Single phase induction motor

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Transcript of Single phase induction motor

  2. 2. DOUBLE FIELD REVOLVING THEORY AC current flows through the Stator two fields are generated 1.f- forward rotating field 2.b-backward rotating field Pulsating field- due to various magnitudes of field at diff time 2
  3. 3. Resultant flux r = 2 x 2 cos 2 2 = cos 3
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  5. 5. Why 1 phase induction motor is not self starting Rotor = squirrel cage type rotor Alternating flux not required to produce rmf 5
  6. 6. Split phase induction motor Two winding Main winding & auxiliary winding 90 degree phase angle Main winding low resistance and high reactance Aux winding- high resistance and low reactance Switch = motor pickup its 75 % of its rated speed. 6
  7. 7. Working. 7 Is lags by V because low reactance and high resistance Im lags V by very large angle due to high reactance Starting torque proportional to sin Disconnect switch after reach its 75 % of rated speed
  8. 8. Capacitor induction motor 1. Capacitor start motor 2. Permanent capacitor motor 3. Capacitor start capacitor run motor 8
  9. 9. Capacitor start motor 9 Electrolytic capacitor 90degree phase angle Im and Is Im lags V due to high reactance of main winding Due to capacitor Is lead V Im and Is angle 90 High starting torque Apps: Lathes, drilling machiine,fan etc
  10. 10. Capacitor start, capacitor run motor 10
  11. 11. Synchronous motor Machine which converts electrical energy into mechanical energy that rotates at a constant speed equal to synchronous speed Alternator can runs as a synchronous motor if AC -> armature winding DC-> field winding 11
  12. 12. Synchronous motor 12 Parts of 3 phase synchronous motor 1. Laminated stator core with 3 phase armature winding 2. Rotating field structure complete with damper winding and slip rings 3. Two end shields to house the bearings that support the rotor shaft
  13. 13. Principle of operation 13
  14. 14. Starting of synchronous motor 1. Dc motor method 2. Pony motor method 3. Damper winding method 4. Starting as a slip ring induction motor 14
  15. 15. Dc motor method Attaching an external motor to it to bring syn. Machine up to full speed Then syn. Machine be paralleled with its power system as a generator Now starting motor can be detached from machine shaft, then its slow down machine change its mode to be motor Once paralleling completed syn. Motor can be loaded down in an ordinary fashion 15
  16. 16. Pony motor method Since starting motor should overcome inertia of syn. machine without a load & starting motor can have much smaller rating since most syn. motors have brushless excitation systems mounted on their shaft, often these exciters can be used as starting motors For many medium-size to large syn. motors, an external starting motor or starting by using exciter may be the only possible solution , because the connected power system source may not be able to feed the required starting current for amortisseur winding 16
  17. 17. Damper winding method most popular method is to employ amortisseur or damper winding armortisseur windings are special bars laid into notches carved in face of a syn. motors rotor & then shorted out on each end by a large shorting ring pole face shown in next slide To understand what a set of amortisseur windings does in a syn. motor, examine salient 2 pole rotor shown next 17
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  19. 19. Starting as a slip ring induction motor Damper winding method of starting doesnt provide high starting torque To get high starting torque instead of shorting the damper winding designed a three phase star winding , end brought to slip ring External rheostat connected in series with rotor circuit. 19
  20. 20. Effect of change in excitation of synchronous motor 20
  21. 21. V Curves Plot armature current as a function of field current or armature current as a function of excitation voltage.
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  25. 25. Applications Synchronous motors are particularly attractive for low speeds (< 300 r.p.m.) because the power factor can always be adjusted to unity and efficiency is high. Overexcited synchronous motors can be used to improve the power factor of a plant while carrying their rated loads. They are used to improve the voltage regulation of transmission lines. High-power electronic converters generating very low frequencies enable us to run synchronous motors at ultra-low speeds. Thus huge motors in the 10 MW range drive crushers, rotary kilns and variable-speed ball mills. 25