JNTU
JNTU B.Tech II PRINCIPLES OF ELECTRICAL ENGINEERING Previous Question Paper (December - 2018 - R15)
Note: This question paper contains two parts A and B. 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 and may have a, b, c as sub questions.
Part A
How transients are produced in an electric circuit?
Answer
Transients are produced in an electric circuit due to the sudden change in the circuit configuration, such as the opening or closing of a switch, or a sudden change in the applied source voltage. These changes force the energy stored in reactive elements (inductors and capacitors) to redistribute, preventing instantaneous changes in current through an inductor or voltage across a capacitor.
Define time constant of RL circuit. Give expression.
Answer
The time constant of an RL circuit is defined as the time required for the current to reach approximately 63.2% of its final steady-state value during a charging process. The expression is:
where L is the inductance in Henrys and R is the resistance in Ohms.
List the various parameter sets that are used to model a two port Networks.
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What is meant by reverse transfer impedance and forward transfer impedance?
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What are balanced attenuators?
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Draw the circuit for symmetrical low-pass π-filters.
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State the voltage and power equation of a d c motor explaining the importance of each term.
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If the speed of the DC motor is above the rated speed which method of speed control do you suggest to bring it to rated speed? Justify your statement with the relevant expressions.
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State the relationships between voltages and currents on primary side and secondary side of a single phase transformer.
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What happens when transformer is connected to a DC supply?
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Part B
Write the differential equations representing the discharge of a capacitance through a resistance.
For the circuit shown in figure 1, find the voltage Vc(t), over the capacitor for all time t>0.
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Write the steps involved in solving simple circuits containing dc sources, resistances, and one energy-storage element for transient analysis.
In the circuit shown in figure 2, find the expression for the transient current and the initial rate of growth of the transient current.
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Draw series-series interconnection of two identical T network.
Show that if two, two-port networks are connected in parallel at input and output, the resulting two-port network will have a [y] matrix that is the sum of [y] matrices of the individual networks.
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Obtain the condition of transmission parameters for two networks connected in cascade.
Test results for a two port network are provided: (i) port 2 open circuited and (ii) port 1 open circuited. Find y-parameters.
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What are attenuators? Classify them.
A prototype LPF has a cut-off frequency of 5kHz and is terminated into matched impedance of 600Ω. Calculate the element values of the filter. Also find attenuation in dB and phase shift in degree at a frequency of 8 kHz.
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What is constant K-filter? Why it is called prototype filter section?
Design π-type attenuator with the following specifications. Attenuation = 20dB, characteristic resistance = 500Ω.
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Give the classification of self excited dc generators along with their connection diagrams.
Explain which dc motor is preferred for the following applications, with reasons: (i) Pumps (ii) Traction
A long shunt d.c compound generator delivers a load current of 50A at 500V and has armature, series field and shunt field resistances of 0.05Ω, 0.03Ω and 250Ω respectively. Calculate the generator voltage and armature current. Allow 1V per brush for contact drop.
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Write the power stages of a dc motor.
An 8-pole dc generator has 500 armature conductors, and a useful flux of 0.05 Wb per pole. What will be the emf generated if it is lap-connected and runs at 1200 rpm? What must be the speed at which it is to be driven to produce the same emf, if it is wave-wound?
Explain which dc motor is preferred for the following applications, with reasons: (i) Punches (ii) rolling mills.
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Draw a no-load phasor diagram of a transformer.
Derive from the first principles, the emf equation for a transformer.
A single phase transformer has 480 turns on primary and 90 turns on the secondary. Calculate (i) The cross-section area of the core (ii) Maximum value of the magnetizing current.
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Write a short note on synchros.
A resistance connected to the secondary of an ideal transformer has a value of 800 ohms as referred to the primary. The same resistance when connected across the primary has a value of 3.125 ohms as referred to secondary. Find the turns ratio of the transformer.
Draw the phasor diagram of Transformer on load assuming the load is a lagging power factor load.
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