Electrical Machines LSEGG216A 9080V
Synchronous Motors     Week 14
Introduction• State the principles of operation of a synchronous motor.• Identify the main parts of a synchronous  alterna...
Motor Types3 Phase               1 Phase             • Reluctance             • Hysteresis             • Permanent Magnet ...
Characteristics•   High operating efficiency•   Smooth constant starting & accelerating torque•   Versatile power factor c...
StatorSame as an induction motor’s stator      Some books may call this the Armature
Rotor• Wound simular to a wound rotor induction motor• When operating DC voltage is placed across this  coil to produce an...
Motor Speed• Magnetic force is obtained from an external source   (In an induction machine rotor’s magnetism is induced fr...
Torque AngleNo Load
Torque Angle                Torque Angle                 Dependant on:                 • Load torque                 • Exc...
Torque Angle      If the load Torque fluctuates                    Or              Changes rapidly• The magnetic “Spring” ...
Amortisseur Windings  Similar to the squirrel cage found in induction machines          Also Known as “Damper “ windings• ...
StartingZero starting Torque   Number of methods:   • Pony Motor   • Low Frequency
Pony Motor                   StartingAn auxiliary smaller motor is used to spin the main motorup to or near Synchronous sp...
Starting Low Frequency• The rotor’s excitation windings are short circuited• Act like a wound rotor induction motor• Suppl...
Motor Uses• Can be used as a standard motor similar to an  induction motor     As an induction machine is cheaper it     i...
Power Factor Correction                               And the Power Factor ImprovesThe stator current will drop           ...
Power Factor Correction                                    And the Power Factor detieriatesThe stator current will increas...
Power Factor Correction                 Curve A = Stator Current         Curve B = Power FactorThese curves are known as  ...
Power Factor Correction These curves are only applicable for a           set load torqueA different load will produce a di...
Power Factor CorrectionIf the bride is over excited she will                  Unity    lead you to the marriage bed      L...
Power Factor CorrectionA motor has full load of 100A and an excitation currentof 8A what will be:• The stator current?• PF...
Power Factor Correction           PF = 0.9 Lagging                   Stator Current             38% X 100A = 38A
Example• A load of 450 kVA operates at a power factor of 0.65  lagging.• An additional synchronous motor is added having a...
Example• A load of 450 kVA operates at a power factor of 0.65  lagging.• An additional synchronous motor is added having a...
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  1. 1. Electrical Machines LSEGG216A 9080V
  2. 2. Synchronous Motors Week 14
  3. 3. Introduction• State the principles of operation of a synchronous motor.• Identify the main parts of a synchronous alternator/motor.• List the methods used to provide the excitation of a synchronous alternator/motor.• List the starting methods of synchronous
  4. 4. Motor Types3 Phase 1 Phase • Reluctance • Hysteresis • Permanent Magnet • Inductor
  5. 5. Characteristics• High operating efficiency• Smooth constant starting & accelerating torque• Versatile power factor control• Constant speed• Considerably more expensive than induction motors• Zero starting torque
  6. 6. StatorSame as an induction motor’s stator Some books may call this the Armature
  7. 7. Rotor• Wound simular to a wound rotor induction motor• When operating DC voltage is placed across this coil to produce an electromagnet Some books may call this the Field Windings
  8. 8. Motor Speed• Magnetic force is obtained from an external source (In an induction machine rotor’s magnetism is induced from the stator)• Rotor poles lock onto the RMF Called “Excitation”• Rotor operates at synchronous speed 120f N sync = = Nrotor P
  9. 9. Torque AngleNo Load
  10. 10. Torque Angle Torque Angle Dependant on: • Load torque • Excitation • The magnetic link between the stator & the rotor can be thought of as a connecting spring. • The excitation can be used to strengthen the springFull Load
  11. 11. Torque Angle If the load Torque fluctuates Or Changes rapidly• The magnetic “Spring” will bounce• Causing large fluctuations in supply current• Amortisseur windings are added to the rotor• Also known as hunting
  12. 12. Amortisseur Windings Similar to the squirrel cage found in induction machines Also Known as “Damper “ windings• When relative movement between the stator and the rotor poles occurs• Voltage is induced into these windings.• Subsequent induced magnetic field tends to slow movement and act like a “shock absorber”• Can be used to aid starting in a simular way to that of the squirrel cage conductors
  13. 13. StartingZero starting Torque Number of methods: • Pony Motor • Low Frequency
  14. 14. Pony Motor StartingAn auxiliary smaller motor is used to spin the main motorup to or near Synchronous speed
  15. 15. Starting Low Frequency• The rotor’s excitation windings are short circuited• Act like a wound rotor induction motor• Supply is applied at reduced voltage & frequency• Rotor builds up speed• Excitation is then applied to windings and rotor locks in Tumit 3 and the Shoalhaven hydro schemes use this system
  16. 16. Motor Uses• Can be used as a standard motor similar to an induction motor As an induction machine is cheaper it is seldom used just as a motor• Main use as a power factor correction device Sometimes called a rotary capacitor
  17. 17. Power Factor Correction And the Power Factor ImprovesThe stator current will drop As we increase the excitation
  18. 18. Power Factor Correction And the Power Factor detieriatesThe stator current will increase If we continue to increase the excitation
  19. 19. Power Factor Correction Curve A = Stator Current Curve B = Power FactorThese curves are known as “Vee Curves”
  20. 20. Power Factor Correction These curves are only applicable for a set load torqueA different load will produce a different set of curves
  21. 21. Power Factor CorrectionIf the bride is over excited she will Unity lead you to the marriage bed Lagging Leading Under Excited Over Excited
  22. 22. Power Factor CorrectionA motor has full load of 100A and an excitation currentof 8A what will be:• The stator current?• PF of the motor?
  23. 23. Power Factor Correction PF = 0.9 Lagging Stator Current 38% X 100A = 38A
  24. 24. Example• A load of 450 kVA operates at a power factor of 0.65 lagging.• An additional synchronous motor is added having an input power of 90 kW and a maximum power factor of 0.85 leading.• Determine reactive power and the overall power factor 450 x cos 49.5°= 292.5kW 49.5° 450 x sin 49.5°= 450kVA 342kVar
  25. 25. Example• A load of 450 kVA operates at a power factor of 0.65 lagging.• An additional synchronous motor is added having an input power of 90 kW and a maximum power factor of 0.85 leading.• Determine reactive power and the overall power factor tan-1 x 286/382.5 = 36.8° 292.5 + 90 = 382.5kW PF = 0.8 Lag 90 x tan 31.8° = 292.5kW 31.8° 55.8kVar 342 – 55.8 = 286kVar 49.5° 90kW 450kVA 342kVar

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