DC generator with neat circuit diagram.
(b) The armature of a 4-pole wave wound d.c generator is required to generate an e.m.f of 480V on open circuit when revolving at a speed of 620 rpm. Calculate the magnetic flux per pole required. The armature has 160 slots with 2 coil sides per slot and each coil consisting of three turns. The armature is wave-wound. May 2011, Set 3

6. (a) What are the classifications of self excited DC generators and explain series generator?
(b) A 4-pole lap wound D.C. shunt generator has a useful flux per pole of 0.06wb. The armature winding consists of 240 turns each of 0.0035 resistance. Calculate the terminal voltage when running at 920 rpm, if the armature current is 60A. Dec 2011, Set 4

7. A separately excited generator running at 1500 rpm supplies 225A at 120V to a current of constant resistance. What will current be when the speed is dropped to 1000 rpm with the field current unaltered? The armature resistance is 0.06 and the total drop at the brushes is 1.5V. Ignore armature reaction. [15] Dec 2011, Set 1

8. (a) What are the applications of DC generators?
(b) The resistance of the field circuit of a shunt excited d.c generator is 200 when the output of the generator is 120 kW, the terminal voltage is 525V and the generated e.m.f is 550V. Calculate
i. the armature resistance and
ii. if the terminal voltage is 540 V at 80 kW of the output what will be the generated emf? [5+10] Dec 2011, Set 3