Jawaharlal Nehru Technological University Hyderabad
Jawaharlal Nehru Technological University Hyderabad B.Tech II ELECTRICAL ENGINEERING Previous Question Paper (July/August - 2021 - R16)
Answer any five questions. All questions carry equal marks.
Main
State and explain Kirchhoff’s laws.
Answer
Kirchhoff’s Current Law (KCL) states that the algebraic sum of currents meeting at any junction or node in an electric circuit is zero, signifying that the total current entering a node equals the total current leaving it. Kirchhoff’s Voltage Law (KVL) states that the algebraic sum of all voltages around any closed loop in a circuit is zero, which is a consequence of the law of conservation of energy.
Calculate the voltage across AB in the network shown in figure 1 below and indicate the polarity of the voltage using Star-Delta transformation.
Answer
To find the voltage across AB, first identify the delta-connected resistors in the network. Convert the delta configuration into an equivalent star (wye) configuration using the transformation formulas: R1 = (Rb*Rc)/(Ra+Rb+Rc), R2 = (Ra*Rc)/(Ra+Rb+Rc), and R3 = (Ra*Rb)/(Ra+Rb+Rc). Once the delta is replaced by the star network, the circuit simplifies into a series-parallel combination. Calculate the equivalent resistance seen by the source, determine the total current, and use the voltage divider rule or nodal analysis on the simplified circuit to find the potential difference between nodes A and B. The polarity is determined by the direction of the current flow through the resulting branch.
Determine the mesh current I1 in the circuit shown below figure 2.
Answer
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Derive an expression for force developed by a current conductor placed in a magnetic field.
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What is self and mutual inductance? Derive a relation for them.
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Explain the method of measuring three phase power in balanced and un balanced three phase circuits.
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With a neat diagram explain the method of finding current in each branch and voltage across each branch when two A.C, RLC series circuits are in parallel.
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Derive the torque equation of DC motor.
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A 220-V, shunt motor, running at 700 rpm, has an armature resistance of 0.45 Ω and takes an armature current of 22 A. What resistance should be placed in series with the armature to reduce the speed to 450 rpm.
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Draw the magnetization and load characteristics of d.c shunt generator.
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Derive an expression of e.m.f produced in a d.c generator.
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A transformer has 500 turns of the primary winding and 10 turns of the secondary winding. i) Determine the secondary voltage if the secondary circuit is open and the primary voltage is 120 V. ii) Determine the current in the primary and secondary winding, given that the secondary winding is connected to a resistance load of 15Ω.
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Find the transformation ratio. State if transformer is step up/step down.
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Explain the principle of operation of a three-phase induction motor.
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Draw and explain various portions of torque slip characteristics of a three phase induction motor.
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Explain the constructional features of an alternator.
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Explain the method of finding regulation by synchronous impedance method for a three phase alternator.
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