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WTGS Operation in Power Systems

  • Zbigniew Lubosny
Part of the Power Systems book series (POWSYS)

Abstract

The connection of the wind turbine generator system to parallel operation with the electric power system influences the system state (operating point) and influences the load flow (real and reactive power). At the same time, nodal voltages and power losses themselves change, too. These quantities, defining the electric power system state, can be assumed to be basic but in fact the spectrum of factors influencing the electric power system as a result of the WTGS connection to the grid is much wider. The factors, which are considered in the following sections in a more detailed form, can be generally characterized as follows:
  1. Location of the wind turbine in the electric power system. The way of connecting it to the electric power system (which in general is an AC system) highly influences the impact of the WTGS (or wind farm) on the power quality. As a rule, the impact on power quality at the consumer’s terminal for the WTGS located close to the load (i.e. connected to an MV system) is higher than one connected “electrically” far away (i.e. connected to an HV or EHV system).

     
  2. Voltage variations of amplitude and frequency. The variations mainly result from the wind velocity, but other factors influencing the generator torque play an important part, too. Voltage variations are directly related to real and reactive power variations. The WTGSs equipped with an asynchronous generator with a squirrel-cage rotor or with a resistor connected to the rotor (in woundedrotor machines) are consumers of reactive power, which can cause additional negative problems for the grid.

     

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Reference

  1. 1.
    Of course, improperly developed control systems of WTGSs can decrease the natural — for asynchronous generators — high damping of any electromechanical oscillations.Google Scholar
  2. 2.
    This is a simplification only.Power losses are considered in Sect. 4.8.Google Scholar
  3. 3.
    The power generated by WTGS, i.e. Swtgs =-Pwtgs +j Qwtgs can be also considered as a change of power generated by the wind turbine during its operation.Google Scholar
  4. 4.
    The maximum power change will take place after disconnecting the fully loaded wind turbine from the power system.Google Scholar
  5. 5.
    The above considerations pertain to an extremely simple power network. In general, these considerations can be treated the WTGS to the network, the power losses in the last branch decrease, then the power losses in the remaining branches of the radial network (when all the loads are inductive) also decrease, which can be treated as a positive feature.Google Scholar
  6. 6.
    The above values are relatively small but it is worth remembering that the decreaseGoogle Scholar
  7. 7.
    Power losses in other branches of the system can be similar. Then the total decrease of the power losses will be higher.Google Scholar
  8. 8.
    The characteristic presented in Fig.6.3 and its extrapolation (above 0.9 MW) is used here.Google Scholar
  9. 9.
    Because modern WTGSs operate with power factor less than 0.3, this case is not realistic.Google Scholar
  10. 10.
    the MV power network? Let us consider the overhead MV transmission line with the cross-sectional area of conductor s = 120 mmGoogle Scholar
  11. An increase of the power generated by the WTGS, for example to 2 MW, causes a decrease of the power losses to about 0.5, which means 66 kW generated by the WTGS (for which the decrease of the power losses is obtained) can be achieved for the fully compensated WTGS (QwTGS = 0).Google Scholar
  12. 12.
    As an example of the above considerations, Fig. 4.27 presents the level of power loss decrease as a function of various values of the load and WTGS power factors tançpl, tamp WIGSGoogle Scholar
  13. 13.
    In the case of WTGS analysis, power variations at maximum can be assumed as equal to the wind turbine rated power . Inpractice, when evaluating flicker, power variations within 95% of the maximum variation band corresponding to a standard deviation are evaluated.Google Scholar
  14. 14.
    The standard does not cover voltage changes less frequent than one per day.Google Scholar
  15. 15.
    IEC 61000–21 standard suggests using values when the data are unknown. For high-rated power modern wind turbines the values are too high.Google Scholar
  16. 16.
    These are values typical for present day WTGSs.Google Scholar
  17. 17.
    The variables in Tables 4.8 and 4.9 are defined in the following pages.Google Scholar
  18. 18.
    The wind turbine should be taken into consideration when, or are satified.Google Scholar
  19. 19.
    The impedances in the example are calculated at the MV power system voltage level the level at the point of common coupling of the wind turbine generator system with the power system.Google Scholar
  20. 20.
    Estimation of the error related to neglecting the resistance is presented later in this section.Google Scholar
  21. 21.
    It is worth remembering that the origin of the conditions is mainly related to the power quality problem.Google Scholar

Copyright information

© Springer-Verlag Berlin Heidelberg 2003

Authors and Affiliations

  • Zbigniew Lubosny
    • 1
  1. 1.Dept. Electrical Power SystemsGdansk University of TechnologyGdanskPoland

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