College : Vardhaman College Of Engineering
Degree : B.Tech
Semester : III
Subject :Elements Of Electrical Engineering
Document type : Question Paper
Website : vardhaman.org
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Vardhaman Elements Of Electrical Engineering Question Paper
B. Tech III Semester Regular Examinations, December – 2013
(Regulations : VCE-R11)
(Common to Computer Science and Engineering & Information Technology)
Date : 4 December, 2013
Time : 3 Hours
Max. Marks : 75
Related : Vardhaman College Of Engineering DC Machines B.Tech Question Paper : www.pdfquestion.in/6309.html
Instructions
Answer ONE question from each Unit
All Questions Carry Equal Marks
All parts of the question must be answered in one place only
Model Questions
Unit – 1 :
1. a)State and Explain Reciprocity theorem. 7M
b) A star connected load has an impedance of (3+j4) ohm in each phase and is connected across a balanced three phase delta connected AC generator having line voltage of 120 V. Obtain the line current of both the load and AC generator. 8M
2. a) Determine Norton’s equivalent circuit at terminals AB for the Circuit shown in fig.1. fig.1 7M
b) Compare single-phase and three-phase supply systems. Deduce the relationship between the phase and line voltages of a 3-phase star-connected system. 8M
Unit – 2 :
3. a) With neat sketch, explain the working principle of DC generator. 7M
b) A shunt motor, fed from a 400 V direct current supply, takes an armature current of 100 A when running at 800 RPM. If the total torque developed remains same, find the speed at which the motor will run if the flux is increased to 120% of its original value and a resistance of 0.8 O is connected in series with the armature. The armature resistance is 0.2 O. 8M
4. a) Briefly discuss about the various types of DC generators. 8M
b) Determine the value of torque in N-M, established by the armature of a 4-pole DC motor having 774 conductors, wave wound, having a flux of 24 mWb per pole when the total armature current is 50 Amperes.7M
Unit – 3 :
5. a) A 600KVA, single phase transformer has an efficiency of 92% both at full load and half load at unity power factor. Determine its efficiency at 60% of full load at 0.8 power factor lag. 10M
b) Draw the equivalent circuit of a transformer. 5M
6.a) Explain the various losses in a transformer. 5M
b) A 20KVA, 440/220V, single phase, 50Hz transformer has iron loss of 324W. The copper loss is found to be 100W when delivering half full load current. Determine the efficiency when delivering a full load current of 0.8p.f lagging. 10M
Unit – 4 :
7. a) Explain the star delta starting method of an induction motor. 7M
b) A 3 phase, 8 pole 60Hz, induction motor has a rotor emf of 10V induced when the rotor is at stand still. Calculate the frequency of the induced emf, when the rotor rotates at 864 rmp. 8M
8. a)Explain the working principle of a stepper motor. 5M
b) Explain a typical slip-torque curve of a 3 phase induction motor. A 6 pole, 50Hz squirrel cage induction motor runs on no load at a shaft speed of 970rpm. Calculate the percentage slip and the frequency of induced current in the rotor. 10M
Unit – 5 :
9. a) Derive the emf equation of an alternator. 7M
b) Find the synchronous impedance and reactance of a single phase alternator in which a given field current produces an armature current of 200A on short circuit and a generated emf of 50V on open circuit. The armature resistance is 0.1O. To what induced voltage must the alternator be excited if it is to deliver a load of 100A at a power factor of 0.8 lagging with a terminal voltage of 200V. 8M
10. a)Explain the working principle of a synchronous motor. 6M
b) A 3 phase, 16 pole alternator has a star connected winding with 144 slots and 10 conduction per slot. The flux per pole is 0.03Wb sinusoidally distributed and the speed is 375rpm. Find the frequency, phase and line emfs. Assume a winding factor of 0.96. 9M