University of Pune 2009 B.Tech Basic Electrical Engineering- - Question Paper
Total No. of Questions : 12] [Total No. of Printed Pages : 6
F. E. (Semester - I) Examination - 2009 BASIC ELECTRICAL ENGINEERING (June 2008 Pattern) kj
Time : 3 Hours] [Maxvwarks : 100
Q.l) (A) Define resistance temperature coefficient # of a conducting material and state its unit. Discuss tbsLeffect of temperature on resistance temperature coefficient.Nj
[06]
A copper coil when connected to aJ40 Volt supply, initially takes current of 4 Amp and hafmean temperature of 20C. After sometime, the current'pwirrg in the coil fall to 3.90 Amp, supply voltage remain samTvFhe mean temperature of coil is then 34C. Determine tfie temperature coefficient of resistance of 0C and 20C. NJ
(B)
[06]
Distinguish betweenwnary and Secondary Cells. What are the indications whi cohfirm that a lead acidic cell is fully charged ? \j
(C)
[06]
Q.2) (A) A single Jtrfpinsulated cable of length L m has its conductor diameter m and the thickness of insulation surrounding the Conductor is t m. Derive the expression for its insuMon resistance, if the resistivity of the insulating material is. p ohm - m.
[06]
(B) "V'X bucket contains 20 liters of water at 20C. A 2.5 KW immersion heater is used to raise the temperature of water to
95C. The overall efficiency of process is 90% and the specific heat capacity of water is 4200 J/KGK. Find the time require for the process. Also find cost of energy (electricity bill) for 365 days if rate of energy is Rs. 3 per unit. [06]
(C) If four cells, each rated for 2V, 0.15A can be connected as a batteries in three different ways. Find voltage and current rating of each type. [06]
Q.3) (A) Explain the following terms with reference to d.c. resistive
networks :
[06]
(1) Unilateral and Bilateral Networks
(2) Linear and Non-linear Networks
(3) Active and Passive Networks
Using Thevenins Theorem find the current .flowing through 8 ohm resistance for the network showKin fig. 1 : [10]
(B)
-/VWW\r
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Fig. 1 |
Define Star aNljDelta Network, hence derive an expression to convert staonnected network into its equivalent delta network. [08]
Q.4) (A) (B)
Using Superposition Theorem find the current flowing through
4 Ohm resistance for the network shown in fig. 2. [08]
Fig. 2
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Compare electric and magnetic circuits stating clearly similarities and dissimilarities between them. 1081
An iron ring has its mean length of flux path as 60 cm and has a circular cross-section of 6.5 cm diameter. Air gap of 2mm is cut in it. A coil of 650 turns is uniformly wound around it and a current of 2.5A passes through it. CalculateV&te flux produced in the air gap and in the iron ring, if '{Aerelative permeability of iron is 1050. Ignore Leakage and Fringing.
Q.5) (A) (B)
[08]
OR
State the factor upon which inductance of a Sul depends. Also obtain an expression for the energy stored in a magnetic field in terms of self-inductance and currsJ
Q.6) (A)
[08]
(B)
The Coils A and B in a Magnetic Cn'suit have 700 and 600 turns respectively. A current of lOAjn coil A produces a flux of .04 Wb. If the Co-efficient/-of Coupling is 0.2.
Calculate : \
(1) Self-inductance of the Coil A when B is open circuit.
(2) Flux Linkage vtthe Coil B.
(3) Mutual InducfQe
(4) E.m.f. ilucpd in the Coil B when the flux linking with
it changes from zero to full value in 0.02s. [08]
Deri&\an expression for the capacitance of a parallel plate capaCTtor with a composit dielectric. [06]
(B) Refine the following terms related to sinusoidal waveform : [04]
\ (1) Form Factor
(2) Crest Factor
P.T.O.
A circuit consist of three parallel branches. The branch currents are given as
i, = 10 sincot, i2 = 20 sin(cot + 60) and i3 = 7.5 sin(cot - 30).
(C)
Find the resultant current and express it in the form i = Imsin (cot + (j)). If the supply frequency is 50 Hz calculate th&jpesultant current when
(1) t = 0 sec. and
(2) t = 0.001 sec.
[06]
A 12(iF capacitor in series with an 1.21*40 resistor is connected across a 100 volt d.c. supply. Detehnine
Q.8) (A)
(1) The time constant of the cirbliit.
(2) The initial value of <argnj current.
(3) The initial rate of ri\0of voltage across the capacitor.
(4) The voltage across\{Jie capacitor 4 sec. after switch on. [06]
What do you undetiQid by dielectric strength and breakdown voltage of a capacitor'? [04]
(B)
(C)
An alternating cihrent of Frequency 60Hz has maximum value of 110 A. (3algulate
V, sec. after the instant current is zero and its
(1)
Its
600
valu decreasing thereafter.
(2) Airne required to reach 90A after the instant current is zero *and increasing positively.
[06]
A
si
sinusoidal voltage of v = Vm sin cot is appalled across a single phase series circuit and current flowing through the circuit is i = Im sin(cat - (j)). Derive an expression for average power consumed by the circuit. Also sketch the wareform of voltage, current and power. [08]
Q.9) (A)
A circuit consist of a pure inductor, a pure resistor and a capacitor connected in series. When the circuit is supplied with 100 volt, 50 Hz supply, the voltage across inductor and resistor are 240 volt and 90 volt respectively. If the circuit takes 10A leading current calculate :
(1) Values of inductance, resistance and capacitaqr*
(B)
(2) Power Factor of Circuit
(3) Voltage Across Capacitor [08]
OR
Q.10) (A)
(B)
(C)
Define the terms Admittance, Conductance and Susceptance as applied to a.c. circuit.
Obtain the expression for resonant frequency is series R-L-C circuit. [04]
A coil having resistance and @jdpctance of 15Q and 8 mH respectively is connected ka paradel with another coil having resistance and inductance and 18 mH. If this parallel
combination is to be rplacea by a single coil, calculate value of resistance, inductance that coil. What value of capacitance should be connectecj parallel with this coil in order to get unity power factor. As&pie operating frequency to be 50Hz. [09]
Explain the folloig terms with reference to polyphase system
Q.ll) (A)
(1) BalancetfLpad
(2) PhaseCsp quence
[04]
(B)
(C)
A single jhase 90 kVA, 3.2 kV/220V, 50Hz transformer has 89% efficiency at unity power factor both at full load and half loadfretermine the efficiency at 70% of full load and 0.8 power factor leading. [06]
ract
iat is an Autotransformer ? State its merits and demerits over a two winding transformer. [04]
Prove that power taken by three phase balanced delta connected load is three times to the power taken by same three phase balanced star connected load. [04]
Derive the e.m.f. equation of Single Phase Transformer. [04]
Three similar coils take a power of 3KW at 0.6 power factor when connected in star to a 3pH, 415 volt, 50Hz supply. Calculate :
Q.12) (A)
(B)
(1) Line Current
(2) Resistance and Inductance of each Coil
With neat circuit diagram explain the direct loadifctest on single phase transformer for finding the voltage regulation and efficiency. vJ [08]
(C)
[3661J-103/6
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| Earning: Approval pending. |
