B.E. All Branches First Semester (C.B.S.) / B.E. (Fire Engineering) First Semester
Basic Electrical Engineering
Time : Two Hours
Max. Marks : 40
Notes : 1. All questions carry marks as indicated.
2. Solve Question 1 OR Questions No. 2.
3. Solve Question 3 OR Questions No. 4.
4. Solve Question 5 OR Questions No. 6.
5. Solve Question 7 OR Questions No. 8.
6. Due credit will be given to neatness and adequate dimensions.
7. Assume suitable data whenever necessary.
8. Illustrate your answers whenever necessary with the help of neat sketches.
9. Use of non programmable calculator is permitted.
1. a) Explain practical voltage source, current source & ideal voltage source, current source.[5M]
b) Find the equivalent resistance of a network shown in figure between the terminals A & B using star delta transformation. All resistances are in ohms.[5M]
2. a) State & explain superposition theorem.[4M]
b) Find the value of current I using super position theorem of the following figure all resistances are in ohms.[6M]
3. a) Explain the similarities & dissimilarities between electric circuit & magnetic circuits.[4M]
b) A circular iron ring of mean circumference of 25 cm & cross sectional area of 5 cm2 has a radia saw out of 1 mm in it. The ring is uniformly would with a coil of 500 turns & current of 2A in the coil produces a flux of 0.5 ×10-3 Wb in the ring. Calculate the relative permeability of iron at this flux density.[6M]
4. a) Draw complete hysteresis loop & explain :[5M]
i) Remanent flux density ii) Residual flux
iii) Retentivity iv) Coercive force
b) A ring is composed of three sections. The cross section area is 0.001 m2 for each section, the mean arc length are la = 0.3m, lb = 0.2m, lc = 0.1m & airgap length of 0.1 mm cut in the ring μr for sections a, b, c are 5000, 1000 & 10,000 respectively. Flux in the air gap is 7.5×10-4 Wb . Find
i) MMF ii) Exciting current if coil has 100 turns
iii) Reluctance of each section. [5M]
5. a) Define the following : [5M]
i) Time period ii) Amplitude
iii) Average value iv) Crest factor
v) Instantaneous value
b) For the circuit shown in fig.[5M]
Calculate the following :
i) Impedance ii) Current flowing through circuit
iii) Power consumed by the circuit iv) Power factor & its nature
v) Draw phasor diagram.
6. a) Define RMS value, and hence show that rms value is 0.707 of peak value of sine wave.
b) An alternator supplies delta connected load. The impedance of load beanch is (8 + j6)  Ω/ph the line voltage is 230V. Determine :[5M]
i) Current in each load beanch ii) Power consumed by load
iii) Power factor
7. a) Describe open circuit test & short circuit test on 1Φ transformer in brief.[4M]
b) A 600 kVA 1Φ transformer has an efficiency of 92% both at full load & half load & at unity p.f. determine the transformer efficiency at 60% of full load & 0.8 p.f. lag.[6M]
8. a) Why a transformer is said to be a constant flux machine ?[4M]
b) A single phase 40 kVA, 6600 V / 250 V transformer has primary & secondary resistances
of 10 Ω & 0.02 Ω respectively. The equivalent leakage reactance referred to primary is 35
Ω. Find full load voltage regulation for the load power factor of –
i) unity p.f. ii) 0.8 lead p.f. [6M]