Important Questions in Electrical Engineering 131307 subject for NOV/DEC 2011 ANNA UNIVERSITY OF TECHNOLOGY AUT EXAMINATIONS FOR II YEAR ECE Students
131307 - Electrical Engineering
1. Draw the experimental set up to predetermine the efficiency of the given DC machine and give the necessary relations to find the efficiency of the machine while it is running as a motor as well as a generator. Also list the advantages and disadvantages of the test.
2. Determine the torque developed and the shaft torque of a 220 v. 4-pole series motor with 800 conductors wave connected supplying a load of 8.2kW by taking 45 amps from the mains.The flux per pole is 25 mWb. And its armature circuit resistance is 0.6 ohm
3. Derive the emf equation of the DC generator when the winding is lap and wave connected
4. Derive the torque equation of a DC motor.
5.. Explain and draw the N-T, N-Ia and T-Ia characteristics of a series, shunt and compound motor.
1. Obtain the equivalent circuit of a 200/400 V, 50 Hz, 1f transformer from the following test data.
OC test: 200 V, 0.7 a, 70 W on LV Side, SC Test: 15 V, 10 A, 85 W on .V side.
2. The primary and secondary windings of a 40 KVA, 6600/250V, 1f transformer has resistances of 10 Ω and 0.02Ω respectively. The leakage reactance of the transformer referred to the primary is 35 Ω. Calculate the full – load regulation at upf and 0.8 lagging pf. Neglect the no-load current.
3. Explain the operation of the 1f transformer under load condition with necessary phasor diagram. \
4. Give the classification of transformer based on primary-secondary combination, rating and application.
1. Draw the slip – torque of 3finduction motor and explain the significance of it.
2. Find the % tapping required on an autotransformer required for a squired – cage motor to start the motor to start the motor against 25 % of full – load torque. The short – circuit current on normal voltage is 4 times the full – load current and full – load slip is 3%.
3. Explain the emf injection method of speed control with a neat diagram.
4. Discuss in detail the principle of three phase induction motor, starting from the production of rotating magnetic field.
1. Explain in detail the MMF method of obtaining regulation of an alternator.
2. Write detailed notes on (i) reluctance motor (ii) stepper motor
3. Explain any one type of stepper motor in detail with connection diagram and different operating modes.
4. An alternator has 18 slots / Pole and the first coil lies in slots 1 and 16. Calculate the pitch factor for fundamental and third harmonics.
1. Draw the single line diagram showing the structure of electric power system and explain each component in detail.
2. Describe the types of DC links.
3. Explain various types of cables with neat diagrams.
4. Derive an expression for string efficiency.