QuestionBankofEEEAC__2013_11_25_17_02_09

8/13/2019 QuestionBankofEEEAC__2013_11_25_17_02_09

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Elements Of Electrical engineering: 2013-14(1st

Sem)

Question bank from My portions:

1.A) Define (i) form factor (ii) peak factor. Obtain the rms value and average

value of half wave rectified sinusoidal voltage wave.

B) Three currents are represented by i1 = 10sint; i2 = 20sin(t /6); i3 =

30sin(t + /4).Find magnitude and phase angle of resultant current.

C) A certain waveform has a form factor of 1.2 and a peak factor of 1.5. If the

maximum value is 100, find rms value and average value.

2.A) Discuss resonance in R-L-C series circuit. Explain how pf, XL and R vary

with frequency.

B) Define power factor. What is the power factor of a pure inductor? Give thedifference between active and reactive power.

3.A) Prove that power in a 3-phase balanced circuit can be deduced from the

readings of two wattmeters. Draw the relevant connection and phasor diagrams.Discuss the nature of power factor (i) when two readings are equal and positive (ii)

when two readings are equal but opposite in sign (iii) when one wattmeter readszero.

B) Three similar coils each of resistance 28 and inductance 0.7H are connected

in (i) star (ii) delta. If the supply voltage is 230V, 50Hz, calculate the line currentand total power absorbed.

4.A) Explain the wiring diagram of a tube light with choke and glow starter.

B) State the different methods of earthing and explain any one of them.

5.A) Add the following currents as waves and as vectors i1 = 7 sin t and i2 = 10sin (t + /3)

B) Voltage and current for a circuit with two pure elements in series are expressedas follows:

v (t) = 170 sin (6280 t + /3) volts i (t) = 8.5 sin (6280 t + /2) amps.


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Sketch the two waveforms. Determine: (i) the frequency (ii) power factor stating

its nature (iii) values of the elements.

C) An inductive coil draws 10 A current and consume 1 KW power from a 200 V,

50 Hz, a. c. supply. Determine: (i) the impedance in Cartesian and polar form (ii)power factor (iii) reactive and apparent power.

6.A) Two impedances given by Z1 = (10 + j5) and Z2 = (8 + j6) are

connected in parallel across a voltage of V = (200 +j0) volts. Calculate the circuitcurrent, branch currents and power factor of each branch. Sketch the vector

diagram with vectors in appropriate proportion.

B) Explain the phenomena of resonance in a.c. parallel circuit. Derive the

mathematical expression of resonant frequency. Sketch the graphical

representation of parallel resonance.

C) Three 100 non-inductive resistances are connected in (a) star (b) delta, across

a 400 V, 50 Hz, 3-phase supply mains. Calculate the power taken from the supply

system in each case.

7.A) Draw a schematic block diagram showing positioning of major equipments in

domestic wiring. Label the diagram. Also draw the circuit for controlling one lampfrom two points (stair case wiring).

B) Give comparison between fuse and MCB with regard to protection in wiringinstallation.

8.A) Derive the relation between phase and line values of voltages and currents in

case of 3-phase (i) star (ii) delta connection.

B) Prove that the sum of readings of two wattmeters connected to measure powerin 3-phase a.c. circuit, gives total power consumed by the circuit.

C) Using schematic block diagram, briefly explain charging of battery from a.c.supply mains.

9.A) A series RLC circuit consists of a resistance of 500 ohm, inductance of 50mHand a capacitance of 20 pF. Find

1. The resonant frequency2. The Q-factor of the circuit at resonance.


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3. The half power frequency.

B) Discuss different methods of representation of vector quantities.

C) Calculate the RMS and average value of the sinusoidal waveform shown in theFig.3 From them, find the peak factor and form factor.

10.A) Discuss how the inductance of a choke coil can be measured using a

rheostate, a voltmeter and an ammeter.

B) Derive the equation of power in a single phase AC circuit in vector form only.

C) In a series parallel circuit, the parallel branches A and B are in series with

branch C. The impedances are ZA = (4+j3) , ZB= (4-j16/3) and ZC= (2+j8)

. If the current Ic = (25+j0) Amp. determine the branch currents and voltages andthe total voltage. Hence calculate the complex power (the active and reactivepowers) for each branch and the whole circuit.

D) Three identical coils each of (4.2 +j5.6) ohm are connected in star across a 415V, 3 phase, 50 Hz AC supply. Find

1. Phase voltage.

2. Phase current.3. Readings of two wattmeters W1 and W2 when they are connected to measure

the total power.

11.A) A delta connected load having branch impedances of (15 +j20) ohm is

connected to a 220V, 3 phase AC supply. Find1. Line currents.

2. Per phase power consumed.

3. What is the phasor sum of the line currents? Why does it have this value?

C) Draw the connection diagram of a tube light and explain its starting andworking.

D) Explain the construction of a three phase cable.


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12.A) A series RLC circuit having resistance of 8 _, inductance of 80 mH and

capacitance of 100 F is connected across 150 V, 50 Hz supply (Fig. 2).

Calculate,(a) the current, (b) the power factor, and (c) the voltages drops in the coiland capacitance.

B)Define following terms in connection with A.C wave forms : (i) Frequency (ii)phase & phase difference (iii) Time Period (iv) form factor (v) R. M. S. Value (vi)

Average Value.

13.A) The circuit, having two impedances of Z1= 8 + j15 and Z2= 6 -j8 inparallel, is connected to a single phase ac supply and the current drawn is 10 A.

Find each branch current, both in magnitude and phase, and also the supplyvoltage.

B) Define the term (1) reactance, (2) inductive reactance and (3) capacitive

reactance and explain how it depends on frequency in an A. C. circuit.

14.A) Derive an expression for the total power for a balanced 3 phase star OR delta

connected load in terms of line voltage line current and power factor.


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B) What is earthing? Explain requirement of earthing for any electrical equipment.

C) Draw the wiring diagram for the staircase wiring.

15.A) List lumens requirements for various categories of illumination. B) Listvarious protective devices used in the electric circuits and compare working of

ELCB with MCB.

16.A) Draw the circuit diagram of tubelight with the wiring of choke and starter.Explain the functioning of the circuit.

B) Explain the biological effect of electric current keeping the electric safety inview. Explain plate earthing.

C) Draw and explain the wiring diagram of supply mains with energy meter anddistribution box.

D) Give the circuit diagram of ELCB. Explain its working in brief.

17.A) The input power to a 3 phase load is measured by two wattmeter method.

The ratio of the readings of the two wattmeters connected for 3 phase balanced

load is 41. The load is inductive. Find the load power factor.

B) Two branches numbered 1 and 2 having impedances of 3 + j4 and 3 j4

respectively are connected to a 230 Volt, 50 Hz rms source. Find out :(i) The total current drawn from the source.

(ii) Power factor of that current.(iii) Draw the phasor diagram for I1, I2, the total current and supply voltage.

18.A) Define following terms with respect to a.c.waveform (i) Frequency (ii)

Power factor (iii) R.M.S. value (iv) Amplitude (v) Average value (vi) Form Factor.

B) A circuit takes a current of 3A at a power factor of 0.6 lagging when connected

to 115V, 50Hz supply. Another circuit takes a current of 5A at a power factor of0.707 leading when connected to same supply. If the two circuits are connected in

series across 230V, 50 Hz supply. Calculate the (i) current (ii) power consumed

(iii) Power factor.

19.A) Explain the method of measuring 3- power by two wattmeters.


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B) Prove that current through pure inductor is always lagging by 90 degree to its

voltage and power consumed is zero.

20.A) Three impedances Z1 = 5-j10 , Z2 =2+j20 and Z3 = 4+j2 are

connected in parallel. If the total current is 20A, Find the current shared by each.

B) Explain in brief (i) Self inductance (ii) Mutual inductance.

C) Compare series and parallel resonance.

21.A) Prove that in a purely capacitive circuit power consumed is zero when a.c.

voltage is applied. Draw relavent phasor diagram and waveforms.

B) An alternating current varying sinusoidally with a frequency of 50 Hz has r.m.s.

value of 10A. Write down the equation for instantaneous value and find this value(i) 0.0025 second and (ii) 0.0125 second after passing through a positive maximumvalue.

22.A) An inductive coil of resistance R and inductance L is connected inparallel with a capacitor of C. Derive an expression for resonant frequency and Q

factor.

B) A resistor of 40 and an inductor of 0.2 H and capacitor of 120 F are

connected in parallel across 230V, 50 Hz supply. Find: (i) the current of each

branch (ii) the resultant current (iii) power factor of the circuit.

C) Establish relationship between line and phase voltages and currents in balanceddelta connection. Draw complete phasor diagram of voltages and currents.

23.A) Three identical coil each having resistance of 10 and reactance of 10

are connected in (i) star and (ii) delta across 400V, 3 phase supply. Find in eachcase line current and the reading of each of the two watt meters connected to

measure the power.

B) Explain the working of earth leakage circuit breaker with diagram.

C) Explain the following wiring systems (i) Cleat wiring (ii) conduit wring

24.A) Explain construction and working of high pressure mercury vapor lamp.

B) Explain the working of a miniature circuit breaker.


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25.A) Draw and explain phasor diagram and Impedance triangle for R-L and R-C series circuit.

B)Discuss resonance in RLC series circuit. Explain how pf, XLand R vary

with frequency.

C) Give the comparison of series resonance and parallel resonance.D) Explain series R-L-C circuit with the phasor diagram for XL>XC; XL

QuestionBankofEEEAC__2013_11_25_17_02_09

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