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Alternator Basic Theory

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  1. 1. Alternator Basic Theory For generating electricity/induction we require Magnet Relative motion between the two Coil N S
  2. 2. Bicycle Dynamo Simplest & most basic form of alternator is bicycle dynamo. Rotor is a Two Pole Permanent Magnet. Voltage ∝ Speed. Voltage ∝ Strength of the magnet. (Can not be adjusted). Alternator Basic Theory Principle
  3. 3. Disadvantages Two Carbon brushes are required to be used. Alternator Basic Theory Brush System Permanent magnet used earlier can be replaced by an electromagnet. Output voltage can be adjusted at the same speed by changing DC supply. Principle
  4. 4. Alternator Basic Theory Brushless Separate excitation System In order to avoid use of brushes we have to use a small alternator named ‘Exciter’. Main Field, Rotating Rectifiers & Exciter Armature are mounted on the same shaft. Excitation supply comes from battery to exciter field instead of main field. In this case the DC power required for excitation is much lesser. Disadvantages This is an open loop system & input to exciter does not vary for variation in output voltage. Principle
  5. 5. Alternator Basic Theory Self Excited & Regulated Shunt System In order to give correction in the exciter input according to the voltage output we have to use AVR. Different Types of AVR’s are being used in DG sets. The one that is being used currently is Basler DECS Principle
  6. 6. Main Armature Main Field Exciter Armature Rotating Rectifiers Exciter Field Surge Suppressor Short Circuit Back Up CT’s Rotor AVR
  7. 7. AVR Booster Unit End
  8. 8. Alternator Basic Theory Stator Winding N S Main Field V AC Back
  9. 9. Alternator Separate Excitation Brush System AC DC Slip Rings Back Stator Winding V Main Field S N + -
  10. 10. Alternator Separate Excitation Brushless System Stator Winding Main FieldN SV AC DC Exciter Rotating Rectifiers Back + -
  11. 11. Alternator Self Excitation Brushless System AC DC Rotating Rectifiers Back ExciterStator Winding Main FieldN SV
  12. 12. SCM CT’S N S Phase Terminals Neutral Terminals AC DC Back