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Posted By: neyha Member Level: Diamond Posted Date: 08 Jul 2008
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2006 Anna University Electronic Instrumentation and Control B.E /B.TECH.DEGREE EXAMINATION : Electrical machines Question paper
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B.E /B.TECH.DEGREE EXAMINATION ,NOV/DEC 2006
Third semester
Electrical machines
Time:3Hrs
Maximum:100 marks
PART A (10 X 2 =20)
1. How is an alternating current converted into unidirectional current in DC generator?
2. Name any two methods of speed control of DC shunt motor.
3. Define he term 'all day efficiency' of a distributor transformer.
4. Why is the coreloss of a transformer practically same for all load conditions?
5. What are the uses of damper windings in synchronous machine?
6. List the different types of torques associated with synchronous motor.
7. Write the torque equatio of an induction motor under running condition.
8. What are the different losses in an induction motor?
9.Why is single phase induction motor not self starting motor?
10. What are the applications of universal motor?
PART B (5 X 16=80)
11(a) (i) Draw and explain the various types of self -excited dc generator with their winding arrangement.
(ii) A four pole wave wound dc shunt generator has 122 slots and 3 conductors per slot in its armature.If the armature is rotated at a speed of 1000 r.p.m in a field of 0.03 Webber per pole. Calculate the E.M.F generated
Or
(b) (i) Explain how a batch emf plays an important role in he operation of a d.c shunt motor
(ii) A 4 ploe d.c series motor has 944 wave connected armature conductors .At a certain load,the fuse per pole is 34.6 mwb and total mechanical torque devloped is 209 newton metrs .Calculate the line current taken by the motor and the speed at which it will run with an applied voltage of 500V .Total motor resistance is 3 ohms.
12(a) (i) Derive the E.M.F equation of a single phase transformer.
(ii) A 33-kVA single transformer is designed to have resistance of 1.5% and maximum efficiency occurs ata load of 173.2 kVA.Find its efficiency when supplying full load at 0.8 p.f.lagging at normal voltage and frequency
OR
(b) (i) Derive the conditon for obtaining maximum efficiency of a sinle phase transformer
(ii) Explain the operation of a single phase transformer on load condition.
13(a) (i) Name the different types of rotors use in alterations .Explain briefly
(ii) Explain the principle of operations of a synchronous motor
OR
(b) (i)Why terminal voltage vary with load inan altrnator? Explain
(ii) Explain the starting method of synchrounouse motor.
14 (a) (i) What are the factors used for determining the maximum torque of a 3-phase induction motor ?
(ii) The power input to a 400 volts ,60 Hz,6 pole,3 phase induction motor running at 1140 rpm is 40 kW at 0,8 p.f lag.Stator losses are 1 kW and the friction and windage losses are 2 kW.Calculate
(1) The slip
(2) The rotor copper loss
(3) The brake h.p
(4) Efficiency
(5) input current
Or
(b) Explain the following of 3 phase induction motor
(i) Squirrel cage rotor
(ii) Phase -wormed rotor
(iii) Slip
(iv) Speed control
15 (a) (i) Explain how a single phase induction motor is self started?
(ii) Explain the working principle of universal motor
OR
(b) Discuss the constructional details of the following motors
(i) Shaded -pole motor
(ii) Capacitor start and run motor
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