Friday, November 30, 2012

Notes - Chapter 8 Summary

The following notes are taken from Wind Turbine Technology by Ahmad Hemami.
  • P = IV
  • Loads
    • Resistive load is a load due to resistors and not dependent on frequency
    • Capacitors and Inductors exhibit frequency dependent resistance called reactance
      • Capacitive and Inductive loads act in opposite directions in phasor diagram can cancel each other's effect
      • cause phase difference between voltage and current
        • preferred value for the phase angle should be as close to zero as possible
        • power factor is the value of the cosine of phase angle
      • electric motors put both inductive and resistive loads into circuit
      • Capacitors in parallel with motors reduce inductive load
  • Current Leading Voltage, means current waveform reaches max or min value before voltage waveform
  • Power types
    • DC power corresponds to resistive load
    • AC 
      • reactive power
        • corresponds to inductive and capacitive loads
        • power stored in each half cycle and sent back to circuit
      • active power
        • resistive loads in AC
        • real power that converts heat or work
      • apparent power
        • provided to maintain a current I in a circuit of voltage V, generator provides apparent power
  • To connect turbine to a grid
    • equal voltages
    • same frequency
    • synchronized waveforms
    • have similar phase sequences
  • Turbine must not lower the power factor of grid
  • The output from all turbines in a wind farm goes to collector substation
    • raises voltage from turbines to grid
  • Power quality
    • perfect sinusoid in AC circuit
    • no fluctuations in voltage and frequency
    • variations, flickers and spikes all indicate lack of quality
  • Harmonics are low-voltage signals that are multiples of the frequency
  • Islanding when a wind farm becomes isolated from the rest of the network which can lead to a drift and voltage and frequency
  • Control actions
    • control voltage
    • control frequency
    • control available current due to power from wind

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