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  2 marks (Questions & Answers) 1.Define Drive and Electric Drive.Drive:  A combination of prime mover, transmission equipment andmechanical working load is called a drive Electric drive:  An Electric Drive can be defined as an electromechanical device for converting electrical energy to mechanical energy to impart motion to different machines and mechanisms for various kinds of process control. 2. List out some examples of prime movers. I.C Engines, Steam engine, Turbine or electric motors. 3. List out some advantages of electric drives .i.Availability of electric drives over a wide range of power a few  watts to mega watts.ii.Ability to provide a wide range of torques over wide range of speeds.iii.Electric motors are available in a variety of design in order tomake them compatible to any type of load. 4.Give some examples of Electric Drives. i.Driving fans, ventilators, compressors and pumps.ii.Lifting goods by hoists and cranes.iii.Imparting motion to conveyors in factories, mines and  warehousesiv.Running excavators & escalators, electric locomotives trains, cars trolley buses, lifts & drum winders etc.. 5. What are the Typical elements of an Electric Drive? Speed & Torque ControlMotor Mechanical LaodGeared CouplingPower Supply  6. What are the types Drive systems? Electric DrivesMechanical DrivesElectromechanical DrivesHydraulic drives. 7. What are the factors that influence the choice of electrical drives? 1. Shaft power & speed11. Speed range2. Power range12. Efficiency3. Starting torque 13. Influence on the supply network 4. Maintenance14. Special competence5. Total purchase cost15. Cost of energy losses6. Influence on power supply16. Environment7. Availability 17. Accessibility 8. Nature of electric supply18. Nature of load9. Types of drive19. Electrical Characteristics10.Service cost20. Service capacity & rating. 8. What is meant by “load equalization”? In the method of “load Equalization” intentionally the motor inertiais increased by adding a flywheel on the motor shaft, if the motor is not to be reversed. For effectiveness of the flywheel, the motor should have a prominent drooping characteristic so that on load there is a considerablespeed drop. 9.List the different types of electrical drives. 1)dc drives 2)ac drives  10.Mention the parts of electrical drives. 1) Electrical motors and load. 2) Power modulator 3) Sources 4) Control unit 5) Sensing unit11. What is meant by regenerative braking? Regenerative braking occurs when the motor speed exceeds thesynchronous speed. In this case the IM runs as the induction m\c isconverting the mechanical power into electrical power which isdelivered back to the electrical system. This method of braking isknown as regenerative braking. 12. What is meant by dynamic braking? Dynamic braking of electric motors occurs when the energy stored in the rotating mass is dissipated in an electrical resistance. This requires a motor to operate as a gen. to convert the stored energy into electrical. 13. What is meant by plugging? It is one method of braking of IM. When phase sequence of supply of themotor running at the speed is reversed by interchanging connections ofany two phases of stator with respect to supply terminals, operationshifts from motoring to plugging region. 14.What are the methods of operation of electric drives? Steady state acceleration including starting deceleration including starting 15. Define four quadrant operation.  The motor operates in two mode: motoring and braking. Inmotoring, it converts electrical energy into mechanical energy which supports its motion. In braking, it works as a generator, converting mathematical energy into electrical energy and thusopposes the motion. Motor can provide motoring and brakingoperations for both forward and reverse directions.  16. What is meant by mechanical characteristics?  The curve is drawn between speed and torque. This characteristic iscalled mechanical characteristics. Write down the equation governing motor load dynamics. COMPONENTS OF LOAD TORQUE  Friction   Windage   Torque required to do the mechanical work  Types of load torques  Passive torque   Active torque Passive torque  oppose the motion.Ex.. Friction torque Active torque  Load torque is constant  Retain its sign always.  Ex.. Force of gravity dt d  J T T or  dt d  J T T   Le Le ω ω  =−+=
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