Bangalore University 2004-2nd Sem B.E Electrical and Electronics Engineering First/ester , y/ust - Question Paper
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First/Second Semester B.E. Degree Examination, July/August 2004
Common to all branches
Time: 3 hrs.] [Max.Marks : 100
Note: 1. Answer any FIVE full questions.
2. All questions carry EQUAL marks.
1. (a) State and explain Faradays Laws of electromagnetic induction. (5 M?rks)
(b) Define
i) Flemings right hand rule
ii) Self inductance
iiij Coefficient of coupling
iv) RMS value of an AC quantity
V) P.f. Of an a.C.Circuit. (5 Marks)
(c) A coil of 1000 turns is wound on a silicon steel ring of relative permeability
1200. The ring has a mean diameter of 10cm and cross sectional area of 12 sq.cm. When a current of 4 amperes flows through the coil, find
i) Flux in the core
ii) Inductance of the coil
iii) the emf induced in the coil if the flux fails to zero in 15 milli seconds.
iv) Now, if another similar coil is placed such that 70% magnetic coupling exists between the coils, find the mutual inductance. (io Marks)
2. (a) An alternating voltage of e s Em sinwt is applied across a pure inductor of L
Henries.
i) Derive an expression for the resulting current.
ii) What is its active power consumption?
iii) Draw the phase diagram.
iv) Show the wave forms of voltage, current and power. (8 Marks)
(b) A single phase voltage of (200 + jO)V at 50Hz is applied to a circuit comprizing of a resistance of 20fi, inductance of 20mH and a capacitance of 150jj,F connected in series. Find,
i) impedance of the circuit
ii) Current drawn from supply
iii) power factor
iv) Power drawn
v) Energy stored in inductor and capacitor
and draw voltage diagram. (12 Marks)
3. (a) State the advantages of 3-phase system. (4 Marks)
(b) Obtain the numerical relationship between the line and phase quantities of a balanced A connected load (6 Marks)
(c) 2 wattmeters are connected to measure the input to a 3-<j>, 20HP. 50Hz Induction motor which works at a full load efficiency of 90% and a power factor of 0.S5. Find the readings of the 2 wattmeters. (io Marks)
(a) With a neat diagram, explain the construction and working principle of a dynamometer wattmeter. (8 Marks)
fbj Define domestic wiring. What important factors are to be considered in domesLic wiring? Mention the different types of wiring in practice. (6 Marks)
(c) What do you understand by Earthing"? With a neat diagram explain plate earthing. (6 Marks)
(a) Make a list of all the parts of a d.c. machine and write the functional use of each part. (6 Marks)
(b) A 4 pole lap connected D.C generator has 600 armature conductors and runs at 1200 rpm. This generator has a total flux of 0.24 wb in it.
i) Derive the emf equation of the generator from fundamentals.
ii) Calculate the emf induced in the above D.C. generator.
iii) Find the speed at which it should be driven to produce the same emf when wave connected: (7 Marks)
(c) A 4 pole, 220V, lap connected D.C. shunt motor has 36 slots, each slot containing 16 conductors. It draws 40Afrom the supply. The field resistance and armature resistances are 110ii and 0.Iii respectively. The motor develops an output power of 6kW. The flux per pole is 40mwb. Calculate
i) the speed
ii) torque developed by the armature and
iii) the shaft torque. (7 Marks)
(a) Explain the necessity of starter for D.C. motor. With a neat internal wiring diagram of a tliree point starter explain how it works. (8 Marks)
(bj Explain the constructional details and types of a synchronous machine.
(7 Marks)
(c) A 6 pole, 3 phase star connected alternator has an armature with 90 slots and 12 conductors/slot. It revolves at 1000 rpm, the flux/pole being 0.5wb. Calculat e the line value of emf generated, if the distribution factor is 0.96 and pitch factor 0.97. (5 Marks)
(a) Derive the emf equation of \-<p transformer. (6 Marks)
fb) Define the transformation ratio and regulation of a transformer. (\ Marks)
!cj A 500kVA transformer has an efficiency of 92% at full load, unity p.f and at half full load. 0.9pf. Determine its efficiency at 80% of full load and 0.95pf
(10 Marks)
(a) Explain the working principle of 3 phase induction motor and state the field of applications of Induction motors. (7 Marks)
(b) What, are the various methods of starting squirrel cage induction motors? With
a neat diagram explain star - delta starter. (7 Marks)
(cj The frequency oi the voltage applied to 4-pole induction motor is 50Hz and that ol (he rotar induced emf is 1.5Hz. What is the slip and at what speed the motor is running? (6 Marks)
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