EVALUATING THE IMPACTS OF WIND FARMS ON POWER SYSTEM OPERATION GÜÇ SİSTEMİ ÜZERİNDE RÜZGAR SANTRALLERİNİN ETKİLERİNİN DEĞERLENDİRİLMESİ

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1 Journal of Naval Science and Enineerin 2010, Vol. 6, No.2, pp EVALUATING THE IMPACTS OF WIND FARMS ON POWER SYSTEM OPERATION Ph.D.Özür Salih MUTLU, Lt. Ministry of National Defence, İzmir Construction & Estate Reional Authority Konak, İzmir, Turkey. Abstract This paper presents evaluation methods to study the impacts of wind enery conversion systems on power system operation Detailed information is iven about the parameters which has essential sinificance in further operation of the wind farm in the power system and their influence on each other. The objective of this study is to determine the methodoloy for studies about power system- wind enery interconnections. GÜÇ SİSTEMİ ÜZERİNDE RÜZGAR SANTRALLERİNİN ETKİLERİNİN DEĞERLENDİRİLMESİ Özetçe Bu makalede rüzar enerjisi dönüşüm sistemlerinin, üç sistemi üzerindeki etkilerinin değerlendirme metotları üzerinde durulmaktadır. Güç sistemindeki rüzar çiftliğinin daha da iyi çalştırılması üzerindeki hayati öneme haiz parametreleri ve birbirlerine olan etkileri hakkında detaylı bili sunulmaktadır. Bu çalışmanın amacı üç sistemi - rüzar enerjisi bağlantıları hakkındaki çalışmalar için metodolojiyi belirlemektir. Keywords: Wind Enery Conversion Systems, Power System, Grid Codes. Anahtar Kelimeler: Rüzar enerjisi dönüşüm sistemleri, üç sistemi, Grid kodları. 166

2 Özür Salih MUTLU 1. INTRODUCTION Sources of enery for the production of electricity are many and varied. Wind power is bein used as a clean and safe enery resource for electricity eneration for nearly a hundred years. The early established wind farms had relatively smaller power rated enerators with respect to conventional power stations. But nowadays, lare power rated offshore wind farms are bein installed to control power system data instead of conventional ones. The wind farms have different impacts and functions on the performance of the rid than conventional power plants, because of variation of wind speed in time. Doubly fed and squirrel cae induction enerators are widely used in wind enery conversion systems. These enerators are usually rid-coupled via power electronic converters in order to control the voltae, frequency and power flow durin the variation of wind speed. As a consequence, wind turbines affect the dynamic behaviour of the power system in a way that miht be different from hydrolic or steam turbines[1]. The increasin percentae of wind enery conversion systems in electrical power production has amplified the need to address rid interation concerns. Power system operators or transmission system operators(tso) need simulation tools and scientific practices before wind power-power system interation to uarantee reliable operation of the system with wind power. Power system reliability consists of system security and adequacy. In order to assure reliable operation, TSO demanded hih short-circuit power capability at wind farm connection buses, like at least 20 times reater than the wind farm nominal power. These reularities impede further penetration of wind power because of power system operational precautions. 167

3 Evaluatin the Impacts of Wind Farms on Power System Operation There are uidelines, recommendations and requirements which deal with the technical data needed to assess the impact of wind turbines on power system and discuss the requirements to be met by networks to which wind turbines are to be connected. Research roups are founded by overments, universities, manufacturers, wind farm owners and power system operators to develop rid codes for wind farm-rid interation. In the last years the trend has moved from installations includin few wind turbines to plannin of lare wind farms with capacity over hundreds of MW. Fiure 1.1 shows impacts of wind power on power systems, divided in different time scales and width of area relevant for the studies. Fiure 1.1 Impacts of wind power on power systems, divided in different time scales and width of area relevant for the studies[2]. At the time of developin the standard IEC : Measurement and assessment of power quality characteristics of rid connected wind turbines, the wind turbines were mainly connected to the distribution rid, and the basic concern was their possible impact on the voltae quality and not on power system operation. This has chaned with the development of 168

4 Özür Salih MUTLU lare power rated wind farms that may form a sinificant part of the power system. In consequence, today s wind turbines are able to control the power (active and reactive) delivered both in transient and steady state, they can cope with power ramp requirements and they have low voltae ride throuh(lvrt) capability. They may even contribute to the primary frequency control, but then on the cost of dissipatin enery. 2. POWER SYSTEM, DISTRIBUTED GENERATION, WECS CONNECTION ISSUES AND GRID CODES The interconnected power system is often referred to as the larest and most complex machine ever built by humankind. This may be hyperbole, but it does emphasize an inherent truth: there is a complex interdependency between different parts of the system. The aim of this complex machine is to produce and deliver to the consumers electric enery of defined parameters, where the main quantities describin the electric enery are the voltae and frequency. It has to be operated to ensure a continuous supply at the consumers terminals. The voltae should be a sinusoidal wave with nominal amplitude and a frequency[3,4]. The power system can be separated into three major subsystems: eneration system, transmission system, and distribution system. The vast majority of eneration is carried out by synchronous enerators. The source of the mechanical power, commonly known as the prime mover, are hydraulic turbines, steam turbines or alternate sources. Hydraulic turbines operate with low speed and their enerators have salient type rotor with many poles. Steam turbines operate relatively hih speeds and coupled with cylindrical rotors. The purpose of the electric transmission system is the optimal hih voltae interconnection of the electric enery producin power plants or eneratin stations with the loads. A three-phase AC system is used for most transmission lines. The distribution system is the part of electric power system between the bulk power source and the consumers service switches. It operates in low and medium voltae levels and includes subtransmission systems; distribution substations; distribution lines; and appropriate protective and control equipment[5]. 169

5 Evaluatin the Impacts of Wind Farms on Power System Operation 2.2 Power System Connection Issues of Wind Enery Conversion Systems The wind farms have different impacts and functions on the performance of the rid than conventional power plants, because of variation of wind speed in time. Many studies have been performed on rid connected wind farms and related power system issues. Different techniques and models have been used for determinin problems; the impacts of wind farms on technical and operational characteristics of power systems and technical requirements for wind farm-rid connections were analyzed. The doubly fed and squirrel cae induction enerators are widely used in wind enery conversion systems. These enerators are usually rid-coupled via power electronic converters in order to control the voltae, frequency and power flow durin the variation of wind speed. As a consequence, wind turbines affect the dynamic behaviour of the power system in a way that miht be different from hydrolic or steam turbines. The factors that cause these affects will be analyzed in this section Location of the Wind Farm in the Electric Power System The point of common couplin(pcc) of wind farms and the power system, includin the parameters of the power system, the parameters of wind farm and the structure of the rid are of essential sinificance in further operation of the wind farm in the power system and their influence on each other. The size and the location of the considered wind farm and the parameters of the rid in that reion hihly influences the appropriate PCC. Wind farms must be located in the reions that have favourable wind conditions. These reions can be shorelines and islands where the power network in these reions can be named as weakly developed. A part of power rid can be named as weak when it is electrically far away from the infinite bus of the interconnected power system. The weak rids have lower short circuit power than stron rids relatively. The short circuit power level in a iven point in the electrical network represents the system strenth. 170

6 Özür Salih MUTLU Fiure 2.1(a) illustrates an example of one line diaram of wind farm connection to a rid and (b) shows phasor diaram. (a) (b) Fiure 2.1 (a) One line diaram of wind farm connection to a rid, (b) Phasor diaram Wind farm is connected to the network with equivalent short circuit impedance, Z k. The network voltae at the assumed infinite busbar and the voltae at the PCC are U s and U, respectively. The output power and reactive power of the wind farm are P and Q, which corresponds to a current I. I S U * P U jq (2.1) 171

7 Evaluatin the Impacts of Wind Farms on Power System Operation The voltae difference, ΔU, between the infinite system and the PCC is iven by U U s U Z. I Rk P X kq U U k ( R k P jq jx k )( ) U P X k Q Rk j U U p j U q (2.2) (2.3) The short circuit impedance, the real and reactive power output of the wind farm determines the voltae difference. The variations of the enerated power will result in the variations of the voltae at PCC. When the impedance Z k is small, then the rid can be named as stron and when Z k is lare, then the rid can be named as weak. Since stron or weak are relative concepts, for a iven electrical wind power capacity P, the ratio, R sc Ssc P U s Z. P k 2 (2.4) stated as the measure of the strenth, where S sc is short circuit power. The rid may be considered as stron with respect to the wind farm installation if R SC is above 20. It is obvious from (2.4) that for lare wind farm-rid connections, the PCC voltae level have to be as hih as possible to limit voltae variations[6]. Local wind farms are the most typical forms of distributed eneration. Althouh distribution systems are planned for unidirectional power flow from transmission system to the consumers, the amount of distributed eneration located at the distribution level of electrical networks is showin rapid rowth worldwide. Issues such as new enery sources, efficiency of local enery production and modularity of small production units are promotin this rowth. On the other hand, lare power rated wind farms connected directly to the transmission level do not actually meet the 172

8 Özür Salih MUTLU definition of distributed eneration since those are named as the members of eneration system[7]. In case of wind farm installations on islands and offshore platforms the underwater transmission of power to the mainland power system has to be performed by cable. For lon distance transmission, the transmission capacity of cables may be mainly occupied by the produced reactive power, therefore ac transmission will meet difficulties. In this situation hih voltae direct current (HVDC) transmission techniques may be used. Fiure 2.2 shows different wind farm connections to rid. Fiure 2.2 Different wind farm connections to a rid Impacts of Wind Farms on Power Quality The currently existin power quality standard for wind turbines, issued by the International Electrotechnical Commission (IEC), IEC : Measurement and assessment of power quality characteristics of rid connected wind turbines, defined the parameters that are characteristic of the wind turbine behavior in terms of the quality of power, and also 173

9 Evaluatin the Impacts of Wind Farms on Power System Operation provides recommendations to carry out measurements and assess the power quality characteristics of rid connected wind turbines. Althouh the standard mainly describes measurement methods for characterizin sinle wind turbines, there are methodoloies and models developed that enable, for well pre-defined conditions, to extrapolate the sinle turbine unit parameters to the typical quality characteristics of wind farms. Since voltae variation and flicker are caused by power flow chanes in the rid, operation of wind farms may affect the voltae in the connected network. On the local level, voltae variations are the main problem associated with wind power. This can be the limitin factor on the amount of wind power which can be installed. If necessary, the appropriate methods should be taken to ensure that the wind turbine installation does not brin the manitude of the voltae at PCC outside the required limits System Stability Stability analysis of the power system is a lare area that covers many different topics. A formal definition of power system stability is provided by IEEE/CIGRE Joint Task Force on Stability Terms and Definitions as the ability of an electric power system, for a iven initial operatin condition, to reain a state of operatin equilibrium after bein subjected to a physical disturbance, with most system variables bounded so that practically the entire system remains intact. Trippin of transmission lines, loss of production capacity and short circuits are named as power system faults which are related to system stability. These failures affects the balance of both real and reactive power and chane the power flow. Thouh the capacity of the operatin enerators may be adequate, lare voltae drops may occur suddenly. The unbalance and re-distribution of real and reactive power in the network may force the voltae to vary beyond the boundary of stability. A period of low voltae may occur and possibly be followed by a complete loss of power. Many of power system faults are cleared by the relay protection of the transmission system either by disconnection or by disconnection and fast reclosure. In all 174

10 Özür Salih MUTLU the situations the result is a short period with low or no voltae followed by a period when the voltae returns. A wind farm nearby will see this event. In early days of the development of wind enery only a few wind turbines, named earlier as local wind turbines, were connected to the rid. In this situation, when a fault somewhere in the lines caused the voltae at the PCC of local wind turbines to drop, local wind turbines were simply disconnected from the rid and were reconnected when the fault was cleared and the voltae returned to normal. Because the penetration of wind power in the early days was low, the sudden disconnection of a wind turbine or even a wind farm from the rid did not cause a sinificant impact on the stability of the power system. With the increasin penetration of wind enery, the contribution of power enerated by a wind farm can be sinificant. If a lare power rated wind farm is suddenly disconnected at full eneration, the system will loss further production capability. Unless the remainin operatin power plants have enouh spinnin reserve, to replace the loss within very short time, a lare frequency and voltae drop will occur and possibly followed by a blackout. Therefore, the new eneration of wind turbines is required to be able to LVRT durin disturbances and faults to avoid total disconnection from the rid. In order to keep system stability, it is necessary to ensure that the wind turbine restores normal operation in an appropriate way and within appropriate time. This could have different focuses in different types of wind turbine technoloies, and may include supportin the system voltae with reactive power compensation devices, such as interface power electronics, SVC, STATCOM and keepin the enerator at appropriate speed by reulatin the power etc[6]. 2.3 Grid Codes for Wind Enery Conversion Systems Modern MW wind turbines currently replace a lare number of small wind turbines and there is a sinificant attention to offshore wind farms, mainly because of hiher averae wind speed and no space limitations. Lare power rated wind farms are started to operate in superior power systems and more lare power rated wind farms are in construction or in the 175

11 Evaluatin the Impacts of Wind Farms on Power System Operation plannin stae all over the world. However, in order to achieve objectives as continuity and security of the supply, a hih level of wind power into electrical network posses new challenes as well as new approaches in operation of the power system. Therefore countries started to issue dedicated rid codes for connectin the wind turbines/farms to the electrical network addressed to transmission and/or distributed system. These requirements have focus on power controllability, power quality, LVRT capability and rid support durin network disturbances. Grid code reulations often contain costly and demandin requirements for wind farm operators due to the increase in share of wind farms in power production. Lare wind farms connected at the transmission level have to act as a conventional power plant and participate in primary (local) and secondary(system level) frequency/power control. The current status of rid codes in Turkey is presented in [8] and discussed with followin headlines; Low Voltae Ride Throuh(LVRT) Capability, Reactive Power and Voltae Variations, Frequency Rane, Control of Frequency and Active Power, Sinals, Control and Communications. 3. TECHNICAL FEATURES OF WIND POWER PLANTS The wind turbine enerator system operation is permanently determined by the speed and variations of the wind. The followin four basic operatin states can be distinuished: Standstill of the turbine as a result of the wind speed value fallin below the cut-in wind speed v < v cut-in. Partial load operation with maximum enery extraction from the wind, when the wind speed v is within the rane v cut-in v v n, where v n is the rated wind speed. Wind turbine enerator enerates the rated power at the rated wind speed. Full load operation with constant and rated load when the wind speed is hiher than the rated wind speed v n < v v cut-out and simultaneously lower than the maxiumum one. The cut-out wind speed is 176

12 Özür Salih MUTLU usually v cut-out = 25 m/s. Standstill of the turbine because of too hih wind speed v > v cut-out. These operatin states of the wind turbine are usually presented in the form of the power versus wind speed characteristics of the wind turbine. An example of such a characteristic is shown in Fiure 3.1[4]. The dashed line shows the power in the wind and the continuous line shows the power that the wind turbine can convert to the rid. The vertical axis is the ratio of power enerated P G, to the rated power of the wind turbine P n, and the horizontal axis is the wind speed. Fiure 3.1 Power versus wind speed characteristics of a wind turbine. The power of an air mass that flows at speed v(m/s) throuh an area A can be calculated as follows; 1 3 Power in wind(watts) Av (3.1) 2 177

13 Evaluatin the Impacts of Wind Farms on Power System Operation where, ρ is air density in (k/m 3 ). As seen from (3.1) the power in wind is proportional to the air density, the interceptin area(the area of the wind turbine rotor), and the speed to the third power. The power in wind is the total avaliable enery per unit of time. The power in the wind is converted into mechanical-rotational enery of the wind turbine rotor, which results in a reduced speed in the air mass. Capacity factor, iven in (3.2), of a wind farm is relatively lower; 0,25 for low wind speed locations and 0,40 for hih wind speed locations, than conventional power plants. This implies that in order to obtain the same enery production from a conventional power plant and a wind farm, the installed wind farm capacity must be sinificantly larer than the capacity of the conventional power plant[9]. W ( Annual) Cap. Fac. (3.2).8760 P rated where W(Annual) is the sum of the enery produced by the wind farm for a year in (kw/h). 4. MODELLING AND SIMULATION OF WIND FARMS FOR POWER SYSTEM STUDIES Wind turbine enerators, control systems, power factor correction equipments, transformers, wind farm substation, inner loops for connections and transmission lines can be listed as wind farm sections that shold be modelled for power system studies. The models of the rid and the wind farms have to comply with common requirements of the simulation platforms for ettin accurate results. Computer simulation makes it possible to investiate a multitude of properties in desin and application phase. The correctness of a computer simulation depends on the quality of the built-in models and of the applied data. In order to investiate the effects 178

14 Özür Salih MUTLU of wind enery conversion systems on power system and vice versa; it is necessary to develop accurate models of both systems. When the aim is to investiate rid interation of wind turbines, there are three main interests; steady-state voltae level influence, rapid voltae fluctuations(flicker), and response to rid disturbances. 4.1 Steady-State Voltae The voltae difference between the infinite system and the PCC of the wind farm is iven by (2.2) and (2.3). The voltae difference, ΔU, is related to the short circuit impedance, the real and reactive power output of the wind farm. Infinite system (or busbar) represents interconnected rid, where voltae never chanes from the desined value. So it is an important decision for us that at which feeder in the model voltae never chanes. Power system components between the infinite system and the PCC of the wind farm; transmission lines/cables and transformers, have to be modelled exactly in the simulation. Otherwise the effect of system X/R ratio(ratio between rid reactance and rid resistance) on wind farm terminal voltae can not be modelled correctly. The first term and real part of the voltae difference ΔU, which is iven in (2.3), is ΔU p : U p R k P X U k Q (4.1) The effect of system X/R ratio on the voltae difference can be examined by monitorin the manitudes of the two terms on the nominator of ΔU p. No-load power factor correction, which means that the wind-farm reactive power consumption will be zero at no load, must be set for a clear examination. With a relatively low X/R value, the first term of ΔU p predominates, and voltae rises over the loadin rane. When X/R value is 179

15 Evaluatin the Impacts of Wind Farms on Power System Operation relatively hih, the second term of ΔU p, which oes neative with increasin reactive consumption, predominates at hiher active power eneration. 4.2 Flicker There are two types of flicker emissions associated with wind turbines. In order to predict the rapid power fluctuations from fixed-speed turbines, there is a need to represent the wind field arrivin at the turbine, since the flicker emission durin continuous operation is mainly caused by fluctuations in the output power due to wind speed variations, the wind radient and the tower shadow effect. Switchin operations like start, stop and switchin between enerators or enerator windins, also produce flicker. When the limits of the flicker emission are iven, the maximum allowable number of switchin operations in a specified period can be examined by appropriate models in simulations. Model of a sinle wind enery conversion system must take into consideration soft starter, capacitor roup, pitch control, and wind speed variations. 4.3 Grid Disturbances When the response to rid disturbances is of interest, it is mainly the enerator description that affects the response of the turbine. For assessin the stability marin of the wind farm-rid interation, small-sinal dynamic model of the system must be formed in simulation platforms. Wind speed, pitch control and input torque to enerator are usually assumed constant for transient analysis, since mechanical system time steps are too larer than time constant of electrical system. The worst case scenario must be defined, like maximum wind speed and minimum load conditions. 180

16 Özür Salih MUTLU 4.4 Areated Modelin Representin a wind farm, which consists of many relatively small power rated wind turbines, by one or few lare power rated wind turbines by addition of power ratins of the small power rated wind turbines, can be stated as areated modelin. When the effect of a wind farm on power systems is studied, the behavior of the wind farm at the PCC to power system can be represented by an equivalent model derived from the areation of wind turbines into an equivalent wind turbine, instead of the complete model includin the modellin of all the wind turbines. The structure of an areated wind farm model should be such, that maximum user friendliness is achieved while keepin the results as close to reality as possible[10]. The advantae of an areated model is that it eliminates the need to develop a detailed model of a wind farm with tens or hundreds of wind turbines and their interconnections, and to specify the wind speed at each individual wind turbine within the wind farm. Groups of wind turbines with similar winds can be areated by an equivalent model which results representin a lare power rated wind farm by a few lare wind turbines. An example of such representation for a fictitious wind farm is shown in Fiure 6.1. There are three sections with identical wind turbines facin similar wind speeds. Power ratins of representative wind turbines are accordin to the addition of the wind turbines inside the sections;1, 2, and, 3. The effective value of the wind is reduced per row of the wind turbines because of shadowin and eneration of turbulence in the wind farm. Areatin just the electrical system of variable speed wind turbines, includin electrical controls and the electrical part of the enerators and to model the mechanical system of each individual turbine and enerator is another option for modellin. This model maintains the nonlinear characteristics, but it reduces calculation speed considerable compared to a fully detailed, non-areated wind farm model[11]. 181

17 Evaluatin the Impacts of Wind Farms on Power System Operation Fiure 6.1 Areated modellin of a wind farm by a few lare wind turbines. 4.5 Validation Procedure of Wind Farm Models Models of rid connected wind farms can be validated with field measurement results to represent correct prediction of wind farm behavior. The response of the areated and the detailed models have to show a hih deree of similarity, both durin normal operation as well as durin disturbances for model validation. Field measurements for validation and data acquisition requires simultaneous electrical and wind speed measurements. The SCADA systems are usually used by wind farm operators to acquire data for operation conditions. However substation-load conditions and different power system faults may not be observed by this way. External measurement system which is capable of aquirin reliable data with optimum equipment should be used for additional measurements. Additional measurement points also can cause synchronization and data storae problems for both wind farm operators and study roups. 182

18 Özür Salih MUTLU 4.6 Case Study Results A case study had been performed accordin to iven information and results were presented[1]. The simulation model of the rid connected wind farm was developed in power system analysis tool, PSCAD/EMTDC. The rid and the electrical components of the wind farm were built with standard electrical component models from PSCAD/EMTDC library. The models of the wind, the aerodynamic and control components of the wind turbine were built with custom components developed in PSCAD/EMTDC. Simulations were performed to analyze the mutual effects of the wind farm with the rid. The case study has iven benficial outputs about a rid connected wind farm. Field measurements were used for PSCAD/EMTDC complete model verification process of the wind farm. PCC of the wind farm is a 34.5 kv substation feeder which was chosen as the electrical measurement point. Grid and load conditions could not be controlled or measured durin electrical measurements. Wind speed measurement results, related to the same period of the electrical measurements, were obtained from early installed wind speed anemometer in the wind farm. The control alorithm of wind turbine was not provided by the system operators for the wind farm considered. Models for the wind farm were iven as Generator Modellin, Control System Model, Turbine Model, Model of Wind, Substation and Power System(Grid). Wind farm simulation results with PSCAD/EMTDC were presented with field measurement results[1] Areated Model of the Wind Farm Areated model of the wind farm and areated model PSCAD/EMTDC simulation results were presented in [12,13] and the effect of main parameters on steady-state stability marin was evaluated and discussed by the help of areated wind farm model results. The results helped to understand the steady-state stability phenomena in wind farms 183

19 Evaluatin the Impacts of Wind Farms on Power System Operation eqquipped with wound rotor induction enerators. The studied parameters were; power system components, rotor resistance control and substation voltae level. The developed areated model of the wind farm was used for simulation studies in PSCAD/EMTDC. Presented simulation results showed that the PCC voltae reduction caused reduction in the maximum mechanical torque that could be applied to the enerator. That meant that the voltae reduction at the PCC in case of hih wind speeds(full power output of the wind farm) could result as losin rotor speed stability and cut out of the wind turbine as a consequence. Also PSCAD/EMTDC simulation results of the developed areated wind farm model were compared with the PSCAD/EMTDC simulation results of complete wind farm model for verification. The effectiveness of the areated model to represent the collective response of the wind farm was demonstrated by comparin the simulation results of areated and complete models both durin standart operation and rid disturbance. 5. CONCLUSIONS The wind farms have different impacts and functions on the performance of power system than conventional power plants, because of variation of wind speed in time. Power system operators have to be sure about the reliability of the system after wind enery interations. As a result; accurate models of wind farms and power system are needed for accurate analysis. Detailed information is iven about the parameters like; location of the wind farm in the electric power system, steady-state voltae level influence, areated modelin and model verification which have essential sinificance about the interation studies of wind farms in power systems. The case study has iven benficial outputs about a real system. The combination of measurements and simulation model makes it possible to 184

20 Özür Salih MUTLU estimate power quality and stability marin of the system that would otherwise be difficult to predict and to measure. With the experiences and results acquired from these interation and modellin studies, future research will be much more detailed. Other existin simulation results, models, and scenarios can be examined with iven headlines. REFERENCES [1] Mutlu, Ö.S., Akpınar, E. and Balıkcı, A. Power Quality Analysis of Wind Farm Connected to Alaçatı Substation in Turkey. Renewable Enery 34 (2009) [2] Holttinen,H., Meibom, P., Orths, A., Hulle F.V.,Ensslin C., Hofmann L., McCann J., Pierik J., Tande J.O., Estanqueiro A., Söder L., Strbac G., Parsons B., Smith J.C., Lemström B.(2006). Desin and Operation of Power Systems with Lare Amounts of Wind Power, First Results of IEA Collaboration. Global Wind Power Conference, Adelaide, Australia [3] Venkatasubramanian, M., & Tomsovic, K. (2004). Power System Analysis. In W. Chen, (Ed.). The Electrical Enineerin Handbook ( ). U.S.A. : Elsevier Academic Press. [4] Lubosny, Z. (2003). Wind Turbine Operation in Electric Power Systems. Berlin : Spriner-Verla. [5] Gönen, T. (2004). Power Distribution. In W. Chen, (Ed.). The Electrical Enineerin Handbook ( ). U.S.A. : Elsevier Academic Press. [6] Chen, Z. (2005). Issues of Connectin Wind Farms into Power Systems. Proc. of IEEE/PES Transmission and Distribution Conference & Exhibition 2005 : Asia and Pacific-China. [7] Mäki, K., Repo, S., & Järventausta, P. (2006). Network Protection Impacts of Distributed Generation A Case Study on Wind Power Interation. Proc. Nordic Wind Power Conference 2006, Espoo, Finland. [8] Mutlu, Ö.S. and Akpınar, E. Assessin the Grid Codes For Wind Power Plants in Turkey. Proc. of 9th World Wind Enery Conference June 2010 Istanbul-Turkey. [9] Manwell, J. F., McGovan, J. G., & Roers A.L. (2002). Wind Enery Explained: Theory, Desin and Application. Great Britain : J.Wiley & Sons Ltd. [10] Slootwe, J. G. & Klin, W. L. (2002). Modelin of Lare Wind-farms in Power System Simulations, Proc. IEEE Power Enineerin Society Summer Meetin [11] Pöller, M., & Achilles, S. (2003) Areated wind park models for analyzin power system dynamics. 4th International workshop on lare-scale interation of wind power and transmission network for off-shore wind-farms, Billund, Denmark. [12] Mutlu, Ö.S.(2009). Effects of Wind Turbines on Power System Operation. Ph.D. Thesis. Dokuz Eylül University. [13] Mutlu, Ö.S. ve Akpınar, E. Elektrik Güç Sistemine Bağlı Rüzâr Enerjisi Dönüşüm Sistemlerinin Bütünleşik Modellenmesi. 5. Yenilenebilir Enerji Kaynakları Sempozyumu.Haziran Diyarbakır-Turkiye. S