Friday, November 30, 2012

Notes - Chapter 6 Summary

The following notes are taken from Wind Turbine Technology by Ahmad Hemami.
  • Electrical Machines
    • Generator converts mechanical energy to electrical energy
      • works based on Lorentz Force, wire moves inside magnetic field generating voltage
    • Motor converts electrical energy to mechanical energy
      • works based on Lorentz Force, current carrying wire inside magnetic field has a force exerted on it
  • AC and DC machines cannot operate interchangeably
    • DC generator connections must have same voltage
    • AC Generator connections must have same frequency, and synchronized
  • Fluid Analogy
    • Electrical voltage is a measure of the level of electricity
    • Current is a measure of the flow of electricity
    • Loads consume electricity, slow the flow, and or reduce the level
    • Source provides electricity or provides movement/flow
  • AC frequency is measured in Hz
    • North America power is provided at 60 Hz
    • European countries power is provided at 50 Hz
  • Voltages of loads and sources must match
    • Power capacity of source must be greater than the power of loads
    • Frequency of load to source must be the same
    • important for attaining required rpm for motors
  • (PM) Permanent Magnets are not often used, usually electromagnets
  • right hand rule
  • DC motor can have any acceptable rpm, AC motor can have speeds at synchronous or close to synchronous speed, dependent on frequency of electricity provided
  • generators can be connected together
  • Wind Turbines don't generate power when wind speed is below cut-in speed, and does not generate electricity over cut-out speed
    • during strong winds wind turbine can be taken out of service, stopped and brakes applied
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