Basic Electrical Engineering - B.Tech 2nd Semester Exam., 2022 (New Course)

2022•Semester 3•Civil-CA•End Semester
Bihar Engineering University, Patna
B.Tech 2nd Semester Exam., 2022 (New Course)

Basic Electrical Engineering

Time: 3 hours Code: 100201 Full Marks: 70

Instructions:

  1. The marks are indicated in the right-hand margin.
  2. There are NINE questions in this paper.
  3. Attempt FIVE questions in all.
  4. Question No. 1 is compulsory.
Q.1 Short answer-type questions (any seven): [14]

  1. State and explain Kirchhoff's laws with an example.

  2. Which winding (LV or HV) should be kept open while conducting OC test? Justify your answer.

  3. Assume that the given transformer has the following name plate ratings: 40 kVA, 440 V/11 kV, 50 Hz. What do these numbers imply?

  4. What is a commutator in d.c. machine?

  5. What is meant by linear network? Explain \(R\), \(L\) and \(C\) as linear elements.

  6. Differentiate among real, reactive and apparent powers.

  7. Calculate maximum value and r.m.s. value of \(v = 10 \sin \omega t - 17.3 \cos \omega t\).

  8. A 250 V bulb passes a current of 0.3 A. Calculate the power in the lamp.

  9. Define unilateral and bilateral elements.

  10. Give some applications of three-phase induction motor.

Q.2 Solve both questions : [14]

  1. An a.c. current varying sinusoidal with frequency 50 Hz has r.m.s. value 20 A. Write equation for instantaneous value and find this value 0.0125 seconds after passing through maximum value.

  2. Calculate the resistance between A and B from the figure given below:

    Question Diagram
Q.3 Solve both questions : [6+8=14]

  1. Explain the r.m.s. value. Solve the \(V_{\text{rms}}\) value of given waveform in the figure.

    Question Diagram

  2. Two coils, connected in series-adding fashion, have a total inductance of 250 mH. When connected in a series-opposing configuration, the coils have a total inductance of 150 mH. If the inductance of one coil (\(L_1\)) is three times the other, then find \(L_1, L_2\) and M. What is the coupling coefficient?

Q.4 Solve both questions : [8+6=14]

  1. Explain the principle of transformer action.

  2. A series circuit consists of a resistance of \(4\,\Omega\), an inductance of 500 mH and a variable capacitance connected across a 100 V, 50 Hz supply. Calculate the capacitance requires for producing a series resonance condition, and the voltages generated across both the inductor and the capacitor at the point of resonance.

Q.5 Solve both questions : [8+6=14]

  1. Define parallel resonance. Calculate at resonance the resultant current and quality factor in terms of the parameters of a circuit.

  2. Explain the advantages of rotating field-type alternator.

Q.6 Solve this question : [14]

  1. A 3-phase, 6-pole, star-connected alternator revolves at 1000 r.p.m. The stator has 90 slots and 8 conductors per slot. The flux per pole is 0.05 Wb. Calculate the voltage generated, if \(K_w = 0.96\).

Q.7 Solve both questions : [8+6=14]

  1. Explain the principle of operation of d.c. motor.

  2. A balanced star-connected load of \((8+j6)\,\Omega\) per phase is connected to a balanced 3-phase, 400 V supply. Find the line current, power factor, power and total volt-amperes.

Q.8 Solve this question : [14]

  1. A 6-pole alternator runs at 1000 r.p.m., and supplies power to a 4-pole, 3-phase induction motor. The frequency of rotor of induction motor is 2 Hz. Determine the slip and speed of the motor.

Q.9 Solve this question : [14]

  1. Two coils, X of 12000 turns and Y of 15000 turns, lie in parallel planes so that 45% of the flux produced by coil X links coil Y. A current of 5 A in X produces 0.05 Wb while the same current in Y produces 0.075 Wb. Calculate (a) the mutual inductance, (b) the coupling coefficient and (c) the percentage of flux produced by coil Y and linking with coil X.