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Posted By: Rajasekaran Member Level: Gold Posted Date: 20 Oct 2007
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2007 Anna University B.E Electronics and Communication EE1211-ELECTRICAL MACHINES Question paper
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BE/B.TECH DEGREE EXAMINATION ,MAY/JUNE 2007
Third Semester
Electronics and Communication Engineering
EE1211-ELECTRICAL MACHINES
(Common to Electronics and Instrumentation Engineering/Instrumentation and
Control Engineering)
(Regulations 2004)
Time:3hrs Maximum: 100marks
Answer ALL questions.
PART A-(10X2=20marks)
1.What is the purpose of commutator?
2.Mention the significance of bac emf.
3.Name the factors on which hysteresis loss depends.
4.Define regulation and efficiency of a transformer.
5.A 6 pole,50Hz, 3phase induction motor has a full load speed of 950rpm, and has rotor copper loss of 5kW.
Calculate rotor input.
6.What will be the effect when stator voltage and frequency of a induction motor are reduced proportionality?
7.Mention some of the applications of stepper motor.
8.Comment on whether excitation affects the power factor of the synchronous motor.
9.What do you meant by one line diagram in electric power system?
10.Name the places where HVDC is used in India.
PART B-(5X16=80 marks)
11.(a)(i)Describe with neat diagram the constructional features of DC machines.(10)
(ii)Write briefly the load characteristics of over compounded generator.(6)
Or
(b)(i)Discuss in detail the methods of control of speed of a DC motor.(12)
(ii)A 4 pole, 500V DC shunt motor has 700 wave connected conductors on its armature.The full load armature
current is 60A and flux per pole is 30mWb.Calculate the full load speed if the rotor armature resistance is 0.2ohms
and the brush drop is 1V per brush.(4)
12.(a)(i)A 2000/200V transformer has primary resistance and reactance of 2 ohm and 4 ohm respectively.The
corresponding secondary values are 0.0025 ohm and 0.04ohm.Determine (1)equivalent resistance and
reactance of primary referred to secondary (2)total resistance and reactance referred to secondary
(3)equivalent resistance and reactance of secondary refereed to primary/(4)total resistance and reactance
referred to primary.(10)
(ii)Draw the vector diagram for an ideal transformer on resistive ,inductive and capacitive load.(6)
Or
(b)(i)Explain with neat diagram the operation of Sumpner's test.(12)
(ii)In a 50kVA transformer the iron loss is 500W and full load copper loss is 800W.Determine its efficiency
at full load (1)unity power factor and (2)at 0.8 p.f .lagging.(4)
13.(a)(i)Derive an expression for the torque developed in a 3 phase induction motor.Sketch a typical torque -speed
characteristics from stand still t synchronous speed.(12)
(ii)A 373kW, 3 phase, 440V, 50Hz induction motor has a speed of 950 rpm on full load.The motor has 6 poles
Calculate slip.How many complete alternations will be the rotor voltage maker per minute.(4)
Or
(b)State and explain double revolving field theory of single phase induction motor.Hence deduce the equivalent
circuit and normal condition.(16)
14.(a)(i)Explain the construction and principle of operation of a synchronous motor.(10)
(ii)A salient pole ,star connected synchronous motor rated at 187kVA, 3phase ,2300V,47A,50Hz,
187.5rpm has an effective resistance of 1.5 ohm and synchronous reactance of 20ohm/phase.Determine
the internal power developed by the motor when it is operating at rated current and 0.8p.f leading.(6)
Or
(b)(i)Explain in detail the different modes of operation of stepper motor.(8)
(ii)With neat sketch,explain the principle of reluctance motor.(8)'
15.(a)With relevant sketches explain, a typical electric power generating using fossil fuels.(16)
Or
(b)Explain in detail various types of insulators and their applications to power transmission.(16)
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