R5220205 Electrical Machines-ii R5 2-2

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Code No: R5220205 II B.Tech. II Semester(R05) Supplementary Examinations, April/May 2009 ELECTRICAL MACHINES-II (Electrical & Electronics Engineering)

Time: 3 hours

Max Marks: 80 Answer any FIVE questions All questions carry equal marks ?????

1. (a) Explain the working principle of operation of single phase transformer under leading load condition with phasor diagram. (b) A 3300/250V, 50Hz single phase transformer is built on a core having an effective crosssectional area of 125cm2 cm and 70 turn on the low-voltage handing calculate i. The valve of maximum flux density. ii. The no. of turn on high voltage winding. 2. (a) Derive the expression for current at maximum efficiency. (b) At 400V and 50Hz the core loss of a transformer was found to be 2400W when the transformer is supplied at 200V, and 25Hz, the core loss in 800w. calculate the hysteresis and eddy current losses at 400V and 50Hz. 3. What is mean by predetermination? What parameters are predetermined by conducting O.C & S.C tests on single phase transformer. Explain with neat circuit diagrams. 4. Explain with the help of connection and phasor diagrams, how the Scott connections are used to obtain Two-phase supply from three-phase supply mains. 5. (a) Explain how the rotating magnetic field is produced in a 3-phase induction motors. (b) The frequency of the emf in the stator of a 4-pole induction motor is 50Hz and that in the rotor in 1.5Hz. What is the slip and at what speed is the motor running? 6. (a) Explain the double cage and deep bar rotors. (b) The power in put to a 3-phase indication motor is 60KW. The Stator losses total is 1KW. Find the total mechanical power developed and the rotor copper loss per phase if the motor in running with a slip of 3% 7. A 50 KW, 6pole, 50Hz, 450V 3 phase slip ring induction motor furnished the following test figures. No load test: 450V, 20A, pf=0.15 Blocked routine test: 200V, 150A, pf=0.3 The ratio of stator to rotor copper losses on short circuit war 5:4. Draw the circle diagram and determine from it (a) The full load current and power factor. (b) The maximum torque and the maximum power input. (c) Slip at full load. (d) Effiency at full load. 8. Explain the principles of operation of induction Generator in detail and what are its limitations ?????

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Code No: R5220205 II B.Tech. II Semester(R05) Supplementary Examinations, April/May 2009 ELECTRICAL MACHINES-II (Electrical & Electronics Engineering)

Time: 3 hours

Max Marks: 80 Answer any FIVE questions All questions carry equal marks ?????

1. (a) Derive the emf equation of single phase transformer. (b) Explain the constructional details and types of single phase transformers. 2. (a) Derive the equivalent circuit parameter of single phase transformer (b) A single transformer working at unity power factor has an efficiency of 90% at both half load and at the full load of 500W. Determine the efficiency at 75% full load. 3. Explain the principle and operation of a Auto transformer in detail. 4. Explain the working principle and constructional details of 3-phase transformer and also explain the possible connections for a 3-phase transformer bank. 5. (a) Determine the rotor emf and reactance under running conditions. (b) A 3-phase, 50Hz, 4pole induction motor has a slip of 4% calculate i. Speed of the motor. ii. Frequency of the Rotor emf. 6. (a) Draw and explain slip-Torque characteristics of 3-phase induction motor. (b) The power input to the rotor of 440v, 50Hz 6pole, 3-phase induction motor in 80KW. The rotor emf in observed to make 100 complete oscillations per minute. Calculate i. ii. iii. iv. v.

The slip. The rotor speed. Mechanical power developed. Rotor copper loss per phase. Rotor resistance per phase if the rotor current in 65A.

7. Explain the starting methods of 3-phase induction motors. 8. How will you control the speed of an induction motor? Explain in detail. ?????

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Code No: R5220205 II B.Tech. II Semester(R05) Supplementary Examinations, April/May 2009 ELECTRICAL MACHINES-II (Electrical & Electronics Engineering)

Time: 3 hours

Max Marks: 80 Answer any FIVE questions All questions carry equal marks ?????

1. (a) Explain the constructional details and types of single phase transformers. (b) How will you minimize the Hysteresis and Eddy current losses that occur in single phase transformers. 2. (a) Define the Regulation of Transformer and also deduce the condition for zero voltage regulation. (b) In a Transformer, the core loss is 100W at 40Hz and 72W at 30Hz. Find the Hysteresis and Eddy current losses at 50Hz. 3. (a) What is mean by predetermination? What parameters are predetermined by conducting O.C& S.C test on transformer? (b) Explain the parallel operation of single phase transformers. 4. What is meant by three phases transformers groups? What is the significance of these groups? What is the possible connections for a 3-phase transformers bank. Explain in detail. 5. (a) Explain the constructional details of 3-phase induction motors. (b) A 3-phase, 6-pole, 50Hz induction motor has a slip of 1% at no load and 3% at full load. Determine i. Synchronous speed. ii. No load speed. iii. Full load speed. 6. (a) What is Crawling and what is cogging? Explain. (b) A 6-pole 50Hz, 3-phase induction motor running on full load develops a useful torque of 150N-m at a rotor frequency of 1.5Hz. Calculate the shaft power output if the mechanical torque lost in friction by 10N-m. Determine i. Rotor copper loss. ii. The input to the motor. iii. The efficiency. 7. Draw the circle diagram for a 3-phase 6-pole, 50Hz, 400V, star connected induction motor from the following data(line values) No load test: 400V, 10A, 1400W Blocked rotor test: 200V, 55A, 7000W The stator loss at stand still is 60% of the total copper losses and full-load current is 30A. From the circle diagram determine (a) Power factor, slip, output, efficiency, speed. (b) Starting torque. (c) Maximum power output and inputs. (d) Maximum torque and slip. 8. Explain the principle of operators of Induction Generator in detail. What are its limitations? ?????

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Code : R5220205 II B.Tech. II Semester(R05) Supplementary Examinations, April/May 2009 ELECTRICAL MACHINES - II (Electrical & Electronics Engineering)

Time: 3 hours

Max Marks: 80 Answer any FIVE questions All questions carry equal marks ?????

1. (a) Explain working principle of operation of a single phase transformer. (b) A transformer with an output voltage of 4000V is supplied at 220V. If the secondary has 2000turns, Calculate the number of primary turns. 2. (a) Derive the condition for maximum efficiency of a single phase transformer. (b) A 10KVA single phase transformer for 2000/400V at no load, has R1 = 5.5Ω, X1 = 12Ω, R2 = 0.2Ω, X2 = 0.45Ω. Determine the approximate value of the Secondary voltage at full load, 0.8 p.f lagging, when the primary applied voltage in 2000V. 3. (a) Explain the procedure to conduct back-to-back on a single phase transformer. (b) What is an Auto transformers? Explain. 4. (a) Explain the advantages of using tertiary winding. (b) Discuss the application of 3-winding transformer. 5. (a) Explain the principle and operations of a 3-phase induction motor. (b) A 3-phase, 50hz, 4 pole induction motor has a slip of 4%. Calculate i. Speed of the motor. ii. Frequency of the motor emf. 6. (a) What is Torque? Deduce the expressions for maximum torque for 3-phase induction motor. (b) A stator loss of 3-phase induction motor is 2KW, when the power input is 90KW. What will be the rotor mechanical power developed and the rotor copper loss if the motor is running with a ship of 4%. 7. Explain the aim and procedure to conduct no load and blocked rotor test on a 3-phase induction motor with neat circuit diagram and also explain the relevant calculations. 8. Explain the speed control methods of 3-phase induction motor in detail. ?????