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    Eee ppt Eee ppt Presentation Transcript

    • PRESENTATION ON
      ELECTRIC MOTOR
    • ELECTRIC MOTOR
      • An electric motor is an electromechanical device that converts electrical energy to mechanical energy.
      • The mechanical energy can be used to perform work such as rotating a pump impeller, fan, blower, driving a compressor, lifting materials etc.
    • BASIC WORKING PRINCIPLE
    • TYPES OF MOTOR LOADS
    • CLASSIFICATION OF MOTORS
      Electric Motors
      Alternating Current (AC) Motors
      Direct Current (DC) Motors
      Synchronous
      Induction
      Self Excited
      Separately Excited
      Three-Phase
      Single-Phase
      Series
      Shunt
      Compound
    • TYPES OF AC MOTORS
      * Electrical current reverses direction
      * Two parts: stator and rotor
      Stator: stationary electrical component
      Rotor: rotates the motor shaft
      * Speed difficult to control
      * Two types
      Synchronous motor
      Induction motor
    • AC MOTOR: INDUCTION MOTOR
      Most common motors in industry
      Advantages:
      Simple design
      Inexpensive
      High power to weight ratio
      Easy to maintain
      Direct connection to AC power source
    • COMPONENTS OF INDUCTION MOTOR
      A3-phase induction motor has two main parts:
      • A stator – consisting of a steel frame that supports a hollow, cylindrical core of stacked laminations. Slots on the internal circumference of the stator house the stator winding.
      • A rotor – also composed of punched laminations, with rotor slots for the rotor winding.
    • COMPONENTS OF INDUCTION MOTOR contd…
      There are two-types of rotor windings:
      • Squirrel-cage windings, which produce a squirrel-cage induction motor (most common)
      • Conventional 3-phase windings made of insulated wire, which produce a wound-rotor induction motor (special characteristics)
    • Induction Motor: Operating Principle
      Operation of 3-phase induction motors is based upon the application of Faraday’s Law and the Lorentz Force on a conductor.
      Consider a series of conductors (length L) whose extremities are shorted by bars A and B. A permanent magnet moves at a speed v, so that its magnetic field sweeps across the conductors.
    • Operating Principle Contd…
      The following sequence of events takes place:
      1. A voltage E = BLv is induced in each conductor while it is being cut by the flux (Faraday’s Law)
      2. The induced voltage produces currents which circulate in a loop around the conductors (through the bars).
      3. Since the current-carrying conductors lie in a magnetic field, they experience a mechanical force (Lorentz force).
      4. The force always acts in a direction to drag the conductor along with the magnetic field.
      Now close the ladder upon itself to form a squirrel cage, and place it in a rotating magnetic field – an induction motor is formed!
    • Induction Motor: Rotating Field
      Consider a simple stator with 6 salient poles - windings AN, BN, CN.
      The windings are mechanically spaced at 120° from each other.
      The windings are connected to a 3-phase source.
      AC currents Ia, Ib and Ic will flow in the windings, but will be displaced in time by 120°.
      Each winding produces its own MMF,which creates a flux across the hollow interior of the stator.
      The 3 fluxes combine to produce a magnetic field that rotates at the same frequency as the supply.
    • Induction Motor: Stator Winding
      In practice, induction motors have internal diameters that are smooth, instead of having salient poles.
      In this case, each pole covers 180° of the inner circumference of the rotor (pole pitch = 180°).
      Also, instead of a single coil per pole, many coils are lodged in adjacent slots.
      The staggered coils are connected in series to form a phase group.
      Spreading the coil in this manner creates a sinusoidal flux distribution per pole, which improves performance and makes the motor less noisy.
    • INDUCTION MOTOR : SLIP
      The difference between the synchronous speed and rotor speed can be expressed as a percentage of synchronous speed, known as the slip.
      s = (Ns – N)
      Ns
      Where s = slip, Ns = synchronous speed (rpm), N = rotor speed (rpm)
      • At no-load, the slip is nearly zero (<0.1%).
      • At full load, the slip for large motors rarely exceeds 0.5%. For small motors at full load, it rarely exceeds 5%.
      • The slip is 100% for locked rotor.
    • Induction Motor: Frequency induced in the rotor
      The frequency induced in the rotor depends on the slip:
      fR = s f
      fR = frequency of voltage and current in the rotor
      f = frequency of the supply and stator field
      s = slip
    • Induction Motor: Active Power Flow
      Efficiency – by definition, is the ratio of output / input power: η = PL / Pe
      Rotor copper losses: PJr = s Pr
      Mechanical power: Pm = ( 1-s)Pr
      Motor torque: Tm = 30Pr
      πNs
      Where: Pe = active power to stator
      Pr = active power supplied to rotor
      PL = Shaft Power
    • Power Losses
    • Induction Motor: Relationship between Load, Speed and Torque
      At 80% of full speed: highest “pull-out” torque and current drops
      At start: high current and low “pull-up” torque
      At start: high current and low “pull-up” torque
      At full speed: torque and stator current are zero
    • PRESENTED BY:-
      • SOURABH RANJAN
      • VYOM DIXIT
      • VIVEK KUMAR JHA
      • MANISH JADAUN
    • THE END