SET - I MODEL QUESTION PAPER 06 ELE 15/25 - BASIC ELECTRICAL ENGINEERING (Answer any 5 questions by selecting at least two

questions from each part.) PART A 1a) State and explain Kirchhoffs laws. [Marks 6] b) Prove the relation between the self and mutual inductance [Marks 6] c) Problem on D.C. circuit/magnetic circuit. [Marks 8] 2a) Define the RMS and AVERAGE value of a sinusoidal emf wave and obtain their expressions. [Marks 8] b) Define i) real power, ii) reactive power and iii) apparent power as applied single Phase a.c circuits. [Marks 6] c) Problem on single phase a.c. circuit. [Marks 6] 3a) List out the advantages of three phase system compared to single phase systems. [Marks 4] b) Show that two watt meters are sufficient to measure total power in three phase Balanced circuit . [Marks 8] c) Problem on three phase circuits 8 4a) Explain with a neat sketch the working of dynamometer type wattmeter. [Marks 6] b) With relevant circuit explain how a lamp can be controlled from three different points and where it is preferred. [Marks 6] c) Explain the necessity of Earthing and with a neat sketch any one method of Earthing[Marks 8] PART - B 5a) Explain with a neat sketch the constructional features of a D.C. machine and mention the functions of each part. [Marks 8 ] b) Explain the principle of the production of torque in D.C. motors. [Marks 6 ] c) Problem on D.C.Motors or Generators. [Marks 6] a) Explain the principle of operation of a single phase transformer. [Marks 4] b) With relevant diagrams distinguish between the core type and shell type transformers [Marks 8 ] c) Problem on transformer. [Marks 8 ] 7a) Mention the different types of synchronous generators and explain the construction of each type with relevant diagram. [Marks 8] b) Derive the EMF equation of an alternator. [Marks 6 ] c) Problem on alternator. [Marks 6] ]8a) Explain why Induction motors never run at synchronous speed. [Marks 6 ] b) Compare the squirrel cage type with the slip ring Induction motor and mention their applications. [Marks 8 ] c) Problem on Induction Motor. [Marks 6 ] BASIC ELECTRICAL ENGINEERING Time-3 hours Max marks-100 Note:Answer any five questions choosing at least two questions from each part. PART-A Q.1 a)explain ohm's law and state its limitations. b)Define coefficient of coupling and establish a relation between self inductance and,mutual inductance with the coefficient of coupling. c)A current of 20A flows through two ammeters A and B in series.The potential difference across A is 0.2V and across B is 0.3V.find how the same current will divide between A and B when they are in parallel. Q.2 a)Sketch the sinusoidal alternating current wave form and denote as well as define the

following termsi)Instantaneous value ii)Peak to peak value iii)Peak amplitude. b)A series RLC circuit is composed of 100 ohm resistance,1H inductance and 5 microF capacitance.A voltage v(t)=141.4Cos377t volts is applied to the circuit.Determine the current and voltages across R,L and C. c)An impedence coil in parallel with a 100 micro farad capacitor is connected across a 200V , 50Hz supply.The coil takes a current of 4A and the power loss in the coil is 600W. calculatei)The resistance of the coil ii)The impedence of the coil iii) The p.f of the entire circuit. Q.3 a)What is the neccesity and advantages of three phase system? b)Show that two wattmeters are sufficient to measure power in three phase balanced star connected circuits with the aid of neat circuit diagram and phasor diagrams. c)A three phase load of three equal impedence connected in delta across a balanced 400W supply takes a line current of 10a a p.f of 0.7 laggaing calculate from the first principlei)The phase circuit. ii)The total power iii)The total reactive KVA. if the windings are connected in star ,what'll be the neew value of phase current and the total power? Q.4 a)Describe the factors affecting the choice of wiring system. b)With a neat connection diagram and switching table explain the TWO POINT CONTROL of a lamp. c)explain construction and principle of operation of dynammometer type wattmeter with a neat sketch. PART-B Q.5 a) Explain the working principle of DC machine as a generator and a motor with diagrams. b)Sketch N-I and T-I characterstics of DCi) Series and ii) shunt motors. mention two applications of each motor. c) A series motor runs at 600rpm when taking 110A from a 250V supply.The resistance of the armature circuit is 0.12 ohm and that of series winding is 0.03 ohm.The useful flux per pole for 110A is 0.024wb, and that for 50A is 0.0155wb.calculate the speed when the current has fallen to 50A. Q.6 a)Derive the expression for the electromotive force induced in the secondry winding of a transformer. b)What are the losses in a transformer? On what factors do they depend? How they are minimized? c)A single phase 25KVA 1000/2000V ,50Hz has maximum efficiency of 98% at full load u.p.f .Determine its efficiency ati)3/4 full load u.p.f (ii)1/2 full load 0.8 p.f (iii)1.25 full load 0.9 p.f. Q.7 a)Enumarate the advantages of having stationary armature and rotating file system in large capacity sychronous generator. b) Explain the terms pitch factor ,distribution factor as applied to an alternator. c)A three phase,star connected sycronous generator driven at 900rpm is required to generate a line voltage of 460V at 60Hz on open circuit.The stator has two slots per pole per phase, and 4 comductors per slot. calculatei)The number of poles (ii)The useful flux per pole. Q. 8 a)With neat sketches explain the constructional detils of squirrel cage and phase wound induction motors. b)Explain the significance of 'Slip' in induction motors. c)if a six pole induction motor supplied from a three phase 50Hz supply has a motor frequency of 2.3Hz.Calculatei)The percentage slip (ii)The speed of the motor.