University of Pune 2010 B.Tech -basic Electrical Engineering - Question Paper
Total No. of Questions : 12] [Total No. of Printed Pages : 4
F. E. (Semester - I) Examination - 2010 BASIC ELECTRICAL ENGINEERING (June 2008 Pattern)
Time : 3 Hours] [Max. Marks : 100
Instructions : VO
(1) In section I, attempt Q. 1 or Q. 2, Q. 3'w*Q. 4, Q. 5 or Q. 6. In section II, attempt Q. 7 or Q. 8, Q. 9 or Q. 10, Q. 11 or Q. 12. \J
(2) Answers to the two sections should fe\written in separate answer-books.
(3) Figures to the right indicate full murks.
(4) Neat diagrams must be drawt{\vherever necessary.
(5) Use of non-programmable electronic pocket calculator is allowed. \J
(6) Assume suitable data, iffn&cessary.
Q.l) (A) How materials are classed as Conductor, Insulator and
Semiconductor. Givo examples of each. [06]
(B) An electric pump difts o'Q m3 of water per hour to a height of 25 meter. The'pijmp efficiency is 86% and motor efficiency is 78%. Thentunp is used for three hours daily. Find energy consumed perweek, if one m3 of water is 1000 kg. [06]
(C) Explain thCharging of Lead Acid Battery with chemical reaction. What are the changes taking place during charging ? [06]
\ * OR
Q.2) (A) Obtathe expression for a2 = o/l + (t2 - tj). [06]
(B) An electric furnace is used to melt aluminum. Initial temperature Mhe solid aluminum is 32C and its melting point is 680C. Specific heat capacity of aluminum is 0.95 kJ/kgK and the heat required to melt 1 kg of aluminum at its melting point is 450 kJ. If the input power drawn by the furnace is 20 kW and its overall efficiency is 60%. Find the mass of aluminum melted per hour. [06]
(C) What is Insulation Resistance ? What are the factors on which insulation resistance of a single core cable depends ? [06]
State and explain Superposition Theorem. [08]
Using Kirchhoffs Laws, find the current delivered by 12V battery as shown in the Fig. 1. [08]
(A)
(B)
Q.3)
 |
nnected Network into |
Derive an expression to convert $tar its Equivalent Delta Network. \) [08]
Q.4) (A)
(B)
Using Thevenins Theorem finite current flowing through 1 ohm resistance connected "between A-B, as shown in the Fig. 2. [08]
10V
Q.5) (A)
iel
Explain the following terms
[08]
(1) MMF*
(1) Pearmeance
Flux Density
(B)*\ A coil M is wound around a magnetic circuit. Explain the phenomenon of self induced emf in it. Define its self inductance and state its unit. Another coil N is wound around the same magnetic circuit. Explain the phenomenon of mutual inductance between the coils and define coefficient of coupling between them.
[08]
OR
Q.6) (A) An iron ring wound with 550 turns solenoid produces a flux density of 0.94 tesla in the ring carrying a current of 2.4 Amp.
The mean length of iron path is 80 cm and that of air gap is 1 mm. Determine :
(1) The relative permeability of iron
(2) Self-inductance
(3) Energy stored in the above arrangement, if thcross sectional area of ring is 25 cms2. "A [08]
(B) Derive the expression for the energy stored invtj)e magnetic
field in terms of energy stored per unit v qkupe. [08]
SECTION - II
Q.7) (A) At instant t = 0, the instantaneous of 50Hz sinusoidal
current is +5 Amp and increases ik magnitude further. Its r.m.s. value is 10 Amp :
(1) Write expression for its ins?ntaneous value.
(2) Find the current at t tf.01 and t = 0.015 second.
(B) Derive Mathematicaj<Bkpression for capacitor voltage and current at any instant auxing charging of capacitor through resistance. Also k|tt$h the graph of capacitor voltage and current withspect to time. [08]
Q.8) (A) A sinusoidaKvoltage of V = Vm sin( t) is applied across a series R-L circuit. Derive the expression for current and average powexNponsumed by the circuit. [08]
(B) A. parallel plate capacitor has plates, each area of 100cm2, parated by a distance of 3cms. The dielectric between the pWes has relative permittivity of 2.2. The potential difference between the plates is lOkV. Find (1) Capacitance of the "A Capacitor (2) The Electric Flux Density, (3) The Electric Field
strength, (4) Energy Stored. [08]
Q.9) (A) Sketch and explain Phasor diagram of an RLC series circuit
when (1) Xc > XL (2) Xc = XL (3) Xc < XL. [08]
3
P.T.O.
(B) A series circuit consisting of a 12Q resistance, 0.3 henry inductance and a variable capacitor is connected across 100V, 50Hz A.C. Supply. The capacitance value is adjusted to obtain maximum current. Find this capacitance value and the power drawn by the circuit under this condition. Now supply frequency is raised to 60Hz, the voltage remaining same at 100 V.
Find the value of inductive and capacitive reactance [08]
Q.10) (A) What is admittance of an AC Circuit ? What are its two components ? State the units of these quantit How is admittance expressed in rectangular and polar form ? [06]
(B) Two circuits the impedances of whicnre given by Zl = (12 + j 16) Ohm and Z2 = (8 -m4) Ohm are connected in parallel across the potential differeitec of (23 + jO) volts. Calculate : (1) The Total Current Drawa (2) Total Power and Branch Power consumed and (3) Qrall Power Factor of the circuit. r [10]
Q.ll) (A) Derive and explain with Phsor diagram the relations between Line Values and Phase Valtfefeof Current and voltages for a 3-phase balanced delta connected lagging power factor load. [08]
(B) The three equal impedah'dbs of each of 10Z600 Ohms are connected in star a#rpss 3-phase, 400 volts 50Hz supply. Calculate : \
(1) Line Voltagsfrfa Phase Voltage
(2) Power ECtor and Active Power consumed
(3) If the same three impedances are connected in delta to the saf source of supply what is the active power consumed ? [06]
(C) Differentiate Shell Type and Core Type Transformer. [04]
OR
Q.12) (A) AS25 kVA, 50 Hz, Single Phase Transformer has the iron loss full load copper loss of 350 and 400 watts respectively.
Find the efficiency of the transformer at (1) 50% of full load at unity p.f. and (2) 75% of full load at 0.8 lagging p.f. [08]
(B) What is an Auto Transformer ? State the advantages, limitations and applications. [06]
(C) Explain the Concept of Balanced Loading. [04]
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| Earning: Approval pending. |
