•W TIET KIEM NANG
L J O N GTIET KIEM NANG LlfCfNG NHIN Tl/ MOI PHIA:
• • •
BO LOC TJCH CUC
Nhffng han che cua bo bu tinh
Cac bd tu bli dvfp'c sii dung rdng rai, dvfp'c coi la giai phdp chii yeu trong viec nang cao he sd' cdng sua't cosq) ciia tai, Idm giam cdng sud't phan khdng, giam tdn that cdng sud't, nang cao chd't lu'Png dien dp va ndng cao kha ndng truyen tai ciia he thd'ng dien. Vi the nganh dien quy dinh gid tri coscp^^.^
^^^^^ > 0,85. Khi lam viec dvfdi gia tri nay trong hda dPn tien dien khach hang phai cdng them tien mua cdng sud't phan khdng (tien phat coscp). Khi tai thay dd'i mach tvf ddng d i l u khiln cdng tac tP, Idm thay dd'i gia trj dien dung C ciia tu bii den gid trj mong mud'n. Neu bii qua cd nguy cP lam dien dp tang cao, anh hu'dng xd'u den cdch dien ciia cdc thiet bj dien.
Tuy nhien bd tu bu cd d i l u khiln bang cdng tac tP chi thich hp'p dd'i vdi cdc tdi cd ddc tinh tuyen tinh, ddi vdi cdc tai phi tuyen mach nay khdng thich hp'p niia (hinh 1).
7
Anh hiidng cua sdng hai bac cao
Cdc tai thvfc te nhvf mdy tinh, bd chinh Ivfu, bien tdn thvfdng sii dung bp bi^'n ddi dien tii cdng sud't, trong do cdc tiristo, IGBT chuyin mach Idm thay ddi dang sdng ddng dien, dien dp. Cdc tai phi tuyen nhvf den phdng dien chd't khi. Id hd quang. Id cam iing ciing la nguyen nhdn lam dang sdng ddng dien, dien dp trd n§n khdng hinh sin (hinh 2).
Sdng khdng hinh sin cd t h i phdn tich thanh tdng cua cdc d i l u hda hinh sin cd tdn sd khde nhau theo cdng thiic Fourier. Sdng hinh sin cd tdn sd' bang tdn sd sdng khdng hinh sin gpi la sdng cP ban, cdn cdc sdng cd tdn sd' ldn hPn sdng cP ban la sdng hai bdc cao. Bien dp ciia sdng hai bac cao giam ddn.
Trong sd' cdc sdng hai thi hai bac ba cd bien dp Idn nhd't. Trong mach ba pha hdi bdc ba ciia cdc pha cd gdc lech pha bdng 3x120° = 360°, nghia la trung pha, chiing hp'p thanh he thd'ng thii tvf khdng vd
"<S< PGS LE VAN DOANH Trudng DHBK Hd Noi
Hinh 1: Bd tu bu AV4000/5000 dilu khiln bang cdng tie td ciia
Schneider
Dong dien i Dien ap u
H'mh 2; Dang sdng ddng dien, di&n dp qua tai phi tuyin
42 Oien A Ddi song
T I E T K I E M N A N G
L U O N G khep m a c h trong d d y t r u n g tinh, lam qud tai hethd'ng trung tinh.
I le so' meo dilu hda THD (Total Harmonic Distorsion)
Trong dd I Id tri sd h i e u d u n g ciia hai bac n, I la trj so hieu d u n g cvia d i l u hda cP b a n . T H D danh gid a n h hvfdng ciia s d n g hai dd'i vdi Ivfdi dien. Theo IEEE 519-1992 dd'i vdi m p i loai tdi quy djnh THD < 5%, rieng dd'i vdi tai ky t h u a t sd THD < 3%.
Cdc sdng hai d d n de'n:
• Tang d d n g dien tai (tdi 50%), gdy qud tai ngudn, cap, mdy bien dp, g i a m hieu sud't ciia ddng cP khdng d d n g bd;
• Gidm dien dp tr§n tai;
• Giam he sd' cdng sud't coscp;
• Gdy cdng hifdng trong m a c h ;
• Gdy nhilu, lam dnh hvfdng tdi cdc thiit bj dien tii.
Vi cac ly do nay ngifdi ta p h a i tim cac bien p h a p giam t h i i u cac hai bac cao.
D l giam cdc hai bdc cao cd t h i sii d u n g cdc giai p h a p :
• Sif d u n g cudn khdng chdn (hinh 3);
• Sii d u n g m a c h lpc thu d d n g (hinh 4);
Hai phvfong dn nay chi cd tdc d u n g b a n
Hinh y. C u o n khdng chan
H i n h 4: M a c h lpc t h u d o n g
ch^ mdt sd' hai bdc cao cho cdc p h u tai cd d a c tinh phi tuyen tinh. Khdng t h i t a n g mdi dien khang cvia cudn chan vi sut dp l a m g i a m cdng sud't ciia tdi. Bd lpc LC cho p h e p gidm T H D tdi 10%, cd t h i tdi 5% khi phd'i h p p vdi dien k h d n g chdn. Dd'i vdi cac p h u tdi d d n g cd ddc tinh p h i
t u y e n tiic thdi l u d n bien d d n g nhu' may ban. Id hd q u a n g cdn sii d u n g bd lpc tfch cifc.
Bo loc tich cvfc
La bd lpc sii d u n g p h a n tif dien tif cdng sua't d l t a o n e n cac s d n g hai bdng vd ngifPc p h a v d i s d n g h a i p h a t sinh trong mach. K i t qua la cdc t h a n h p h a n s d n g hai bj triet tieu d o d d d a n g s d n g ciia n g u d n se t h u d n tiiy hinh sin. Tai h i n h 5 ta thdy t d n g ciia s d n g hai do n g u d n I^ ^^^ vd s d n g h a i d o bd lpc tich cifc phdt ra I|^^ b a n g k h d n g . Tuy n h i e n cdc sdng nay l u d n t h a y dd'i, d o do bd lpc tich cifc can difp'c d i l u k h i l n theo tin h i e u d a n g sdng n g u d n va d a n g s d n g tai va dvfp'c p h a n a n h qua p h a n h d i d d n g dien. N h d bd lpc tich cifc chdt lifpng d i e n d p ciing difp'c n d n g len va tcin hao cdng s u a t t r o n g Ivfdi se g i d m di (hinh 5).
S6ng ngu6n S6«ig hA. \ut> S6ng hii M loc S(yig ting trong
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Tii phi tuydnBflpc ttdiqic
Hinh 5: N g u y e n ly bd lpc tfch cifc S P dd bd tu bii dvfpc d i l u k h i l n bdng phan tli dien tii cdng sud't nd'i song song ngifpc d hai p h a A, B. Cdc tiristo difp'c d i l u k h i l n sao cho gidm t h i i u cdc hdi bac cao phii h p p vo'i sif bien
A B r thien ciia tdi (hinh 6).
K i t ludn: Bd lpc tich cifc cd tdc d u n g ndng cao chat Ivfp'ng dien dp va giam tdn hao cdng sua't trong mach cd p h u tai phi t u y i n . Day la bd t i l t kiem dien, cd the tilt kiem 4-5% dien ndng Nhifpc d i l m la gia thanh tifPng dd'i cao, tuy nhien loi ich ciia tiet kiem se nhanh chdng hoan vdn.
1 ^ ^
Hmh 6: Bd tu bli ddng
