Name of the College : Sphoorthy Engineering College
University : JNTUH
Department : ELECTRICAL AND ELECTRONICS ENGINEERING
Subject Code/Name : 09A50206/ELECTRICAL MACHINES – III
Degree : B.Tech
Year/Sem : III/I
Website : sphoorthyengg.com
Document Type : Model Question Paper
Download Model/Sample Question Paper : https://www.pdfquestion.in/uploads/sphoorthyengg.com/4849-09A50206%20-%20ELECTRICAL%20MACHINES%20-%20III.pdf
Electrical Machines–III Question Paper :
B. Tech III Year I Semester Examinations, December-2011
Time: 3 hours
Max. Marks: 75
Related : Sphoorthy Engineering College 09A50301 Managerial Economics & Financial Analysis B.Tech Question Paper : www.pdfquestion.in/4846.html
Answer any five questions :
All questions carry equal marks :
1.a) Discuss the constructional details of synchronous machine.
b) Mention the differences between salient pole and non salient pole synchronous machine. [7+8]
2. Derive the emf equation of alternator, explain the coil span factor, distribution factor and derive the expressions? [15]
3.a) What are the causes of harmonics in the voltage waveform of an alternator?
b) Enumerate various methods used for minimizing harmonics in turbo-alternator.
c) Explain the effect of “armature reaction” in alternators for lagging power factor load, with mmf diagram. [15]
4. A 3-phase, star-connected alternator is rated at 1600 kva, 13500v. The armature effective resistance and synchronous reactance are 1.5O and 30O respectively per phase. Calculate the percentage regulation for a load of 1280kw at power factors of 0.8 leading 0.8 lagging. [15]
5. Two three-phase alternators operate in parallel. The rating of one machine is 50MW and that of the other is 100MW. Both alternators are fitted with governors having a droop of 4%. How will the machines share a common load of 100MW? [15]
6. Explain V – curves and ? – curves of 3-phase synchronous motor. [15]
7. Explain the double field revolving theory of single phase induction motor. [15]
8. Explain the operation of universal motor. [15]
R09Code No: 09A50206
SET-2
1. Describe with neat sketch, the constructional details of salient pole alternators. [15]
2. A 3-phase, 8-pole, 750 rpm star – connected alternator has 72 slots on the armature. Each slot has 12 conductors and winding is short chorded by 2 slots. Find the induced emf between lines, given the flux per pole is 0.06 wb. [15]
3. What is armature reaction? Explain the effect of armature reaction on the terminal voltage of an alternator at
i) Unity power factor load
ii) Zero loading P.F load
iii) Zero lagging P-F load and draw the corresponding phasor diagrams. [15]
4. A straight – line law connects terminal voltage and load of a 3-phase star – connected alternator delivering current at 0.8 P.f lagging. At no load, the terminal voltage is 3500V and at full load of 2280kw, it is 3300v.
Calculate the terminal voltage when delivering current to a 3-phase, star- connected load having a resistance of 8O and a reactance of 6O per phase. Assume constant speed and field excitation. [15]
5. A synchronous generator operates on constant – voltage constant frequency bus bars. Explain the effect of variation of a) excitation b) steam supply on power output ,power factor, armature current and load angle of the machine. [15]
6. Explain the effect of varying excitation on armature current and power factor in a synchronous motor. Draw V – curves and state their significance. [15]
7. A 3000V, 3-phase synchronous motor running at 1500 y.p.m has its excitation kept constant corresponding to no – load terminal voltage of 3000V.
Determine the power input, power factor and torque developed for an armature current of 250A if the synchronous reactance is 5O per phase and armature resistance is neglected. [15]
8. Discuss the principle of operation of single phase capacitor start and capacitor run motors. [15]
Electrical Machines – III :
1. What are the different types of ac generators in use? Explain their constructional features and essential differences in their construction. [15]
2.a) Calculate the distribution factor for a 36-slot, 4-pole single layer 3-phase winding.
b) Derive the emf equation of synchronous generator from the fundamental principles. [7+8]
3.a) Explain the effect of load power factor on the armature reaction of alternator.
b) Explain briefly load characteristics of alternator. [8+7]
4. A 3-phase, 1500 kvA, star-connected, 50-Hz, 2300v alternator has a resistance of 0.12Ω. A field current of 70A produces a short – circuit current equal to fuel load current of 376A in each line. The same field current produces an emf of 700V on open circuit. Determine the synchronous reactance of the machine and its full load regulation at 0.8 lagging power factor.