Electric Motor


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Electric Motor- primary concepts, history, types, composition, working, use tec

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Electric Motor

  1. 1. ` 1 SUBJECT: ELECTRO-MAGNETIC THEORY “ELECTRIC MOTOR” : Submitted By : Rajvi Trivedi (131039) Shailaja Sampat (131046) What is an Electric Motor? Electric motor has brought one of the biggest advancements in the fields of engineering and technology ever since the invention of electricity. Electric Motor is a simple device that produces rotational force or more generally Electric Motor is an electro-magnetic device that converts electrical energy into mechanical energy. Electric Motor Symbol
  2. 2. ` 2 Principle: Electric motor works on the principle of a magnetic interaction between a current-carrying conductor and an external magnetic field to generate rotational motion. Current carrying coil placed in electro-magnetic field rotates continuously due to torque acting on the coil. When the coil rotates, the shaft attached to it also rotates and thus it can result in doing mechanical work. Electric Motor – Timeline : Conversion of electrical energy into mechanical energy by mutual induction Michael Faraday (1821) The most primitive D.C.motor (very expensive and not used for practical purposes) William Sturgeon (1832) First electrical motor which was capable of rotating at a constant speed under a varied range of load Frank Julian Sprague (1886) Electric Motor - Timeline
  3. 3. ` 3 Electric Motor – Parts : Electric motor consists mainly with five parts;  Armature or Rotor Armature is a rectangular coil made up of insulated copper wire wound on a soft iron core. It is placed between the magnetic poles.  Commutator Commutator is a copper ring split into two parts C1 and C2. They rotate along with the coil. Battery is connected to the rings by brushes in-between.  Brushes (B1 and B2) Two small strips of carbon, known as brushes are used to connect power source with Commutator.  Magnets  Power Supply
  4. 4. ` 4 Operational Principle- Fleming’s left hand rule : Fleming’s left hand rule- Place index finger, middle finger and thumb of our left hand in such a way that the electric current carrying wire is placed in a magnetic field (index finger) and perpendicular to the direction of current (middle finger), then the conductor experiences a force in the direction (represented by the thumb) mutually perpendicular to both quantities. Working of Electric Motor:
  5. 5. ` 5 Due to applied external DC source, electric current starts flowing through the Armature. As the conductor is carrying current inside a magnetic field, the left side of the armature is pushed away from the left magnet and drawn towards the right causing rotation. It will experience a force and torque which tends to rotate the Armature. Rotation of a coil due to torque When the coil turns through 900 , the Brushes lose contact with the Commutator and the current stops flowing through the coil however the coil keeps turning because of its own momentum. Now when the coil turns through 1800 , the sides get interchanged. As a result the Commutator ring C1 is now in contact with brush B2 and Commutator ring C2 is in contact with brush B1. Therefore, the current continues to flow in the same direction. We can find magnitude of Force by F= ILB sinө and direction by applying Fleming’s Left hand Rule. At any instance of time, forces experienced by the conductors are in such a direction that they tend to rotate the Armature due to forces of same magnitude but opposite direction. Fl = ILB Sin (90°) = BIL (Force on left part of Armature) Fr = (− I) LB Sin (90°) = − BIL (Force on right part of Armature)
  6. 6. ` 6 Types of Electric Motor :  DC: driven by Direct Current  AC: driven by Alternate Current  Synchronous motor: always runs at synchronous speed.  Induction motor / Asynchronous motor: whose speed is governed by varying the slip.  3 phase induction motor: contains 3 phase supply and runs on the principal of e.m.f. induction due to flux.  Single phase induction motor: contains single phase supply and runs on the principal of established theories, namely the Double Revolving field theory and the Cross field theory. ELECTRIC MOTOR AC MOTOR DC MOTOR SYNCHRONOUS MOTOR INDUCTION MOTOR / ASYNCHRONOUS MOTOR Single Phase INDUCTION MOTOR 3 Phase INDUCTION MOTOR SEPARATELY EXCITED SELF EXCITED SERIES COMPOUND SHUNT
  7. 7. ` 7  Shunt: field windings are shunted to, or are connected in parallel to the armature.  Compound: field windings are connected in series to the armature. Applications of electric motors :  3 phase Induction motor: conveyers, crushers, cranes, elevators, compressors, blowers, fans, machine tools, centrifugal pumps etc.  Single phase Induction motor: domestic applications mainly used in Hair dryers, fans, washing machine, ac fans, dairy machinery, small power tools, small farming equipment, vacuum cleaner, mixers etc.  3 phase Synchronized motor: variable speed applications such as high power and high speed compressors, blowers etc. Special Types of Motors :  Reluctance motors - electric clocks timers, signaling devices, recording devices etc.  Hysteresis motors - electric clocks and timing devices  Permanent magnet DC motor – portable vacuum cleaner, drills  Servomotors - robotics, radars, computers, machine tools, etc.  DC motors - DC series motor is also used in lifts, fans etc.  DC Shunt motors - mill machines, conveyors.