* T B TNH (SVC) t vn :Cc nh my cn thp, nh my xi mng, ... (s dng nhiu ng c cng sut ln c tc quay lun thay i, khng n nh trong qu trnh lm vic), nh my luyn thp (cc l h quang in) sinh ra cc sng hi bc 2, 3, 5, 7, ...

Cc sng hi ny lm tng tn tht cng sut, gy dao ng in p, nhp nhy in p, gy ting n, gim h s cng sut, mt n nh in p, gim kh nng qu ti ca my bin p, ... lm nh hng ti hiu qu hot ng ca thit b cng nh li in ln cn.

=> V vy yu cu cn c mt thit b khc phc cc nhc im trn.V SVC l mt thit b nh vy.

SVC l g? SVC (Static VAR Compensator) hay cn gi l T b tnh c dung lng thay i l mt thit b b cng sut phn khng tc ng nhanh trn li truyn ti in p cao.

SVC l thit b t ng iu chnh in khng, c ch to iu chnh in p ti cc nt t SVC v iu chnh cng sut phn khng. - Nu h thng tha cng sut phn khng hay in p ti nt cao hn gi tr cho php, SVC s ng vai tr l cc khng b ngang. Khi , SVC s tiu th cng sut phn khng t h thng v h thp in p ti nt iu chnh.

Ngc li, nu h thng thiu cng sut phn khng, cc t b ngang s c t ng ng vo. => Do , cng sut phn khng c bm thm vo h thng, in p ca nt c ci thin.

Tm li, chc nng c bn ca h thng SVC gm: - Nng cao h s cng sut.

- Ngn chn sng hi. - n nh in p. - Khc phc dao ng in p. - Khc phc nhp nhy in p. - Gim s lm vic trc trc ca thit b. - Cn bng pha. - Tng cng sut. - Tit kim in cc v gim tn nng lng.

Mt s hnh nh v cc t b tnh:

H thng b v lc sng hi trung v h th SVC cho nh my thp

H thng b v lc sng hi - SVC trong nh

H thng b v lc sng hi SVC (Static VAR Compensator)

Cu to & nguyn tc hot ng:Mt SVC in hnh gm cc t b ngang c ng ct ring bit, c kt ni vi cun dy in cm (c hoc khng c li st) c iu chnh bng thyristor. Nh vic thay i gc dn ca thyristor m in khng ng tr ca SVC c th thay i lin tc c. Do , cng sut phn khng ca li in c th c bm vo hay ht i mt cch lin tc.S 1 si ca mt SVC in hnh; mt cun dy in cm c iu khin bng thyristor (TCR) c ni vi ba b t ng ct

Theo cu trc ny, cc t in s iu chnh th, sau , cc thyristor s iu chnh gi tr cm khng, kt qu l gi tr in khng ng tr l mt gi tr lin tc. iu chnh trn hn v linh hot hn c th thc hin c bng cch s dng b t in c ng ct bng thyristor hay TCCS (thyristor-controlled capacitor switching).

Li ch:Li ch chnh ca vic s dng SVC so vi cc t b c ng ct c kh l chng phn ng gn nh tc thi vi s thay i in p ca h thng. V l do ny, chng thng hot ng gn st nt iu chnh t hiu qu iu chnh cao nht khi c nhu cu. SVC ni chung r hn, c dung lng cao hn, iu chnh nhanh hn v tin cy hn so vi cc thit b b khc nh my b ng b.