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# Second Lesson Induction Motor

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### Second Lesson Induction Motor

1. 1. CLIL experience Content and Language Integrated Learning 2 nd Second lesson
2. 2. Induction Motor ( Asyncronous motor ) <ul><li>Why induction motor (IM)? </li></ul><ul><ul><li>– Robust; No brushes. No contacts on rotor shaft </li></ul></ul><ul><ul><li>– High Power/Weight ratio compared to Dc motor </li></ul></ul><ul><ul><li>– Lower Cost/Power </li></ul></ul><ul><ul><li>– Easy to manufacture </li></ul></ul><ul><ul><li>– Almost maintenance-free, except for bearing and other mechanical parts </li></ul></ul><ul><li>Disadvantages </li></ul><ul><ul><li>– Essentially a “fixed-speed” machine </li></ul></ul><ul><ul><li>– Speed is determined by the supply frequency </li></ul></ul><ul><ul><li>– To vary its speed need a variable frequency supply </li></ul></ul>
3. 3. Cutaway of a three-phase induction motor
4. 4. 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.).
5. 5. Three-phase induction motor <ul><li>2P; 50Hz </li></ul><ul><li>n 0 = 60f/2P </li></ul><ul><li>P=coppia polare </li></ul><ul><li>1500 rpm </li></ul>Squirrel cage rotor Stator windings Laminated Stator
6. 6. Construction stator stator
7. 7. 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.
8. 8. Construction stator & rotor
9. 9. Connections <ul><li>Star </li></ul>Delta E E Star connection RL=2 Rph Delta connection RL=2/3 Rph V A + V A + V A + V A +
10. 10. 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)
11. 11. 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.
12. 12. Tesla polyphase induction motors <ul><li>A polyphase induction motor consists of a polyphase winding embedded in a laminated stator and a conductive squirrel cage embedded in a laminated rotor. </li></ul><ul><li>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. </li></ul><ul><li>Unlike single phase motors, polyphase induction motors are self-starting. </li></ul><ul><li>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. </li></ul><ul><li>Three phase motors will run on single phase, if started. </li></ul><ul><li>A static phase converter is three phase motor running on single phase having no shaft load, generating a 3-phase output. </li></ul>
13. 13. Power flow diagram
14. 14. Determination of machine parameters <ul><li>The following tests are usually carried out to determine the parameters of an asyncronous machine. </li></ul><ul><li>Ohmic resistance measurement </li></ul><ul><li>No-Load Test </li></ul><ul><li>Locked-Rotor Test </li></ul><ul><li>The aims of the no–load test are to determine: </li></ul><ul><li>Stator ohmic/copper losses Pcu(s) </li></ul><ul><li>Stator core losses due to hysteresis and eddy current </li></ul><ul><li>Rotational losses due to friction and windage </li></ul><ul><li>Magnetizing reactance. </li></ul><ul><li>The blocked–Rotor Test provide information necessary to determine: </li></ul><ul><li>The winding resistances </li></ul><ul><li>The leakage (dispersion) reactances </li></ul>
15. 15. Translate the following words: <ul><li>No brusches …………………………. </li></ul><ul><li>Rotor shaft ………………………………… </li></ul><ul><li>Squirrel cage rotor……………………… </li></ul><ul><li>Bearing …………………………… </li></ul><ul><li>Stator windings………………………………. </li></ul><ul><li>Delta connection …………………………………. </li></ul><ul><li>Air-gap……………………………….. </li></ul><ul><li>Rotor torque …………………………….. </li></ul><ul><li>Rotor slips …………………………….. </li></ul><ul><li>Terminals ……………………………… </li></ul><ul><li>hysteresis and eddy current ……………………………….. </li></ul><ul><li>winding embedded in a laminated stator …….................. </li></ul><ul><li>......................................................................... </li></ul>
16. 16. Answer to the following questions <ul><li>Which are the advantages of the induction motor? </li></ul><ul><li>Which are the disadvantages? </li></ul><ul><li>What are the main parts of the induction motor? </li></ul><ul><li>How can the connecting terminals of the IM be connected? </li></ul><ul><li>How does the IM work? </li></ul><ul><li>What are the main tests that have to be carried out in order to determine the parameters? </li></ul>
17. 17. Fill the gaps <ul><li>Speed is determined by ………………………………… </li></ul><ul><li>Stator core losses due to ………….…. and ……..…. current </li></ul><ul><li>Rotational losses due to ……..…….. and ……….……. </li></ul><ul><li>Stator core losses due to …………………. and eddy current </li></ul><ul><li>Rotational losses due to friction and ……….……… </li></ul>
18. 18. Complete the power flow diagram