Aalborg Universitet. Published in: Proceedings of the 5th Nordic Wind Power Conference. Publication date: 2009

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1 alorg Universitet oordination etween Fault-Ride-Through apaility and Overurrent Protetion of DFIG Generatorsfor Wind Farms ak-jensen, irgitte; Kawady, Tamer.; del-rahman, Mansour H. Pulished in: Proeedings of the 5th Nordi Wind Power onferene Puliation date: 9 Doument Version Pulisher's PDF, also known as Version of reord Link to puliation from alorg University itation for pulished version (P): ak-jensen,., Kawady, T.., & del-rahman, M. H. (9). oordination etween Fault-Ride-Through apaility and Overurrent Protetion of DFIG Generatorsfor Wind Farms. In Proeedings of the 5th Nordi Wind Power onferene Tehnial University of Denmark (DTU). General rights opyright and moral rights for the puliations made aessile in the puli portal are retained y the authors and/or other opyright owners and it is a ondition of aessing puliations that users reognise and aide y the legal requirements assoiated with these rights.? Users may download and print one opy of any puliation from the puli portal for the purpose of private study or researh.? You may not further distriute the material or use it for any profit-making ativity or ommerial gain? You may freely distriute the URL identifying the puliation in the puli portal? Take down poliy If you elieve that this doument reahes opyright please ontat us at vn@au.aau.dk providing details, and we will remove aess to the work immediately and investigate your laim. Downloaded from vn.aau.dk on: oktoer 8, 8

2 oordination etween Fault-Ride-Through apaility and Overurrent Protetion of DFIG Generators for Wind Farms irgitte ak-jensen, Tamer. Kawady, MIEEE, Mansour H. del-rahman, strat Due to the inreasing penetration of wind farms in power systems, staility issues arise strongly for power system operation. Douly-Fed Indution Generators (DFIG) are haraterized with some unique features during normal/anormal operating onditions as ompared with singly-fed ones. Fault ride- Through (FRT) mainly aims to delay a disonneting of the DFIG units during grid faults for a possile time to restore the system staility if the fault is leared within a permissile time. This strategy may, however, affet the performane of related protetive elements during fault periods. In this paper, the oordination etween Fault Ride-Through apaility and Overurrent Protetion of DFIG Wind Generators in MV Networks is investigated. Simulation test ases using MTL-Simulink are implemented on a 5-MW wind farm in L-Zaafarana, Egypt. The simulation results show the influene of FRT apaility on protetive relaying oordination in wind farms. Index Wind farms Protetion, Dynami modeling, MTL- Simulink, Fuse. I. INTRODUTION Owing to the rapid inrease of the gloal population and their energy needs, traditional means to satisfy the urgeoning energy demands need areful reevaluation. oupled with the uneven distriution of resoures around the world, the importane of renewale resoures of energy is ovious. mong these resoures, wind eletri onversion has emerged as the leader at the present time. The impressive growth in the utilization of wind energy has onsequently spawned ative researh ativities in a wide variety of tehnial fields. Moreover, the inreasing penetration of wind energy into onventional power systems highlights several important issues suh as reliaility, seurity, staility, power quality, et. The essential enefits from a dediated protetion funtions are to avoid possile loal damage resulting from inident faults and minimize the impat of these anormal onditions on the other sound parts of the network. This redues the This work was made possile y the EU UPWIND (Integrated Wind Turine Design) projet No 995 under the SIXTH FRMEWORK PROGRMME PRIORITY 6. Sustainale development, gloal hange and eosystems. The authors aknowledge with thanks. Tamer.. Kawady is with the Department of Eletrial Engineering., Menoufiya University, Egypt ( t_kawady@ieee.org). Mansour H. del-rahman ( mhar@iet.aau.dk) irgitte ak-jensen ( j@iet.aau.dk) oth are with the Institute of Energy Tehnology, alorg iversity, Denmark assoiated negative impats of the faults on the servie ontinuity and the system staility. onsequently, it enhanes the reliaility and dependaility of the overall grid performane. Wind farms still utilize surprisingly simple and noneintegrated protetion methodologies []. lso, researh efforts regarding wind farm protetion are still limited in the literatures s reported y auske et al. in [], different levels of damage were reorded resulting oasionally from the drawaks of the assoiated protetion system. onventionally, wind turines were separated from the grid following grid faults leading to loss of an undesirale portion of power generation. Hene, utilities nowadays require Fault Ride-Through (FRT) apaility for grid-onneted wind farms. FRT aims mainly to enale the wind farm to withstand severe voltage dips at the onnetion point resulting from the ourring grid faults. Hene, wind farm is required to remain grid- onneted during grid faults for a ertain time so that it an diretly ontriute with ative power to the grid. This leads to support the overall system staility. This is nowadays essentially required y almost all known grid odes for modern variale speed DFIG []. DFIGs have nowadays the superiority for wind farms as ompared with onventional IGs. This is mainly eause these units are distintive with different advantages inluding aility to ontrol voltage and reative power, low short iruit ontriution and supporting the system staility. These grid odes were issued mainly to define the asi requirements of wind turines during grid faults onsidering their operation modes and ontrol strategies. On the other hand, different prolems arise for the assoiated generator/onverter protetion and ontrol issues. During these voltage dips, the delivered ative power to the grid y the farm is remarkaly redued. onsequently, the mehanial power exeeds the delivered ative power resulting in inreasing the rotor speed. Then, the ontrol sheme of the DFIG variale-speed wind turines emraes oth the wind turine ontrol for preventing over-speeding of the wind turine and the ontrol and protetion of the power onverter during and after the grid faults []. lthough the FRT enale the overall system to restore its staility without losing large amounts of power generations after fault learing, these ontrol strategies may influene the related protetive elements. Relay miss-oordination or missoperation may our due to the resulting hanges of fault urrent profile. The aim of this paper is to investigate the ehavior of overurrent protetion used with wind generating units during the operation of the FRT proedure. These investiga-

3 tions are arried out ased on well prepared simulation examples. mong the known pakages for dynami simulation purposes MTL [7] was employed for developing a suessful dynami simulation of a wind farm that is used to arry out this study due to its modeling apailities and superior development failities. Results of a 5-MW wind farm in Egypt is onsidered as a simulation example for this study showing the influenes of FRT apaility on the onventional overurrent protetion used ommonly in wind farms. II. ONVENTIONL PROTETION SYSTEM FOR WIND FRMS Fig. Shemati of the onventional protetion system Fig. shows a shemati of a typial wind farm onsisting of (n) units of wind turines. Nowadays, modern wind farms inlude to 5 units with typial size from.5 MW to MW wind turine generators. Larger sizes up to 5 MW are reently availale in the market, in whih they were suessfully installed in some European ountries. The use of indution generators in wind farm installations is today a standard pratie, due to its suitale harateristis for the wind turines. The typial generator terminal voltage may range from 575 to 69 V with a frequeny of 5 (or 6) Hz. The generator terminal voltage is stepped up to the olletor us system with typial voltage of to.5 kv. The step up transformer is normally oil ooled, pad mounted unit loated at the ase of the wind turine unit. Sometimes, the step up transformer is mounted in the turine naelle. These transformers are usually vitims to remarkale virations due to the wind load hitting the wind turine. ertain onsiderations should e applied for avoiding harmoni effets. The transformer tanks have vertial and horizontal reinforements to redue viration and resonane. lso, the ore/oil assemly will e highly lamped and seured in the tank, restriting any movement in any of the three dimensions. The typial wind farm olletor system onsists of a distriution sustation olleting the output of the distriuted wind turine generators through the inoming feeders. Usually some reative power ompensation units are provided y a olletion of swithed apaitors. Finally, the olleted power is transferred to the utility side via an interonnetion step up transformer. The wind farm protetion system is usually divided into different protetion zones inluding the wind farm area, wind farm olletion system, wind farm interonnetion system and the utility area. First, the indution generator protetion is typially aomplished via the generator ontrolling system overing some ertain protetion funtions suh as under/over voltage, under/over frequeny, and generator winding temperature (RTDs). The generator ontrol system does not ontriute to the interonneting system or the utility zone. The generator is proteted against short iruits with its iruit reaker, whih is pratially dimensioned to - times the generator rated urrent. The generator step up transformer is usually proteted with fuses dimensioned to - times its rated urrent. The olletor feeder protetion is simplified onsidering it as a radial distriution feeder using overurrent protetion (5/5). asi hallenge arises due to the distriuted generators onneted together to the radial feeder in determining the minimum faulty zone. That is in order to keep the remaining sound parts of the farm supplying the power. On the other hand, the protetion of the wind farm sustation olletor us and main power transformer onsists of a multifuntion numerial relay system inluding main transformer differential relay, transformer akup overurrent relay, olletor us differential relay and reaker failure relay. Further details are availale in the literatures [5]-[7]. It should e onsidered that, the wind farm interonnetion would e applied to MV distriution network, HV system... et. Therefore, the oordination of utility relays and the wind farm will e quite different. ommuniation systems with dediated SD are quite important for wind farm operation. Nowadays, the data from eah wind generator ontrol is transmitted via opti ales and spread to the main sustation for general ontrol and monitoring purposes. This provides an ideal situation for providing them with an integrated monitoring and ontrol system. Fig. FRT apaility urve profile III. PROLEM IDENTIFITION. Fault Ride-Through fundamentals for DFIGs Historially grid odes allowed the wind turines to e disonneted instantaneously with voltage sag elow.8 per unit. In, E.ON and VET (Germany) introdued the first FRT ode requirements. Later, other international wind energy assoiations introdued their similar odes as well. Generally speaking, the grid odes required that grid onneted wind turines should withstand voltage dips on any or all phases in the transmission system as long as the voltage measured at the high-voltage terminals of the grid-onneted transformer, or in other words at the ommon oupling point (P), remains aove the predetermined level of the grid ode [8]-[]. Different enefits are expeted to e gained with FRT apailities

4 inluding enhaning the system staility and fast restoration of system servie if the fault is leared during the allowale time. These apailities an e ahieved y an adapted ontrol strategy.. rowar system protetion The rowar omprises of some ertain thyristors that short-iruit the rotor winding and hene therey limit the rotor voltage and provide an additional path for the fault urrent. When a disturane is introdued, high urrents are indued into the rotor iruitry from the stator side affeting the dlink voltage as well. Then, the d-link over-voltage protetion will stop the rotor onverter/inverter unit, meanwhile it turns on the rowar ontrol thyristor. Similarly, the rowar an e triggered ased on the ourring overurrent through the rotor iruity. The rotor is now onneted to the rowar and remains onneted until the main iruit reaker disonnets the stator from the grid [], []. fter learane of the fault the generator an e line-synhronized again and started in a normal operation mode. When oth these voltages are low enough, the rowar is turned off. fter a short delay for the deay of the rotor urrents, the rotor-side inverter is restarted and the reative power is ramped up in order to support the grid.. FRT ehavior during disturanes Fig. shows different fault loations ourring on either the wind farm MV distriution network or the HV transmission system onneting the farm to the grid. These fault positions are designated with (), (), () and (D) respetively. Ideally, suessful FRT operation is restrited to those faults that our outside the wind farm in order to support the system staility. For those faults ourring inside the farm, the FRT sheme should not operate in order to enale the assoiated protetion system to respond orretly. Referring to Fig., solid three phase faults at positions () and () are normally haraterized with larger voltage dips (down to % of the nominal voltage) whih may e loalized elow the FRT harateristi edge. Hene, these faults may not trigger the FRT mehanism to operate. On the other hand, other external faults suh as those ones at positions () and (D) are haraterized with relatively smaller voltage dips (aout % of the nominal voltage). Then, the FRT mehanism should operate orretly. Sine, the ore for the rowar mehanism depends mainly on the ourring rotor overurrent to start, the aforementioned ehavior of the FRT is expeted to funtion properly for solid three phase faults as desried earlier. This however, an not e guaranteed for non-solid faults or for unalaned ones. Fig. rowar protetion system for DFIG units erodynami part Rotor otroller IG ().. Fuse. Point of ommon oupling olletor feedr The ore of the rowar operation was desried y khmatov, Xiang, Holdsworth, Ekanyaki and Niiranen as reported in [9] -[7]. Tehnially, two types of rowar systems are known inluding passive and ative ones. For passive ones, the rowar onsists of a diode ridge that retifies the rotor phase urrents and a single thyristor in series with a resistor Rrow. The thyristor is turned on when the D link voltage Ud reahes its maximum value or the rotor urrent reahes its limit value. Simultaneously, the rotor of the DFIG is disonneted from the rotor-side frequeny onverter and onneted to the rowar. The rotor remains onneted to the rowar until the main iruit reaker disonnets the stator from the network. When the grid fault is leared, the rotor-side onverter is restarted, and after synhronization, the stator of the DFIG is onneted to the network. In ontrast to a onventional passive rowar, the ative rowar is fully ontrollale y means of a semiondutor swith. This type of rowar is ale to ut the short-iruit rotor urrent whenever needed and thus the DFIG wind turine is ale to ride through a network disturane. If either the rotor urrent or d link voltage levels exeed their limits, the IGTs of the rotor-side inverter are loked and the ative rowar is turned on. The rowar resistor voltage and d link voltage are monitored during the operation of the rowar. Other wind turine units Fault position () DFIG () DFIG () Fault position () Fault position (D) Fig. Fault positions during faults for wind generating unit IV. DEVELOPMENT OF THE SYSTEM MODELING Fault position () Modeling of DFIGs is well desried in the literatures [5]-[7]. 5-MW wind farm was reently estalished in l- Zafarana ( south east of airo, Egypt) and onneted to the Egyptian kv grid. This area is distintive with different features suh as an average annual wind speed of 9.5 m/s, and its exellent geographial and environmental features. The farm was strutured through seven stages of,,, 7, 8 and 85, MW respetively as desried in Fig. 5. Exept the latter two stages, other stages are with fixed speed and variale pith operation. The fifth stage of the farm was seleted as a simulation example in the paper. It onsists of wind turines (with a 85 KW DFIG units for eah turine) providing a total power of 85MW The DFIGs were dis-

5 triuted at seven feeders as illustrated in Fig.. Eah wind turine is onneted to a 69V: KV loal step-up transformer. The olleted power are then fed to the kv network through three 75 MV, / kv step-up transformers. Main Step up transformers Feeder Fig. 6 shows the detailed shemati diagram of eah wind unit onstruted with the uilt-in wind turine model in MTL. The relatively large numer of wind turine units, in whih eah of them was onstruted with different individual items Turine, generator, loal transformer, feeding ale, inreased remarkaly the orresponding soure of ode. This is haraterized with a huge operation time (around 5 min. for eah single running on a. GHz, G-RM mahine). This resulted in an impratial testing profile for those simulation purposes that are haraterized with huge amounts of simulation ases. Moreover, the aforementioned prolem is signifiantly exaggerated for larger systems. Therefore, the need for reduing the overall wind farm model is ovious. On the other hand, the redued model should e onditioned with the following restritions: Model uray for eah individual power system element should e kept in its higher level The essential onepts for distriuted generation must e satisfied. Equivalene of urrents for eah individual unit as well as overall farm urrents for oth detailed and redued model should e realized Equivalene of the generated power for eah individual unit as well as for the overall farm for oth detailed and redued model should e realized. Total power losses (due to onneting ales) should e onsidered. Feeder [Va_] [Ia_] Feeder Feeder a a [Ia_stator] [Tm ] Tm m a <Rotor speed (wm)> <Rotor angle thetam (rad)> [wr] [angle _rotor] _stator synhronous Mahine pu Units Feeder 6 Feeder 5 Feeder 7 ) Fig. 5 Desription of the fifth stage of l-zafarana Farm Geographial distriution of l-zafarana farm Shemati of the fifth stage of l-zafarana Farm The turine operation was haraterized with the wind speed, the generator speed and its individual pith ontrol, where its nominal wind speed was assigned to 9.5 m/se the annual average wind speed in its orresponding loation and the ut-in wind speed was assigned to e.5 m/se. Eah wind turine was equipped with its indution generator model ased on the asynhronous mahine uilt-in model in MTL [8]. The operation of the rowar was modeled y deativating the onverters upon the detetion of rotor urrent magnitude aove the urrent protetion limit and shortiruiting the generator rotor. ( [Va_] Qref (pu ) Iq_ref (pu) Va_ Q_ref Iq_grid_onv_ref hoke Pulses_grid_onv a _grid _onv [Ia _grid _onv] g + Universal ridge g Universal ridge [wr] [eta ] Wind (m/s) Fig. 6 Simulink-ased diagram of a single unit diagram a _rotor _onv Generator speed (pu) Pith angle (deg) Wind speed (m/s) Wind Turine [Ia _rotor ] Fig. 7 illustrates the proposed redued model for the fifth stage of l-zafaranna wind farm. The first six olleting feeders were lumped with their power equivaleny with total lumped equivalent generators for eah feeder respetively. For the latter olleting feeder, among its wind turine generators, generators were represented with their equivalent lumped generator, whereas the rest ones (the first, seond and last units) were represented individually for keeping the distriuted generation onept. For those lumped units, ale lengths were onsidered for keeping the total power losses equal to those resulted with the orresponding detailed model. The re- Tm (pu) [Tm ]

6 sponse of the redued model was validated ompared with the orresponding detailed one via different simulation examples for oth faulty and non-faulty operating onditions. Details for the proposed modeling methodology were fully addressed in [7]. () Fig. 8 Simulation response due to a solid -phase grid-fault at position () without rowar initialization. Stator phase voltage, pu. Rotor phase urrents, pu. () Stator phase urrent, pu. WT *85KW WT *85KW WT 5*85KW WT 5*85KW WT 5*85KW WT 5*85KW Rotor urrents, p WT *85KW WT *85KW WT *85 KW urrent, pu - WT5 *85KW WT *85KW Fig. 7 Shemati of the redued wind farm model. V. SIMULTION RESULTS Depending on the developed redued model in the preeding setion, the ehavior of the DFIG units in onjuntion with the related FRT mehanism was thoroughly investigated under various faulty and non-faulty operating onditions. These ases were applied on the seventh olleting feeder as desried in Fig.. Four different fault loations were onsidered: eyond the loal step-up transformer (position ), along the onneting ale (position ), eyond the grid-onneting transformer (position ) and along the HV transmission line (position D). For eah ase, voltage and urrent quantities for oth stator and rotor iruitries were reorded as desried in the following su-setions.. Grid faults Voltage, pu. Rotor urrents, pu. urrent, pu time, se Fig. 9 Simulation response due to a solid -phase grid-fault at position () with rowar initialization. Rotor phase urrent, pu. Stator phase urrent, pu. During grid faults, the ourred faults resulted in a suffiient drop of phase voltage so that the assoiated rowar mehanism was initiated to protet the rotor windings from the exessive fault urrent. s illustrated from Fig. 8, oth rotor and stator windings suffered from the inreased urrents resulted from a solid -phase grid fault ourring at position (). On the other hand, initiated rowar mehanism resulted in shorting the rotor winding rapidly after the fault ineption after seonds as well as deativating the rotor ontroller as remarked from Fig. 9, meanwhile the DFIG reat similarly to the onventional single infeed mahines. Rotor urrents were dereased to zero avoiding the possile winding damage, whereas the stator urrents were dereased to zero due to the loss of reative power ompensation. This was fully addressed for thee phase faults for single infeed mahines in [7]. When the fault was leared at.5 seond, the DFIG was restarted again.. Solid Wind farm faults In order investigate the ehavior of the DFIG equipped with rowar mehanism, a solid -phase fault was applied efore the loal transformer at position (). s illustrated from Fig., the resulting low voltage ondition at the generator terminals inhiited the rowar operation. This was owing to the relatively larger voltage drop loated lower than the FRT edge from the shown harateristis in Fig.. Similarly, the DFIG response for a -phase solid fault at the same position eyond the loal step-up transformer at position () was investigated as shown in Fig.. s remarked from the results, the ourred voltage drop initiated the rowar mehanism. s noted from Fig. (), the resulted stator fault urrent was kept low the predetermined setting of the utilized fuse element seleted typially from to times the rated urrent. Repeating the same fault with deativating the rowar

7 mehanism is illustrated in Fig. and, in whih the fault resulted in a relatively larger fault urrent as noted from the assoiated Disrete Fourier Transform (DFT)-ased peak detetor of the fault urrent. These aforementioned results raise the effets of the FRT mehanism on the performane of employed overurrent protetion with DFIG mahines equipped with FRT mehanisms. Voltage, pu. urret, pu. urrent-dft profile, pu () Fig. Simulation response due to a solid -phase fault at position () with rowar initialization. Stator phase voltage, pu. Stator phase urrent, pu. () Stator phase urrent peak profile with DFT. Non-solid wind farm faults t non-solid faults usually the fault urrent dereases due to an inreased fault resistane. These faults should e onsidered for evaluating the ehavior of the DFIG mahines equipped with FRT mehanisms. When a fault resistane is inserted into the fault urrent path, the derease of the fault urrent is aomplished with a derease of the ourring voltage drop at the generator terminals. onsequently, the FRT mehanism may inorretly e initiated for faults ourring inside the wind farm. This results in inhiiting the operation of the related overurrent protetion due to the redued fault urrent. This is illustrated in Fig. for a -phase fault ourring at position () through a Ω fault resistane with utilizing rowar operation. Whereas the DFIG response, for the same fault ondition, with deativating the rowar mehanism is shown in Fig.. s onluded from oth results, the rowar operation redued the fault urrent rapidly, whereas the fault urrent was kept at a remarkale level with the FRT operation. Hene, the impat of the FRT operation on the performane of overurrent relays for suh situations is ovious. urrent, pu Voltage, pu urrent, pu time, pu. urrent - DFT profile, pu Fig. Simulation response due to a solid -phase fault at position () without rowar initialization. Stator phase urrent, pu. Stator phase urrent peak profile with DFT urrent-dft profile, pu () Fig. Simulation response due to a solid -phase fault at position () with rowar initialization. Stator phase voltage, pu. Stator phase urrent, pu. Stator phase urrent peak profile with DFT VI. ONLUSIONS DFIG generators represent nowadays the most ommon generator type for wind farms using either onshore or offshore turines. Owing to the inreasing penetration of wind farms into power system grids, FRT apailities is reently required y all known ommon grid odes. ommon FRT strategies for DFIGs are usually performed with shorting the rotor winding of the faulted DFIG and deativating the rotor onverter immediately after deteting the ourring fault. The DFIG ehaves, therefore, exatly as onventional SFIGs during the fault period. This results in lower levels of fault urrents as ompared with ontinuous DFIG operation during the fault. This onsequently affets the ehavior of onventional overurrent protetion elements against network faults ourring

8 into the loal onneting iruitry of the wind farm. Fault resistane in onjuntion with FRT strategies, even with small values, shows a signifiant effet perturing the performane of the overurrent protetion as well. The results orroorate the need for new or modified oordination rules for overurrent elements inorporated with DFIGs and FRT apaility tools. Voltage, pu. urrent, pu. urrent-dft profile, pu () Fig. Simulation response due to a -phase fault at position () with rowar initialization and fault resistane of Ω. Stator phase voltage, pu. Stator phase urrent, pu. () Stator phase urrent peak profile with DFT urrent, pu. urrent-dft profile, pu Fig. Simulation response due to a -phase fault at position () without rowar initialization and fault resistane of Ω. Stator phase urrent, pu. Stator phase urrent peak profile with DFT [] Stefan aushke, lemens Okirher, Georg hleitner, Lothar Fikert and Manfred Sakulin, "Improved Protetion system for eletrial omponents in wind energy plants, 5 th International onferene on Power System Protetion, PSP '6, led-slovenia, 6-8 Sept. 6. [] I. Erlih, Memer, IEEE, W. Winter,. Dittri, "dvaned Grid Requirements for the Integration of Wind Turines into the German Transmission System", IEEE General Meeting, GM6. [] I. Erlih, H. Wrede, and. Feltes, " Dynami ehavior of DFIG-ased Wind Turines during Grid Faults", Power onversion onferene - Nagoya, 7. P '7, -5 pril 7 pp. 95. [5] S. Haslam, P. rossley and N. Jenkins, Design and evaluation of a wind farm protetion relay, Generation, Transmission and Distriution, IEE Proeedings, Volume 6, Issue, Jan. 999, pp. 7. [6] R. Fuhs, Protetion shemes for deentralized power generation, Developments in Power System Protetion,. Eighth IEE International, 5-8 pril, Vol., pp. 6. [7] Tamer. Kawady, Naema Mansour, del-maksoud Taala, "Performane Evaluation of onventional Protetion Systems for Wind Farms IEEE/PES General Meeting, GM-8, Pittsurg, - July, 8. [8] ndreas Dittrih lexander Stoev, "omparison of fault ride-through strategies for wind turines with DFIM generators", Power Eletronis and ppliations, 5 European onferene on, Dresden, Germany. [9] V. khmatov, nalysis of Dynami ehaiour of Eletri Power System with Large mount of Wind Power, PhD Thesis, Eletri Power Engeneering, Orsted DTU Tehnial University of Denmark, pril, Denmark. [] Niiranen, J.. Voltage Dip Ride Through of Douly-Fed Generator Equipped with tive rowar, Nordi Wind Power onferene, - Marh, halmers University of Tehnology, Göteorg, Sweden. [] Niiranen, J. 5. Experienes on Voltage Dip Ride through Fatory Testing of Synhronous and Douly Fed Generator Drives, Proeedings of th European onferene on Power Eletronis and ppliations. Dresden, Germany, - Septemer 5. [] na D. Hansen and Gariele Mihalke, "Fault ride-through apaility of DFIG wind turines", Renewale Energy, Elsevier, Vol. (7), pp [] Niiranen, J. 6. out the tive and Reative Power Measurements in Unsymmetrial Voltage Dip Ride Through Testing, Nordi Wind Power onferene, - May 6, Espoo, Finland. [] Xiang, D., Ran, L., Tavner, P.J., umy, J.R.. ontrol of a Douly-fed Indution Generator to Ride-through a Grid Fault, Proeedings of IEM, raow, Poland, 5-8 Septemer. [5] Petersson,., Thiringer, T., Harnefors, L., Petru, T. 5. Modeling and Experimental Verifiation of Grid Interation of a DFIG Wind Turine, IEEE Transations on Energy onversion, Vol., Issue, De. 5, pp [6] Ekanayake, J.., Holdsworth, L., Wu, X.G., Jenkins, N.. Dynami Modeling of Douly Fed Indution Generator Wind Turines, IEEE Transation on Power Systems, Vol. 8, Issue, May, pp [7] Holdsworth, L., Wu, X.G., Ekanayake, J.., Jenkins, N., a. omparison of Fixed Speed and Douly Fed Indution Wind Turines during Power System Disturanes, IEE Proeedings - Generation, Transmission and Distriution, Vol. 5, No., May, pp [8] The MathWorks In., MTL, Ver. 7., 6, " VII. REFERENES [] D. Hornak, N. hau, Green power - wind generated protetion and ontrol onsiderations, Protetive Relay Engineers, 57th nnual onferene for Mar- pr, pp..

9 VIII. IOGRPHIES irgitte ak-jensen (M 88) reeived her M.S. degree in Eletrial Engineering in 986 and a Ph.D. degree in Modeling of High Voltage omponents in 99, oth degrees from Institute of Energy Tehnology, alorg University, Denmark. From , she was with Eletrolux Elmotor /S, alorg, Denmark as an Eletrial Design Engineer. She is an ssoiate Professor in the Institute of Energy Tehnology, alorg University, where she has worked sine ugust 988. Her fields of interest are modeling and diagnosis of eletrial omponents, power quality and staility in power systems. During the last years, integration of dispersed generation to the network grid has eome one of her main fields, where she has partiipated in many projets onerning wind turines and their onnetion to the grid. Mansour H. del-rahman (M 79) was orn in Egypt in 97. He reeived the.s. and M.S. degrees in eletrial engineering from airo University in 97 and 975, respetively, and the Ph.D. degree in eletrial engineering from the University of Manhester Institute of Siene and Tehnology (UMIST), U.K., in 979. He has een a Full Professor at the University of El-Mansoura, Egypt, sine 987. He spent visiting assignments, teahing and researhing, at the University of Toronto, anada, University of Windsor, anada, the University of amridge, U.K., where he was a Fellow of hurhill ollege, University of Western ustralia, ustralia, Doshisha University, Japan, Helsinki University of Tehnology, Finland, University of Ieland, University of alorg, Denmark, Jordan University, Jordan, and Kuwait University, Kuwait. His researh interests inlude eletromagneti transients in power system networks and mahines, steady-state and dynami analysis of power systems, and the appliation of artifiial intelligene in power systems. Dr. del-rahman reeived the John Madsen Medal for the est paper sumitted to the Institute of Engineers, ustralia, in 989, the IEEE Industry ppliation Soiety First Prize Paper in 988, and the IEEE Industrial and ommittee Prize Paper in 987. Tamer. Kawady (MIEEE ) was orn in Shein El-kom, Egypt on Sept., 97. He reeived his.s. (honors) and M.S. degrees in Eletrial Engineering, Menoufiya University, Egypt, Ph.D. degree (exellent) from Tehnial University Darmstadt, Germany in 995, 999 and 5 respetively. Dr. Kawady is urrently an assistant professor at Menoufiya University, Egypt sine pril 5. Dr. Kawady has tens of pulished journal and onferene papers and he is now a reviewer for various IEEE and IET journals. His interests are in digital protetion, Power system simulation using the Eletromagneti Transient Program (ETP) and rtifiial Intelligene appliations to power system protetion.