TECHNICAL AREA Project: Study and simulation systems of wind generation at Sotavento. Energetic efficiency and electromagnetic compatibility

The great penetration of wind energy in our country is forcing us to consider, in this type of installations, determined aspects related to the quality of the generated wave, its influence on the electric network and the behaviour in the continuity of supply when facing determined network contingencies (tension gaps and microcuts).

Sotavento Galicia is aware of it and by utilizing the advantages that its installations offer, as there are different wind technologies on the wind farm, it pretends to make a comparative study of them by real measuring in reference to wave quality and continuity of generation in case of perturbation.

To do this, there have been different meetings with the Electrotecnia and Electric Network Group of the University of Vigo in the year 2004, in order to fix the details of the accomplishing of this project by this institution.

The aims of the above mentioned study include the following aspects in the wind generators at Sotavento:

• Comparative study of the wave quality according to the type of wind generator and at farm level (power fluctuation, inter-harmonics...)
• Simulation of the influence on the electric network (flicker, harmonics, tension variations...) of farms with these different technologies. Comparison with the values obtained during the measuring stage.
• Study of the energetic efficiency of the farm and of the different technologies of wind generators.
• Analysis and simulation of the behaviour of wind generators in case of perturbation in the electric network ( tension gaps, frequency variations...)
• Investigation of the possible effects on the electric network that wind farms, based on some of the existing technologies at Sotavento, would have.
• Valuation of the capacity of the different technologies to adapt themselves to the technical requirements present in the latest standards, especially those referred to in the RD 436/2004.

8 models of wind generators, which can be enclosed in 5 different technologies will be studied. The proposed studies go beyond the individual behaviour of each machine, as we will evaluate by means of simulation, the behaviour of farms composed by each of these technologies, taking as a reference the results obtained from the machines at Sotavento.

The wind generators to be studied are the following:

• ECOTECNIA 44 / 640 KW
• NEG MICON 900 KW
• IZAR 600 KW
• MADE 660 KW
• MADE 1300 KW : Asynchronous two speeds and fixed shovel move
• IZAR 1300 KW : Asynchronous two speeds and variable shovel move (active aerodynamic loss)
• GAMESA G47 / 660 KW : Asynchronous doubly fed generator and variable shovel move
• MADE 800 KW Synchronous generator and variable shovel move

The proposed study has been divided into the following phases, which will be commented now:

PHASE 0 : Previous documentation

PHASE A: Measuring campaign and wave quality

PHASE B : Study of the energetical efficiency

PHASE C : Simulation of the behaviour in case of electric perturbation

PHASE D: Simulation of the impact on the electric network

• Previous documentation
  
  The previous step before the study is the knowledge of the present configuration of Sotavento farm, being the most relevant facts:
  • Electric and mechanic characteristics of the wind generators
  • Characteristics of the transformers and underground lines as far as the sub-station
  • Characteristics of the sub-station
  • Characteristics of the evacuation lines of electric energy
  • As for its behaviour, it is essential to know the basic electric parameters of the performance of the installations, not only on the level of the machine but also of the farm, in different wind conditions, namely:
  • Historical parameters of the wind conditions on the level of farm and machine
  • Active and reactive power on the level of farm and machine
  • Behaviour of tension at the different points of the installations
  
  All this documentation has been offered to the University of Vigo by Sotavento.
• PHASE A : Measuring campaign and wave quality
  
  The first phase consists in the accomplishing of a measuring campaign directed towards aspects of details of the wave and supply quality , on the level of the farm as well as on the level of the machine. The aim of this measuring campaign is divided according to the special characteristics of the measurings to be carried out. On the one hand there is the study of the classical parameters which Spanish standards refer to ( UNE-EN 50160:2001: Characteristics of the tension supplied by the general distribution network), which will be done by a commercial equipment. This measuring includes aspects like:
  • Tension variations (slow and fast ones )
  • Valuation of harmonic distortion
  • Unbalanced condition in the feeding tension
  • Tension impulses
  
  The influence of the wind generators on the electric network goes beyond the classical aspects of the wave quality such as the ones recollected in the section above, making it necessary to measure more variables. These are some of these points:
  • The aleatory nature of wind causes the power injected into the network to follow a similar pattern. Therefore it will be necessary to superpose effects such as the shadow of the tower, which cause low frequency oscilations which are superposed to the mentioned aleatory behaviour.
  • The influence of the electronic power equipments which present wind generators are equipped with are not only a source of harmonics but also of inter-harmonics, even at frequencies which are higher then the ones collected in the present standard. It is therefore necessary to have an equipment capable of detecting harmonics of high frequency, which are usually excluded from the specifications of most equipments.
  • The doubly fed wind generators or the ones connected to network by AC/AC link make a show of control of the power put into the network. Thus, the fluctuations of the power injected into the electric network are diminished considerably, as well as the efforts that the mechanical elements bear in case of wind variations. Nevertheless it is necessary to record the power at the exit of the wind generator, as in this case the ability of obtaining the purposes mentioned above depends to a great extent on the adequate choice of the algorhythms of control employed. All the mentioned aspects must be considered when we study the influence of an increasing wind energy on the electrid network
  
  In this case, the measuring to be carried out has to be based by a specific registering that allows a show of high frequency and long endurance of the wave forms at the exit of the wind generator. This project therefore implies the use of equipments developed at the department of Electric Engineering that cover these aspects. This measuring campaign includes only those wind generators considered representative for a determined technology. The measuring period for each of the wind generators has to be long enough to get representative situations of their performance.
• PHASE B : Study of energetical efficiency
  
  One of the basic aspects of every energy - producing system is the evaluation of the energetical efficiency, that is to say, the grade of exploitation of the available energetical resources. The first aspect to evaluate will be the one related to energy loss at the different points related with its evacuation, namely: transformers, conductors, lines... At this point we will evaluate the effects of the power converters in those technologies which include them. This last aspect will be of great importance due to the increasing market penetration of doubly fed or synchronous wind generators with AC/AC link. Another aspect related to efficiency will be to compare the production of the different technologies under similar wind conditions. In this part of the study it is essential to have all information of available historical values at Sotavento, especially the fact of their synchronization, both of the power injected into the network and of the different wind measuring.
• PHASE C: Simulation of the behaviour in case of electric perturbation
  
  The increasing penetration of wind energy into the electric network makes it necessary to know its behaviour in case of its usual perturbances. Furthermore there is an increasing demand that wind farms should guarantee a certain immunity in order to contribute to the maintenance of the network stability. A fact that is emphasized by both European and national standard tendencies. The behaviour in these perturbances, especially those related to tension variations, is closely related to the employed technology. Thus, in case of tension diminution, an asynchronous wind generator reacts with intensities similar to the direct starting of an engine, whereas, for a doubly fed system, the most probable reaction is its disconnection, so as to protect the electronic from power. This project will study the simulation that allows not only to establish which is the behaviour of the machines at Sotavento, but also to predict the behaviour of a farm with machines of identical technology, as it occurs on other farms.
  
  In this phase we will evaluate the possibilties of the analyzed technologies to adapt themselves to the new technical requirements made by the regulating organisms, as the ones referred to in the RD 436/2004. Requirements, which can be extended or complemented by other standards that may appear during the development of the project. The study of these requirements should lead to the obtention of the present capacities of the new technologies, such as they are proposed for the state of connection to the electric network (protections, reactive compensation...) Moreover, possible control strategies to improve the performance of wind generators will be studied.
• PHASE D : Simulation of the impact on the electric network
  
  A complementary aspect to the ones in the last section is the impact that the different technologies of wind generators have on the electric network. In order to look for a generalization of conclusions, it is necessary to simulate farms with different technologies exclusively and under different conditions : both wind and electric ones, by using the obtained values from the study at Sotavento farm. As for the electric conditions it is of special importance to study the different characteristics of the electric network the farm is connected to. In this case we study the influence as for the characteristics of the connecting point according to the standards in force.
  
  Both phases mentioned above (Phase C and Phase D) require an important simulation effort of the performance of the different technologies of wind generators. This is associated to a modelling for which it is necessary to recollect both electrical and mechanical values from the different wind generators, values which are available at Sotavento wind farm.

In November 2004, the first phase of measuring began by installing a TOPAS analyzer and our own one (U.Vigo) to show high frequency and long duration of the generated wave in wind generator number six (6) by Made. In addition, an anemometer was installed in the axle box accomplishing with the period of measuring in that wind generator, so as to record the immediate values from the variables of wind incidence and to see its influence on the quality of the generated electric energy. It is significant that the wind measuring of the anemometer, which each wind generator is equipped with, is only stored in ten-minute-average, which means that they are not useful fot the dynamic analysis pretended with this project.

This period of measuring will be extended from one wind generator to another until all 8 of them are completed, once all kinds of winds and network conditions to be evaluated have occurred.

The pursuit of the project is meant to be executed during the year 2005, without taking into account possible conditionings by new technical standards which may make us introduce new fields or concepts to study, thus lengthening the period of the project.