Ti sao cn ci thin h s cng sut:

I.Ti sao cn ci thin h s cng sut: 1. Gim gi thnh tin in: - Nng cao h s cng sut em li nhng u im v k thut v kinh t, nht l gim tin in. - Trong giai on s dng in c gii hn theo qui nh. Vic tiu th nng lng phn khng vt qu 40% nng lng tc dng (tg > 0,4: y l gi tr tho thun vi cng ty cung cp in) th ngi s dng nng lng phn khng phi tr tin hng thng theo gi hin hnh. - Do , tng nng lng phn khng c tnh tin cho thi gian s dng s l: kVAr ( phi tr tin ) = KWh ( tg 0,4) - Mc d c li v gim bt tin in, ngi s dng cn cn nhc n yu t ph tn do mua sm, lp t bo tr cc t in ci thin h s cng sut. 2. Ti u ho kinh t - k thut - Ci thin h s cng sut cho php ngi s dng my bin p, thit b ng ct v cp nh hn V.Vng thi gim tn tht in nng v st p trong mng in. - H s cng sut cao cho php ti u ho cc phn t cung cp in. Khi y cc thit b in khng cn nh mc d tha. Tuy nhin t c kt qu tt nht, cn t t cnh cnh tng phn t ca thit b tiu th cng sut phn khng. * Ci thin h s cng sut

- ci thin h s cng sut ca mng in, cn mt b t in lm ngun pht cng sut phn khng. Cch gii quyt ny c gi l b cng sut phn khng. -Ti mang tnh cm c h s cng sut thp s nhn thnh phn dng in phn khng t my pht a n qua h thng truyn ti phn phi. Do ko theo tn tht cng sut v hin tng st p. - Khi mc cc t song song vi ti, dng in c tnh dung ca t s c cng ng i nh thnh phn cm khng ca dng ti. v vy hai dng in ny s trit tiu ln nhau IC = IL. Nh vy khng cn tn ti dng phn khng qua phn li pha trc v tr t t. - c bit ta nn trnh nh mc ng c qu ln cng nh ch chy khng ti ca ng c. Lc ny h s cng sut ca ng c rt nh (0,17) do lng cng sut tc dng tiu th ch khng ti rt nh.

II. Cc thit b b cng sut: 1. B trn li in p Trong mng li h p, b cng sut c thc hin bng : - T in vi lng b c nh (b nn). - Thit b iu chnh b t ng hoc mt b t cho php iu chnh lin tc theo yu cu khi ti thay i. Ch : Khi cng sut phn khng cn b vt qu 800KVAr v ti c tnh lin tc v n nh, vic lp t b t pha trung p thng c hiu qu kinh t tt hn.

2. T b nn B tr b gm mt hoc nhiu t to nn lng b khng i. vic iu khin c th thc hin: - Bng tay: dng CB hoc LBS ( load break switch ) - Bn t ng: dng contactor - Mc trc tip vo ti ng in cho mch b ng thi khi ng ti. Cc t in c t: - Ti v tr u ni ca thit b tiu th in c tnh cm ( ng c in v my bin p ). - Ti v tr thanh gp cp ngun cho nhiu ng c nh v cc ph ti c tnh cm khng i vi chng vic b tng thit b mt t ra qu tn km. - Trong cc trng hp khi ti khng thay i. 3. B t b iu khin t ng ( b ng ng ) - B cng sut thng c hin bng cc phng tin iu khin ng ngt tng b phn cng sut. - Thit b ny cho php iu khin b cng sut mt cch t ng, gi h s cng sut trong mt gii hn cho php chung quanh gi tr h s cng sut c chn. - Thit b ny c lp t ti cc v tr m cng sut tc dng v cng sut phn khng thay i trong phm vi rt rng. v d: ti thanh gp ca t phn phi chnh, ti u ni ca cc cp trc chu ti ln.

Cc nguyn l v l do s dng b t ng: - B t b gm nhiu phn v mi phn c iu khin bng contactor. Vic ng mt contactor s ng mt s t song song vi cc t vn hnh. V vy lng cng sut b c th tng hay gim theo tng cp bng cch thc hin ng hoc ct contactor iu khin t. Mt rley iu khin kim sot h s cng sut ca mng in s thc hin ng v m cc contactor tng ng h s cng sut c h thng thay i ( vi sai s do iu chnh tng bc ). iu khin rle my bin dng phi t ln mt pha ca dy cp dn in cung cp n mch c iu khin. Khi thc hin b chnh xc bng cc gi tr ti yu cu s trnh c hin tng qu in p khi ti gim xung thp v do kh b cc iu kin pht sinh qu in p v trnh cc thit hi xy ra cho trang thit b. - Qu in p xut hin do hin tng b d ph thuc mt phn vo gi tr tng tr ngun. Cc qui tc b chung - Nu cng sut b t ( kVar ) nh hn hoc bng 15% cng sut nh mc my bin p cp ngun, nn s dng b nn. - Nu trn mc 15%, nn s dng b kiu t ng. - V tr lp t t p trong mng in c tnh n ch b cng sut; hoc b tp trung, b nhm, b cc b, hoc b kt hp hai phng n sau cng. - V nguyn tc, b l tng c ngha l b p dng cho tng thi im tiu th v vi mc m ph ti yu cu cho mi thi im. - Trong thc tin, vic chn phng cch b da vo cc h s kinh t v k thut.

V tr lp t t b: 3.1 B tp trung : p dng cho ti n nh v lin tc. Nguyn l : b t u vo thanh gp h p ca t phn phi chnh v c ng trong thi gian ti hot ng. u im: - Gim tin pht do vn tiu th cng sut phn khng . - Lm gim cng sut biu kin. - Lm nh ti cho my bin p v do n c kh nng pht trin thm cc ph ti cn thit. Nhn xt : - Dng in phn khng tip tc i vo tt c l ra t phn phi chnh ca mng h th. - V l do ny kch c dy dn , cng sut tn hao khng c ci thin ch b tp trung. 3.2 B nhm ( tng phn on ). B nhm nn s dng khi mng in qu ln v khi ch ti tiu th theo thi gian ca cc phn on thay i khc nhau. Nguyn l : b t c u vo t phn phi khu vc . hiu qu do b nhm mang li cho dy dn xut pht t t phn phi chnh n cc t khu vc c t t c th hin r nht. u im:

- Lm gim tin pht do vn tiu th cng sut phn khng. - Lm gim cng sut biu kin yu cu. - Kch thc dy cp i n cc t phn phi khu vc s gim i hoc vi cng dy cp trn c th tng thm ph ti cho t phn phi khu vc. Nhn xt : - Dng in phn khng tip tc i vo tt c dy dn xut pht t t phn phi khu vc. - V l do ny m kch thc v cng sut tn hao trong dy dn ni trn khng c ci thin vi ch b nhm. - Khi c s thay i ng k ca ti, lun lun tn ti nguy c b d v km theo hin tng qu in p. 3.3 B ring: B ring nn c xt n khi cng sut ng c ln ng k so vi mng in. Nguyn l: b t mc trc tip vo u dy ni ca thit b dng in c tnh cm ( ch yu l cc ng c ). B t nh mc ( kVAr) n khong 25% gi tr cng sut ng c. B b sung ti u ngun in cng c th mang li hiu qu tt. u im : Lm gim tin pht do tiu th cng sut phn khng (kVAr) Gim cng sut biu kin yu cu.

Gim kch thc v tn hao dy dn i vi tt c dy dn. Nhn xt : Cc dng in phn khng c gi tr ln s khng cn tn ti trong mng in. 3.4 Mc b ti u Phng php chung Bng s liu tnh ton cng sut phn khng cn thit trong giai on thit k. qua c th xc nh cng sut phn khng v cng sut tc dng cho mc b khc nhau. Vn ti u ho kinh t k thut cho mt mng in ang hot ng. Vic tnh ton nh mc b ti u cho mt mng tn ti c th thc hin theo nhng lu sau: + Tin in trc khi t b + Tin in tng lai sau khi lp t b. + Cc chi ph bao gm : - Mua t b v mch iu khin. - Lp t v bo tr - Tn tht trong t v tn tht trn dy cp, my bin p sau khi lp t b.

III. Chn T B : 1. Phng php tnh n gin: ( chn t b cho mt ti no th ta cn bit cng sut(P) ca ti v h s cng sut (Cos ) ca ti ): Gi s ta c cng sut ca ti l P H s cng sut ca ti l Cos 1 tg 1 ( trc khi b ) H s cng sut sau khi b l Cos 2 tg 2. Cng sut phn khng cn b l QC = P (tg1 tg2 ). T cng sut cn b ta chn t b cho ph hp trong bng catalog ca nh cung cp t b. d hiu ta s cho v d minh ho nh sau: Gi s ta c cng sut ti l P = 270 (KW). H s cng sut trc khi b l cos1 = 0.75 tg1 = 0.88 H s cng sut sau khi b l Cos2 = 0.95 tg2 = 0.33 Vy cng sut phn khng cn b l Qb = P ( tg1 tg2 ) Qb = 270( 0.88 0.33 ) = 148.5 (KVAr) T s liu ny ta chn t b trong bng catalog ca nh sn xut gi s l ta c t 25KVAr. b cho ti th ta cn b 6 t 25 KVAr tng cng sut phn khng l 6x25=150(KVAr) vi 6 t b ny ta chn b iu khin 6 cp nh s hnh v:

2. Phng php b ti u da vo iu kin khng ng tin pht: Xt ho n tin in lin quan n dung lng kVArh tiu th v ghi nhn s kVArh phi tr tin sau , chn ho n tin gi kVArh cao nht phi tr (khng xt n trng hp ngoi l). V d: 15965 kVArh trong thng ging Tnh tng thi gian hot ng trong thng v d : 220h s gi xt tnh l nhng gi m h thng in chu ti ln nht v ti t gi tr nh cao nht. ngoi thi gian k trn vic tiu th cng sut phn khng l min ph. Gi tr cng sut cn b: [kVAr] = = Qb kVAr : s kVAr phi tr tin. T : s gi hot ng Dung lng b thng c chn cao hn gi tr tnh ton mt cht. Mt s hng cung cp qui tc thc loga thit k t bit cho vic tnh ton ny theo cc khung gi ring. Cng c trn v cc d liu km theo gip ta chn la thit b b v s iu khin thch hp, ng thi rng buc ca cc sng hi in p trong h thng in . cc sng hi ny i hi s dng nh mc t d (

lin quan n gii nhit, nh mc p v dng in ) v cc cun khng hoc mch lc sng hi.