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Lesson 21: Alternator Capabilities and Mechanical Power Control

Lesson 21: Alternator Capabilities and Mechanical Power Control. ET 332b Ac Motors, Generators and Power Systems. Learning Objectives. After this presentation you will be able to: Explain the power balance in and alternator. Identify the operating region of an alternator’s capability curve.

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Lesson 21: Alternator Capabilities and Mechanical Power Control

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  1. Lesson 21: Alternator Capabilities and Mechanical Power Control ET 332b Ac Motors, Generators and Power Systems Lesson 21_et332b.pptx

  2. Learning Objectives • After this presentation you will be able to: • Explain the power balance in and alternator. • Identify the operating region of an alternator’s capability curve. • Explain how a governor controls mechanical power input to an alternator • Compute governor droop. Lesson 21_et332b.pptx

  3. Power Balance in Alternators Alternator Ratings Alternators rated in kVA or MVA at a specified power factor Typical: 100 kVA, 480 V at 80% power factor Active power supplied by prime mover Reactive power determined by machine excitation Lesson 21_et332b.pptx

  4. Power Balance in Alternators Prime mover sized to handle largest active power load expected plus losses Maximum active power load occurs When Fp =1.0 so Srated= Pout Generally Most alternators supply reactive power also so Fp changes up to approximately 80% leading Prime Mover :Diesel Engine Lesson 21_et332b.pptx

  5. Alternator Capability Curve Reactive power output limited by machine excitation system Operating Range In this diagram + kVARs are delivered - kVARs are absorbed. 80% lead 80% lag Lesson 21_et332b.pptx

  6. Mechanical Power Input Control Governor - electromechanical speed control used to maintain constant speed as machine power load changes Power transfer between parallel alternators is controlled by change in prime-mover power input and speed. If speed remains constant, then torque increases as developed power increases n= constant Mechanical Power In Speed Increasing Torque Electric Power Out Torque Lesson 21_et332b.pptx

  7. Governor Characteristic and Speed Regulation Governor Speed Regulation Where nnl = no-load speed of machine (rpm) nrated = rated machine speed (rpm) frated = rated frequency (Hz) fnl = no-load frequency (Hz) Prime-mover Governor Characteristic – relates speed (frequency) change to alternator power output Lesson 21_et332b.pptx

  8. Governor Characteristic Curve fnl and nnl 61.2 Hz 3672 rpm rated f and n 60 Hz 3600 rpm GD f (Hz) n (rpm) rated P out 0 0 500 kW P (kW) Governor Droop-the slope of the governor control characteristic. Units - Hz\W or Hz\kW or Hz\MW Formula Lesson 21_et332b.pptx

  9. Governor Characteristic Curve Example Example 21-1: Find the speed regulation and the governor droop for the machine that has the curve shown 61.2 Hz 3672 rpm 60 Hz 3600 rpm GD f (Hz) n (rpm) 0 0 500 kW P (kW) Lesson 21_et332b.pptx

  10. End Lesson 21: Alternator Capabilities and Mechanical Power Control ET 332b Ac Motors, Generators and Power Systems Lesson 21_et332b.pptx

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