a hybrid system of wind-pv at ntt kume juma radio relay station

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  • 7/27/2019 A Hybrid System of Wind-PV at NTT Kume Juma Radio Relay Station


    34 1

    A Hybrid System Composed of a Wind Powerand a Photovoltaic System at NTT Kume-jima

    Radio Relay StationKazuh iro KURO ZUM I*, Takeru TAWARA*, Tosh ikazu TAN-*,Yuji KAWAGOE*, Ta kash i YAMAN=*, Hiroaki IKEBE*,Kazuhiko SHINDOU **, and Tetsuo MIYAZATO**

    3-9-11, Midori-cho,Mu sashino-shi, Tokyo, 18 0-0012 JapanTe1:+81-422-37-7643,Fax:+81-422-37-7650,E-mail:kurozu22@bn.ntt-f.co.jp2-2 -2, Otemachi, Chiyoda-ku, Tokyo, 100-0004JapanTe1:+81-3-5200-6888,Fax:+81-3-5200-9118,E-mail:t-miyaza@mbd.mbc.ntt.co.jp

    NTT Power and Building Facilities Inc.**Nippon Telegraph and Telephon e Corporation

    bstract This paper describes a 250 kWhybrid system composed of two systems whichuses clean energy sources, a wind power systemand a photovoltaic (PV) system. The hybridsystem has been installed in the radio relaystation at NTT in Kume-jima (a small island inthe south-west of Japan). The hybrid systemconsists of a 230 kW wind turbine, a 50 kWresistor, a 230 kW bidirect ional converter withstorage batteries, 20 kW PV modules, and a 20kW interactive inverte r. The power genera tedin this system is supplied to telecommunicationsequipment at the ra o relay station and to th epower grid by reversing power flow. One of theadvantages of this system is that it suppressesrapid change in the output power of the windpower system. This rapid change causes t he gridvoltage and the grid frequency to fluctuatebecause t he grid capacity in Kume-jima is low.

    1. IntroductionEquipment used in multimediatelecommunications must have the capacity to

    manage large amounts of information rapidlyand must have air conditioners to cool theequipment effectively. These feat ures result inincreased power consumption. Effective use ofenergy and reduction of +its consumption are

    important issues for companies, who have aresponsibility to protect th e environment.

    In cooperation with NTT Power and BuildingFacihties, Inc. IT has started a Total PowerRevolution (TPR) campaign to reconsider itsenergy consumption policy and reduce powerconsumption in telecommunications equipment.This ha s involved the introduct ion of cleanenergy sources, an example of which is theinsta llation of PV systems in telecommunicationsbuildings. [11[2]

    Our most recent clean energy system, acombination of a wind power system and a PVsystem has been installed in Kume-jima, alocation particularly suited to this laid of systemowing to its good wind and sunshine conhti ons.The hybrid system is connected in the grid andits generated power is supplied, by reversingpower flow to the telecommunicationsequipmentat the radio relay station and to the grid. Therapid change in output power o the hybridsystem may cause the grid voltage and gridfrequency to fluctuate, owing to the low gridcapacity in Kume-jima. We have thereforedeveloped a system which uses a resistor and abidirectional converter to suppress fluctuationin the grid.

    0-7803-5069-3 /98/$10.00 01 99 8 IEEE 785

  • 7/27/2019 A Hybrid System of Wind-PV at NTT Kume Juma Radio Relay Station


    2.Configuration of the hybridsystem

    The configuration and external view of thehybrid system are shown in Figs. 1and 2. Thesystem consists of a 230 kW wind power systemand a 20 kW PV system a nd makes the most ofthe advantages of each. The wind powersystem consists of a wind turbine, a resister, abidirectional converter, and storage batteries (2V, 500Ah, 180cells). The PV system consists ofPV modules and an interact ive inverter.

    The power generated by the hybrid system issupplied to the telecommunications equipmenta t the radio relay station and to the grid.

    3. Wind power systemThe rapid change in the output power of the

    wind turbine causes the grid voltage and gridfrequency to fluctuate because the grid capacityis low in Kume-jima (power consumption on awinter night there is as low as 3000 kVA).

    Therefore, considering the characteristics of thepower grid's diesel engine generator(investigated in rapid load change experiments),we estimate that the grid frequency cannot meetthe requirement (59.7-60.3Hz) when thegenerated power changes by more than 160kW.

    Wind pow er system

    Fig. 2 Hybrid system composed of the windpower and the photovoltaic system.

    Photovoltaic svstem


    AC6600V 3-phase 60HzTransformer

    . I Radio relay station

    Fig. Configuration of the hybrid system.


  • 7/27/2019 A Hybrid System of Wind-PV at NTT Kume Juma Radio Relay Station


    There are two conditions in which the powergenerated by the wind power system changesrapidly. When the wind velocity changesrapidly ,and when t he wind turb ine stops.(a) Counte rmeasure of rapid change in

    wind velocityWaveform of the power generated by the wind

    turbine is shown in Fig. 3. When the increaseof power generated by wind turbine is 130 kWduring 10 seconds and th e ra te of increase is 30kW/s at the same time, the switch S1 turns onand the resistor consumes the power a s shown inFig. 4.

    When the decrease of power generated is 130kW during 10 seconds and the rate of decrease is30 kWls at the same time, the bi-hrectionalconverter's mode of operation changes fromcharging to discharging an d t,he storage batte rysupplies the power to the grid and the radio relaystation, as shown in Fig. 5.

    .-Suppressed power

    Rapid increase Rapid dccrcnseFig. 3 Operation of the hybrid system when

    the wind power rapidly changes.

    The operation data of the bi-directionalconverter is shown in Fig. 6. The waveformsshown in Fig. 6 can be described as follows.When the power generated by the wind turbinedecreased rapidly, the bi-du-ectional converterstopped charging the batteries at point A.Its mode of operation changes to discharging andits output current increases a t point B. After 10seconds, its output current gradually decreasesto OA at point C and it took another 10 secondsto sta rt charging the batteries again a t point D.These results verify the operation of the bi-Iirectional converter.

    Gridv.iipp.Power_sY femIt

    converter I


    C6600V, -phase, 60Hz

    Radio relay stationFig. 4 Operation of the wind power system when

    the generated power increases rapidly.GridWind PP1wP_ _?Fs_fern

    66WV, -phase 60Hz


    Rablor 5OkW

    Fig. 5 Operation of the wind power system whenthe generated power decreases rapidly.

    Fig. 6 Operation data of the bi-directional converter.


  • 7/27/2019 A Hybrid System of Wind-PV at NTT Kume Juma Radio Relay Station


    @ C o u n t e r m e a s u r e o w i n d turbine cut-off

    The wind turbine cuts off to protect itself if thewind velocity is more than 25 mls for 10minutes.The generated power then decreases from 210kW to 0 kW within 50 mihseconds. Operationof the wind power system in these conditions isshown in Fig. 7.

    After receiving a pre-alarm signal from thewind turbine, the bi-directional converterchanges to a waiting mode in which the currentdose not flow between the grid and the storagebatteries, and th e S1 turns on causing the powergenerated by the wind turbine to be consumed.10 seconds afte r receiving the pre -alarm signal,the bi-directional converter receives the cut-offsignal. Its mode of operation changes fromwaiting to discharging and its output powerincreases from 0 kW to 210 kW within 300milhseconds. Its output power graduallydecreases, to reach 0kW after 10 seconds.

    Therefore, this system can suppress thechanges in output power as well as thefluctuations of the grid voltage and the gridfrequency.

    4 Photovoltaic systemThe PV system uses an interactive inverter to

    convert DC power generated by the PV modulesinto AC power which is then supplied to thetelecommunications equipment. The externalview and specifications of the interactiveinverter are shown in Fig. 8andTable1.

    Protection of th e. natu ral enGironment wastaken into account in the installation of thissystem. Instead of digging the hdlside toprepare t he horizontal are a necessary for the PVsystem, we took advantage of the na tur al slope toprepare bases and set PV modules. Thismethod was also cost-effective.

    The capacity of the photovoltaic system wasdecided by installation are a of the PV modules.

    Pre.durn? - P l - P 3PII k P l - P Zi

    i i Tmc;iFig. 7. Operation of the wind power system

    at the wind turbine cut-off.

    Fig. 8 Externa l view of the interactiveinverter.

    Table 1 Specifications of interactiveinver te r .

    Rated capacityRated voltageVoltage rangeRated voltage


    Convertion efliaencySue


    ~ ii tion250 360260



  • 7/27/2019 A Hybrid System of Wind-PV at NTT Kume Juma Radio Relay Station


    5. ConclusionNTT and NTT Power and Building Facilities

    Inc. have been working on the introduction ofclean energy and have installed clean energysystems in telecommunications buildings. Thetotal capacity of these energy systems hadincreased to 1350 kW by March, 1998.

    A 250 kW hybrid system composed of a 230kW wind power an d a 20 kW photovoltaic systemwas installed at NTT Kume-jima radio relaystation for which we developed the technology tosuppress grid power fluctuations.

    6. References[ l] Y. Kawagoe, K. Nakamura, D. Ikeda and S.Torigoe Field Investigation of a PhotovoltaicPower System for a TelecommunicationsSystem, INTELEC 91 November, 1991[2] K. Kurozumi, Y. Kawagoe, T. Yamanaka andT. Hidaka Dev