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Second Lesson Induction Motor
 

Second Lesson Induction Motor

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Lezione sul MAT - CLIL

Lezione sul MAT - CLIL

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    Second Lesson Induction Motor Second Lesson Induction Motor Presentation Transcript

    • CLIL experience Content and Language Integrated Learning 2 nd Second lesson
    • Induction Motor ( Asyncronous motor )
      • Why induction motor (IM)?
        • – Robust; No brushes. No contacts on rotor shaft
        • – High Power/Weight ratio compared to Dc motor
        • – Lower Cost/Power
        • – Easy to manufacture
        • – Almost maintenance-free, except for bearing and other mechanical parts
      • Disadvantages
        • – Essentially a “fixed-speed” machine
        • – Speed is determined by the supply frequency
        • – To vary its speed need a variable frequency supply
    • Cutaway of a three-phase induction motor
    • Three-phase induction motor Squirrel cage rotor Stator windings The stator consists of wound 'poles' that carry the supply current to induce a magnetic field that penetrates the rotor. In a very simple motor, there would be a single projecting piece of the stator (a salient pole ) for each pole, with windings around it; in fact, to optimize the distribution of the magnetic field, the windings are distributed in many slots located around the stator, but the magnetic field still has the same number of north-south alternations. The number of 'poles' can vary between motor types but the poles are always in pairs (i.e. 2, 4, 6, etc.).
    • Three-phase induction motor
      • 2P; 50Hz
      • n 0 = 60f/2P
      • P=coppia polare
      • 1500 rpm
      Squirrel cage rotor Stator windings Laminated Stator
    • Construction stator stator
    • Construction squirrel cage rotor The most common rotor is a squirrel-cage rotor. It is made up of bars of either solid copper (most common) or aluminum that span the length of the rotor, and are connected through a ring at each end.
    • Construction stator & rotor
    • Connections
      • Star
      Delta E E Star connection RL=2 Rph Delta connection RL=2/3 Rph V A + V A + V A + V A +
    • How does it work? The relationship between the supply frequency, f , the number of poles, p , and the synchronous speed (speed of rotating field), ns is: where n = Revolutions per minute (rpm) f = AC power frequency (hertz) p = Number of poles per phase (an even number)
    • Rotating Magnetic Field Look at magnetic field component. Blu, yellow and red vector rappresente the fields generated by trhee windings. Black vector is rotating field as result in every moment.
    • Tesla polyphase induction motors
      • A polyphase induction motor consists of a polyphase winding embedded in a laminated stator and a conductive squirrel cage embedded in a laminated rotor.
      • Three phase currents flowing within the stator create a rotating magnetic field which induces a current, and consequent magnetic field in the rotor. Rotor torque is developed as the rotor slips a little behind the rotating stator field.
      • Unlike single phase motors, polyphase induction motors are self-starting.
      • Motor starters minimize loading of the power line while providing a larger starting torque than required during running. Line current reducing starters are only required for large motors.
      • Three phase motors will run on single phase, if started.
      • A static phase converter is three phase motor running on single phase having no shaft load, generating a 3-phase output.
    • Power flow diagram
    • Determination of machine parameters
      • The following tests are usually carried out to determine the parameters of an asyncronous machine.
      • Ohmic resistance measurement
      • No-Load Test
      • Locked-Rotor Test
      • The aims of the no–load test are to determine:
      • Stator ohmic/copper losses Pcu(s)
      • Stator core losses due to hysteresis and eddy current
      • Rotational losses due to friction and windage
      • Magnetizing reactance.
      • The blocked–Rotor Test provide information necessary to determine:
      • The winding resistances
      • The leakage (dispersion) reactances
    • Translate the following words:
      • No brusches ………………………….
      • Rotor shaft …………………………………
      • Squirrel cage rotor………………………
      • Bearing ……………………………
      • Stator windings……………………………….
      • Delta connection ………………………………….
      • Air-gap………………………………..
      • Rotor torque ……………………………..
      • Rotor slips ……………………………..
      • Terminals ………………………………
      • hysteresis and eddy current ………………………………..
      • winding embedded in a laminated stator ……..................
      • .........................................................................
    • Answer to the following questions
      • Which are the advantages of the induction motor?
      • Which are the disadvantages?
      • What are the main parts of the induction motor?
      • How can the connecting terminals of the IM be connected?
      • How does the IM work?
      • What are the main tests that have to be carried out in order to determine the parameters?
    • Fill the gaps
      • Speed is determined by …………………………………
      • Stator core losses due to ………….…. and ……..…. current
      • Rotational losses due to ……..…….. and ……….…….
      • Stator core losses due to …………………. and eddy current
      • Rotational losses due to friction and ……….………
    • Complete the power flow diagram