Facts File Tv

Chng 1. Vai tr ca cc b bin i bn dn cng sut trong h thng in

1

Chng 1 Vai tr ca cc b bin i bn dn cng

sut trong h thng in

1.1. m bo tnh n nh ca h thng nng lng

Tnh n nh ca h thng nng lng c nh ngha l kh nng ca h thng

trong trng thi cn bng trong iu kin lm vic bnh thng v c th quay v c

trng thi cn bng chp nhn c sau nhng bin ng nhiu tc ng. Khi mc

phc tp ca h thng nng lng ngy cng tng ln do ngy cng c nhiu loi ngun

pht tham gia vo h thng v nhiu loi ph ti kiu in t cng sut tc ng nhanh

th h thng nng lng cng phi lm vic gn n gii hn ca n nh.

n nh ca h thng nng lng chia lm hai dng chnh: n nh gc ph ti

ca cc my pht v n nh in p. Vn th nht lin quan ch yu n li truyn

ti, trong khi vn th hai c tnh cc b hn, lin quan n li phn phi. n nh

gc ph ti l n nh tn s hay m bo tnh ng b. n nh in p l m bo mc

dao ng trong phm vi cho php, khng qu +/- 10% quanh gi tr nh mc trong

iu kin bnh thng v kh nng quay v phm vi ny sau khi c bin ng sy ra,

trnh trng hp in p st gim dn n hiu ng dy chuyn. m bo in p cn

p ng ng cng sut phn khng cho li v iu khin cc mc in p ph hp

bng cc cp cun dy my bin p.

n nh gc ph ti rotor li chia thnh n nh vi bin ng ln (s c xy ra ti

l no ) v n nh vi bin ng nh (s thay i ph ti). V bn cht vt l c hai

trng hp trn u lin quan n vn n nh cc dao ng c in do tng tc gia

cc qu trnh in v c trong h thng bin i c nng thnh in nng. Qu trnh bin

i ny c trng bi phng trnh ng hc cho my ng b nh (1.1)

2

22m e

d dT T H D

dt dt

(1.1)

Vi ,eT K V

Trong Tm v Te l mmen c v mmen in t, H mmen qun tnh quy v

trc my in, D h s dp dao ng, K hng s v l gc rotor. Vi bin ng nh

phng trnh (1.1) c th tuyn tnh ha quanh im lm vic cn bng, dn n:


2

2

022 cosm e

d dT T H D K

dt dt

(1.2)

40

1 sincos

Dt

HmT e tK

(1.3)

Gii phng trnh (1.2) tm ra gc rotor nh (1.3), trong tn s dao ng xc

nh bng (1.4):

2

0cos

2 4

K D

H H

(1.4)

T phng trnh (4), thay nhng tham s tiu biu ca cc t my vo, c th thy

tn s dao ng trong khong 0,1 2,5 Hz.

Nhng dao ng ny c th pht sinh do nhng bin ng nh v tip din lin tc

trong h thng. Nhng dao ng vng tn s cao, khong 0,7 2 Hz, thng din ra

cc b ti mt t my, khng nh hng n ton b li in, gi l dao ng cc b.

Nhng dao ng vng tn s thp, 0,2 0,8 Hz, din ra gia cc t my vi nhau v rt

kh b dp tt. Chng sinh ra cc qu trnh trao i cng sut thng qua li truyn ti

gia cc nh my v cc t my vi nhau, gia vng ny vi vng kia ca li in. Cc

dao ng ny xut hin trong nhiu li in, ti nhiu ni trn th gii. Hu qu ca cc

dao ng lin vng ny l xung ng ln cc rotor ca cc t my, lm mi cc c cu c

kh, dn n nhng hng hc cc b phn iu khin, a n nhng chi ph kh lng.

Dao ng lin vng lm gim kh nng truyn ti ca li in, c th dn n gi li

trong mt s trng hp.

dp tt dao ng cn dng cc b iu khin. Cc b iu khin cc b l b

n nh cng sut h thng (Power System Stabilizer PSS) kt hp cng h thng iu

khin kch t my pht. PSS pht cc tn hiu cng pha vi s thay i ca tc rotor

sao cho cc dao ng ny b dp tt. Trn hnh 1 l cu trc b iu chnh PSS, gm bn

khu ni tip: khu khuych i, khu lc thng thp pht hin s thay i vi tn s

thp, hai khu lead/lag to sm pha cn thit cho tn hiu a vo mch kch t.


3

Hnh 1.1. B iu chnh PSS chng dao ng h thng.

u vo l tn hiu bin ng tn s quay rotor, u ra l tn hiu ph tc ng vo

mch iu chnh kch t my pht.

dp dao ng lin vng s cn cc h thng FACT, nh SVC, STATCOM.

SVC hay STATCOM l cc thit b b song song, c th c tc ng iu chnh in p

ti im kt ni theo hng b lm tt dao ng. B iu chnh ca SVC c thm u

vo Additional input phn nh s dao ng ca li (tn s ), u ra tc ng thay i

dn B ca SVC nh biu din trn hnh 1.2.

Hnh 1.2. B iu chnh cho SVC c tc dng dp dao ng trn li.

Trn hnh 1.3 l cu trc b iu chnh ca STATCOM, c thm u vo phn nh

s dao ng ca li (tn s ), u ra tc ng thay i gc lch pha gia in p ra

ca STATCOM so vi im kt ni. T c th a vo hay ly ra cng sut, b li s

dao ng ca li in.


4

Hnh 1.3. B iu chnh cho STATCOM c tc dng dp dao ng trn li.

Ngoi ra cc thit b FACTS khc nh TCSC, TCPS, UPFC, cng u c th

chnh nh c tc dng chng dao ng.

1.2. iu khin cht lng in nng

Nhng vn chnh lin quan n cht lng in nng l:

- n nh in p;

- Sng hi;

- Lm in p;

- Qu in p;

- in p nhp nhy,

Tuy nhin ngy nay khi nim cht lng in nng mang ngha rng hn. Cht

lng in nng bao hm ton b cc quan h phc tp gia nh sn xut v ngi tiu

dng in, t nh my n khch hng cui cng. Trong sn xut v trong i sng hng

ngy xut hin nhiu loi thit b, my mc c yu cu cao v n nh, tnh lin tc

ca ngun in cung cp. Cc h thng dch v v sn xut cng thay i mi quan h

gia hot ng sn xut, kh nng cung cp dch v p ng cc nhu cu ca khch hng

nh mt trong nhng mi quan tm hng u. Tm li nhng trc trc nh trong h thng

cung cp nng lng c th dn ti nhng tn tht ln v kinh t. Chnh v vy ngy nay

khch hng t ra nhng tiu chun m nh sn xut v phn phi in phi p ng.

Khch hng thng c lin h vi nh cung cp in ngay t nhng khu u tin trong

qu trnh thit k, xy dng, lp t cng nh s dng hng ngy c m bo cung

cp in ph hp nht.


5

Ngi s dng s chu nh hng mnh nht ca cc hin tng: lm in p, mt

ngun ngn hn v sng hi.

- Lm in p: hin tng in p st gim xung ti 0,1 n 0,9 p.u. trong thi

gian 0,5 chu k in p li (10 ms 50 Hz) n 1 pht. Lm in p thng xut

hin do c s c trn ng truyn ti hoc ng phn phi lm cc thit b bo

v tc ng, do cc ng c cng sut ln khi ng. Do lm in p nhiu thit

b s b ngng hot ng, nh cc cng tc t, cc bin tn, thit b iu khin in

t, dn n c dy chuyn c th phi dng li. iu ny c th gy nn nhng

hu qu nghim trng.

- Mt in ngn hn xy ra khi in p gim n 0 trong 1s n 5 pht. Cc hu qu

sy ra cng ging nh lm in p, tuy nhin vic khc phc s phc tp hn

nhiu.

- Vn sng hi tr nn nghim trng hn do ngy cng c nhiu loi ph ti phi

tuyn c s dng nh cc b bin i bn dn, cc ph ti mt pha hoc do cc

qu trnh ph ti bin ng nhanh.

Sng hi c trng bi h s mo phi tuyn tng th:

ax

2

2

1

mh

h

h

M

M

THDM

(1.5)

Trong h l bc ca sng hi, s nguyn ln tn s c bn. mo phi tuyn

sng hi i vi dng in th hin r nht tc ng ca mo phi tuyn i vi cc thit

b trong h thng v dng in mi phn nh c cng sut.

ax

2

2

mh

h

h

I

L

I

TDDI

(1.6)

Trong IL l dng ti ln nht tn s c bn, ly gi tr trung bnh cho ph ti

trong 12 thng cui cng.


6

1.2.1. Kim sot lm in p

gim thiu cc tn tht kinh t do lm in p mang li cn thc hin mt s

bin php. Lm in p pht sinh ch yu do cc s c xy ra trn mng in, v vy bin

php u tin l loi tr cc nguyn nhn dn n s c. Trong li truyn ti cn m

bo s vng chc ca cc ct ng dy, lm sch s , lp t cc my ct tc ng

nhanh v cc cun chn tip t. Trong li phn phi cn ct ta cy gn ng dy, lp

t cc b by ng vt, thit k h thng theo mch vng ch khng phi hnh sao, lp

t cc thit b bo v nhanh, Tuy cc bin php p dng cng khng th m bo

loi tr c ht cc s c.

Cc bin php tip theo cn p dng l s dng cc thit b gip vt qua cc lm

in p. Cc thit b FACTS (SVC, DVR, STATCOM) c th dng cho nhng mc ch

ny. Tuy nhin cc thit b ny tng i t tin. V li khng phi h tiu th no cng

cn mc bo v nh nhau v dch v vi gi thnh cao cho cc ph ti khng yu cu

khc nghit v cht lng in p s b phn i. V vy cc thit b tng t nh

FACTS nhng c thit k ph hp cho lui phn phi, p dng ring cho nhng ph

ti quan trng, vi cng sut nh hn, gi thnh thp s c tim nng ng dng nhiu

hn.

Ngoi nhng bin php trn vi cng sut va phi c th dng nhng loi thit b

khc, l nhng thit b tch tr nng lng in. Thit b tch tr nng lng hot ng

theo nguyn tc tch nng lng lc ti nh v a ra nng lng lc cn thit, p ng

nh ph ti, c th l ch trong mt thi gian ngn. Cc thit b ny c th l:

- H thng tch tr nng lng bng acquy (BESS);

- H thng dng bnh vnh cu (Flying Wheel);

- H thng tch tr nng lng dng cun cm siu dn (SMESS);

- H thng cp in lin tc (UPS).

c im ca cc h thng tch tr nng lng trn y l kh nng pht huy cng

sut trong thi gian rt ngn, c 0,1ms n 1s, ph hp vi thi gian xy ra lm in p

hay nhy in.

1.2.2. Kim sot thnh phn sng hi

Sng hi xut hin trong li in do nhiu nguyn nhn, do ti phi tuyn nh cc

b bin i bn dn, do mt s lng ln cc ph ti mt pha, do qu trnh ng ct ngu

nhin ca cc loi ph ti, Sng hi s i qua nhiu khu suy gim trc khi n c


7

ph ti. V d qua s phi hp cch u dy my bin p, tam gic hoc sao, qua cc

cun cm chn pha u vo. Cch suy gim sng hi tt nht l ti ch c th pht sinh

sng hi bng nhng thit k ph hp. K thut gim sng hi ph bin nht trong cc b

bin i l phng php bin iu b rng xung PWM.

Khi sng hi pht sinh vi cng sut ln cn nhng thit b lc. Thit b lc th

ng thch hp vi li phn phi (trung th), va lc va c tc dng b cng sut

phn khng. Lc th ng ch yu dng mch song song, ni ti nhng im c th ngn

chn s xm nhp ca sng hi vo ti. Do c tc dng b cng sut phn khng nn khi

thit k ban u cn chn dung lng t cn thit tn s c bn. Sau s tnh ton

in cm mc ni tip vi t to thnh mch cng hng tn s sng hi cn phi

dp, tiu biu l cc tn s bc 2, 4, 5, 7, Cui cng l thnh phn in tr cn a vo

mch to c tnh suy gim dao ng v chn lc v tn s ca b lc. Thng

thng vi cng sut ln cc mt lc sng hi bc 2, 4, 5, 7, c thit k v lp t

ring, ti im nt ni vi li. Mc d lc th ng c p dng tng i rng ri

nhng nhc im chnh ca cc h thng ny l c th gy cc dao ng trong li khi

c cc bin ng mnh xy ra.

Cc mch lc tch cc trn c s cc b bin i bn dn cng sut c kh nng

lc ht sng hi. Thng thng lc tch cc c cng sut nh hn nhiu so vi lc th

ng v thng c lp t ngay ti im c pht sinh sng hi. Do ch c chnh nh

vi thnh phn sng hi nn cng sut lc tch cc c th nh hn.

1.3. B v iu chnh in p

thy c nguyn l b v iu chnh in p ta xt mng in c mch tng

ng n gin trn hnh 1.4. Trn hnh 1.4 ngun in c s.. E truyn theo ng dy

c tng tr khng bng Rs + jXs. Trn thanh ci in p V c ti P + jQ, mch b c cng

sut Q. th vector cho trn hnh 1.5.


8

Hnh 1.4. Mch in tng ng.

Hnh 1.5. th vector ca mch in trn hnh 1.4.

Theo th vector c th tnh c st p trn ng dy bng:

V=E V =ZsI (1.7)

Lu cc k hiu ch in m, khng nghing, th hin l cc vector, cc ch

nghing th hin cc gi tr thng thng.

Dng ti bng:

P jQI

V (1.8)

Cc thnh phn ca st p c th xc nh bng:


9

V s s s ss s R XR P X Q X P R QP jQ

R jX j V j VV V V

(1.9)

Nh vy st p gm hai thnh phn, VR ng pha vi V v Vx vung pha vi

V. St p ph thuc c vo phn cng sut thc v cng sut phn khng. S ph thuc

ca in p vo dng in gi l ng c tnh ti, th hin trn hnh 1.6. Mc d st p

ph thuc vo dng in nhng trong thc t do mc in p ch c php thay i

trong gii hn cho php nn trn trc honh ca c tnh ti ngi ta hay dng cng sut

phn khng Q thay cho dng in I. Nh vy c tnh ti th hin s ph thuc in p

vo cng sut phn khng, khi tiu th cng sut phn khng (Q > 0, ti cm) in p

gim so vi khi khng ti E, khi pht cng sut phn khng (Q < 0, ti dung) in p

dng ln cao hn E.

Hnh 1.6. ng c tnh ti.

1.3.1. B gi in p khng i

Bng cch ni song song vi ti mt tr khng b c th t c bin in p

bng in p khi khng ti,

|V| = |E|. (1.10)

T th vector c th thy rng:

2 22

E s s s s s sR P X Q X P R Q

VV V

(1.11)


10

Gii h hai phng trnh trn c th lun lun xc nh c nghim Q cn thit

ca mch b bin in p lun bng gi tr lc khng ti, |V| = |E|. iu ny th

hin trn th vector hnh 1.7. Nh vy, nu mch b c th thay i mt cch lin tc

trong mt phm vi nht nh c th lun m bo in p khng i khi ti thay i.

1.3.2. B gi h s cng sut bng mt

Nu Q = Q th mch s c h s cng sut bng mt.

T y cng c th thy rng khng th dng mch b n nh in p v hiu

chnh h s cng sut cng mt lc.

1.3.3. ng c tnh ti

C th thy rng trong h truyn ti phn in tr thun ng dy rt nh so vi

cm khng, c th coi Rs ~ 0. Mt khc c th b qua phn st p VX v phn ny ch

lm thay i gc pha ca in p. V vy ta c:

2V sR

X QV QV hay

V V S

(1.12)

1Q

V ES

(1.13)

Nh vy in p V t l nghch vi cng sut phn khng Q nh th hin trn

ng c tnh ti nh trn hnh 1.6.

Hnh 1.7. B gi in p khng i.


11

1.4. iu khin cng sut v tn s

S mt h thng truyn ti c minh ha trn hnh 1.8, vi cc thnh phn

ngun cng sut s cp (turbine), my pht, ti. T s ta s a ra cc biu thc ch r

quan h h gia cng sut thc, cng sut phn khng, gc ti v gc pha ca ti.

Gc gia Es v Er gi l gc ti . Gc pha gia dng ti v in p Er l . C th

b qua thnh phn thun tr Rs. V vy st p do tr khng ng dy s l jXsI, vung

gc vi dng in I.

Hnh 1.8. H thng truyn ti vi turbine, my pht v ph ti. in p c hai u

ng truyn coi l u c iu khin nn k hiu nh s.. qua Es v Er.

Hnh 1.9. th vector.

T th vector trn hnh 1.9 c th vit c:


12

os sin

sin cos

s r s

s s

E c E X I

E X I

(1.14)

Cng sut ti bng:

os sinr r r rP jQ E I E Ic jE I (1.15)

T ta c phng trnh dng cng sut:

sins r

s

E EP

X

(1.16)

V phng trnh cho cng sut phn khng pha u thu:

coss rr r

s

E EQ E

X

(1.17)

Do ng truyn gi s khng b tn tht nn P = Ps = Pr. Pha u pht ta c:

os sins s s r sP jQ E Ic jE I (1.18)

Cng sut phn khng pha u pht bng:

sin os cos sin

sin cossin cos

cos

s s

s s rs s

s s

s rs

s

Q E I c

E E EE E

X X

E EE

X

(1.19)

V d 1: Gi s sE = rE =1.0 p.u v P =1.0 p.u . ng dy truyn ti c sX = 0.1

p.u v sR l khng ng k. Ta c sin.

.

s

s r

P X

E E = 0.1 nn = 5.739o v cos =0.995. T

ta c sQ = +0.05 p.u v rQ = -0.05 p.u. Do , u pht v u thu u pht cng sut

phn khng .

V d 2: Gi s sE = 1.0 p.u trong khi in p ti u thu gim xung rE = 0.95

p.u vi P = 1.0 p.u. v sX = 0.1 p.u .Khi sin.

.

s

s r

P X

E E =0.105 v = 6.042o , ln hn

gc ca v d 1 v rE gim i 5%. Mt khc sQ = +0.553 p.u v rQ = 0.422 p.u. Khi

sQ dng, u pht pht ra VArs. rQ cng dng c ngha u thu li hp th VArs.

Trong v d 2, in p gim i 5% gy ra s trao i ln v cng sut phn khng

gia u pht v u thu. iu ny chng t rng in p trn ng truyn ti ph thuc

rt mnh vo cng sut phn khng. iu tng t cng xy ra khi gc pha ca ti thay

i ln. Khi cng sut thc thay i, in p thay i khng nhiu nhng gc ti li


13

thay i nhiu. iu ny c th thy c t phng trnh dng cng sut, sin ~ P, khi

nh th sin ~ .

1.5. Kt lun

Trong chng ny nhc li nhng vn c bn ca h thng in, tnh n

nh ca h thng nng lng v nhng vn lin quan n cht lng in nng, i

cng vi l vai tr to ln ca cc b bin i in t cng sut trong lui in.

Cc b bin i bn dn c th s dng cho cc mc tiu sau y:

iu khin dng cng sut trn cc ng dy theo mun.

Gi c ti ca cc ng dy gn gii hn nhit.

Nng cao kh nng truyn cng sut gia cc phn ca h thng, do ,

gim d tr chung ca h thng.

Phng nga c s c lan truyn.

Gim dao ng in p.

Chng 2. Tng quan v b trong h thng truyn ti in

14

Chng 2 Tng quan v b trong h thng truyn ti

in

2.1. Yu cu c bn i vi h thng truyn ti

H thng truyn ti in phi m bo hai yu cu c bn, l:

1. m bo ng b: yu cu v m bo tn s;

2. m bo bin dng in p.

m bo ng b l yu cu cc my pht u a ra tn s chnh xc, v d 50

Hz, vi sai lch cho php trong phm vi +/-0,1 Hz. iu ny ch c th t c nu

mi my pht u hot ng trong gii hn n nh ch xc lp. Khi c bin ng h

thng iu khin phi c tc ng ng a c h thng v li trng thi cn bng

mi. Cc bin ng li chia ra lm bin ng nh v bin ng ln.

m bo bin dng in p l gi c in p ti mi im kt ni trn h truyn

ti trong phm vi cho php. C th thy rng bin ng in p lin quan n dng cng

sut phn khng, thay i theo din bin ca ph ti v ch hot ng ca h thng

nh kt ni ngun, sa thi ph ti hoc chuyn hng ng truyn, Mi din bin

qu in p hoc thp p u dn n nhng hu qu v kinh t, k thut. Gia hai

trng hp ti hn l khng ti v ngn mch i hi nhng bin php bo v khn cp

c rt nhiu bin php iu chnh m bo bin dng in p. Nhng bin php ny

tm tt trong bng di y. Mt s bin php c th c nhiu hiu qu khc nhau v c

th phi hp tc dng gia chng.


15

2.2. Cc c tnh ca ng dy cha b khng ti

2.2.1. Dng in, in p trn ng dy di l tng

Hnh 2.1. S ng truyn ti tham s ri vi cm khng ni tip v dung khng song

song.

Mch in tng ng ca ng dy di tham s ri cho trn hnh 2.1. Trn s

hnh 2.1, a l chiu di tuyn dy, x l chiu di dc tuyn ng dy. Cc thng s

ri ca ng dy: l in cm (H/m); c t in (F/m). Phng trnh vector in p V(x)

v dng in I(x) vit c theo (2.1).

Vdx

Vd 22

2

vi ( )( )r j l g j c (2.1)

Trong (2.1), r l in tr trn mt n v chiu di (/m), ni tip vi tr khng l

(H/m); g l in dn trn mt n v chiu di (S/m) song song vi c; l tn s gc

(rad/s); ). l s sng; l tc lan truyn, hi nh hn tc nh sng

(30000km/s); trong l bc sng. Vi tn s 50 Hz, =

30000/50 = 6000 km v = 1,047. 10 -3 rad/km = 6o/100km.

Nghim ca phng trnh (2.1) i vi vector in p v dng in th hin trong

(2.2), (2.3).

V(x) =Vrcos )( xa + jZ0Ir sin )( xa (2.2)

I(x) = j0Z

Vr sin )( xa +Ircos )( xa (2.3)

Z0 = cl / [], gi l tr khng surge. i vi dng dy cao th gi tr tiu biu

ca Z0 c 250 .


16

Tr khng ca ng truyn l Z(x)=V(x)/(I(x) biu din c nh (2.4).

0

0

[ cos ( - ) sin ( )]( )( )

( ) [ cos ( - ) sin ( )

Z I I a x j a xV x r rZ x ZI x I I a x j a xr r

(2.4)

V(x) v I(x) ng pha trn sut cc im trn ng dy nhng gc pha cng thay

i:

( )( )

( )( )

j a xV x V er

j a xI x I er

Tr khng surge Z0 l tr khng ca ng dy di v tn.

th vector c dng nh trn hnh 2.2. Bin dng in p, V(x) thay i theo x,

c dng nh trn hnh 2.3.

Hnh 2.2 th vector.

Cng sut truyn trn ng dy trong trng hp ny gi l ti t nhin v gi tr

bng:

00

2VP

Z (2.5)

ngha ca tr khng Z0 v ti t nhin phi hiu l thc ra ti ch l gi nh, nu

cui ng dy trn hnh 2.1 c mt ti c gi tr cng sut tc dng P0 th ti ny s nhn

thy ng dy di tr khng Z0.


17

Hnh 10.3 Bin dng in p trn ng dy cha b.

2.2.2. c tnh h mch ca ng dy truyn thng cha b, khng tn

tht trn ng dy

Trn ng dy khng ti, khng tn tht, dng v p trng pha nhau, khng c

cng sut phn khng:

( ) ( )V x V a xr (2.6)

0

( ) sin ( )VrI x j a xZ

(2.7)

th vector c dng nh trn hnh 2.4, bin dng in p v dng in th hin

trn hnh 2.5.

Hnh 2.4. th vector ng dy di khng ti.


18

Hnh 2.5 Bin dng dng in v in p trn ng dy khng ti (h mch) 300 km.

in p tng ln cui ng dy n 1,05 p.u. Nu ng dy di n 1500 km

in p h mch s tng n v cng, khng th chp nhn c. My pht phi cung cp

dng np cho ng dy vi gc pha vt trc, ngha l vi dng kch t nh hn nh

mc. iu ny c th dn n h thng bo v kch t tc ng.

2.3. ng dy cha b c ti

2.3.1. ng dy truyn thng vi in p c nh pha nhn

Gi s pha cui dng dy c ti c cng sut P+jQ. Dng in c dng:

*r

r

P jQI

V

(2.8)

in p u v cui ng dy lin h vi nhau theo phng trnh:

0 *cos sins r

r

P jQE V jZ

V

(2.9)

Gii hai phng trnh trn c th xc nh c in p vn hnh V*r.


19

Hnh 2.6. th bin in p ca ng dy di 300 km ph thuc cng sut P/P0, ti

cc h s cng sut khc nhau.

Vi mi h s cng sut c mt gi tr cng sut Pmax ng vi im lm vic n

nh gii hn (statedy state stable limit). Khi P < Pmax c hai gi tr Vr, mt ng c

tnh tng i phng pha trn v mt pha di. Thng thng im pha trn l im

lm vic vi in p trn di mt cht so vi 1,0 p.u.

2.3.2. ng dy cha b i xng

Hnh 2.7. S ng dy i xng.

in p v dng in mt na u pha pht:

0cos sin2 2

s m mE V jZ I

(2.10)

0

sin cos2 2

ms m

VI j I

Z

(2.11)


20

Ph ti ni im gia ng dy:

*

m m mP jQ V I P (2.12)

Cng sut phn khng t mi pha pht ra Qs = - Qr:

2 22

00 2 2 2

0 0

sin

2

ms

m

V VPQ P

P V V

(2.13)

Hnh 2.8. th vector ng dy i xng.

Bng 2.1 nh hng ca cng sut truyn ti ln bin dng in p v yu cu

cng sut phn khng.

Trng hp in p Cng sut phn khng

P sE , rE C s d tha dng cng sut phn khng, c hp

th cui ng dy: sQ 0.

P>P0 mV > sE , rE C s thiu ht dng cng sut phn khng, c

cung cp cui ng dy: sQ >0 v rQ


21

E (cos sin )j

E e E js s s

(2.14)

trong gc gi l gc ti hay gc truyn ti. Khi cng sut truyn ti s l:

0

sinsin

s rE EPZ

(2.15)

Nh vy ta c cng sut ln nht c th xc nh:

0

ssin

s rE EPZ

(2.16)

Cng sut pht ph thuc gc ti theo th. im cng sut ln nht xc nh

gii hn n nh xc lp. Theo th c th coi cng sut pht ph thuc gc ti .

Tuy nhin trong thc t cn coi vi mi gi tr cng sut P cn iu chnh gc ti ph

hp sao cho gi c d tr n nh cn thit. Thng thng gc ti bng = 30o v

sin =0,5 c d tr n nh 100%.

Cng sut phn khng hai u ng dy l:

0

( cos cos )

sin

r s rr

E E EQ

Z

(2.17)

0

( cos cos )

sin

s r ss

E E EQ

Z

(2.18)

Trong mi trng hp P < Pmax. Nu P < P0 , Es = 1,0 p.u, gc < , Qs < 0, Qr >

0. Ngha l c hai u u thu cng sut phn khng. Nu P > P0 c hai u u pht cng

sut phn khng.


22

Hnh 2.9. c tnh cng sut theo gc truyn ti.

2.4. ng truyn ti c b

B trong h thng truyn ti c mc tiu:

- Gi bin dng in p phng vi mi cng sut truyn;

- m bo n nh tng dung lng ng truyn;

- Cung cp cng sut phn khng theo mt mc tiu kinh t k thut nht nh.

Cc h thng b c th l b th ng v b tch cc. B th ng ngha l ng

ct mt lng khng hoc t c nh. B tch cc l kh nng a vo hoc tiu th mt

lng b va m bo c tnh truyn ti trong mi ch , ni chung l m bo

bin dng in p phng. V d my b ng b, cc thit b b c iu khin.

Cc h thng v thit b b ph bin bao gm:

- B bng khng hoc t song song. Khng song song c tc dng b dung khng

ng dy khi ti nh in p khng tng qu mc. T song song c tc dng

b phn khng cho ti khi ti nng.

- H thng b ni tip: b cho di ng dy.

Gii hn n nh xc lp


23

2.4.1. B tnh song song

Hnh 2.10. S mch b tnh bng khng song song.

Hnh 2.11. Bin dng in p v dng in trong b khng song song.

H thng b tnh song song c s nh trn hnh 2.10. Bin dng in p t

c th hin trn hnh 2.11.

V d:

Vi ng dy di 300km, vi f=50hz,v 0 1.0 .sE V p u , in p im gia l

1.0125 p.u. v cng sut phn khng hp th cui ng dy l 0.158 P0. Nhng gi tr

ny nn c so snh vi in p cui ung dy 1.05 p.u v cng sut phn khng

im u hp th sQ =0.329 P0 khi khng c b song song. Vi nhim v b song song

ung dy 500 kV khng ti, cng sut ca cun khng thng l 53 MVAr trn mi

pha, nu Z0=250 .

Nguyn l b song song trn ng dy di, vi bin dng in p c th t

c, th hin trn hnh 2.12. Trn hnh c th thy rng c th t c bin dng in

p tng i phng nu sau mi 300 km ng dy c mt mt b.

My ct Khng b

in p

Dng in


24

Hnh 2.12. B song song theo ng dy di.

H thng b song song c th dng cho mc ch iu chnh in p trn ng

dy nu kt hp c cun khng v t song song. Nguyn l iu chnh in p bng b

song song c th thy r trn hnh 2.13.

Hnh 2.13. Nguyn l iu chnh in p bng b song song.

Bin dng in p(p.u)

Cha b

Cha b

Ngun

Ti


25

2.4.2. B gia ng dy

Hnh 2.14. Mch b gia ng dy.

Nguyn l b gia ng dy cho trn hnh 2.14.

Bnh thng khi cha b:.s r

L

E EP sin

X (2.19)

Sau khi b gia ng dy: .

22

s r

L

E EP sin

X

(2.20)

Nh vy cng sut max tng gp 2 ln bnh thng, kh nng truyn ti v d

tr n nh cng tng gp i. c tnh ng truyn cho trn hnh 2.15.

Hnh 2.15. c tnh ng truyn c mch b gia ng dy. Cng sut truyn ln gp

i so vi khi khng b.

Cha b

b


26

2.4.3. B tnh ni tip

T b mc ni tip c th trung ha phn cm khng ca ng dy, gim gc ti

, do gim dng np cho ng dy, dn n c th tng c cng sut ti t nhin.

Do tr khng ng dy gim nn c th cn n thnh phn cm song song nh th hin

trn hnh 2.16. B ni tip thng dng cho ng dy rt di nhng cng c th dng

cho mch nhnh song song ca ng truyn hiu chnh dng cng sut. th vector

th hin trn hnh 2.17.

Hnh 2.16. Mch b ni tip.

Hnh 2.17. th vector mch b ni tip.

C th xc nh cng sut truyn ln nht nh sau:

Theo th vector c th xc nh cng sut truyn P = ImVm nh sau:

00

sin2

sin ( os sin )2 2 2 2

s mE VPXc Z

Z cX

(2.21)


27

Vi

0os os sin os2 2 2 2

s m r

ZE c V c E c

X

(2.22)

Khi m bo iu kin Es = Er ta c:

0

sin

sin (1 os )2

s rE EPXc

Z c

(2.23)

Vi

0 0sin1 1 tan1 os 2

Z Z

X c X

(2.24)

T nhng phng trnh trn mi mi mc cng sut truyn ti c th xc nh gc

ti , gi tr in p Vm, V1, V2, VC.

Trng hp n gin ha nu c th b qua c in cm ng dy, khng tnh

n in cm song song jX, biu thc cng sut c dng n gin nh sau:

2

sinL

EP

X Xc

(2.25)

2.5. Tnh ton dng cng sut

Tnh ton dng cng sut l xc nh ch xc lp ca h thng truyn ti.

Qu trnh nghin cu cn xc nh dng cng sut thc, cng sut phn khng vo ra, gi

tr in p, gc pha ti cc nt ca li.

Cc gi tr tnh ton c ph thuc cu hnh v cc bin php iu khin trn

li.Nu cng sut tnh ton vt qu gi tr gii hn cc bin php iu khin cn c

tnh ti. Nu gi tr in p ra khi phm vi cho php cn tnh ti cc bin php b.

2.5.1. Phng trnh mng li c bn

Kt hp nh lut Ohm v nh lut Kirchhoff v dng in gia hai nt l v m.

Ta c, phng trnh quan h gia nt l v m:


28

.m l k kV V Z I => l m

k

k

V VI

Z

= .kY V (2.26)

Trong 1

k

k

ZY

l tng tr gia hai nt l v m, kI l dng in chy t nt l sang

nt m.

Ti nt i, gi s c q dng vo ra:

1

q

i k

k

I I

(2.27)

Trong iI l dng in ti nt i, k l s nhnh ni vi nt i. Tt nhin, kI l

dng in ti nhnh k.

Kt hp phng trnh (2.26) v (2.27) ta c:

1

q

i k l m

k

I Y V V

(2.28)

Ta c th bin din (2.28) theo phng trnh ma trn sau:

1 111 12 13 1

2 221 22 23 2

31 32 33 33 3

1 2 3

...

...

...

. . . . .. .

. . . . .. .

...

n

n

n

n n n nnn n

I VY Y Y Y

I VY Y Y Y

Y Y Y YI V

Y Y Y YI V

(2.29)


29

VD1: Ta xt 1 v d gm cc nt a,b,c,d nh hnh v v tng tr cc nhnh u l

Y.

Theo nh lut Ohm ta c:

I1=Y(Va-Vc)

I2=Y(Va- Vb)

I3=Y(Vb-Vd)

I4=-Y(Vc-Vd)

I5=-Y(Va-Vc)

I6=-Y(Vb-Vc)

Theo nh lut Kirchhoff v dng in ta c:

2 1 5

2 6 3

1 6 4

5 3 4

a

b

c

d

I I I I

I I I I

I I I I

I I I I

T ta c:


30

a b c d a

a b c d b

a b c d c

a b c d d

YV YV YV YV I

YV YV YV YV I

YV YV YV YV I

YV YV YV YV I

Hoc dng ma trn:

a a

b b

c c

d d

I VY Y Y Y

I VY Y Y Y

I Y Y Y Y V

Y Y Y YI V

T phng trnh ma trn (2.29) ta c:

1 111 12 13 1

2 221 22 23 2

31 32 33 33 3

1 2 3

...

...

...

. . . . .. .

. . . . .. .

...

n

n

n

n n n nnn n

V IZ Z Z Z

V IZ Z Z Z

Z Z Z ZV I

Z Z Z ZV I

Vi:

1

11 12 13 1 11 12 13 1

21 22 23 2 21 22 23 2

31 32 33 3 31 32 33 3

1 2 3 1 2 3

... ...

... ...

... ...

. . . . . . . . . .

. . . . . . . . . .

... ...

n n

n n

n n

n n n nn n n n nn

Y Y Y Y Y Y Y Y

Y Y Y Y Z Z Z Z

Y Y Y Y Z Z Z Z

Y Y Y Y Z Z Z Z


31

2.5.2. L thuyt dng cng sut

Trong l thuyt dng cng sut, cc nt uc chia lm 3 loi, nh vic phn loi

ny m ta c th tnh ton thng s cc nt, t xc nh dng cng sut thc, cng

sut phn khng vo ra, gi tr in p, gc pha ti cc nt ca li thc hin cc

phng php iu khin.

a. Nt iu khin in p: Nu cng sut phn khng ti nt ,in p ti nt c

th iu chnh c v nt s l nt kiu iu khin in p. My b ng b hoc cc

b thit b b tnh SVCs l thit b dng iu chnh in p. Trong trng hp my b

ng b th cng sut tiu th c cho bit, con vi SVCs cng sut tiu th bng 0. Ti

nt, cc thng s cha bit l gc pha in p v cng sut phn khng ca mng. Nt

kiu ny uc gi l nt PV.

b. Nt ti: nu khng c ngun cp c s ti nt, l dng nt ti. Dang nt ny

cng sut tiu th v cng sut phn khng c xc nh,in p v gc pha l bin

cha bit. Nhng nt kiu ny cn c gi l nt PQ. Nu khng c s pht in v

lng nhu cu mt nt ring bit no th nt ny thuc loi PQ vi lng cng sut

bm vo l bng 0. Bin in p ti khng th iu chnh uc nu ngun pht khng

p ng yu cu cng sut. Trong vn hnh thc t th im nt thay i t loi PQ

sang PV.

c. Sack node: Kiu nt th 3 khi nghin cu v dng cng sut l Slack node. S

cn thit xc nh nt slack t thc t tn tht cng sut tiu th v cng sut phn khng

trong mng u khng bit. My pht ni vi nt Slack s cung cp cng sut b mt

trn ng truyn ti, nng cao d tr ca mng li. nt Slack, in p v gc pha

bin, cng sut tiu th v cng sut phn khng l bin cn xc nh.

2.5.3. Biu din li in thng thng.

Cc thit b ca mt mng li in trong cc m hnh dng cng sut chy

thng gm c: cc my pht, cc my bin p, h thng dy truyn ti, ti v cc thit b

b song song v ni tip.

Nt pht:


32

ng dy truyn ti:S thay th hnh II

S thay th my bin p:

S thay th t b ni tip:


33

2.5.4. Phng php dng cng sut Newton-rapson.

Ti nt l: Ta c cng thc

Sl=Pl+jQl=VlI*

l (2.30)

Trong : lS l cng sut phc a vo nt l,

lP l cng sut tc dng a vo nt l,

lQ l cng sut phn khng a vo nt l,

lV l in p phc ti nt l,

lI l dng in phc a vo nt l.

Gi s c n nhnh dng in ni vi nt l , ta c:

1

n

l lm m

m

I Y V

(2.31)

Trong : Ylm = Glm + jBlm

T (4.37) v (4.38) ta c:

* *

1

n

l l l lm m

m

P jQ V Y V

(2.32)

Mt khc : lV = | lV |`lje

v mV = | mV |

mje

nn thay vo (2.32) ta c:


34

( )( )

1

jn mlP jQ V V G jB eml l l lm lmm

(2.33)

( ) cos( ) sin( )1

l m l m

nP jQ V V G jB jml l l lm lmm

(2.34)

cos( ) sin( )1

nP V V G Bm m ml l lm l lm lm

(2.35)

sin( ) cos( )1

nQ V V G Bm m ml l lm l lm lm

(2.36 )

trong , | lV | v | mV | l cc bin in p im nt ti nt l v m, cn l v m l cc gc

pha in p ti nt l v m.

Ta tuyn tnh ha cc phng trnh (2.35) v (2.36) ta c:

2 2 2 2 2 2

2 3 2 3

3 3 3 3 3 3

2 3( ) 2 32

3

2 3 2 3

22 2 2 2

32 3

P P P P P P

VV Vn n

P P P P P P

VV Vn nrP

PP P P P P Pn n n n n n

VV Vn nPn

QQ Q Q Q

QVn

Qn

( )

2

3

22 2

32 3

3 3 3 3 3 3

2 3 2 3

2 3 2 3

r

n

VQ Q

VVV n

Q Q Q Q Q QVnVV Vn n

Q Q Q Q Q Qn n n n n nVV Vn n

(2.37)

( )r

Trong :


35

Pl = netlP

calc

lP l cng sut tc dng sai lch ti nt l.

lQ = net

lQ calc

lQ l cng sut phn khng sai lch ti nt l.

calc

lP v calc

lQ l cng sut tc dng v phn khng tnh ton c ti nt l.

net

lP = gen

lP load

lP l cng sut tc dng d tnh ti nt l.

net

lQ = gen

lQ load

lQ l cng sut phn khng d tnh ti nt l.

gen

lP v gen

lQ l cng sut tc dng v phn khng c pht ra ti nt l.

load

lP v load

lQ l cng sut tc dng v phn khng c tiu th bi ti ti nt l.

l v | lV | l thay i v bin v gc pha in p im nt ti nt l.

(r) biu th bc lp th r v l = 2, 3, 4,..,n.

Cc thnh phn ca ma trn Jacobian c th c xc nh bng cch ly vi phn

cc phng trnh (4.42) v (4.43) theo l, m, |Vl| v |Vm|.

Khi l = m:

2 2sin( ) cos( )l l l ll l l lll

nPV V G B V B Q V Bm ml lm l lm lm l

(2.38)

cos( ) sin( )l lm l ll l lll

nP PV G B V G V Gm mlm l lm l Vm lV

l

(2.39)

2 21

cos( ) sin( )l m l ll l l llnQ

V V G B V G P V Gm ml lm l lm lm l

(2.40)

sin( ) cos( )l lm l ll l lll

nQ QV G B V B V Bm mlm l lm l Vm lV

l

(2.41)

Khi l m:


36

1 sin( ) cos( )P

V V G Bm m ml lm l lm lm

(2.42)

11 1cos( ) sin( )P Q

V G Bm ml lm l lm lV Vm m m

(2.43)

1 cos( ) sin( )Q

V G Bm ml lm l lm lm

(2.44)

11 1sin( ) cos( )Q P

V G Bm ml lm l lm lV Vm m m

(2.45)

Ta tin hnh gii lp, gi s bit v bin v gc pha ca in p im nt ti

cc nt PQ, cc gc pha in p ti cc nt PV tnh ton cng sut tc dng v phn

khng a vo bng cc phng trnh (2.35) v (2.36). Khi m gi s sai th cc cng

sut bm vo tnh c s khng ng vi cc cng sut xc nh bit.

Cc vector cng sut sai lch c th c xc nh nh sau:

( ) ,( ) ,( )( )

r gen calc r calc rload netP P P P P P (2.46)

( ) ,( ) ,( )( )

r gen calc r calc rload netQ Q Q Q Q Q (2.47)

Khi ta c:

( 1) ( ) ( )r r r

(2.48)

( 1) ( ) ( )r r rV V V

(2.49)

C th lp i lp li cc php tnh ca cc phng trnh t (2.35) n (2.36) v t

(2.46) n (2.49) cho n khi sai lch cng sut P v Q l nh trong dung sai chp

nhn c, v d khong = 1210 .

Ta c th tm tt ton b qu trnh trnh trn bng s sau:


37


38

V d:

Mch in bao gm 2 nt, mt ngun pht, ng dy v mt ti. Ti c gi tr

1+j0.5 pu v in khng ca ng dy l 0.1 pu. Bin v gc pha in p ti im

ngun pht (nt Slack) c gi ln lt ti 1 pu v 0 radians.

S dng phng php dng cng sut Newton-Raphson, bin v gc pha in

p im nt ti nt 2 s c xc nh bng cch s dng bin in p 1 pu v gc pha

0 radians pha ti lm iu kin ban u.

Ma trn tng dn im nt c nh dng cho h thng ny nh sau:

10 10

10 10

j jY G jB

j j

Note: Z = R + jX, Y = G + jB, Y = 1/Z, G = 1/R v B = 1/X

Cng sut tc dng v phn khng ca mng c tnh ton nh sau:

?

.1

net gen loadP P P p u

?.

0.5

net gen loadQ Q Q p u

- Bc lp u tin

S dng cc gi tr in p ban u | 1V | = | 2V | = 1, 1 = 2 = 0 v cc gi tr ma trn

tng tr im nt cc phng trnh (2.35) v (2.36), cc cng sut c tnh nh sau:


39

2 2 1 21 2 1 21 2 1 2 2 22 2 2 21 2 2

2 2 1 21 2 1 21 2 1 2 2 22 2 2 21 2 2

{ os( ) sin( )}+ { os( ) sin( )}

{ sin( ) os( )}+ { sin( ) os( )}

calc

calc

P V V G c B V V G c B

Q V V G B c V V G B c

Theo cc phng trnh (2.46) v (2.47) ta c:

(1)

1 1 1

2 2 2

(1)

1 1 1

2 2 2

?.

1

?.

0.5

net calc

net calc

net calc

net calc

P P Pp u

P P P

Q Q Qp u

Q Q Q

Mt khc theo cc phng trnh t (2.38) n (2.45) vi 2calP = 0 v

2

calQ =0 ta

c:

2

2

10P

2

2

0P

V

2

2

0Q

2

2

10Q

V

Kt qu ca h thng tuyn tnh ha ca phng trnh l:

(1) (1)(1)

2 22

2 22

10 0 0.1 0 1 0.1

0 10 0 0.1 0.5 0.05

P

V VQ

Theo phng trnh (2.48) v (2.49) kt qu ca bc lp 1 l:

(1) (0) (1) (1)

2

2

0 0.1 0.1.

1 0.05 0.95p u

V

- Bc lp th 2

S dng thng tin v in p c cp nht | 1V | = 1, | 2V | = 0.95, 1 = 0 v 2 =

-0.1 cc phng trnh (2.35) v (2.36), cc cng sut tc dng v phn khng mi c

tnh ton nh cc kt qu sau:

2

2

0.94841 . .

0.4275 . .

calc

calc

P p u

Q p u

Cc phng trnh v sai lch cng sut nh sau:


40

(2)

1 1 1

2 2 2

(2)

1 1 1

2 2 2

? ? ?. .

1 0.94841 0.051583

? ? ?

0.5 0.4275 0.07246

net calc

net calc

net calc

net calc

P P Pp u

P P P

Q Q Q

Q Q Q

. .p u

Ta nhn thy rng cc sai lch v cng sut gim nhiu v bin so vi cc

gi tr sai lch bc lp 1.

Cc thnh phn Jacobian ca nt 2 l:

2

2

9.45254P

;

2

2

0.998334P

V

;

2

2

0.948417Q

;

2

2

8.574958Q

V

.

Kt qu h thng tuyn tnh ha ca phng trnh l

(2)(2)

22

22

(2) (2)

2

2

9.45254 0.998334

0.948417 8.574958

0.107042 0.012462 0.051583 0.006425

0.011839 0.113996 0.07246 0.009161

P

VQ

V

Theo phng trnh (2.48) v (2.49) kt qu ca bc lp 1 l:

(2) (1)

2

2

0.1 0.006425 0.106425

0.95 0.009161 0.940839V

n y, xc nh c cc in p ti nt 1 v 2 nh sau:

(2)

1

2

1 0. .

0.940839 0.106425

Vp u

V

Cc in p ny kh l gn vi cc kt qu thc. Nu qu trnh tnh ton c lp

li nhiu hn 2 bc lp th 2P v 2Q s nh hn 610

Chng 3.Tng quan v h thng truyn ti in xoay chiu linh hot (FACTS)

41

Chng 3 TNG QUAN V H THNG TRUYN TI IN XOAY CHIU LINH HOT (FACTS)

3.1. Gii thiu chung

H thng nng lng in bao gm ba b phn chnh: ngun pht, h thng truyn

ti (in p cao) v h thng phn phi (trung th v h th). Cc ngun pht c xy

dng v pht trin thng xa cc trung tm ph ti ln, chng hn nh cc nh my

thy in xy dng ngun nc ni c ct p v lu lng dng chy ln, cc nh my

nhit in xy dng gn ngun nhin liu, cc nh my a nhit v thy triu ch c th

xy dng mt s a im, cn nh my in ht nhn th c xy dng xa khu th.

a in nng i xa cn c li in truyn ti cao p, kt ni tt c cc ngun pht

to nn li in quc gia. Cc h thng phn phi s kt ni vi li truyn ti ti gn

cc h ph ti. H thng truyn ti c vai tr c bit quan trng trong m bo an ninh

nng lng v phi c pht trin ph hp vi yu cu pht trin kinh t x hi ca

quc gia. H thng truyn ti phi m bo tin cy, an ton v c d tr nht

nh v dung lng p ng cc nhu cu pht trin ca ph ti.

H thng truyn ti in thng l 3 pha xoay chiu, vn hnh cc cp in p

khc nhau (thng thng l 230kV tr ln). Vi yu cu ngy cng tng v cng sut v

khong cch truyn ti, cc cp in p truyn ti cng ngy cng tng ln gim tn

tht.

Kh nng ti ca h thng

truyn ti ph thuc vo cc yu t

sau:

- Gii hn v nhit;

- Gii hn v cch in;

- Gii hn v n nh.

Cc gii hn ny xc nh cng

sut ti a truyn ti c m khng

gy nguy him n cc ng dy

truyn ti v cc thit b in. V c

bn, gii hn ca cng sut truyn ti

c th gii quyt bng vic xy dng thm cc tuyn truyn ti mi. Tuy nhin iu ny


42

dn n tn km v vn xy dng, thi gian thi cng v mt qu t cho cc hnh lang

an ton ca tuyn ng dy. V th khi h thng in pht trin nhanh i hi nhng

cng ngh mi khai thc trit cc kh nng ca h thng in hin c m khng

nh hng n s an ton ca h thng. p ng nhu cu ny, cc nghin cu v thit

b iu chnh linh hot h thng truyn ti in xoay chiu FACTS (Flexible AC

Transmission Systems) c tin hnh vo cui nm 1980 nhm gii quyt hai vn

chnh l nng cao kh nng truyn ti ca cc h thng truyn ti v gi cng sut trong

khong gii hn nh trc. Vi s pht trin vt bc trong lnh vc iu khin t

ng, cng vi s pht trin nhanh chng ca cc phn t bn dn cng sut ln to ra

cc b bin i bn dn in t cng sut ln cho php iu khin, khng ch cc dng

nng lng gn nh tc thi, gip cho qu trnh iu khin h thng in c th thc hin

c theo cc cch thc m cc phn t c kh, in t trc khng th m bo

c. Cng ngh FACTS l duy nht c kh nng iu khin nhanh mt cch linh

hot cng sut tc dng v phn khng ca h thng in. Cc thit b FACTS khc nhau

c cc thng s iu khin khc nhau v c cc m hnh vt l khc nhau iu khin

cng sut. iu khin cng sut mt cch c hiu qu trong h thng in, cn xem

xt n cc yu t gii hn kh nng truyn ti v xc nh r li ch t c khi p

dng cc thit b iu khin FACTS.

3.2. Cc thit b b ngang SVC, STATCOM

3.2.1 SVC (Static Var Compensator)- B b tnh

SVC l ngun pht hoc b tiu th cng sut phn khng c th thay i c, c

th c iu chnh trao i dng in in cm hoc in dung duy tr hoc iu

khin cc thng s c th ca h thng in ti im kt ni (in hnh l in p nt).

SVC bao gm b in cm v t in (reactor hoc capacitor) ng m hoc iu

khin bng thyristor. SVC dng cc thyristor iu khin khng hon ton thng thng,

ngha l c th iu khin m bng cc iu khin nhng kha li mt cch t nhin khi

dng qua n bng khng. in khng c ng m hoc iu khin bng thyristor dng

tiu th cng sut phn khng v t in ng m bng thyristor cung cp cng

sut phn khng.

Trong trng hp chung, SVC c cu to t cc phn t c bn, nh th hin

trn hnh 3.2, TCR (Thyristor Controlled Reactor), TSR (Thyristor Switched Reactor),

TSC (Thyristor Switched Capacitor), mt hay nhiu b lc LC c hiu chnh cho cc

sng hi bc 3, 5, 7,


43

Hnh 3.2 Cu to chung ca SVC.

- TCR (Thyristor Controlled Reactor) Cun khng iu chnh bng thyristor: l

cun cm c iu khin bng thyristor, mc song song, in khng ca n thay

i lin tc bng cch iu chnh gc dn ca van thyristor (thit b khng c tham

s c iu chnh trn).

- TSR (Thyristor Switched Reactor) Cun khng ng m bng thyristor: l cun

cm ng m bng thyristor, ni song song, m in khng ca n c thay i

theo bc theo trng thi dn dng hoc khng dn dng ca van thyristor.

- TSC (Thyristor Switched Capacitor) T ng ct bng thyristor: l t in ng

ct bng thyristor, mc song song, in dung ca n c th thay i dng bc

thang bng cch ng hoc kha cc thyristor.

Phi hp 3 loi phn t trn cho php to ra c nhng khng b ngang thay i

c lin tc thng s (in khng, cng sut) trong phm vi rng (du m v dng)

vi gi thnh h.

Cc chc nng chnh ca SVC bao gm:

- n nh in p trong nhng h thng c bin ng ln, nhanh ca ph ti, nh

cht lng in p c nng cao ng k.

- iu khin dng cng sut phn khng ti nt c b.

- Gim qu in p khi xy ra s c ngn mch trong h thng.

- iu khin qu trnh qu , nng cao tnh n nh cho h thng.


44

- Gim dao ng cng sut khi xy ra s c trong h thng nh ngn mch, mt ti

t ngt...

- Nng cao gii hn truyn ti ca ng dy theo iu kin n nh tnh.

- Gim tn tht cng sut v in nng.

3.2.2. STATCOM (Static synchronous Compensator)- B b ng b tnh

STATCOM ging nh mt my pht ng b tnh, hot ng nh mt b b tnh

mc song song, dng in cm hoc dung c th c iu khin c lp i vi in p

h thng. Khc vi SVC dng in hay cng sut phn khng ph thuc vo mc in p

ti im kt ni, dng v cng sut ca STATCOM c th c iu khin c lp vi

in p, nh kh nng ca STACOM cao hn nhiu so vi SVC.

Hnh 3.3 Cu to ca STATCOM.

STATCOM l mt trong nhng loi b iu khin FACTS quan trng, xy dng

trn c s b nghch lu ngun p (VSI) hoc ngun dng (CSI), nh minh ha trn hnh

3.3. V gi thnh cc VSI c th c xy dng trn cc module mch lc c sn nn

c dng nhiu hn.

Vi b nghch lu ngun p, in p u ra xoay chiu ca n c th c iu

chnh v bin v v gc pha sao cho ph hp vi dng cng sut phn khng theo yu

cu tng ng vi in p ti im kt ni, in p pha mt chiu trn t s c iu

chnh t ng theo yu cu hot ng nh ngun p cho b bin i. STATCOM cng

c th c thit k cng hot ng c nh mt b lc tch cc lc cc sng hi.

STATCOM c nh ngha theo IEEE, l mt tp hp cc b iu khin ni song

song bao gm c cc ngun cng sut tc dng hoc ngun d tr bn pha mt chiu


45

sao cho dng in bm vo c th cha cng sut tc dng. Nhng b iu khin nh

vy bao gm:

- SSG (Static Synchronous Generator) My pht ng b tnh: b chuyn i

cng sut c kha bn dn hai chiu c cung cp t mt ngun nng lng ph

hp, c th to ra mt lot cc in p u ra nhiu pha c th iu chnh c,

kt hp cng h thng in xoay chiu cho mc ch trao i cng sut tc dng

v phn khng mt cch c lp.

R rng l SSG l s kt hp ca STATCOM v mt ngun nng lng no

cung cp hoc tiu th cng sut, nh minh ha trn hnh 3.4. Ni chung SSG c lin

kt vi bt k mt ngun nng lng no , c th l acquy, t in mt chiu cng sut

ln, cc b bin i, chnh lu khc, ... Mt b bin i DC DC ng vai tr l giao

din gia ngun nng lng v b nghch lu DC - AC. i vi b nghch ngun p VSI

ngun nng lng np in cho t thng qua giao din in t ny v duy tr in p t

in theo yu cu.

Hnh 3.4 H thng BESS.

SSG cng bao gm BESS (H thng d tr nng lng Battery).

- BESS (Battery Energy Storage System) - H thng d tr nng lng acquy: Mt

h thng d tr nng lng di dng ha nng, s dng b nghch lu ngun p,


46

ni song song c kh nng iu chnh nhanh chng lng in nng cung cp hoc

tiu th t h thng.

- i vi ng dng truyn ti, kch c ca b d tr ca BESS c xu hng nh

(hng chc MWh) v nu nh cng sut b bin i ln, n c th phn phi

cng sut tc dng vi t l MW/MWh cho n nh qu

.

B bin i c th tiu th hoc pht cng sut phn khng trong kh nng dung

lng MVA ca b bin i. Khi khng cung cp cng sut tc dng cho h thng, b

bin i thng c s dng np cquy vi tc c th chp nhn c.

Nhng b d tr nng lng khc, ph hp cho cc ng dng truyn ti, c th

c s dng l h thng d tr nng lng t cun cm siu dn SMES

(Superconducting Magnetic Energy Storage), c nh ngha bi IEEE nh sau:

- SMES (Superconducting Magnetic Energy Storage)- B d tr nng lng t

cun cm siu dn: l mt thit b d tr nng lng in t siu dn c cha cc

b bin i in t, c kh nng bm vo hoc tiu th cng sut tc dng, phn

khng mt cch nhanh chng hoc iu khin ng dng cng sut trong h thng

in xoay chiu.

V dng in mt chiu trong mch t khng th thay i nhanh chng, nng

lng u vo hoc u ra c thay i nh vic iu khin in p ca hai u ni vi

giao din in t ni vi STATCOM.

Cc chc nng chnh ca STATCOM cng ging nh ca SVC nhng kh nng

iu chnh, iu khin cc thng s ca STATCOM mc cao hn, bao gm cc chc

nng sau:

- iu khin in p ti nt kt ni STATCOM n nh in p, nh cht

lng in p c nng cao.

- iu khin dng cng sut phn khng ti nt c b.

- Gim qu in p khi xy ra s c (ngn mch, mt ti t ngt...).

- Gim qu in p khi xy ra s c ngn mch trong h thng in.

- iu khin qu trnh qu , nng cao tnh n nh cho h thng.

- Gim dao ng cng sut khi xy ra s c trong h thng nh ngn mch, mt ti

t ngt...

- Nng cao gii hn truyn ti ca ng dy theo iu kin n nh tnh.


47

- Gim tn tht cng sut v in nng.

Ngoi ra STATCOM cn c cc c im ni tri so vi SVC l:

- C kh nng vn hnh trong ch s c v tip tc iu khin khi loi tr s c.

- C th pht cng sut phn khng khi in p thanh ci nh hn in p li v

ngc li, tiu th cng sut phn khng khi in p thanh ci ln hn in p

li.

- Khi trang b thm ngun cng sut tc dng hoc cc thit b d tr nng lng

pha mt chiu, STATCOM c th trao i cng sut phn khng v cng sut tc

dng vi h thng, do nng cao kh nng n nh ng v chng dao ng

cng sut.

Nhng khi nim khc ca b iu khin theo IEEE bao gm:

- SVG (Static Var Generator or Absorber) - b tiu th hoc my pht tnh: l mt

thit b hoc h thng in c kh nng ly ra dng in dung hoc cm t h

thng in v do pht hay tiu th cng sut phn khng. N thng cha TCR

v/hoc TSC.

SVG, theo nh ngha ca IEEE, l mt ngun cng sut phn khng m, nu iu

khin ph hp, c th chuyn i thnh b b ngang cng sut phn khng theo mt mc

ch c th no hoc a mc ch. V th c SVC v STATCOM u l cc my pht

tnh c trang b vng iu khin ph hp thay i u ra p ng i tng b c

th.

- SVS (Static Var System) h thng thay i tnh: l s kt hp ca cc b b c

th thay i c kha ng m c kh tnh khc nhau v u ra c phi hp.

- TCBR (Thyristor Controlled Braking Resistor) in tr hm iu khin bng

thyristor): l in tr ng ct bng thyristor, mc song song, c th c iu

khin gip n nh ca h thng in hoc lm gim gia tc nng lng ca

khi pht in trong lc c nhiu.


48

Hnh 3.5 B TCBR

TCBR lin quan n vic ng m theo tng chu k ca in tr (thng l in

tr tuyn tnh) vi mt thit b ng ct xoay chiu da trn thyristor v khng iu

khin gc pha, nh minh ha trn hnh 3.5. gim chi ph, TCBR c th l cc thyristor

khng c iu khin gc pha, tuy nhin vi vic iu khin gc pha theo tng na chu k

c th lm gim dao ng tn s thp mt cch c la chn.

3.3. Cc thit b b dc

3.3.1. SSSC (Static Synchronous Series Compensator) B b ni tip ng b tnh

SSSC l mt my pht ng b khng c ngun nng lng in bn ngoi, hot

ng nh mt thit b b ni tip m in p u ra c th iu khin c lp v vung

pha vi dng in trn ng dy nhm mc ch tng hoc gim in p dung khng ri

trn ng dy v v th iu khin cng sut truyn ti. SSSC c th cha b d tr

nng lng hoc cc thit b tiu th nng lng nhm tng cng kh nng n nh

ng ca h thng in bng cch b thm cng sut tc dng tc thi, tng hoc gim

in p ri trn ng dy.

SSSC l mt trong nhng b iu khin FACTS quan trng nht. N ging nh

STATCOM, nhng khc l in p u ra ac ni tip vi ng dy, nh biu din trn

hnh 3.6. N c th da trn b bin i ngun p hoc b bin i ngun dng. Thng

in p ni tip a thm vo l kh nh so vi in p ng dy, v cch in i vi

t kh ln. Vi cch in ph hp gia cun s cp v th cp ca my bin p, cc

thit b chuyn i c t in th mt t tr khi cc thit b ny c t trn mt


49

phng c cch in vi t. T s my bin p c bin i sao cho thit k b bin

i kinh t nht. V khng c ngun in thm ngoi, SSSC ch c th a thm vo 1

in p ri thay i nhanh pha hn hoc chm pha hn so vi dng in 1 gc 90 .

Cun s cp ca bin p v do c cun th cp cng nh b chuyn i phi mang

c dng in trn ng dy khi y ti, k c dng lm vic khi s c, tr khi b

chuyn i c i vng qua mt cch tm thi trong khi c s c nghim trng.

Hnh 3.6 SSSC da trn b bin i ngun p v SSSC c ngun d tr.

B d tr in hoc d tr t siu dn cng c th c ni vi b iu khin ni

tip a thm vector in p vi cc gc pha khc nhau vo ni tip vi ng dy.

Chc nng chnh ca SSSC l:

- iu chnh dng in.

- Gii hn dng in s c.

- Gim dao ng cng sut.

- Nng cao n nh ng v n nh qu .

- n nh in p.

3.3.2. IPFC (Interline Power Flow Controller) b iu khin dng cng sut lin ng dy

IPFC l mt khi nim mi c a ra, do cha c nh ngha theo IEEE. Mt

nh ngha c th chp nhn c nh sau: IPFC l s kt hp ca 2 hay nhiu SSSC,

lin kt vi nhau thng qua phn mt chiu chung trao i dng cng sut tc dng

theo c hai chiu gia cc u ra ca SSSCs, v c iu khin cung cp b cng

sut phn khng cho s iu chnh ca dng cng sut tc dng trn mi ng dy v

duy tr phn phi dng cng sut phn khng theo yu cu gia cc ng dy. Cu trc

ca IPFC c th bao gm mt STATCOM, kt hp vi phn mt chiu chung ca IPFC,


50

cung cp b cng sut phn khng ngang v cung cp hay tiu th lng cng sut tc

dng thiu ht ca cc b SSSC.

3.3.3. TCSC (Thyristor Controlled Series Capacitor) T ni tip iu khin bng thyristor

TCSC l mt b b in khng mang tnh cht dung khng, c cha mt b cc t

in ni tip v b ny song song vi khng in iu khin bng thyristor (TCR) nhm

cung cp in dung c th iu chnh trn, nh minh ha trn hnh 3.7.

TCSC da trn thyristor thng thng. N l mt s la chn khc cho SSSC v

cng ging nh SSSC, l mt thit b FACTS quan trng. Mt khng in c th thay i

in khng nh TCR c ni song song vi b t. Khi gc pha ca TCR l 180o, khng

in s khng dn in na v khi b t c in khng bnh thng ca n. Khi gc

pha thay i t 1800 v nh hn 1800, in khng dung s tng ln. Khi gc pha l 900,

khng in tr nn dn in hon ton, in khng tng s mang tnh cht cm, bi v

in khng ca khng in c thit k nh hn nhiu so vi in khng ca b t.Vi

gc pha l 900, TCSC c th hn ch dng s c. TCSC c th l mt khi ln, n l

hoc cha vi t in kch c bng hoc khc nhau c th hot ng mang li hiu qu

tt hn.

3.3.4. TSSC (Thyristor- Switched Series Capacitor) - T in ni tip ng m bng thyristor

TSSC l b b in khng mang tnh cht dung cha b t ni tip v b t ny

song song vi mt in khng ng m bng thyristor cung cp s iu khin theo

bc cho in khng, nh cng c minh ha trn hnh 3.7.

Hnh 3.7 Cu to chung ca TCSC v TSSC.

Thay v iu khin trn dung khng, in khng ca khng in khi gc pha l 00

hoc 900 (khng iu chnh gc pha) c th lm gim chi ph v tn tht cho b iu


51

khin. Rt hp l khi sp xp mt trong cc module c iu khin thyristor, trong khi cc

module khc th ch ng ct thyristor.

3.3.5. TCSR (Thyristor- Controlled Series Reactor) in khng ni tip iu khin bng thyristor:

TCSR l mt b b cm khng c cha b cc khng ni tip v mc song song

vi in khng iu khin bng thyristor nhm iu chnh cm khng mt cch lin tc,

minh ha trn hnh 3.8.

Khi gc pha ca TCR l 900, n s khng dn in, in khng khng c iu

khin s hot ng nh 1 b hn ch dng s c. Khi gc pha gim xung di 900, in

khng tng s gim cho n khi gc pha l 00, in khng tng l hai in khng song

song vi nhau. Cng ging nh TCSC, TCSR c th l mt khi ln ring l hoc mt

vi khi nh hn.

3.3.6. TSSR (Thyristor- Switched Series Reactor) khng in ni tip ng m bng thyristor)

TSSR l b b cm khng c cha b cc khng ni tip v mc song song vi

in khng ng ct bng thyristor nhm iu chnh cm khng theo bc. Ging nh

TCSR, nhng kha thyristor ch ng hoc ct (khng c iu khin gc pha), s cng

c minh ha trn hnh 3.8.

Hnh 3.8 Cu to chung ca TCSR v TSSR.

Cc b iu khin ni tip ni chung c cc chc nng tng t nhau, tuy nhin

mc iu khin v iu chnh in p, dng cng sut, n nh ng, n nh tnh l

khc nhau ty thuc vo tng loi b iu khin khc nhau. Cc chc nng chnh l:

- iu chnh dng in.

- Gii hn dng in s c.


52

- Gim dao ng cng sut.

- Nng cao n nh ng v n nh qu .

- n nh in p.

3.4. B iu khin kt hp ni tip- song song

3.4.1. UPFC (Unified Power Flow Controller)

UPFC l s kt hp ca STATCOM v SSSC vi phn mt chiu chung, cho

php dng cng sut tc dng theo c hai chiu gia cc u ra ni tip ca SSSC v cc

u ra song song ca STATCOM, v c iu khin cung cp b cng sut phn

khng v tc dng mt cch ng thi m khng cn ngun in bn ngoi. UPFC, bng

cch a thm vo in p ni tip mt cch t nhin, c kh nng iu khin, ng thi

hoc c la chn, in p ng dy truyn ti, in khng, gc pha, hoc dng cng

sut tc dng, phn khng chy trn ng dy. UPFC c th cung cp b phn khng

ngang c iu khin mt cch c lp.

Trong UPFC bao gm STATCOM v SSSC, cng sut tc dng cho khi ni tip

(SSSC) ly t li thng qua khi song song STATCOM. SSSC cng c dng iu

chnh in p bng cch iu chnh cng sut phn khng. y l b iu khin y ,

c th iu chnh c c dng cng sut phn khng v tc dng, cng nh in p

ng dy.

Hnh 3.9 Cu to chung ca UPFC.

B d tr nng lng b sung nh BESS hoc SMES c th c ni vi thanh

ci mt chiu thng qua giao din in t s cung cp cch thc tng cng thm hiu

qu ca UPFC. Nh nhc n trong cc phn trn, s trao i dng cng sut tc dng

c iu khin vi ngun bn ngoi, chng hn nh b d tr, hiu qu hn rt nhiu


53

trong vic iu khin ng h thng hn l ch iu bin s trao i cng sut trong cng

mt h thng.

V chc nng, UPFC c cc chc nng ca STATCOM v SSSC, l:

- iu khin dn cng sut tc dng v phn khng ti nt b.

- Tng cng tnh n nh tnh v n nh ng ca h thng.

- Gim dao ng cng sut khi xy ra s c trong h thng.

- C kh nng vn hnh trong ch s c v tip tc iu khin khi loi tr

c s c.

3.4.2. TCPST (Thyristor- Controlled Phase Shifting Transformer)

TCPST - bin p dch pha iu khin bng thyristor, l mt bin p dch pha c

iu chnh bng kha thyristor thay i gc pha mt cch nhanh chng, nh biu din

trn hnh 3.10.

Hnh 3.10 Cu to chung ca TCPST.

Ni chung, dch pha t c bng cch thm vector in p vung gc ni tip

vi pha. Vector ny ly t hai pha cn li thng qua bin p mc ngang song song. in

p ni tip vung pha c to ra c th thay i bng rt nhiu loi cu trc in t

cng sut. B iu khin ny cn c gi l TCPAR (Thyristor- Controlled Phase Angle

Regulator).

TCPST c cc chc nng ging nh cc b iu khin FACTS khc, tuy nhin,

chc nng chnh ca n l iu chnh gc lch pha ca in p pha ca ng dy, v n

c kh nng iu khin dng cng sut rt cao.


54

3.4.3. TCVL (Thyristor- Controlled Voltage Limiter) B gii hn in p iu chnh bng thyristor

TCVL l mt bin tr oxit kim loi (MOV) c s dng gii hn in p hai

u trong qu trnh qu .

Hnh 3.11 TVCR

Kha ng m thyristor c th c ni ni tip vi chng st van khng khe h,

hoc nh trn hnh 3.11, mt phn ca chng st van khng c khe h (10-20%) c th

c ni vng qua mt kha thyristor lm gim mc gii hn in p. Ni chung,

MOV c ngha quan trng hn so vi chng st van. Nh trn hnh 3.11, TCVL thng

thng c dng hn ch qu in p ng, nu khng c s ngn cn ny th qu

in p ng c th din ra trong hng chc chu k.

3.4.4. TCVR (Thyristor- Controlled Voltage Regulator) b iu chnh in p iu chnh bng thyristor

TCVR l mt bin p c th cung cp in p cng pha vi kh nng iu chnh

trn. Trong thc t, thit b ny c th l bin p thng thng vi u iu chnh iu

khin bng thyristor hoc vi b bin i in p xoay chiu sang xoay chiu iu khin

bng thyristor a thm vo in p xoay chiu thay i c ca cng mt pha ni

tip vi ng dy, nh biu din trn hnh 3.12.


55

Hnh 3.12 TCVR loi da trn u phn p v loi da trn s a thm in p vo

ng dy.

3.5. Kt lun

H thng truyn ti in xoay chiu linh hot FACTS c ng dng rt rng ri

trong vic nng cao kh nng truyn ti, nng cao mc n nh tnh, n nh ng, n

nh in p v gim cc dao ng trong h thng in.

Cc thit b FACTS c thit k v ch to vi nhiu loi khc nhau tng

ng vi cc loi iu khin v cc thng s iu khin trong h thng in. Nhn chung

thit b FACTS c chia thnh cc thit b iu khin dc, ngang v t hp gia chng.

Cc thit b b dc c iu khin ch yu s dng iu khin dng in cng nh

dng cng sut trong h thng truyn ti. Ngoi ra chng cn c s dng tng

cng mc n nh v gim dao ng ca h thng in. Cc thit b b ngang c

iu khin ch yu s dng iu khin v gi in p ti cc im nt ca h thng

in, ngoi ra cn c tc dng b cng sut phn khng, nng cao n nh tnh v n nh

ng, gim cc dao dng trong h thng in.

Cc thit b FACTS c thit k, ch to v lp t ph bin trn th gii vi

rt nhiu chng loi tng ng vi cc thng s iu khin trong h thng in. Vic la

chn thit b ph thuc vo mc ch iu khin, hin trng lin kt li in v tnh ton

cc chi ph u t xy dng v li ch v kinh t m thit b FACTS mang li.

Ni chung cc thit b FACTS u t tin, nht l cc thit b iu khin hn hp,

c th b dc ln b ngang. Chnh v th cc thit b iu khin hn hp nh UPFC,

TCPST,... t c ng dng trong thc t. Trn th gii hin nay, c 2 loi thit b

FACTS c lp t nhiu v chng t c hiu qu hot ng ca chng, l

TCSC b dc v SVC b ngang.

Chng 4.Cu to v nguyn l lm vic ca thit b b tnh SVC

56

Chng 4 Cu to v nguyn l lm vic ca thit b b tnh STATIC VAR COMPENSTATOR (SVC)

SVC (Static Var Compensator)- L thit b b tnh c dung lng b thay i c, ni

song song vi li in, cng sut u ra ca n c th c iu chnh trao i dng

in in cm hoc in dung duy tr hoc iu khin cc thng s c th ca h thng

in (in hnh l in p nt).

4.1. Vai tr ca SVC

Mt s ng dng ca SVC:

Hnh 1:mt s chc nng ca SVC

a. Chc nng c bn ca SVC l iu khin in p v tro lu cng sut

phn khng ti im m n c ni vo li in.

Cng sut phn khng c nh hng ln ti in p, m SVC l mt thit b c

kh nng to ra hoc tiu th cng sut phn khng.

Trong h thng in vi cc s c ngn mch hay cc ng dy di c

khong cch ln th cht lng in p b nh hng bi s thay i ca cng

sut ti.Vi cng sut ti ln th in p s b gim ng k. Qu p l nguyn


57

nhn gy nn hin tng bo ha mch t ca my bin p,v lm tng vt cc

thnh phn sng hi trong cc my pht in. Cc thnh sng hi ny cng

hng vi cc t v in cm k sinh trn ng dy dn n c th ph hng

cc thit b in.

b. Chc nng quan trng nht l gii hn thi gian v cng qu p khi

xy ra s c bnh thung nh mt ti t ngt ti 1 im trn ng dy

hoc ngn mch yu.V SVC c th phn ng trong vng 10ms,nn thi gian

qu p s c gim xung thp hn thi gian chnh nh bo v ca h thng

R le.Do cc R le khng cn tc ng v tnh cht ti in lin tc s uc

nng cao. c im ny rt quan trng i vi cc ng dy co p v siu

cao p nc ta v n c chiu di ln nn nhiu trng hp phi ngn mch

1 pha cc on ng dy nn c th dn n hin tng qu p.

c. n inh dao ng cng sut hu cng.

Dao ng cng sut hu cng l 1 hin tng c th xay ra sau 1 qu trnh qu

,v d nh mt ti thnh lnh, gim bt cng sut pht in ti ngun hoc t

ng ng li sau s cH thng ti in cng yu th hin tng ny cng

d xy ra.

Khi c dao ng cng sut hu cng, SVC s iu khin n nh bng cch

m gc m Thyristor ca TCR gn nh tc thi n inh cng sut hu

cng.

d. Gim cng dng in v cng v nh th s gim bt i tn tht gy

ra bi dng in ny trn ng dy m cc nh my pht in phi cung

cp.Ni chung l tit kim nng lng v tng nng sut ca ca h thng in.

e. Tng kh nng ti ca ng dy v tng d tr n nh.Cng sut

truyn ti ca h thng in thng c gii hn bi cp in p v in

khng ca cc my bin p trong h thng.Gi s b gia ng dy:


58

Bnh thng khi cha b:.s r

L

E EP Sin

X

Sau khi b gia ng dy: .

22

s r

L

E EP Sin

X

Nh vy cng sut max tng gp 2 ln bnh thng, kh nng truyn ti v

gi tr n inh tng gp i.

g. Cn bng cc ph ti khng i xng do SVC c kh nng gi in p n

nh theo tng pha ring r nn n lm cho s khng i xng ca ph ti

gim xung. S khng i xng v s xut hin ca cc ti 1 pha c nh

hng n cht lng in p trong h thng in. V vy cn bng ph ti l 1

nhim v quan trng.

h. Ci thin n nh sau s c.

cho h thng in gi uc trng thi n nh sau cc nhiu lon ln do

vic loi tr cc s c bng tc ng ca cc phn t bo v. H thng phi gi

cng sut truyn ti nh hn gi tr cng sut gii hn n nh. Khi thit b


59

SVC uc ng dng th kh nng ti ca uc dy c tng ln,v theo gi

tr cng sut gii hn n nh tng ln. Mt khc, thng qua SVC ta c th gi

cng sut truyn ti bng cch thay i gc m Thyristor ca TCR.

4.2 Cu to ca SVC

-V mt cu to th SVC c 2 dng cu hnh chnh l: TCR/FC v TCR/TSC.

Cu hnh TCR/FC Cu hnh TCR/TSC

Hnh 2:Cc cu hnh SVC

-TCR bao gm cun khng v cc van Thyristor. Nhnh TCR iu khin mt cch

lin tc cng sut phn khng bng cch thay i bin ca dng in chy qua

cun khng.

-TSC bao gm cc van thyristor, t in v cun khng hn ch tng dng qua

van (surge current). TSC ch c iu khin ng hoc ngt t ra khi h

thng.

-B lc FC dng pht mt lng c nh cng sut phn khng v lc sng hi

dng in to ra bi TCR

4.3 Nguyn l hot ng ca TCR


60

Dng in trong in khng c th c iu khin t gi tr ln nht ti 0 bng cch

iu khin gc m

Hnh 3: dng sng vn hnh vi cc gc m

Bin IL() ca thnh phn dng in c bn iL() c th c biu th l hm ca

gc nh sau:

2 1( ) (1 sin 2 )L

VI

L

(4.1)

Trong V l bin ca in p ngun, L l in cm ca in khng iu khin

bng thyristor, l tn s gc ca in p ngun.


61

Hnh 4: Bin thin bin cc dng in thnh phn c bn qua TCR

ph thuc gc m

TCR c th iu chnh dng in c bn chy qua in khng, v nu nhn t pha li

th TCR c th coi l 1 in dn cm khng c th thay i gi tr. V th, in dn cm

khng hiu dng ca TCR c xc nh t cng thc (2.2), l hm ca gc nh

sau:

)2sin12

1(L

1)(BL

(4.2)

ngha ca (2.3) l vi mi gc iu khin , in dn BL() c xc nh, n xc

nh bin ca thnh phn dng in c bn ILF() trong

TCR 1 in p ngun cho trc. Trong ng dng thc t,

bin ln nht ca in p ngun v ca dng in b gii

hn bi gi tr nh mc ca cng sut m cc thnh phn

(in khng, van thyristor) s dng. V th, TCR trong

thc t c th vn hnh bt c im no trong vng V-I xc

nh, ng bin ca n xc nh bng in dn ln nht c

th t c, in p v dng in nh mc, nh minh ha

trn hnh 4. Gii hn ca TCR c thit lp khi thit k t

yu cu vn hnh thc t.

Hnh 4: c tnh V-I


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Nu kha TCR b gii hn gc iu khin c nh, thng = 0 th n s tr thnh

TSR-Thyristor-Switched Reactor (in khng ng ct bng thyristor). TSR to ra 1 in

dn cm khng c nh v do , khi c ni vi h thng li xoay chiu, dng in

chy qua n s t l vi in p ngun. Mt vi TSR c th to ra in dn iu chnh

c gin on theo bc. Nu TSR vn hnh = 0, dng in xc lp c dng hnh sin.

-Sng hi: iu khin gc dn dng (c tnh vn hnh ca TCR) dn n kt qu l

dng sng ca dng in khng cn l hnh sin. Ni cch khc, ngoi thnh phn c bn,

TCR cn sinh ra cc sng hi. Trong na chu k dng in dng, m xc nh, ch c

cc sng hi bc l mi c to ra. Bin ca cc sng ny l hm ca gc iu khin

, c th hin trong cng thc:

)1n(n

)nsin(cosn)ncos(sin4

L

V)(I

2Ln (4.3)

vi n = 2k+1, k = 1, 2, 3,...

Hnh 5: Bin cc thnh phn dng in bc cao ca TCR so vi .

Trong h thng 3 pha, ngi ta s dng 3 b TCR 1 pha v ni tam gic. Trong iu

kin cn bng, dng in hi vi bc l bi ca 3 chy qun trong b TCR ni tam gic

v khng i vo h thng in.


63

Ngoi ra t c yu cu k thut v kinh t hoc cc l do thc t khc, ngi ta s

s dng b lc sng hi. Thng thng, cc b lc ny l cc nhanh LC v LCR ni tip

vi nhau v song song vi TCR v ha hp vi cc sng hi chim u th ln, nh bc 3,

5, 7, v i khi l bc 11,13.

4.4 Nguyn l hot ng ca TSC

Trong ch xc lp, khi thyristor dn v TSC c ni vi ngun p xoay chiu,

v = Vsint th dng in trong nhnh s l tcosC1n

nV)t(i

2

2

trong

C

L

2 X

X

LC

1n

Bin ca in p t l V1n

nV

2

2

C

(3.4)

Nhnh TSC c th khng c ni vo HT (b ngt ra) lc dng in bng 0. Khi dng

in qua gi tr 0, in p t in t gi tr cc i th ta c:

V1n

nv

2

2

0i,C

T in khng c ni s gi in p mc ny v dn n in p ngc t ln

thyristor thay i t 0 ln n gi tr bin dao ng kp (peak to peak) ca in p

ngun.

Nu in p ca t khi b ngt vn khng i, TSC c th ng li m khng c qu

trnh qu , ti gi tr nh ph hp ca in p ngun.

Hnh 6: Dng sng minh ha qu trnh ng ct khng c qu trnh qu ca TSC.


64

Thng thng, cc bn t in b phng in sau khi b ngt ra khi ngun, v th vic

ni li cc t in ny s phi thc hin vi phn in p d trn t nm trong khong

gia gi tr 0 v gi tr ln nht ca t V1n

nv

2

2

0i,C

. iu ny c th i km vi nhiu

qu nh nht nu thyristor ng nhng thi im in p d trn t v in p

ngun bng nhau, ngha l khi in p qua thyristor bng 0.

Cc qu trnh qu ny gy ra bi thnh phn dv/dt khc 0 thi im ng, nu nh

khng c in khng ni tip s to ra dng in tc thi ic=Cdv/dt (Dng in ny biu

th cho gi tr tc thi ca dng in qua t ch xc lp ti thi im ng kha). Tc

ng qua li gia t in v in khng hn ch dng in, cng vi in tr, sinh ra dao

ng qu , c th thy trn dng sng ca in p v dng in. (Ch l qu trnh qu

khi ng t in phng in hon ton th phc tp hn so vi khi t in mi

phng in 1 phn v thnh phn dv/dt ca in p ngun t gi tr ln nht im qua

gi tr 0 ).

Nhng iu kin ng t in khng qu :

1. Nu in p d trn t in thp hn nh in p ngun (Vc V) th thi

im ng s l khi in p ngun t cc i, khi

in p t ln thyristor l nh nht.

T cc phn tch trn ta thy, gc iu khin ln

nht ng cc bn t l c chu k ca in p

ngun, ngha l khong thi gian t nh dng

(hoc m) n nh dng (hoc m)

V cng c th thy rng iu khin gc m

khng p dng i vi t in, vic ng t in ch

c th din ra thi im c th trong mi chu k

m cc iu kin qu trnh qu din ra phc tp nht. V l do ny m TSC ch

c th cung cp s thay i theo bc dng in dung (gi tr ln nht hoc 0). Ni cch

khc, nhnh TSC biu th cho 1 in dung hoc l ni hoc l ngt ra khi h thng.

Dng in trong nhnh TSC thay i tuyn tnh vi in p ngun ty thuc vo in

dung ca t in. in p ngun ln nht v dng in tng ng b gii hn bi nh

mc ca cc thnh phn TSC (t in v thyristor)


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xp x s thay i dng in, ngi ta thng s dng mt vi TSC song song nhau

(lm tng in dung bc), hoc phi hp vi 1 nhnh TCR.

4.5 Nguyn l hot ng ca FC.

Nhnh FC (Fixed Capacitors) ca SVC bao gm t in v cun khng hot

ng nh mt b lc xoay chiu. FC lc cc thnh thnh sng hi dng in do s

hot ng ca TCR to ra. Ngoi ra nhnh FC cn c kh nng pht mt lng

cng sut phn khng nht nh ln li.

Documents

Facts File Tv