KHOA HOC CONG NGHE Q Nghien cuu anh huang cua song hai tren l iM phan phoi toi chat luong lien oaoo Tdm tdt Cdc tieu ctnudn ve chdt lUdng dien ndng iiien tai cua Viet Nam chUa quan tam nhieu d§''''n sdng[.]
KHOA HOC - CONG NGHE Q Nghien cuu anh huang cua song hai tren liM phan phoi toi chat luong lien oaoo PHUNG ANH TUAN - NGUYEN THANH KHANG Dai hoc Bdch Khoa Ha Noi Tdm tdt - C d c tieu ctnudn ve c h d t lUdng dien ndng iiien tai c u a Viet Nam chUa q u a n t a m nhieu d§'n sdng hdi vd c d c t d c hgi c u a nd SU ton tgi v d lan truyen sdng hdi tren lUdi p h d n phd'i g d y t d n t h d t dien n d n g rdt Idn Ngodi ra, c h u n g c d n g d y suy g i d m c h d t lUcJng dien ndng m o t c d c h d d n g ke SU xudt hien c u a sdng hdi tren lUdi p h d n phdi c d nguon g d c c h u y e u Id d o sU p h d t trien khdng kiem sodt c u a c d c p h u tdi phi t u y e n c o n g sudt Idn Viec khdng c h e p h d t thdi sdng hdi tren lUdi p h d n phdi, t h d m chf phdi c h u d n hda thdnh q u y p h q m trd t h d n h nhu c d u bOc thiet Mdt sdng dien ap dieu hda bat ky U(t) cd chu ky 271 deu cd the bieu dien dUdi dang tdng vd han cua sdng dien ap dieu hda cd ban va cac bdi sd cua nd vdi cac he sd tQdng Qng : f^(') = V + Z[f^-.'^os(ằ/) + C/,.sm(ô0] ã^ ,1=1 Trong dd f C/„^ =— ("f/(T).cos(«r).a'r «>0 'r C/„^ = — \U(T) sin(« T).dT L n>l Gl(3l THIEU Nhiem vu cua he thdng dien la truyen tai va phan phdi dien nang theo mdt chat iQdng phuc vu biet trQde Chat iQdng phuc vu d day dUdc hieu la cac tieu chuan cu the ve dien ap, tan sd va dp tin cay cung cap dien [1 ] Cac tieu chuan ky thuat dQdc quy chuan cu the mang tinh phap ly, cdn dp tin cay cung cap dien la mdt sU thda thuan giQa nha cung cap va ngUdi sCf dung nang iQdng Trong cac tieu chuan ky thuat, dieu ma ta quan tam nhat bai bao la mot chi tieu thupc ve chat lUdng dien ap [2]: dd la dp khong sin hay meo dien ap Cd nhieu nguyen nhan gay nen sU meo dien ap he thdng dien : n g i n mach dot nhien, cdng suat tai tang dot ngpt, qua dien ap quyen Trong bai bao nay, trQde het ta se de cap den ban chat va ngudn gdc tao nen sdng hai Sau dd, ta se di nghien cQu viec lan truyen sdng hai tren dQdng day cua he thdng phan phdi Mo hinh md phdng dUdc xay dung nham cu the hda cac Udc iQdng Cac tinh toan ve thong sd cua may bien ap, thdng sd dQdng day, thong sd cua phu tai va anh hudng cua chung den dp meo dang sdng dien ap dUPc lam rd IT SONG HAI A A fX^ a— 74 ^\ /' V? n.>-;/ Hinh Mdt ham so dieu hda bat ky deu phan tich tong mdt chudi cac ham sin va cos Ddi vdi ddng dien cdng nghiep tan sd 50 Hz, ngQdi ta thQdng quan tam den mdt vai sdng hai dac biet nhu cac sdng hai bac le 3, 5, 7, l o Su tham gia cua cac p h i n sdng bac cao vao sdng cd ban lam cho dang sdng cua sdng tdng hdp bj bien dang MQc dp tham gia cua cac sdng bac cao cang Idn thi dang sdng tdng hdp cang khac vdi dang sdng sin dieu hda [3] [4] Trong trQdng hdp ta gpi la meo dang sdng Ta cd the t i m thay meo dang sdng d ca ddng dien va dien ap Oe Qde iQdng dp meo dang sdng, ngQdi ta dung cac chi tieu tdng meo hai dien ap va tdng meo hai ddng dien nhQ sau : Dien dt D&i song 11 S KHOA HOC - CONG NGHE • Tdng meo hai dien ap : Ta cd the ke den cac bd ngudn may tinh vdi ddn vj hang ty chiec, tivi, cac he thdng may van phdng (photocopie, scanner, may in) Cd the ndi cQ vdi moi mdt thiet bj tieu thu cdng suat, ta cd mdt he thong chinh IQU dau vao Tuy thupc vao tieu chuan cua tQng nudc ma cac he thdng chinh iQu cd dUdc thiet ke de kiem soat phat thai sdng hai hay khdng HU THD,^ h>] u' Tdng meo hai ddng dien : CO THD, - ;i>i Trong dd cac gia trj U^ va 1^ (h>1) la gia trj hieu dung cua dien ap va ddng dien bac h Gia trj hieu dung toan phan dUPc tinh toan theo cdng thQc sau : U,,,,,= lY.(U;)=U,^l I^.,s-]'t(Il)=^^ + THD, + THD, Ta de dang nhan thay quan he giQa gia tri hieu dung toan phan, gia trj hieu dung sinh cong bac nhat va dp meo sdng hai tdng hdp Op meo hai cang Idn, mQc dp tham gia sinh cdng cua sdng cd ban cang giam di Hay ndi khac di, nhiem sdng hai cang Idn, kha nang truyen tai cdng suat tren dudng day cang giam di Hinh Cau true mdt he chinh lUu cd bien ap nguon cung cap Tuy nhien, thiet ke lam tang chi phi cho vat tu thiet bj Va dd vi muc dich giam chi phi dau vao va tang ldi nhuan ma da sd cac nha san xuat bd qua van de thiet ke Trong phan tiep theo, ta se xem xet den cac nguyen nhan gay d nhiem sdng hai chu yeu ludi phan phdi in NGU6N GOC CUA SONG HAI Cac Net ke dQdi day se xem xet cac ngudn gdc gay nhiem sdng hai tren iQdi phan phdi Danh sach khdng liet ke het tat ca cac ngudn gay nhiem ma chi chu yeu tap trung vao xac djnh rd cac ngudn nhiem cd ban, nang ne nhat Cac phu tai cd dac trUng quan he khdng tuyen tinh giQa ddng dien va dien ap thQdng gap la cac Id hd quang, Id luyen thep cam Qng, cac he thdng chinh iQu cdng suat, den phdng dien, cac he thdng dieu khien tdc dp ddng cd v v A Cac he thong chinh luu Tat ca cac he thdng chinh iQu d mpi mQc cdng suat deu la nhQng ngudn phat thai sdng hai Ngay nay, vdi sU phat trien manh me cua cdng nghe ban d i n va dien tCf cdng suat Qng dung, cac he thdng ngudn chinh lUu cd m§t d khap mpi ndi 12 Dien dt D&i song Hinh Dang sdng dien ap va ddng dien dau vao cua bd chinh luu Khi quan sat dang sdng cua ddng dien phia trUdc bd chinh iQu, ta de dang nhan thay dUdc mQc dp bien dang cua ddng dien va anh hudng cua nd den dien ap Tuy nhien, meo dien ap xuat hien meo ddng dien gay se dQdc xem xet d phan IV bai bao B Cac he thong dieu khien gdc md thyristor PhQdng phap thay ddi gdc md thyristor nham dieu khien gia tri trung binh dien ap dau PhQdng phap cd mpt Qu diem la cd the dat dUdc dai dieu chinh rpng va trdn Tuy nhien, viec bam sdng dien ap d cac gdc md khac d i n den dang sdng dau xau, mang nhieu nhieu KHOA HOC ' CONG NGHE Q I V LAN TRUYEN S(DNG HAI TR^N LU(3l PHAN PHOI C Bien tan Bien tan la mdt thiet bj bien ddi nang lUdng dien tQ tan sd sang tan sd khac theo mdt quy luat dieu khien phu hdp vdi yeu cau cua phu tai Oo dd, nd cho phep dieu khien ddng cdng suat truyen tQ ngudn den phu tai mdt each linh hoat nhat Bien tan dac biet phu hdp vdi cac he truyen ddng can dieu khien tdc dp (bdm nUdc, quat gid, bang chuyen, o) A Md hinh phu tai phi tuyen Ta xem xet mdt md hinh dien hinh cua mpt he chinh lUu ddn gian, cdng suat Idn Ta cd the gap md hinh d bat cQ mpt cd sd san xuat cdng nghiep cd trung binh nad (dac biet la san xuat thep, dien phan,o) Uif TRANSMISSION LINE DiSmiBUnON TRANSFORMER A ini„„ lUI n,,n u Hinh Sa dd nguyen ly lam viec cua bien tan Oau vao phd thdng cua bien tan la he chinh luu diode va tu Ipe nham dn djnh tang dien ap mot chieu Nhu ta da biet d tren, vdi mot tang chinh iQu dau vao ddn gian khong kem theo giai phap giam thieu sdng hai, bien tan chinh la mdt tac nhan gay nhiem sdng hai tram trpng tren ludi phan phdi Hinh So dd nguyen ly cua he thong thi nghiem lan truyen sdng hai Md hinh bao gdm mdt he thdng truyen tai 110 kV, dien ap trung ap 22 kV dQdc phan phdi den cac phu tai thong qua cac he thdng dudng day tren khdng, phu tai phi tuyen se dUdc sii dung mdt may bien ap rieng n h i m each ly vdi cac phu tai khac Ta se giam sat cac dai lUdng dien ap va ddng dien trUdc bd chinh iQu Vg^^j^, l^^^^i^iphu tai), trUdc may bien ap chuyen dung V^, 1^ va dau ngudn V^ ,,^,,., ^ SAMONT Ddi vdi bien tan, cac nhieu loan tren dien ap iQdi cd the khdng lam anh hQdng den che dp lam viec cua ban than bien tan Tuy nhien, cac nhieu loan lai cd anh hudng dang ke den nhOng phu tai nhay cam khac mac song song cung vdi bien tan Hien nay, vdi sU phat trien cua cac ky thuat dieu khien thong minh va cac vi xd ly manh, cac bien tan hien dai cd kha nang hap thu sdng hai Tuy nhien, cung phai ndi them rang dieu lam tang them chi phi tUdng ddi nhieu cho nha san xuat D Cac phu tai phi tuyen khac NONLINEAR LOAD UTtUTY TRANFORMER • ^ ^ »»« \ J ^ r1 I JI IZ ,.» Hinh Dien ap va ddng dien tai tieu thu V^,,,,,, L„,„, r- ^ • SVAL' SAVAL Cac phu tai phi tuyen khac ma ta cd the liet ke nhu cac ngudn phat thai sdng hai la cac he thdng den dng phdng, cac Id luyen thep dung cdng nghe hd quang va cam Qng, cac may bien ap lam viec d che dp bao hda Ta nhan thay rang cac phu tai gay nhiem sdng hai nhieu nhat chinh la cac bd bien ddi tinh Cdng suat cua cac loai cd the rat Idn vdi sd lUdng nhd hoSc cdng suat nhd vdi sd lUdng rat Idn Nhin chung, chung la tac nhan gay nhiem sdng hai chu yeu tren ludi phan phdi Hinh Dien ap va ddng dien chay tren dUdng day V^/j va dien ap nguon V.^ SAMONT Dien dt D&i song 13 S KHOA HOC • CONG NGHE Ta cd the de dang nhan thay meo dang sdng cua ddng dien va dien ap trudc phu tai, tren dudng day mac du phia dau ngudn cap cd dang sin chuan Meo dang sdng dien ap tren phu tai cd dang 16m Idn Su meo dien ap se cd nhOng anh hQdng xau nhat djnh ddi vdi nhung phu tai nhay cam dau ndi song song vdi phu tai phi tuye'n chinh d tren E Ban chat hien tuang meo dien ap song hai Oe di tim ban chat cua hien tupng tren, ta xet sd dd mot sdi cua nd nhU sau : gia tri Z ve zero dupc Cdn giai phap tang tiet dien day ro rang lam tang chi phi xay dUng • Khdng che ddng meo cua phu tai phi tuyen mdt khoang gidi han cho phep Theo tieu chuan cua uy ban ky thuat dien qudc te IEC-61000 hoac tieu chuan IEEE-519 [5][61, trQ nhQng trUdng hdp dac biet, dp meo ddng dien tdng yeu cau tQ phia phu tai khong dUPc vUpt qua 5% phu tai dd mudn da'u ndi vao he thdng phan phdi • Cach ly phu tai phi tuyen b i n g each nhdm cac phu tai nhQng cum rieng biet va cung cap bang nhQng dudng day rieng Giai phap cung lam tang chi phi xay dUng he thdng mot each dang ke V TAC HAI CUA S(DNG HAI A Anh huang den he thong dien ap Hinh Mo hinh mdt sol nghien cuu meo dien ap sdng hai Ta gia thie't rang nguon cung cap cd dang hinh sin tuyet ddi: f/^(/) = f/^.sin(wO Cac ddng dien tai l,(t), l.,(t) tUdng Qng vdi cac phu tai tuyen tinh va phi tuye'n Do dd, chung se cd dang sin tuyet ddi hoac khong sin Tdng cua chung cung se la m p t dang khong sin Ddng dien khong sin chay tren day dan, gay nen m o t sut ap khong sin #U tren tdng trd cua dUdng day Theo djnh luat Kirchhotf II, ta cd : Us{t) = AU +11,(1) Dieu dan tdi dien ap dat tren phu tai U|_ se bi meo dang sdng MQc dp meo cua dien ap tren phu tai se phu thuoc true tiep vao cUdng dp ddng dien meo chay tren dudng day, muc dp meo cua ddng dien phu tai phi tuyen, dd Idn cua tdng trd dudng day, cong suat cua ngudn, :> Ta nhan tha'y rang de giam bdt dp meo dien ap tren phu tai ta cd the dung mot sd bien phap sau : Giam tdng trd dudng day ve gan tdi zero Oieu ddng nghTa vdi viec xda bd dudng day hoac tang tiet dien Rd rang dieu la khdng the bdi vi dudng day dam bao lien ke't vat ly giua phu tai va ngudn d nhQng khoang each nha't dinh Ta khong the giam 14 Dien dt D&i song Anh hudng da dupc ta phan tich d tren Ro rang la vdi sU lan truyen cua sdng hai tren dudng day, meo dien ap se xuat hien sut ap tren tdng trd cua day dan MQc dp meo se phu thupc vao Idn cua ddng dien hai, dp sut ap tren dudng day, cong suat ngan mach ngudn Anh hudng thdng dien den cac phan cua he Ngoai viec gay meo dang dien ap tren ludi phan phdi - la mpt tac hai nhin thay duoc, dem dUpc, sdng hai cdn cd mpt sd cac tac hai tuPng ddi dai lau hdn Ta cd the ke de'n nhQ 1) May bien ap nguon Sdng hai lam phat ndng phu tren may bien ap cung cap day ta phai hieu ri ng ke ca may bien ap chuyen dung cung cap true tiep cho phu tai phi tuye'n cung nhu may bien ap phan phdi d phia d i u dudng day Hai dien ap gay tdn hao phu loi thep cua may bien ap Tdn hao cang Idn neu meo dien ap cang Idn (tdn hao tang theo tan sd) Tdn hao chinh la tdn hao s i t tang them Hai ddng dien gay phat ndng phu trpi tren day quan cac phia cua may bien ap Tdn hao ty le vdi binh phQdng ddng dien va cd ban chat la ton hao tren day quan Cac tdn hao phu trpi tren lam tang nhiet dp va dd, de dam bao vd an toan va tudi thp, kich thudc cua may bien ap phai tang len Cac may bien ap dupc thiet ke dung cho cac tai chinh luu, tai phi KHOA HOC - CONG NGHE Q tuyen manh phai dudc tang cong suat tinh toan thie't ke can phai tinh den cac tdn hao dang ke [7] Hoac neu ta cd mdt may bien ap cd cong suat biet trudc, neu dung may de nudi cho tai phi tuye'n, cong suat thuc nudi cho tai phi tuyen dd phai giam di He sd giam tai phu thuoc trUc tiep va phan tram ddng hai tai va tdn hao ddng xoay cupn day 2) Dgng ca xoay chieu Dpng cd xoay chieu dat dudi dien ap meo se bi tang tdn hao ddng xoay loi thep nhU trUdng hdp ddi vdi may bien ap Tuy nhien, meo dien ap cdn cd mpt anh hudng nghiem trpng hdn : Od la gay dao dpng momen tren true BAC SONG HAI VA THANH P H A N T H O T U Bdc song hdi so vdi thdnh phdn thii lit ddi xiCng Bdc song hdi Thii tu- 1.4.7,10,13,16.19 ThQ tQ thuan 2,5,8,11,14,17,20 ThQ tQ ngliich 3,6,9,12,15.18,21 ThQ tQ kliong Cac sdng hai bac le nhU 5, 11 dac biet nhay cam ddi vdi cac phu tai quay nhu dpng cd vi chung tao tQ trudng thQ tQ nghich quet ngQpc chieu quay cua dpng cd, gay rung, dn va cd the dan tdi pha hdng dpng cP Da sd cac thie't bi dem deu duoc che tao de van hanh d tan sd cong nghiep chuan (d nudc ta la 50 Hz) Neu khong cd sU tdn tai cua sdng hai, cac thie't bi dem se cho ta hinh anh chinh xac trang thai cua he thdng (gia trj ddng dien, dien ap) Tuy nhien, sU tdn tai cac p h i n sdng hai ddng dien can lam cho cac thiet bi khong cdn chinh xac nQa Cd the ly giai mot each ddn gian nhU sau : • tan sd chuan, bang thong cua thiet bi rat ldn Khi tdn tai sdng hai, bang thong hep lai Do dd, thdng tin cua thie't bj khong phan anh chinh xac va day du ddi tUdng nQa • Ddng dien hai chay qua sd cap cua bien ddng se lam bao hda sdm thiet bj dem Do dd, gia tri chi thi cua bien ddng se khong cdn chinh xac nQa VI KET LUAN Ta thay rang nhiem sdng hai la tac nhan chu ye'u gay nhieu loan dien ap d nhQng diem dau ndi chung Nguon gdc cua meo sdng hai ddng dien la sU tham gia mot each khdng kiem soat cua nhQng phu tai phi tuyen vao he thdng phan phdi MQc dp nhiem phu thupc vao cau true cua ludi phan phdi, mQc dp meo cua ddng dien hai Dp meo dien I p sdng hai se cang tang meo cua ddng dien cang ldn NhQng nghien cQu bai bao cho t h i y mQc dp anh hQdng tram trpng cua sdng hai neu khong dUdc kiem soat mot each chat che 3) Tu dien Phan Idn cac phu tai cong nghiep cung nhU sinh hoat mang tinh cam Va dd tu bu cong suat phan khang dUdc sii dung nhieu de cai thien he sd cong suat Dien khang cua tu dien ty le nghjeh vdi tan sd Do dd, mac tu bu vao lUdi, ngudi ta can phai dac biet chu y tdi kha nang cpng hudng cd sU tham gia cua tu va dien cam phdi hpp tdng trd Ro rang la vdi sU cd mat cua cac sdng hai tren ludi, viec lUa chpn mdt gia trj thich hpp cua tu bu de vQa dam bao yeu cau ve cdng suat phan khang, lai vQa p h i i dam bao yeu cau ve cpng hudng la rat khd Hon nQa, dien khang cua tu ddi vdi tan sd cao rat be, dieu cd the dan den viec qua tai tu, tham chi mpt sd trQdng hpp cdn cd the gay bao ve tac dpng nham vdi ngan mach TAI LIEU THAM KHAO [11 Tran Bach, Lu6i dien & He thong dien, tap 2, Nha xuat ban Khoa hpc ky thuat, 2004 [21 Thiet ke may bien ap, Pham Van Binh, Le Van Doanh, NXB Khoa hoc va ky thuat, 2003 [31R.C Dugan, M.F McGranaghan, H.W Beaty, Electrical Power Systems Quality, McGraw-Hill, NewYork, 1996 [4] Parihar, P.; Liu, E.; "Identification, Classification and Correlation of Monitored Power Quality Events" Power Engineering Society 1999, Winter Meeting Vol 1, PP 437-441 [51 CIGRE WG 36.05; "Equipment producing harmonics and conditions governing their connection to the mains power supply" Electra N 23.March 989, pp 21-37 C Anh hudng den thiet bi lUdng, bao ve [6] IEEE Std 519-1992 IEEE Recommended Practices and Requirements for Harmonic Control in Electrical Power Systems Su tdn tai cua sdng hai ddng dien tai cd nhung anh hudng nhat djnh tdi dd chinh xac cua thie't bi dem va bao ve [71 IEEE Working Group on Nonsinusoidal Situations, "Practical Definitions for Powers in System with Nonsinusoidal Waveforms and Unbalanced Loads: A Discussion", IEEE Transactions on Power Delivery Dien dt D&i song 15