JNTU
JNTU B.Tech II ELECTRICAL SYSTEMS Previous Question Paper (April/May - 2023 - R13)
Note: i) Question paper consists of Part A, Part B. ii) Part A is compulsory, which carries 25 marks. In Part A, Answer all questions. iii) In Part B, Answer any one question from each unit. Each question carries 10 marks and may have a, b as sub questions.
PART - A
State Kirchhoff’s laws.
Answer
Kirchhoff’s Current Law (KCL) states that the algebraic sum of currents entering a node (or junction) is zero, meaning the sum of currents entering a node equals the sum of currents 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.
State Thevenin’s theorem.
Answer
Thevenin’s theorem states that any linear, bilateral, active two-terminal network containing multiple voltage sources, current sources, and resistances can be replaced by an equivalent circuit consisting of a single voltage source in series with a single resistor connected to the same two terminals.
The equivalent voltage, known as the Thevenin voltage (Vth), is the open-circuit voltage measured across the two terminals. The equivalent resistance, known as the Thevenin resistance (Rth), is the equivalent resistance of the network measured across the same terminals with all independent voltage sources replaced by short circuits and all independent current sources replaced by open circuits.
Define active power.
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Explain the concept of power factor.
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Define voltage regulation of a transformer.
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What are the various losses of a transformer?
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What is the function of a commutator in a d.c generator?
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Draw the circuit diagram of a d.c compound motor.
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Explain the necessity of starter in a d.c motor.
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Explain the working principle of split phase single phase Induction Motor.
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PART - B
State and explain Norton’s theorem.
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Use Thevenin’s theorem to find the current flowing in the 10Ω resistor for the circuit shown in figure 1 below.
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State and explain Maximum power transfer theorem.
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Replace the delta-connected network shown in figure 2 below by an equivalent star connection.
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An alternating voltage is given by v = 282.8 sin 314t volts. Find (i) the r.m.s voltage, (ii) the frequency and (iii) the instantaneous value of voltage when t = 4 ms.
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Derive an expression for resonant frequency of R-L-C series circuit excited by A.C source of variable frequency.
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Obtain an expression for a transient current in a R-L series circuit excited by d.c supply at t = 0.
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Three coils each having resistance 3Ω and inductive reactance 4Ω are connected in star to a 415 V, 3-phase supply. Calculate (i) the line and phase voltages and (ii) the phase and line currents.
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Give the constructional details of single phase transformer.
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Derive the condition for maximum efficiency of a single phase transformer.
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Draw the phasor diagram of single phase transformer at lagging p.f load.
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A 2400 V/400 V single-phase transformer takes a no load current of 0.5 A and the core loss is 400 W. Determine the values of the magnetizing and core loss components of the no load current.
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Draw the External characteristics of d.c shunt generator.
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A d.c generator is connected to a 60 Ω load and a current of 8 A flows. If the armature resistance is Ω determine (i) the terminal voltage, and (ii) the generated e.m.f.
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Explain the working principle of a d.c motor.
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An 8-pole D.C. motor has a wave-wound armature with 900 conductors. The useful flux per pole is 25 mWb. Determine the torque exerted when a current of 30 A flows in each armature conductor.
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Explain the double field revolving theory.
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Explain the disadvantages of low power factor. State methods to improve the power factor of a system.
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Two wattmeters connected to a 3-phase motor indicate the total power input to be 12 kW. The power factor is 0.6. Determine the readings of each wattmeter.
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Explain the constructional details of a 3-phase Induction Motor.
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