Cochin University of Science and Techology (CUST) 2002 B.Tech Civil Engineering Electrical Engineering I - Question Paper

(b) What is meant by neutral shift? Explain any one method of solving an unsymmetrical system feeding an unbalanced load.    (8)

MODULE - V

IX.    (a) With a neat diagram explain the working of an induction

type energymeter.    (10)

(b)    Compare moving coil and moving iron instruments. (4)

(c)    What is the use of shunts and multipliers in the field of electrical measurements?    (6)

OR

X.    (a) A moving coil instrument has a resistance of 10Q and

gives fullscale deflection when carrying a current of 100mA. Show how it can be used to measure voltages . upto 1000V and currents upto 50A.    (10)

(b) What are the different torques in an electrical instrument?

Explain.    (10)

B.TECH. DEGREE I SEMESTER (SUPPLEMENTARY) EXAMINATION IN INFORMATION TECHNOLOGY/COMPUTER SCIENCE AND ENGINEERING/ELECTRONICS AND COMMUNICATION ENGINEERING/MECHANICAL ENGINEERING (CAD/CAM)/ SAFETY AND FIRE ENGINEERING, FEBRUARY 2002

IT/CS/EC/ME/SE 104 ELECTRICAL ENGINEERING I

(Old Scheme)

Time: 3 Hours    Maximum Marks: 100

MODULE - I

(a) Using super position theorem calculate the current through the 30 resistance of the circuit drawn below:    (15)

(b) State and explain Kirchoffs laws.    (5)

OR

(a) Using Thevenins theorem compute the current through

the 6Q resistance of the circuit below:    (15)

JVW1 ,

(Turn over)

MODULE - II

The equivalent inductance of the series combination of

2 coils is measured as 5H. If the equivalent inductance remains the same, after halving the number of turns of the first coil and doubling the number of turns of the second coil, calculate the possible values of mutual inductance between the coils and separate inductances. (12) Establish analogy between electric and magnetic circuits. Also list out the differences.    (8)

OR

An iron ring has mean circumferential length of 80cm and cross sectional area of 4cm². It is wound with a coil of 100 turns. An airgap of 2mm in width is cut in the ring. Determine the current required to produce a flux of 0 48mWb in the airgap. Assume leakage factor of 1.05. B-H data of iron is as follows:    (12)

B(Wb/m²) : 0.9 1.0 1.1 1.2 1.3

H (AT/m) : 450 500 550 600 620

Derive expressions for the energy stored in a magnetic field and lifting power of a magnet.    (8)

Contd..................3.

V.    (a) A pure inductor, a non inductive resistor and a capacitor

are connected in series in that order. The supply emf is 85 V at 50Hz, the pd across the capacitor and resistor together is 85 V and that across the inductor is 40V. If the circuit current is 5A, calculate the value of all the components and pf of the circuit.    (16)

(b) If two ac voltages of equal value adds to 15V, calculate

the phase angle between them.    (4)

OR

VI.    . (a) A 50Hz, 250V single phase power line supplies the follow

ing loads:

(i)    4KW at a pf of 0.8 lagging.

(ii)    6KVA at 0.6 pf lagging.

(iii)    5KVA which includes 1.2 KVAR leading.

Determine the overall pf of the system, total load in KVA and the capacitance to be connected in parallel to improve the overall pf to unity.    (15)

(b) Draw and explain the vector diagram of a series RLC

circuit.    (5)

MODULE . IV

VII. (a) Discuss different methods of interconnection of 3 phase

systems and compare them.    (8)

(b) The power of a 3 phase balanced load supplied from a symmetrical 3 phase system is measured using

2 wattmeter method. If the reading of one wattmeter is 250W, what are the possible values of total power.

Assume that the load pf is 0.866 lagging. Also calculate the corresponding reactive powers.    (12)

OR

Contd.................4.