**B.E. All Branches First Semester (C.B.S.) / B.E. (Fire Engineering) First Semester**

**Basic Electrical Engineering**

**NRT/KS/19/3284/3933**

**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. Use of non programmable calculator is permitted.

1. a) Explain ideal voltage source and practical voltage source.[4M]

b) Determine the Equivalent resistance between terminals A and B in the network shown in

figure. All resistances are in ohms.[6M]

**OR**

2. a) State and Explain Kirchoff’s laws for DC electric circuit.[4M]

b) Find the current through branch AB using super position theorem.[6M]

3. a) Define the following terms related to magnetic circuit.[4M]

i) Flux density ii) Reluctance

iii) Permeance iv) MMF

b) An iron core is rectangular in shape and has a mean length of 50cm. It has a saw cut in one of its lengths of 2mm width. One of the limbs of this core has a coil on it having 100 turns. Find the current required to flow in the coil to produce an air gap flux density of 2 0.75wb/ m^{2} . Neglect fringing. Relative permeability is 600.[6M]

**OR**

4. a) Define and explain the following terms with appropriate diagram.[4M]

i) Magnetic fringing ii) Magnetic leakage

b) A metal ring of mean diameter of 80cm is made out of two semi circular pieces of cast iron and cast steel having same cross section and separated at junctions by pieces of copper each of 1mm thickness. If the ring is uniformly wound with 1000 turns. Calculate the value of current required to produce a flux density of 0.85wb/ m^{2} in the ring. Given that relative permeability of cast iron as 200, that of cast steel is 1200 and for copper, μr =1.[6M]

5. a) Define RMS value. Derive the expression for rms value of sinusoidal voltage.[4M]

b) For the series circuit shown in Fig. and with the current and voltages as indicated, calculate the values of R, r and L and the frequency of the applied voltage and its magnitude.[6M]

**OR**

6. a) Prove that a three phase balanced load draws three times as much power when connected in delta, as it would draw when connected in star.[4M]

b) Three similar coils, connected in star, take a total power of 1.5kw at a p.f of 0.2 lagging from a three phase 440V, 50H supply. Calculate the resistance and inductance of each coil.[6M]

7. a) Derive the EMF equation of two winding single phase transformer.[4M]

b) A 400/200V, single phase transformer is supplying a load of 50amp at the power factor of 0.866 lagging. The no-load current is found to be 2 ampere at 0.208Pf. lagging. Calculate the current and power factor on primary side of transformer.[6M]

**OR**

8. a) Derive the condition for maximum efficiency of 1Φ transformer.[4M]

b) A 5kVA, 250/500V, 50Hz, 1 phase transformer gave following test results:[6M]

No load | 250V | 0.75A | 60W | (L.V. side) |

Short Circuit | 9V | 6A | 21.6W | (H.V. side) |

Calculate the equivalent circuit components.

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