JNTUH
JNTUH B.Tech I Year BASIC ELECTRICAL ENGINEERING Previous Question Paper (May/June - 2019 - R18)
Part A is compulsory which carries 25 marks. Answer all questions in Part A. Part B consists of 5 Units. Answer any one full question from each unit. Each question carries 10 marks.
PART- A
State Thevenin’s theorem.
Answer
Thevenin’s theorem states that any linear, bilateral, active two-terminal network containing multiple energy sources and resistances can be replaced by an equivalent circuit consisting of a single voltage source in series with a single resistor. The equivalent voltage source, known as Thevenin voltage (Vth), is the open-circuit voltage across the terminals, and the equivalent resistance, known as Thevenin resistance (Rth), is the equivalent resistance of the network looking into the terminals with all independent sources replaced by their internal resistances.
What is meant by apparent power?
Answer
Apparent power is the product of the root-mean-square (RMS) voltage and the RMS current in an AC circuit. It represents the total power that appears to be delivered to the load, measured in volt-amperes (VA). It is defined by the formula:
where S is the apparent power, V is the RMS voltage, and I is the RMS current.
Why the copper losses are more in a transformer?
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What is necessity of rotating magnetic field in the induction motor?
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What is the difference between fuse unit and switch fuse unit?
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What is meant by capacitor charging current, obtain its expression in terms of its time constant in case of R-C circuit?
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An alternating voltage e = 300 sin(πt + π/3), what is its instantaneous voltage at t = 5 ms and 10 ms for 50 Hz frequency?
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What is the difference between ideal transformer and practical transformer?
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What are the advantages of armature winding placing in its stator?
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What are the characteristics of batteries for longer life?
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PART-B
State Kirchhoff Current Law and Voltage law, determine the values for IX and VY in the given circuit.
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In the given circuit, calculate i) v1, v2, v3 and ii) power delivered to R1, R2 and R3.
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Find the Norton equivalent circuit of the given circuit with respect to the terminals ‘a-b’.
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State and explain superposition theorem.
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Describe phasor representation of RL series circuit. If admittance of a series circuit is (0.010 + j0.004) S, determine the values of the circuit components for the frequency of 50 Hz.
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Balanced Y-connected load of 10 kW at 0.8 power factor lagging supplied by a 50-Hz, 300-V, three-phase system. Find the line current delivered by the source. Draw the phasor diagram.
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Explain how the sinusoidal waveform is represented as phasor quantity with example.
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A coil is connected in series with a capacitor of 20 µF to a 200 V variable frequency supply. The current is a maximum at 50 A, when the frequency is set to 50 Hz. Determine the resistance and inductance of the coil.
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Draw and explain the phasor diagram of single phase transformer on lagging load.
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A 50 kVA, 1000/10000 V, 50Hz single phase transformer has iron loss of 1200W. The copper loss with 5 A in the high voltage winding is 500 W. Calculate the efficiency at i) 25%, ii) 50%, iii) 100% of normal load at power factor of 0.8.
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Describe the principle of operation of auto transformer, what is the saving of copper in this transformer when compared with two winding transformer?
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Discuss the various three phase transformer groups and their significance.
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Describe the constructional details of three phase slip ring induction motor.
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Describe the torque speed characteristics of separately excited dc motor.
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What are the various losses occurs in the three phase induction motor in their operation?
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Describe briefly construction details of any three phase synchronous generator.
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Describe the operation of ELCB with its schematic diagram.
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What are the drawbacks of low power factor, describe how it is improved?
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What is the difference between MCB and MCCB, describe their schematic diagrams?
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Calculate total energy consumed per day by the use of following loads: i) 5 number of 40 W lights operated 5 hours per day ii) 1 h.p. motor is operated 2 hours per day iii) 1 k.W heater is operated 1 hour per day iv) 1 computer is used for 6 hours per day with printer about 30 minutes.
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