Currently, there is a lack of technical material in Brazil that could help power engineers in the analysis of the impacts of grid connected wind turbines, and also orientate the grid connection design of wind turbines and wind farms in the national electrical network. The course: “Interconnecting wind farms to the national power system”, held in August 2001 in Recife, Pernambuco, Brazil, identified, through the specialists’ debates, this lack of material.
The “Guidelines on Grid Connection for Wind Farms”, published in 2004, aim to fill this gap by presenting the main methods for designing the connection of wind farms and the tools used for the estimating their impact upon local power quality. The evaluation of wind turbine operation and the analyses of protection to avoid undue operations are also included.
Wind Turbine at Fernando de Noronha, Brazil. © WWEA e.V.
The Guidelines have been developed in the form of a Guide with the intention of helping electrical power system engineers to design the grid connection of wind farms. It also includes descriptions of the main parameters related to the grid connection of wind farms and introduces means of assessing the impact of the wind farms on the power quality of the existing network.
The text is divided into two large sections:
The issues relating to the grid connection of wind farms can be classified in the following way:
These aspects identified above are not always relevant; common sense and experience are relevant in decisions on the main analyses to be performed.
Nonetheless, in general terms, the first four aspects of the above list are necessary for defining the grid connection of a wind Farm. The last three topics are important; however, they are more relevant in the analysis of large-scale wind energy penetration in the regional power systems.
The electrical parameters described in this work are in accordance to: wind turbine generator systems – Part 21: Measurements and assessment of power quality characteristics of grid connected wind turbines (IEC 61400-21) prepared by the International Electrotechnical Commission – IEC.
The IEC 61400-21 specifies the most relevant parameters related to the power quality and grid connection of wind turbines/farms. It also presents methods on how to assess the power quality and to give an estimation of the voltage quality influenced by the wind turbines.
With these parameters, it is possible to estimate the impact of wind turbines on the power quality at the point of common coupling – PCC.
In spite of there being recommendations for the maximum permitted values and limits of the parameters such as flicker and voltage deviations, each project should also be analysed in the light of the local network characteristics and must also respect the local operator’s limits and recommendations for power quality and stability from connection of dispersed generation.
In the guidelines, there are also some annexes included. The first annex presents the different technologies of modern wind turbines and their main characteristics. The second annex presents a description of the basic notions of electrical engineering and energy and transmission. Finally, the last annex presents a schematic diagram of all the phases of the wind farm’s grid connection project.
The main procedures and methods presented in this work apply to wind farms connected to large electrical power systems. The application of this Guide for the installation of wind turbines/farms in isolated power systems is not advised, nor for hybrid power systems where the Wind Power has a considerable participation (typically above 15 %). (Electrical) frequency deviation and stability parameters of synchronous machines (e.g. phase angle stability) of the power systems are not considered in the methodology presented here.
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The guidelines are available at Brazilian Wind Energy Centre. www.eolica.com.br