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Ac motors and their types

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Ac motors and their types

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Ac motors and their types

  1. 1. AC Motors & Their Types GroupMembers: MAbdullah (p12-6322) SalmanSyed (p12-6403) YasarHayat (p12-6405)
  2. 2. Topic Introduction  Electromechanical device that converts electrical energy to mechanical energy.  Mechanical energy used to e.g.  Rotate pump impeller, fan, blower  Drive compressors  Lift materials  Motors in industry: 70% of electrical load.  What is an Electric Motor?
  3. 3. Principle of how motors work
  4. 4. Structural Design  An electric motor is all about magnets and magnetism: A motor uses magnets to create motion.  A motor is consist of two magnets.
  5. 5. Classification of Motors Electric Motors Alternating Current (AC) Motors Direct Current (DC) Motors Synchronous Induction Three-PhaseSingle-Phase Self ExcitedSeparately Excited Series ShuntCompound
  6. 6. AC Motors Alternating Current (AC) Motors Synchronous Induction Three-PhaseSingle-Phase
  7. 7. AC Motors  Electrical current reverses direction  Two parts: stator and rotor  Stator: stationary electrical component  Rotor: rotates the motor shaft Two types • Synchronous motor • Induction motor stator rotor
  8. 8. Induction motors Induction motors can be classified into two main groups: single-phase induction motors three-phase induction motors Single-phase induction motors: These only have one stator winding, operate with a single-phase power supply... Three –phase induction motors: The use three sets of stator coils the rotating magnetic field drags the rotor around with it.
  9. 9. Induction motors •Induction motors are the most common motors used for various equipments in industry. Components Rotor • Squirrel cage • Wound rotor Stator
  10. 10. Single Induction motor •Single phase motors are very widely used in home, offices, workshops etc. as power delivered to most of the houses and offices is single phase. In addition to this, single phase motors are reliable, cheap in cost, simple in construction and easy to repair.
  11. 11. 3 phase Induction Motor • Stator As its name indicate stator is a stationary part of induction motor. A three phase supply is given to the stator of induction motor. • Rotor The rotor is a rotating part of induction motor. The rotor is connected to the mechanical load through the shaft. The rotor of the three phase induction motor are further classified as • Squirrel cage rotor • Slip ring rotor or wound rotor or phase wound rotor
  12. 12. Squirrel Cage Induction Motor
  13. 13. • Advantages of squirrel cage induction rotor 1. Its construction is very simple and rugged 2. as there are no brushes and slip ring, these motors requires less maintenance. • Applications: Squirrel cage induction motor is used in lathes, drilling machine, fan, blower printing machines etc
  14. 14. Slip Ring Induction Motor • Slip ring or wound three phase induction motor : In this type of three phase induction motor the rotor is wound for the same number of poles as that of stator but it has less number of slots and has less turns per phase of a heavier conductor.The rotor also carries star or delta winding similar to that of stator winding. The rotor consists of numbers of slots and rotor winding are placed inside these slots.
  15. 15. • Advantages of slip ring induction motor 1. It has high starting torque and low starting current. 2. Possibility of adding additional resistance to control speed • Applications: Slip ring induction motor are used where high starting torque is required i.e in hoists, cranes, elevator etc
  16. 16. Synchronous motor  As the name suggests Synchronous motors are capable of running at constant speed irrespective of the load acting on them.  Synchronous motors have got higher efficiency than its counterparts. Its efficiency ranges from 90 – 92%.
  17. 17. AC Synchronous motor Stator: It carries three phase winding and is fed from 3-phase supply. Rotor: It carries permanent magnet poles that rotate exactly with same speed as that of the stator magnetic field, hence the name synchronous motor. It is not self starting.
  18. 18. Synchronous Motor-Principle 22 The rotor acting as a bar magnet will turn to line up with the rotating magnet field. The rotor gets locked to the RMF and rotates unlike induction motor at synchronous speed under all load condition
  19. 19. Synchronous Speed Speed at which RMF rotates or Synchronous speed can easily be derived as follows, speed of synchronous motor can be very accurately controlled. This is the reason why they are suitable for high precision applications.
  20. 20. Why Synchronous motors are not self starting ? North Pole of the Rotor will obviously get attracted by South Pole of RMF, and will start to move in the same direction. But since the rotor has got some inertia, this starting speed will be very low. So it will give repulsive force. This will make the rotor move backward. As a net effect the rotor won’t be able to start.
  21. 21. Making Synchronous Motor Self Start • To make synchronous motor self start, a squirrel cage arrangement is cleverly fitted through pole tips. They are also called as damper windings. At the starting rotor field coils are not energized. So with revolving magnetic field, electricity is induced in squirrel cage bars and rotor starts rotating just like an induction motor starts.
  22. 22. Out of Synchronism •Synchronous motors will produce constant speed irrespective of motor load only if the load is within the capability of motor. If external torque load is more than torque produced by the motor, it will slip out of synchronism and will come to rest. Low supply voltage and excitation voltage are other reasons of going out of synchronism
  23. 23. Application of Synchronous Motor • Synchronous motor having no load connected to its shaft is used for power factor improvement. it is used in power system in situations where static capacitors are expensive. • Synchronous motor finds application where operating speed is less (around 500 rpm) and high power is required. For power requirement from 35 kW to 2500KW, the size, weight and cost of the corresponding induction motor is very high. Hence these motors are preferably used. Ex- Reciprocating pump, compressor, rolling mills etc

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