Dc machines for Mechanical engineering students, Exercises of Electrical Engineering

Download Dc machines for Mechanical engineering students and more Exercises Electrical Engineering in PDF only on Docsity! CENTRAL COLLEGE OF ENGINEERING AND MANAGEMENT SUBJECT: ELEMENTS OF ELECTRICAL ENGINEERING QUESTION BANK UNIT-1(DC NETWORKS) 1 .Define Thevenin’s Theorem. List the steps for obtaining Thevenin’s equivalent circuit. 2 .Define and explain Norton’s theorem. 3 .Define kirchoff’s Law. 4 .Use nodal analysis method to find current in the various resistors of the circuit shown in fig. 5 . Give the comparison between magnetic and electric circuit? 6 . Write down the statement of Thevenin's theorem Also write the various steps to find the Thevenin's equivalent? 7. State Kirchhoff’s current law and Kirchhoff’s voltage law. 8. Define Hysteresis and Eddy current losses. How these losses are reduced, practically in electric machines? 9. State Norton theorem? 10. State the superpositiontheorem? 11. Use nodal method to find current in branch a b of circuit shown in Fig. All resistance in ohms. 12. For the network shown below, draw a Norton’s equivalent circuit and Determine the current flowing through 18.75ohms resister. 13. Find the current in different branches of the network shown in Fig.Using superposition theorem. 14. The Circuit Shown in Fig. contains two voltage sources and two current sources. Calculate (i) Vth (ii) Rth Betweenthe open terminals A & B of the circuit. UNIT -4(SINGLE PHASE TRANSFORMER AND DC MACHINE) 2 marks questions-> 1. Derive the torque equation of D.C. machine. 2. Derive the EMF equation of a D.C. machine. 3. A series motor never be started without load on it. Give reason. 4. Explain function of commutator. 8/7 marks questions-> 1. Enlist various parts of a D.C. machine and explain the function of each part. 2. Describe the principle of three phase induction motor 3. Suggest the appropriate motor for following applications:-  Ceiling fan  Electrical traction lathes  Crane &hoists  Blower and fan  Floor mill  Tape recorder  Tube well pump. 4. Write the application of D.C. generator .The armature of a 12-pole D.C. shunt generator has 50 slots and is wave wound with 12 conductor per slots .The generator is running at a speed of 625 rpm and supplies a resistiv load of 15Ω at a terminal voltage of 300 v. The armature resistance is 0.5Ω and field resistance is 60Ω.Find the armature current, the generated EMF and flux per pole. 5. Derive the expression for maximum torque and draw the torque –slip curve. 6. Define slip and sate its importance. 7. A 4 pole , 3 phase induction motor operates from a supply whose frequency is 50 Hz. Calculate:  The speed at which the magnetic field of the stator is rotating.  The speed of the rotor when the slip is .04.  The frequency of rotor current when slip is 0.03.  The frequency of the rotor current at stand still. 8. Derive the expression for developed torque in a 3-phase induction motor. 9. With usual notation, derive the torque equation of O.K. motor. 10. A 120v decent motor has an armature resistance of 0.2 Ω and a field resistance of 60Ω. It runs at 1800rpm it is taking a full load current of 40 A. Find the speed of the motor when it is operating at half full load. 11. A 4 pole, 500 V, shunt motor has 720 wave connected conductors on its armature . The full load armature current is 100A and flux pee pole 0.03 Wb. The armature resistance is 0.2 ohm. Calculate full load speed of the motor. 12. The voltage applied to a stator of 3 phase 6 pole induction motor has a frequency of 50Hz. The frequency of the EMF induced in the rotor is 2 Hz. Calculate the slip and speed at which motor is running. 13. Draw the circuit diagram of the following :  D.C. shunt motor.  D.C. series motor  Three phase induction motor(slip ring)  Single phase shaded pole motor Give the application of each motor with appropriate reason. 14. A 3-phase, 6 pole, 50Hz induction motor has a slip of 1% at no load and 3% at full load. Determine:  Synchronous speed  No-load speed  Full load speed  Frequency –load speed  Frequency of rotor current at stand still.  Frequency of rotor current at full-load 15. A 250 V shunt motor on no load runs at 1000rpm and takes 5A. 16. The total armature and shunt field resistances are 0.2hm and 250 ohm respectively . Calculate the speed .When loaded taking a current of 50A, if the armature reaction weakens the field by 3%. 17. A 230 V D.C. shunt motor on no load runs at 1000 rpm on full load, drawing a current of 10A. The shunt field resistance is 230 ohm and armature resistance is 0.5 ohm. Calculate the resistance to be inserted in series with the armature so that the speed at full load is 650 rpm. 18. A 3- phase induction motor runs at 290 rpm at full load with 50 Hz supply. Find the no. Of poles of motor and slip. 19. A 4 pole d.c. shunt motor takes 22 A from 220V. The armature and field resistance are 0.5 and 100 ohm respectively. The armature lap connected with 300 conductors. If the flux per pole is 20mWb , calculate speed and gross torque developed. 20. Derive an expression for the torque of 3 phase induction motor. Plot the torque slip characteristic of motor and show the position of maximum torque. 21. Derive an expression for the torque developed by D.C. motor. Give the torque speed characteristic for D.C. series and D.C. shunt motor. 22. Explain working principle of 3-phase induction motor. Draw torque/slip curve for two different values of rotor resistance. 23. The no load armature current of 230V shunt motor is 2A at speed of 1200rpm. If the full load armature current is 40A, find full load torque and speed. Take armature resistance=o.25 ohm and field flux unchanged from no load to full load. 24. Describe the classification of D.C. motor. Explain their torque /slip characteristic. Derive the expression for torque developed by D.C. motor. Give the torque speed characteristic for D.c. series and D.C. shunt motors. 25. . What is a transformer? Give classification of the transformer. 26. Derive e.m.f. equation of a single phase transformer. 27. Explain maximum efficiency of a single phase transformer. UNIT- 5(ELECTRICAL MEASURING INSTRUMENTS) 2 marks Questions -> 1. Define damping. Name 3 different types of damping torque used in electro mechanical instruments. 2. State the essential requirements of indicating type instrument. Explain in brief 3. How do you extend the range of an armature? 4. What is creeping error? 7/8 marks Question 5. Describe the following torque and explain why they are required in electrical measure in system. a. Deflecting torque b. Controlling torque c. Damping torque 6. Draw a neat diagram of PMMC instrument and explain its working. 7. Explain essentials of indicating instruments 8. A millimetre with a resistance of 4 ohm is connected with a shunt of 0.005 ohm . what will be the current flowing through the instrument if it is connected to a circuit in which a current of 10A is flowing? 9. What is the principle of moving iron voltmeter? 10. Explain the operation of amoving iron voltmeter. 11. What do you understand by shunt and multiplier. How these are useful for extension of instrument? Explain.