enggzc111 ec-1r 1-10

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Birla Institute of Technology & Science, Pilani Work-Integrated Learning Programmes Division First Semester 2010-2011 Mid-Semester Test (EC-1 Regular) Course No. Course Title Nature of Exam Weightage Duration Date of Exam Note: : ENGG ZC111 : ELECTRICAL & ELECTRONICS TECHNOLOGY : Closed Book : 40% No. of Pages =1 : 2 Hours No. of Questions = 5 : 29/08/2010 (AN)

1. Please follow all the Instructions to Candidates given on the cover page of the answer book. 2. All parts of a question should be answered consecutively. Each answer should start from a fresh page.3. 4. Mobile phones and computers of any kind should not be used inside the examination hall. Use of any unfair means will result in severe disciplinary action.

Q.1. Find the voltage across the 4 resistor in the network shown in Fig. Q.1 using (a) Nodal analysis (b) The superposition theorem (c) Thevenins theorem [15]

4

22V

8

2A

Figure Q.1 Q.2. The power dissipation across and the current in a circuit are represented by (100+j200) V and (10+j5) A respectively. Calculate the active power and the reactive power. [4]Q.3. A parallel network consists of branches A, B and C. If IA=10 -60o A, IB=5 -

30o A, and IC=10 90o A, all phase angles, being relative to the supply voltage, determine the total supply current. [7]

Q.4. A 100 kVA transformer has 400 turns on primary and 80 turns on secondary. The primary and secondary resistances are 0.3 and 0.01 respectively, and the corresponding leakage reactances are 1.1 and 0.035 respectively. The supply voltage is 2200V. Calculate the per-unit and the percentage resistance and leakage reactance drops of the transformer. [7] Q.5. A coil having a resistance of 8 and a constant inductance of 4 H is connected across a 40 V dc supply. Calculate 5.1. The time constant 5.2. The final value of current 5.3. The value of current 2 s after it is connected to supply 5.4. The time taken by current in circuit to grow 4.32A after it is connected to supply. [7]