Bu Cong Suat SVC

LUN VN THC S K THUT

PHN TCH NH GI HIU QU KINH T K THUT CA VIC NG DNG THIT B B C IU KHIN SVC TRONG H THNG IN CA KHU GANG THP

THI NGUYN

Ngnh : THIT B MNG V NH MY IN M s :23.04.3898

V TH THY NINH

Thi nguyn 2008

MC LC

S ha bi Trung tm Hc liu i hc Thi Nguyn http://www.lrc-tnu.edu.vn

MC LC

Cc ch vit tt v k hiu

M u

Chng I: c im tiu th in ca li in cng nghip

cng sut ln

I.1: c im tiu th in ca li in cng nghip cng

sut ln

I.2: B cng sut phn khng cho ph ti trong li in

cng nghip

I.2.1. H s cng sut v s iu chnh

I.2.1.1. H s cng sut

I.2.1.2. iu chnh h s cng sut

I.2.2: iu chnh in p

I.2.2.1: Nguyn tc iu chnh in p

I.2.2.2. Cng thc gn ng cho vic iu chnh in p.

I.2.2.3. c tnh gn ng ca cng sut phn khng

Chng II: Tng quan v cng ngh FACTS

II.1. t vn

II.2. Li ch khi s dng thit b FACTS

II.2.1. Cc u im khi s dng thit b FACTS

II.2.2. Phn loi thit b FACTS

II.3. Mt s thit b FACTS

II.3.1. Thit b b tnh iu khin bng thyristor

(SVC)

II.3.2. Thit b b dc iu khin bng thyristor

(TCSC)

II.3.3.Thit b b ngang iu khin thyristor (STATCOM)

Trang

1

2

6

6

7

8

8

9

11

11

14

16

28

28

28

28

29

30

30

32

33

MC LC


II.3.4. Thit b iu khin gc pha bng thyristor

(TCPAR)

II.3.5. Thit b iu khin dng cng sut hp nht

(UPFC)

II.4. Kh nng p dng thit b FACTS ti Vit Nam

Chng III: Cc thit b b cng sut phn khng v hot

ng ca thit b b ngang c iu khin (SVC)

III.1: Cc thit b b cng sut phn khng

III.1.1: B cng sut phn khng trong h thng in

III.1.2: Cc thit b b iu khin bng thyristor

III.2: Hot ng ca thit b b ngang c iu khin SVC

III.2.1: c tnh iu chnh ca SVC

III.2.2: c tnh lm vic ca SVC

III.3: Mt s nh hng ph ca SVC

Chng IV: nh gi hiu qu s dng SVC ti khu gang

thp Thi Nguyn

IV.1: M u

IV.2: Cn c thit k h thng SVC

IV.2.1: Cc thng s trm bin th Gia Sng

v trm bin th cp in ca Gang thp

IV.2.2: Cc thng s ca bin p l in

IV.2.3: Tr khng v in khng hn dng ca

mch ngn l in

IV.2.4: Ch tiu k thut cn t c

IV.2.5: H thng cp in ca Cng ty Gang

thp Thi Nguyn Vit Nam

IV.3. Phn tch nh hng ca cm l in h quang

ti cht lng in ca li in cung cp in

35

36

38

40

40

40

43

48

48

57

59

61

61

62

63

63

64

64

67

71

MC LC


IV.3.1: nh hng cht lng in trong li

cp in hin nay ca Cng ty Gang thp Thi Nguyn

IV.3.2: nh hng ca h thng cp in

tng lai khng c SVC i vi cht lng

in nng ca li in

IV.4: Xc nh phng n SVC

IV.5: Kh nng c ci thin v cht lng

in nng ca mng in i vi h thng cung

cp in gang thp sau ny khi d c lp

thm SVC

IV.6: nh gi hiu qu kinh t khi s dng SVC

ti khu gang thp Thi Nguyn.

Kt lun chung

Ti liu tham kho

Ph lc

72

77

84

84

86

95

96

97

CC CH VIT TT V K HIU


1

CC CH VIT TT V K HIU

CXL

CSPK

CSTD

HT

HTCC

FACTS

GTO

MBA

STATCOM

SVC

TCPAR

TCR

TCSC

TSR

TSC

UPFC

Ch xc lp

Cng sut phn khng

Cng sut tc dng

H thng in

H thng cung cp in

Flexible AC Transmission Systems - H thng truyn ti

in xoay chiu linh hot

Gate Turn - Off Thyristor - Kha ng m

My bin p

Static Synchronous Compensator - Thit b b ngang iu

khin bng thyristor

Static Var Compensator - Thit b b tnh iu khin bng

thyristor

Thyristor Controlled Phase Angle Regulator - Thit b iu

chnh gc lch pha ca in p

Thyristor Controlled Reactor - khng in iu khin bng

thyristor

Thyristor Controlled Series Compensator - Thit b b dc

iu khin bng thyristor

Thyristor Switched Reactor - Khng in ng m bng

thyristor

Thyristor Switched Capacitor - T in ng m bng

thyristor

Unified Power Flow Control - Thit b iu khin dng

cng sut hp nht

M U


2

M U

1. Mc ch nghin cu v l do chn ti

Trong ch vn hnh bnh thng ca HT (vn hnh trng thi n nh)

vic sn xut cng sut tc dng (CSTD) phi p ng c nhu cu tiu th (k c cc

tn tht), nu khng th tn s h thng s b thay i. Cng vy, c mt s gn b cht

ch gia iu kin cn bng cng sut phn khng (CSPK) vi in p cc nt h

thng. Cng sut phn khng mt khu vc no qu tha th s c hin tng

qu in p (in p qu cao), ngc li, thiu CSPK in p s b st thp. Ni khc

i, cng nh i vi cng sut tc dng, CSPK lun phi c iu chnh gi cn

bng. Vic iu chnh CSPK cng l yu cu cn thit nhm gim nh tn tht in

nng v m bo n nh h thng.

Tuy nhin c s khc nhau c bn gia iu chnh CSTD v iu chnh CSPK.

Tn s h thng s c m bo bng vic iu chnh CSTD bt k my pht in

no (min sao gi c cn bng gia tng cng sut pht v cng sut tiu th).

Trong khi , in p cc nt h thng khng bng nhau, chng ph thuc iu kin

cn bng CSPK theo tng khu vc. Nh vy ngun CSPK cn c lp t phn b v

iu chnh theo tng khu vc. iu ny gii thch v sao, ngoi cc my pht in cn

phi c mt s lng ln cc thit b sn xut v tiu th cng sut phn khng: My

b ng b, t in, khng in... Chng c lp t v iu chnh nhiu v tr trong

li truyn ti v phn phi in (gi l cc thit b b CSPK).

Trc y, vic iu chnh CSPK ca cc thit b b thng c thc hin n

gin: Thay i tng nc (nh ng ct bng my ct c kh) hoc thay i kch t

(trong my b ng b). Chng ch cho php iu chnh th hoc theo tc chm. K

thut thyristor cng sut ln m ra nhng kh nng mi, trong vic ra i v ng

M U


3

dng cc thit b b tnh iu chnh nhanh cng sut ln - SVC (Static Var

Compensator), TCSC (Thyristor Controled Serie Capacitor) gii quyt c nhng

yu cu m cc thit b b c in cha p ng c, nh t ng iu chnh in p

cc nt, gim dao ng cng sut nng cao n nh h thng.

Vic ng dng cc thit b b CSPK cht lng cao iu khin bng thyristor

tr thnh mt nhu cu cp thit nhm nng cao tnh n nh v hiu qu s dng ca h

thng cung cp in (HTCC) ni chung cng nh i vi cc ph ti c cng sut

phn khng thay i nhanh nh l nung h quang in.

Vi ngha trn, mc ch ca ti lun vn c xc nh l:

+ Nghin cu tm hiu cc c im, tnh nng hot ng, ch lm vic v

m hnh tnh ton ca cc thit b t ng iu chnh linh hot (FACTS) c bit l

thit b b iu chnh nhanh (SVC) trong HTCC

+ Nghin cu, nh gi, xc nh hiu qu kinh t - k thut ca SVC khi c

lp t vo HTCC khu Gang thp Thi Nguyn.

2. Ni dung lun vn

Vi mc tiu nu trn, lun vn c trnh by trong bn chng:

Chng I : c im tiu th in ca h thng in cng sut ln v l thuyt

c bn v b cng sut phn khng.

Chng II: Tng quan v cng ngh FACTS

Chng III: Cc thit b b cng sut phn khng v hot ng ca thit b b

ngang c iu khin

M U


4

Chng IV: nh gi hiu qu s dng SVC ti khu Gang thp Thi Nguyn.

3. i tng v phm vi nghin cu

Hiu qu ca vic ng dng cc thit b b ti li in khu Gang thp Thi

Nguyn.

4 Phng php nghin cu

thc hin nhim v nghin cu trn s dng phi hp cc nhm phng

php:

Nhm phng php nghin cu l thuyt: Tham kho cc t liu k thut

phn tch, tng hp nhng vn c lin quan ti ti.

Nhm phng php nghin cu thc tin ti x nghip Nng lng: iu tra,

kho st, lp t k thut,... cng c thm tin cy, chnh xc ca kt qu nghin

cu.

5. ngha khoa hc v thc tin ca lun vn

Cc kt qu nghin cu ca lun vn nhm tm hiu su v cng ngh FACTS,

c bit ch cng ngh SVC v m hnh ho cc thit b FACTS trong cc phng

trnh c bn tnh ton ch xc lp (CXL) ca HTCC. i su nghin cu cc nh

hng ca ch lm vic l h quang i vi h thng cung cp in nh: Dao ng

in p, mo hnh sin, nh hng ca sng, sung kch v cng, tc hi ca th t

nghch (m)... T ng dng SVC i vi ph ti khu gang thp Thi Nguyn

gim thiu cc tc ng nu trn v nghin cu tnh ton hiu qu kinh t ca SVC i

vi h thng in khu gang thp Thi Nguyn.

M U


5

Tc gi xin chn thnh cm n cc thy gio v c gio trong b mn H thng

in Trng i hc K thut Cng nghip Thi Nguyn v Trng i hc Bch khoa

H Ni, cc bn b ng nghip gip v to iu kin thun li trong thi gian

thc hin lun vn. c bit tc gi xin by t lng bit n su sc vi Thy gio TS.

Nguyn Mnh Hin, ngi quan tm, tn tnh hng dn gip tc gi xy dng v

hon thnh lun vn ny.

CHNG I: C IM TIU TH IN CA LI IN CNG NGHIP

CNG SUT LN


6

CHNG I

C IM TIU TH IN CA LI IN CNG NGHIP

CNG SUT LN

I.1: c im tiu th in ca li in cng nghip cng sut ln

in nng l dng nng lng ch yu ca cc x nghip cng nghip, ni tiu

th khong 50 sn lng in nng ca c nc. V vy, vic cung cp v s dng

in hp l trong lnh vc ny c ngha rt to ln i vi s pht trin ca nn kinh

t quc dn.

Cc x nghip cng nghip c c im chung l c ph ti in ln; yu cu

tin cy cung cp in cao; thit b dng in c tp trung vi mt cao, lm vic

vi ti gn nh mc, dng c in p xoay chiu v in p mt chiu, tn s cng

nghip (50Hz); lm vic lin tc trong sut nm v t ph thuc vo tnh cht ma v.

Tuy vy, do qu trnh cng ngh ca x nghip rt khc nhau nn c im tiu th

in v h thng cung cp in ca chng cng mang nhiu c im ring bit khc

nhau. Trong phn ln cc ph ti in cng nghip th l nung h quang in l loi

ph ti tiu th in ln nht, qu trnh vn hnh ca n thng ko theo s dao ng

in p v dao ng cng sut rt ln.

s dng in nng c hiu qu trong cc l h quang luyn thp th cc vn

phi c gii quyt mt cch tng th v ng b, c bit l cn phi quan tm

n cc vn n nh in p, hiu chnh h s cng sut v lc sng iu ho ...

n nh in p ci thin ng k ch vn hnh ca l luyn, lm gia tng

cng sut cc i dn n tng nng sut sn phm. Ngoi ra, trong trng hp l h

quang ngn cng cho php l lm vic vi cng mt mc cng sut cc i, nhng

gim thiu c mc kh nng chy ca v bc bn ngoi phi thp, gip hn ch

chp nhy in p.


CNG SUT LN


7

Cc gii php c s dng n nh in p bao gm: vic u ni l vo

li c in p cao hn hoc s dng cc thit b ph tr nh my b ng b vi in

khng m, thit b iu khin thyristor tc cao hin i hoc in khng bo ho.

u ni l in vo li in c in p cao hn thng rt t v i khi l khng

thc t. p ng nhanh ca thit b b tc cao gip gii quyt vn i nghch

gia c tnh l in v vic gim chp nhy ca t hp my b ng b vi in

khng m. V vy, c th ni trong mt s trng hp, vic s dng thit b b iu

khin bng thyristor hoc b bng in khng bo ho s l gii php n nh in p

l in mang li hiu qu kinh t - k thut cao nht.

I.2: B cng sut phn khng cho ph ti trong li in cng nghip

Mc tiu u tin ca l thuyt b ph ti l gii thch mi quan h gia h

thng cung cp in (HTCC), ph ti v thit b b nhm t ba mc tiu:

+ iu chnh h s cng sut

+ Cng c s iu p

+ Cn bng ph ti.

C th nu c trng hoc thit lp m hnh ca h thng cung cp, ph ti v

thit b b theo nhiu cch. H thng cung cp c th c c trng nh mt mch

tng ng Thevenin vi mt in tr h mch, mt tng tr ni tip cc yu cu v

dng in hay cng sut, cng sut phn khng ( hay h s cng sut). Thit b b c

th c m hnh ho thay i hay mt ngun cng sut phn khng. Vic la chn m

hnh s dng cho mi thnh phn c th thay i theo yu cu v c kt hp theo

nhiu cch. Cc m hnh khc nhau ca mi thnh phn tng ng vi nhau c th

chuyn i qua li.

u tin, l thuyt c pht trin cc iu kin tnh hay gn tnh vi gi thit

l cc ti v cc c tnh h thng c hiu ngm l chng khng thay i hay thay


CNG SUT LN


8

i chm s dng cc phng trnh pha. iu ny lm vic phn tch tr nn n

gin hn. Trong hu ht cc trng hp thc t, cc phng trnh pha tnh hay gn tnh

xc nh cc c tnh bn ngoi v nh mc ca thit b b. i vi cc ph ti

c cng sut v cng sut phn khng thay i rt nhanh (chng hn nh l h quang

in), cc phng trnh pha hon ton khng hiu qu, nghin cu chng cn s

dng cc phng php c bit.

I.2.1. H s cng sut v s iu chnh

I.2.1.1. H s cng sut

C th m t mt pha nh hnh 1a, ta c tng dn YL = GL + jBL c cung cp t

in p U, dng in ti l IL, ta c:

IL = U.( GL + jBL ) = U.GL + jU.BL = IR + jIX (1)

C U v IL u l cc phn t pha v phng trnh (1) c th hin trong th

pha hnh 1b, trong U l vc t in p chun.

Dng in ti IL c thnh phn tc dng IR cng pha vi in p U v

thnh phn phn khng IX vung gc vi U gc gia U v IL l L

Cng sut biu kin: SL = U.IL = U2.GL- j U

2.BL = PL + jQL (1.2)

b

Hnh 1.1 a)

QL

SL

L

c

GL + jBL

U

IS

IR

IL IX

L

PL

~ . *


CNG SUT LN


9

Cng sut biu kin c mt thnh phn thc PL ( cng sut biu kin c ch

chuyn thnh phn nhit, cng c hc, nh sng hoc cc dng khc ca nng lng )

v mt thnh phn cng sut phn khng QL ( cng sut phn khng khng chuyn

c thnh cc dng nng lng c ch, nhng s hin din ca n l mt nhu cu cn

thit ca ti ). Quan h gia SL, PL, v QL c th hin hnh 1.1c. i vi ti tr (

cm ng ) theo qui c PL dng v QL m.

Dng in IS = IL do h thng cung cp l ln hn dng in cn thit cung

cp ring cho cng sut thc, bi h s:

R

L

I

I =

Lcos

1 (1.3)

y cosL l h s cng sut, gi th l v:

cosL =

L

L

S

P =

22

LL

L

QP

P (1.4)

Nh vy cosL l t l ca cng sut biu kin c th chuyn i mt cch hu

ch cc dng nng lng khc.

I.2.1.2. iu chnh h s cng sut

Nguyn tc iu chnh h s cng sut l b cng sut phn khng, tc l cung cp

ti ch bng cch ni song song vi ti mt thit b b c tng dn phn khng n

thun jBL. minh ho iu ny xem hnh 1.2 minh ho vic iu chnh h s cng

sut.

Q1

Hnh 1.2

Q1 Q2 = Q1 - Qc

P1 P1

Ti

a) S1

S2

P1

Qc

Q2

b)

2 1


CNG SUT LN


10

Mt ph ti P1 + jQ1 c h s cng sut cos 1 = 2

1

2

1

1

QP

P, khi c cung cp

mt lng cng sut phn khng QC, h s cng sut c ci thin t cos 1 thnh

cos2, vi cos

2 =

2

1

2

1

1

)( CQQP

P (1.5)

Hnh 1.3 v 1.4 minh ho s thay i ca thnh phn cng sut phn khng khi

tng thm vi mi 10 thay i ca h s cng sut. Lu , trong minh ho hnh 1.3,

ngay c khi h s cng sut l 0,8 th cng sut phn khng vn ln do nguyn nhn gia

tng thm 25 trong cng sut biu kin

( kVA ) ca ng dy. h s cng sut ny, 75 kVA ca thit b b l cn thit

kh 75 kVAr ca thnh phn chm sau.

100

kW 100

kW

48,43

kVA

r

100

kW

75

kVAr

100

kW

102

kVAr

100

kW

133,33

kVAr

100 kVA cos = 1,00

142,86 kVA cos = 0,70

111,11 kVA cos = 0,90

125 kVA cos = 0,80

166,67 kVA cos = 0,60

Hnh 1.3. Minh ho s gia tng nhu cu ca cng sut biu kin v cng sut phn khng l mt hm s ca h s cng sut, khi gi cng sut tc dng l mt hng s

100

kW 90

kW 80

kW 70

kW 60

kW

43,59

kVAr 60

kVAr 71,41

kVAr 80

kVAr

Hnh 1.4. Minh ho s thay i cng sut tc dng v cng sut phn khng

l mt hm s ca h s cng sut, khi gi cng sut biu kin l mt hng s


CNG SUT LN


11

C th quan st t hnh 1.2b, cng sut biu kin v cng sut phn khng trc

v sau khi b c biu th l S1 ( kVA ) n S2 ( kVA ) v

Q1 ( kVAr ) n Q2 ( kVAr ) bng vic cung cp cng sut phn khng QC, d nhin

vic gim dng in phn khng a n lm gim dng in tng lm gim tn tht

cng sut. Vy, vic hiu chnh h s cng sut a n tit kim v mt kinh t l

gim chi ph u t v chi ph nhin liu thng qua vic gim cng sut v gim tn

tht cng sut trong tt c cc phn t gia im lp t thit b b v ngun pht,

bao gm ng dy phn phi v trm bin p. H s cng sut kinh t l im m ti

hiu qu ca vic lp t thm thit b b va ng bng chi ph ca thit b b.

Trc y, h s cng sut kinh t ny vo khong 0,95. Ngy nay, do chi ph ca nh

my v nhin liu cao nn ngi ta tm cch a h s cng sut kinh t ln n 1.

Tuy nhin khi h s cng sut tng gn n 1th hiu qu thit b b trong vic ci

thin h s cng sut, gim vic truyn ti cng sut biu kin, tng kh nng ti, gim

tn tht do vic tng dng ti trn ng dy cng gim r rt. Do vy vic hiu chnh

h s cng sut ln n 1tr nn t hn so vi chi ph kinh t ca vic lp t t b.

I.2.2: iu chnh in p

I.2.2.1: Nguyn tc iu chnh in p

Vic iu chnh in p c xem nh l thay i t l ( hay trn mi n v )

vi bin in p cung cp i km vi mi thay i ca dng ph ti c xc nh (

ngha l t khng ti n y ti ). iu ny to nn s st p trn tng tr cung cp

mang dng in ti. Nu h thng cung cp c biu din bng mch tng ng

Thevenin mt pha hnh 1.5 th vic iu chnh in p c cho bi:

UUEU

UE

/ vi U l in p pha chun.


CNG SUT LN


12

Khi khng c thit b b, s thay i ca in p cung cp do dng in ph ti

IL gy ra c biu din hnh 1.5b l U :

U = E U = ZS.IL vi ZS = RS + jXS ( 1.6 )

T phng trnh 1.2 ta c:

IL = U

jQP LL

U = ( RS + jXS )U

jQP LL

Do vy:

Hnh 1.5: a) Mch tng ng ca ph ti v h thng cung cp. b) th vc t pha cho hnh 1.5a ( cha c b ).

c) th vc t cho hnh 1.5a ( b cho in p khng i )

a)

E

U

IS

ZS = GS + jBS

YL = GL + jBL

IL

E

U

IL

RU

XU U

ISRS

jISXS

L S

b)

U

U

E

ISRS

jISXS

IC

IS

L

IL c)

Hnh 1.5


CNG SUT LN


13

U = U

QXPR LSLS .. + jU

QRPX LSLS .. = UR + j UX ( 1.7 )

S thay i in p c thnh phn UR cng pha vi U v thnh phn UX

vung gc vi U, c biu din trn hnh 1.5b. iu ny c ngha l bin v pha

ca U c lin quan n in p cung cp E, l cc hm s ca bin v pha ca

dng in ph ti, hay ni cch khc s thay i in p ph thuc vo c cng sut

tc dng v cng sut phn khng ca ph ti.

Khi thm thit b b ni song song vi ti, c th lm cho E = U , tc l lm cho

s thay i in p bng khng hay gi cho bin in p khng i gi tr E khi

c ti. iu ny c th hin trn hnh 1.5c i vi thit b b phn khng thun.

Cng sut phn khng QL phn trnh ( 1.2 ) c thay bng tng: QS = QL + QC v

QC c chnh nh sao cho lm quay th vect pha U cho n khi E = U .

T phng trnh ( 1.6 ) v ( 1.7 ) ta c:

2E =

2..

U

QXPRU SSLS +

2..

U

QRPX SSLS ( 1.8 )

Gi tr yu cu ca QC c xc nh bng cch gii phng trnh ( 1.8) theo QS

vi E = U, khi QC = QS QL .

T ( 1.8 ) suy ra: a2QS2

+ bQS + c = 0 ( 1.8 )

Vi: a = RS2 + XS

2, b = 2U

2XS, c = ( U

2 + RSPL )

2 + XS

2PL

2 E2U2

Gii phng trnh ( 1.8 ) ta c: QS =

a

acbb

2

42

Ta thy rng y lun lun c p s cho QS bt k gi tr no ca PL.

iu ny dn n cc kt lun quan trng sau y:

Mt thit b b phn khng thun tu c th loi b s bin thin ca in p

ngun cung cp gy ra bi s thay i cng sut tc dng v cng sut phn khng


CNG SUT LN


14

ca ti, min l c th iu khin d dng cng sut phn khng ca thit b b trong

mt phm vi va ( ni chung k c chm sau hay vt trc ). mt tc va

th thit b b c th hot ng nh mt b iu p l tng ( cn phi tha nhn rng

ch c bin in p l iu khin c, cng gc pha ca n thay i lin tc theo

dng ph ti ).

phn trc chng ta bit l thit b b c th gim cng sut phn khng do

h thng cung cp v khng nh th no. l, thay v lm chc nng iu chnh in

p, thit b hot ng nh mt thit b hiu chnh h s cng sut. Nu thit b c

thit k lm iu ny, chng ta c th thay i phng trnh ( 1.7 ) bng: QS = QL +

QC = 0. in p thay i l:

U = U

PjXPR LSLS = ( RS + jXS ).U

PL ( 1.9 )

Gi tr ny c lp vi QL v khng b thit b b iu khin.

V vy: Thit b b cng sut phn khng thun tu khng th mt lc va duy tr

in p bng khng i va duy tr h s cng sut ng nht.

Ngoi l duy nht i vi qui tc ny l PL = 0, nhng iu ny ni chung khng

thc t. iu quan trng cn ch l nguyn tc ny p dng cho h s cng sut tc

thi, cng c th c mt thit b b cng sut phn khng khng thun tu dng duy

tr c in p khng i v h s cng sut trung bnh ng nht.

I.2.2.2. Cng thc gn ng cho vic iu chnh in p.

Cch biu din ca UX v UR trong phng trnh ( 1.7 ) i lc c cho

dng hu ch khc nh sau:

Nu mt h thng b ngn mch thanh ci ph ti th cng sut ngn mch

biu kin s l:


CNG SUT LN


15

SSC = PSC + jQSC = E.ISC = *

2

SCZ

E ( 1.10 )

Trong :

ZSC = RS + jXS

ISC dng ngn mch

V: *SCZ = ZSC, ta c:

RS = SCZ .cos SC = SCS

E 2cos SC ( 1.11 )

V: XS = SCZ sin SC = SCS

E 2sin SC ( 1.12 )

Vi: tg SC = XS / RS ( 1.13 )

Thay ( 1.11 ) v ( 1.12 ) v o ( 1.7 ), bin i UX v UR theo U v gi thit

E / U 1, ta c:

SC

R

SU

U 1( PL cos SC + QL sin SC ) ( 1.14 )

SC

X 1

U S

U( PL sin SC - QL cos SC ) ( 1.15 )

UX thng c b qua, ch v n c khuynh hng to ra s thay i mt

pha ti in p im cung cp, s thay i v bin c th hin bi UR. Phng

trnh ( 1.14 ) tuy gn ng, song li c li v n c biu din theo cc i lng

thng thng, l: mc s c hay mc ngn mch SSC, t s X/R ( tc l

tg SC ), cng sut tc dng v cng sut phn khng ca ph ti PL v QL

c kt qu chnh xc, cch biu din phng trnh (1.14) phi nhn vi

2

2

U

E. n y cc phng trnh c vit ra nh th U gn lin vi s thay i ton

b t 0 n PL hay t 0 n QL trong ph ti.Cc phng trnh (1.7), ( 1.14 ) v (1.15)

cng c gi tr i vi cc thay i nh ca PL v QL, do vy:

~ *


CNG SUT LN


16

SC

R

SU

U 1( PL cos SC + QL sin SC ) ( 1.16 )

Nu in tr RS nh hn nhiu so vi in khng XS th cho php b qua cc

thay i in p gy ra bi cc thay i ca cng sut tc dng P. Do , vic iu

chnh in p c thc hin theo phng trnh:

U

RU

U

U =

SC

LSC

SC

L

S

Q

S

Qsin ( 1.17 )

Ngha l, s thay i in p trn mi n v bng t s thay i cng sut phn

khng theo mc ngn mch ca h thng cung cp.Quan h ny c biu din

bng th nh hnh 1.6 v cho thy c tnh in p ca h thng cung cp

( hay ng ti ca h thng ) gn nh tuyn tnh. Mt cch th hin khc l:

USC

L

SC

L S

QE

S

Q

E1

1

( nu Q


CNG SUT LN


17

Trong phn ny chng ta suy on cc thuc tnh ca mt my b l tng

dng cng c vic iu p vi ti cm ng thay i.

Ti c gi thit l ba pha, cn bng v bin thin chm c th s dng

th vc t mi pha hay phng trnh gn tnh, bin thin ca ti c gi thit l nh

cho U


CNG SUT LN


18

QL

1,0

Ump

QCmax

QCmax QLmax - QLmax 0

c)

E

U

QL QC

QS QLmax 0

b)

QS

QCmax

QC

U

0

d) Hnh 1.7.

a) Mch tng ng mt pha cua ph ti c b. b) c tnh gn ng in p / cng sut phn khng ca h thng c b hon ton. c) c tnh gn ng in p / cng sut phn khng ca h thng c b mt phn. d) c tnh gn ng in p / cng sut phn khng ca thit b b l tng . e) th cn bng cng sut phn khng ( bin thin ca Q S v QC theo QL ).

e)

QL

QLmax

QCmax

QCmax QLmax - QLmax

QC

QS

QS

0

U

ZS = RS + jXS

QS

QC QL

Thit b b Ti

a)

E


CNG SUT LN


19

S iu p U / U ch c th gi bng khng nu nh mc cng sut phn

khng ca thit b b bng hay vt qu QLmax, nu cng sut phn khng ca thit b

b b gii hn bi QLmax ( nh hn QLmax ), nh vy khi

QL = 0 th thit b b hp th QLmax v s iu p s bng:

SC

CL

S

QQ

U

U maxmax ( 1.23 )

Tnh hung ny c m t hnh 1.27c, y l b mt phn. Phng trnh

(1,23) m t tc ng n by m thit b b nh hng ln in p h thng trong

gi tr ti a ca U / U c th gy ra bi s thay i cng sut phn khng ca thit

b b t 0 n ti a c cho bi QLmax / SSC. nh mc ti thiu ca thit b b c

th c chn sao cho QLmax / SSC va p ng vi thay i in p ti a cho php

U, do :

QCmax = QLmax SSC.U

U mp ( 1.24 )

By gi chia 1.7 ra hai thnh phn ring bit nh hnh 1.7c, 1.7d, iu ny c

thc hin nh s h tr ca s cn bng ca cng sut phn khng nh hnh 1.7e.

Hnh 1.7c cho thy s bin thin ca in p ti im cung cp vi QL: N th hin c

tnh ca h thng c b v cn c so snh vi c tnh ca h thng khng b ca

hnh 1.7b. Thit b b c nh mc QCmax < QLmax v c iu khin mt cch l

tng sao cho gi QS khng i nh phng trnh ( 1.22 ), min l khng vt qu gii

hn nh mc ca n, tc l thit b b hot ng vi chc nng mt thit b iu p l

tng.

Hnh 1.27c cho thy nh mc cng sut phn khng ca thit b b

khng cn ln hn lng bin thin ca cng sut phn khng ca ph ti,

nhm gi cho in p cung cp khng i khi ti thay i. Vic ny gip ta

tit kim dung lng my b trong cng sut phn khng ca ph ti thay i gi

cc gi tr ti a v mt vi gi tr thp phn, v d 0,5 cho mi n v, min l thit b


CNG SUT LN


20

b c nh mc theo phng trnh ( 1.24 ) th d cng sut phn khng ca ph ti

bng bao nhiu i na th s bin thin in p cung cp khng vt qu Ump.

Hai thnh phn ca hnh 1.7c c th xc nh nh mt phm vi khng c iu

chnh vi 0 < QL < ( QLmax - QCmax ) v mt phm vi c iu chnh vi ( QLmax - QCmax )

< QL < QLmax. Trong phm vi khng iu chnh, thit b b hp thu QCmax v hn ch s

gia tng ca in p n mc ti a cho php Ump, trong phm vi c iu chnh, thit

b b duy tr QS = hng s v

U = 0.

c tnh iu chnh ca thit b b c biu din hnh 1.7d, v khng c s

thay i in p vi 0 < QC < QCmax, ng c tnh ny phng trong phm vi iu

chnh. Nu QL nm di phm vi iu chnh, thit b b ch hp th khng i QCmax

bt k in p l bao nhiu.

* Ci thin h s cng sut

H s cng sut trung bnh ca ti cm ng v c bn xu hn h s cng sut

ca ti, v d, nu cng sut phn khng trung bnh ca ti QL bng 1 /2 gi tr ti a

th cng sut phn khng trung bnh do ti cung cp bi h thng ph ti c b l

2QL, tc l gp i.

c s iu p l tng cng nh h s cng sut trung bnh n v, th thit

b b dung khng l cn thit, thay v gi cho QS = hng s = QLmax nh phng

trnh( 1.22 ), thit b b phi gi cho QS = hng s = 0 ( 1.25 ).

B qua tc ng s thay i v cng sut ph ti theo trnh t nh

mc (a) s cho thy c tnh in p/ cng sut phn khng ca thit b b l

tng, cc hnh 1.8a n 1.8d minh ho qu trnh. Hnh 1.8c cho thy c tnh thit b

b l tng. Dung lng in dung ti thiu ca thit b b c cho bi phng trnh

( 1.24 ) v ngoi phm vi iu chnh ca n thit b b c gi thit pht ra cng sut


CNG SUT LN


21

phn khng khng i QCmax. in p ng nht by gi c nh ngha l p ng

iu kin b hon ton, c qui nh phng trnh ( 1.25 ) v im vn hnh trung

bnh l U = 1,0 cho mi n v vi QS = 0.

im vn hnh

U 1,0

QC QL

QL

QLmax QCmax a)

QC QCmax

U

1,0

0

c)

QS

QS

QLmax

QCmax

QC

U

1,0

Ump

0

QLmax QCmax

QL

iu p Khng iu p

b)

d)

Hnh 1.8:

a) c tnh in p / cng sut phn khng gn ng ca h thng

cha b.

b) c tnh in p / cng sut phn khng gn ng ca h thng c

b.

c) c tnh in p / cng sut phn khng ca thit b b l tng.

d) th cn bng cng sut phn khng ( bin thin ca QS v

QC theo Q ).


CNG SUT LN


22

Thay v hp th cng sut phn khng to tng QL = QC n QLmax th

thit b b tr thnh in dung thun tu. Nu thit b b c thit k lm thit b

b iu chnh in p l tng th QS khng phi lun lun bng khng v cng sut

ph ti thay i. Ni chung tc ng ny nh.

* dc ca cng sut phn khng

Nu cng sut phn khng ca ph ti c th thay i t vt trc

( pht ) n chm sau ( nhn ) th cn c thit b b c c tnh iu chnh in p

cng sut phn khng m rng v c hai gc phn t ca hnh 1.9a. c tnh cm ng

ca thit b b hnh 1.7c c th hng theo cch ny bng cch s dng t b ngang

c nh

QCmax vt trc QCmax chm sau

a) Vt trc Chm sau

U

Q

T in

th hiu

dch

Thit b b

cm ng

bin thin

b)

Thit b b

in dung bin thin

in khng

th hiu dch

c) Hnh 1.9:

a) c tnh in p / cng sut phn khng gn ng ca kh nng vt trc

v chm sau cng sut phn khng ca thit b b l tng.

b) in dung th hiu dch ca thit b b cm ng bin thin.

c) in khng th hiu dch ca thit b b in dung bin thin.


CNG SUT LN


23

( hnh 1.9b ) ln th my b cm ng c th hng vo gc phn t chm sau ( tr )

bng in cm c nh nh hnh 1.9c. Nu t b ngang hnh 1.9b ln th my b

cm ng c th hng sao cho ng c tnh ca n nm hon ton gc phn t

vt trc ( sm ). Khi c kt hp vi t b ngang thit b b cm ng c kh nng

duy tr in p khng i v h s cng sut trung bnh ng nht cho ph ti cm ng.

S phn bit gia thit b b cm ng v thit b b in dung c th nh gi to,

nhng theo quan im thc t th y l mt im quan trng bi v tt c cc thit b

b thc t ( tr my b ng b ) lm vic bng cch iu khin cc dng in trong

mt cm t in hay trong t hp cc in cm. Thit b b in khng bo ho chng

hn, t nht n cng thng hng mt phn vo gc phn t vt trc nh cc t

in. Mt in khng c nh mc song song s c li hn mt thit b b bin thin c

cng nh mc cng sut phn khng. i khi tit kim cn xc nh kch c thit b

b sao cho ph hp vi s bin thin cng sut phn khng trong ph ti theo hng

thm mt in khng c nh mc song song nhm t c h s cng sut trung bnh

cn c.

cc hnh 1.7, 1.8, 1.9 ng c tnh in p / cng sut phn khng ca thit

b b v h thng cung cp u khng tht thng v c dng ton phng. Chng c

biu din gn nh ng thng, vi gi thit rng U khng chnh lch ng k so vi

mt n v cng sut, nhng tnh ton chnh xc hn i hi cc dng chnh xc ca

phng trnh ( 1.7 ) v ( 1.8 ), ni cch khc, c th lm vic ny i vi cc dng in

v cng sut phn khng.

* Thit b b ph ti lm chc nng thit b iu p.

Cc c tnh iu khin hnh 1.7d v hnh 1.8c c th c c trng bi ba

thng s:

1. in p im khp ( knee point ): Uk.


CNG SUT LN


24

2. Cng sut phn khng nh mc hay ti a: QCmax.

3. li: KC.

li ny c th nh ngha l mc thay i cng sut phn khng QC chia cho

mc thay i in p U, ngha l KC = dU

dQC ( 1.26 ) v nu c tnh iu khin l tuyn

tnh, th vi QC < QCmax, n c biu th bng phng trnh:

U = Uk + C

C

K

Q ( 1.27 )

hnh 1.7d v 1.8c li KC l v nh, thit b b hp th hoc pht ra mt

lng cng sut phn khng va ng duy tr in p khng i ti im cung cp

khi ti thay i.

By gi ta xc nh c tnh iu chnh in p ca thit b b c li iu p.

Xc nh KC, vn hnh h thng cung cp c mc ngn mch xc nh SSC, vn

quan trng l bin in p im cung cp bin thin nh th no vi ph ti (c

bit vi cng sut phn khng ca ti ).

Thit b b l tng dng iu chnh in p c li KC l v nh. Trong

thc t him c cc gi tr KC qu cao. N c khuynh hng lm gim tnh n nh ca

im vn hnh thit b b, i vi mt s loi thit b b, thit k c gi tr KC cao kh

tn km. Do vy c tnh KC xc nh l quan trng.

Phn tch trn c s tng pha vi gi thit iu kin cn bng. Gi thit t s XS /

RS l cao v b qua cc dao ng cng sut, h thng c biu din hnh 1.7a, s

cn bng cng sut phn khng c cho bi:

QL + QC = QS (1.28 )

ng c tnh in p h thng cung cp hay ng ti c cho gn ng

phng trnh (1.20 ):

U SC

S

S

Q1.


CNG SUT LN


25

Trn hnh 1.10a, gradient ca ti biu din nhy thc ca in p cung cp

i vi s thay i v cng sut phn khng QS, do :

SCS

E

dQ

dU

S

(1.29 )

Mc ngn mch SSC cao lm gim nhy in p, lm ng ph ti phng,

lc h thng c gi l cng. Trong trng hp khng b,

QC = 0 v QS = QL do nhy in p i vi cng sut phn khng ca ti QL bng

vi nhy thc -SCS

E. Khi c thit b b, t phng trnh ( 1.19 ) v

( 1.28 ) ta c:

U SC

CL

S

QQE 1 ( 1.30 )

U

0 QS

a)

c tnh in p h thng

U = E(1-QC/SSC)

U

Uk

QC b)

0

c tnh thit b b

U = Uk+QC/KC

Hnh 1.10:

a) c tnh in p / cng sut phn khng gn ng ca h thng cung cp.

b) c tnh in p / cng sut phn khng gn ng ca thit b b l

tng.


CNG SUT LN


26

V v QC l hm ca U, nhy s c hiu chnh. Cng sut phn khng ca

my b QC c xc nh bi lch in p ( U Uk ) theo phng trnh( 1.27 ) (

xem hnh 1.10b ), do :

QC = KC ( U Uk ) ( 1.31 )

Ta bit rng li my b KC cao th c ng c tnh U/Q phng, l

c tnh in p khng i. Tnh theo n v ( p.u ), nu li khong 40 n v c

ngha l cng sut phn khng ca my b thay i t 0 n 1 n v ng vi thay i

ca U Uk ( hoc U ) l 1/40 hay 0,025 n v. Trong cc tnh ton cho tin ta s

dng h thng tnh n v tng i, trong QCmax l cng sut phn khng c bn v

E l in p c bn.

nh hng ca my b c xc nh bng cch thay QC t phng trnh (1.31)

vo phng trnh ( 1.30 ) v rt gn li c:

U = E

SCSC

C

SC

S

.1

S

K1

S

.1

EK

S

QUK

C

SC

LkC

( 1.32 )

Phng trnh ( 1.32 ) cho thy in p im cung cp U, bin thin nh th no

theo cng sut phn khng ca ph ti QL, khi c my b min l vi QC < QCmax, d

ch gn ng n cng trc tip cho thy nh hng ca tt c cc thng s chnh khc

nh: Cng sut phn khng ca chnh ph ti, c tnh my b Uk v KC, c tnh h

thng E v SSC.

Nu ph ti khng c b, chng ta c KC = QC =0 v phng trnh

(1.32) rt gn thnh phng trnh ( 1.20 ). My b c hai tc ng r rng trong

phng trnh ( 1.32 ): Thay i in p im cung cp khng ti v thay i s nhy

cm ca in p im cung cp vi cng sut phn khng ca ph ti, nu li ca

my b KC > 0 th tnh nhy cm in p gim xung:


CNG SUT LN


27

LdQ

dU= -

SCS.1

EK

S

E

C

SC ( 1.33 )

Cc tnh ton v cng sut b cho trm SVC ca cng ty gang thp Thi

Nguyn c th da vo l thuyt b va trnh by trn.

CHNG II: TNG QUAN V CNG NGH FACTS


28

CHNG II

TNG QUAN V CNG NGH FACTS

II.1. t vn

Trc y cc thit b b thng khng c t ng iu chnh in p, hoc c

iu chnh nhng rt chm (my b ng b ) hoc b tng nc. Vi s pht trin vt

bc trong lnh vc iu khin t ng, c bit k thut in t cng sut nh thyristor

cng sut ln cho php thc hin c c thit b b iu khin nhanh, thc t cc thit

b b dng thyristor c th thay i cng sut t 0 n tr s nh mc khng qu 1/4

chu k tn s in cng nghip.

FACTS l h thng truyn ti in xoay chiu linh hot s dng thit b in t

cng sut hot ng ch t ng vi d ng in v in p cao, cho php iu

khin b cng sut phn khng gn nh tc thi, ngn cn dao ng n nh in

p, h s cng sut ca h thng mt cch nhanh chng.

Mt khc vic nh hng pht trin h thng c cn c trn c s d bo

ph ti, tuy nhin trong qu trnh vn hnh khng phi lc no cng m bo cn bng

gia cung v cu dn n tnh trng h thng in s c thi im b qu ti. Thm vo

, do kh nng ti ca ng dy b gii hn bi cc yu t nhit , in dung v

n nh, nu khng c s iu khin hp l, s khng tn dng ht kh nng ti ca cc

ng dy. Vic s dng thit b FACTS s gp phn gii quyt vic vn hnh h

thng in mt cch khoa hc, nng cao hiu qu ng dy ti in hin c, p ng

yu cu thc t t ra. c bit nhng ni yu cu v cung cp in an ton v tin

cy.

II.2. Li ch khi s dng thit b FACTS

II.2.1. Cc u im khi s dng thit b FACTS



29

S dng thit b FACTS cho php:

+ Nng cao kh nng gi n nh in p, gim dao ng cng sut lm cho

vic vn hnh HT linh hot v hiu qu hn.

+ iu khin tro lu cng sut phn khng theo yu cu

+ Tng kh nng ti ca ng dy gn ti gii hn nhit

+ Tng tin cy, gim tn tht h thng

Tuy nhin gi thnh cc thit b FACTS l rt cao so vi kh nng ti chnh

nc ta hin nay. Do , khi nghin cu p dng thit b FACTS cn phi phn tch

cc ch tiu kinh t, k thut la chn gii php ph hp.

II.2.2. Phn loi thit b FACTS

Cc thit b FACTS c th phn ra lm bn loi:

1, Thit b iu khin ni tip ( Series Controllers ): Loi thit b ny cho php

thay i tng tr ng dy bng t in, in khng, hoc bin i ngun c tn s

bng tn s li nh thit b bn dn cng sut. V nguyn l, tt c cc thit b iu

khin ni tip ch cung cp hoc tiu th cng sut phn khng bin i.

2. Thit b iu khin song song (Shunt Controllers): Loi thit b ny cho php

thay i tng tr, thay i ngun hoc kt hp c hai. Tt c cc thit b iu khin

song song b dng in vo h thng ti im nt.

3. Thit b iu khin kt hp ni tip vi ni tip ( Combined series series

Controllers ): y l s kt hp cc thit b iu khin ni tip ring r, c cng cch

thc iu khin c s dng trong h thng nhiu dy dn hoc c th l thit b iu

khin hp nht. Trong nhng thit b iu khin ni tip cng sut phn khng c b

c lp cho mi ng dy, tuy nhin cng sut tc dng gia cc ng dy c

trao i qua ngun lin kt. Kh nng chuyn cng sut tc dng ca thit b iu



30

khin ni tip ni tip hp nht to ra s cn bng c dng cng sut tc dng v

cng sut phn khng trong cc dy dn, tn dng ti a h thng truyn ti.

4. Thit b iu khin kt hp ni tip vi song song ( Combined series shunt

Controllers ): y l s kt hp cc thit b iu khin song song v ni tip ring r

c iu khin kt hp hoc iu khin hp nht dng nng lng vi cc phn t ni

tip v song song. V nguyn l, nhng thit b iu khin song song v ni tip kt

hp b dng in v h thng vi nhng phn t iu khin song song v b in p

trn ng dy vi nhng phn t b ni tip.

II.3. Mt s thit b FACTS

II.3.1. Thit b b tnh iu khin bng thyristor ( SVC )

SVC (Static Var Compensator) l thit b b ngang dng pht hoc tiu th

cng sut phn khng c th iu chnh bng cch tng hay gim gc m ca thyristor,

c t hp t hai thnh phn c bn:

_ Thnh phn cm khng tc ng v mt cng sut phn khng ( c th pht

hay tiu th cng sut phn khng tu theo ch vn hnh ).

_ Thnh phn iu khin bao gm cc thit b in t nh thyristor, cc ca

ng m ( GTO Gate turn off )...

SVC c cu to t ba phn t chnh bao gm:

+ Khng iu chnh bng thyristor ( TCR Thyristor Controlled Reactor ): C

chc nng iu chnh lin tc cng sut phn khng tiu th.

+ Khng ng m bng thyristor ( TSR Thyristor Switched Reactor ): C

chc nng tiu th cng sut phn khng, ng ct nhanh bng thyr istor.

+ B t ng m bng thyristor ( TSC Thyristor Switched Capacitor): C

chc nng pht cng sut phn khng, ng ct nhanh bng thyristor.



31

S dng SVC cho php nng cao kh nng ti ca ng dy mt cch ng k

m khng cn dng n nhng phng tin iu khin c bit v phc tp trong vn

hnh. Cc chc nng chnh ca SVC bao gm:

UN

IL IC

Biu hot ng

hnh 2.1: Cu to v nguyn l hot ng ca SVC

TSR TCR TSC

MBA b

S nguyn l



32

_ iu khin in p ti nt c t SVC c th c nh gi tr in p.

_ iu khin tro lu cng sut phn khng ti nt c b.

_ Gii hn thi gian v cng qu in p khi xy ra s c ( mt ti, ngn

mch.. ) trong HT.

_ Tng cng tnh n nh ca HT.

_ Gim s dao ng cng sut khi xy ra s c trong HT nh ngn mch, mt

ti t ngt...

Ngoi ra , SVC cng c cc chc nng mang li hiu qu kh tt cho qu trnh

vn hnh HT nh:

_ Lm gim nguy c st p trong n nh tnh.

_ Tng cng kh nng truyn ti ca ng dy.

_ Gim gc lm vic lm tng cng kh nng vn hnh ca ng dy.

_ Gim tn tht cng sut v in nng.

II.3.2. Thit b b dc iu khin bng thyristor ( TCSC )

Cng tng t nh phn t SVC, phn t TCSC ( thyristor Controlled Series

Capacitor ) l thit b iu khin tr khng nhanh ca ng dy v hot ng trong

iu kin n nh ca h thng in, n c t hp t mt hay nhiu modul TCSC,

mi mt modul bao gm hai thnh phn c bn:

_ Thnh phn cm khng c th thay i c in dung nh b iu chnh van

thyristor.

_ Thnh phn iu khin bao gm cc thit b in t nh cc van thyristor , cc

kho ng m GTO...

Ngoi ra, TCSC cng c mt s thit b ph nh b lc F nhm lc b cc sng

hi bc cao, thit b ng ngt phc v cc ch vn hnh ca TCSC trong cc ch

khc nhau ca HT.



33

S nguyn l cu to v hot ng ca TCSC nh hnh 2.2:

Cc chc nng chnh ca TCSC bao gm:

_ Lm gim nguy c st p trrong n nh tnh.

_ Gim s thay i in p.

_ Tng cng kh nng truyn ti ca ng dy

_ Tng cng n nh ca HT.

_ Gim gc lm vic lm tng cng kh nng vn hnh ca ng dy.

_ Hn ch hin tng cng hng tn s thp trong HT.

Ngoi ra, TCSC cng c nhiu chc nng khc c th tng tnh linh hot trong

vn hnh, tu theo yu cu v chc nng ca chng trong tng HT c th m ta c

th p dng cc phng php, mch iu khin TCSC cho ph hp vi cc ch vn

hnh trong HT.

II.3.3. Thit b b ngang iu khin thyristor ( STATCOM )

Hnh 2.2: Cu to v nguyn l hot ng ca TCSC

S nguyn l HT iu Khin

Thyristor

L

I

C

MOV

90

Cm khng

180

Vng khng H

Dung khng

Biu hot ng

Z



34

STATCOM l s hon thin ca thit b b tnh SVC, bao gm cc b t in

c iu chnh bng cc thit b in t nh thyristor v kho ng m GTO, so vi

SVC, n c u im l kt cu gn nh hn, khng i hi din tch ln nh SVC v

c bit l n iu khin linh hot v hiu qu hn.

Cc tnh nng ca STATCOM cng nh ca SVC nhng kh nng iu chnh,

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

_ iu khin in p ti nt t STATCOM c th c nh gi tr in p.

_ iu khin tro lu cng sut phn khng ti nt c b.

_ Gii hn thi gian v cng qu in p khi xy ra s c ( mt ti, ngn

mch... ) trong HT.

MBA lin kt

Biu hot ng

IL IC

UN

Hnh 2.3: Cu to v nguyn l hot ng ca STATCOM

DD

C L

S nguyn l



35

_ Tng cng tnh n nh ca HT.


ti t ngt...

Ngoi ra, STATCOM cng c c im ni tri so vi SVC nh sau:

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

c s c.

_ C th pht CSPK khi in p thanh ci nh hn in p li v ngc li,

tiu th CSPK khi in p thanh ci ln hn in p li.

II.3.4. Thit b iu khin gc pha bng thyristor ( TCPAR )

Thit b TCPAR l mt khi nim mi ng dng thyristor iu chnh gc

lch pha ca in p pha ca ng dy.

MBA NI TIP

U U,

UQ

1 3

MBA KCH THCH

9

Hnh 2.4: Nguyn l cu to ca TCPAR

U U

, U

Q



36

V mt cu to n nh mt my bin p 3 cun dy ni song song vi ng

dy truyn ti v c th iu chnh gc lch ca in p Uf truyn ti trn ng dy

Cc tnh nng ca TCPAR cng nh ca cc thit b b c iu khin khc

nhng chc nng ca n l iu chnh gc pha ca in p trn ng dy.

Kh nng iu chnh tro lu cng sut l rt cao, cc tnh nng ca TCPAR bao

gm:

_ iu khin tro lu cng sut phn khng ti nt c b

_ Tng cng tnh n nh tnh, tnh n nh ng ca HT.


ti t ngt...

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

c s c.

II.3.5. Thit b iu khin dng cng sut hp nht ( UPFC )

HT iu khin

S nguyn l

Converter 1

MBA2

mba1

ub

ua

vdc

Converter 2

Hnh 2.5: Nguyn l cu to ca UPFC



37

ua

ub

ut

vect in p

UPFC l mt khi nim mi ng dng cc thit b b a chc nng iu

khin in p ti cc thanh ci c lp, dng cng sut tc dng P v phn khng Q

trn cc ng dy truyn ti, UPFC l thit b lm cho li in vn hnh rt linh hot

v hiu qu.

V nguyn l cu to, UPFC c hiu nh s kt hp thit b b dc lm thay

i gc pha ( Static Synchoronous Series Compensator ) l thit b b ngang

STATCOM, n c cu to t hai b chuyn i ( Converter ) iu khin thyristor c

ca ng m GTO. Mi mt b chuyn i gm c van ng m ( GTO ) v MBA

trung gian in p thp ( xem hnh 2.5 ).

MBA ni vi b chuyn i qua

thanh ci lm vic v my ct c

m t trn hnh. Mi mt b chuyn

i c th ngng hot ng v

bt c nguyn nhn no , b

chuyn i cng li c th iu khin

vn hnh c lp.

V nguyn l, UPFC c ba ch vn hnh ,

bao gm:

Ch 1: Ch iu khin tr khng XC.

U = XCjI2

P = sin2

CXX

X

X

U

Ch 2: Ch iu khin in p trc giao U .

U = UCjI2 2I

P =

2cossin

2

U

U

X

U C



38

Ch 3: Ch iu khin gc pha in p C.

U = 2.

2exp

2sin

1

1

j

U

UU

P =

2.

2cos2sin.2

tg

X

U

Trong : +, I2: Vc t dng ca UPFC.

+, XC: in khng b.

+, U1: Vc t in p nhn

+, : Gc lch pha gia U2 v U1.

+, X: in khng ca ng dy truyn ti.

+, : Gc lch pha gia in p u v cui ng dy

Trong 3 ch vn hnh trn ca UPFC th ch 2 v ch 3 c u im

hn ch 1 v c th iu khin dng cng sut tc dng P ngay c khi gc pha rt

nh. Trong ch 1, nu dng trong thnh phn b dc ( Series Compensator ) gim

th kh nng iu khin ca UPFC cng gim theo. Hn na, trong ch 1 v ch

2, cng sut ca thnh phn b ngang ( Shunt Compensator ) c th gim ti thiu v

dng cng sut i qua lin kt mt chiu ( DC link ) gn nh bng 0.

Ngoi ra, thnh phn b ngang c th iu khin ng thi c dng cng st

phn khng Q v cng sut tc dng P truyn ti trn ng dy.

II.4. Kh nng p dng thit b FACTS ti Vit Nam

Sau khi kho st nguyn l lm vic v tnh nng ca cc thit b FACTS, cho

thy vic ng dng cc thit b ny trong h thng in c kh nng iu chnh gn nh

tc thi thng s h thng, tng cng n nh in p v gim dao ng cng sut.



39

Trong cc loi thit b FACTS, SVC l loi thit b c nhiu u im u vit

hn c, nn n c s dng rng ri trn th gii ci thin ch vn hnh v nng

cao kh nng n nh tnh ca HT.

CHNG III: CC THIT B B CNG SUT PHN KHNG V HOT

NG CA THIT B B NGANG C IU KHIN SVC


40

CHNG III

CC THIT B B CNG SUT PHN KHNG V HOT NG CA

THIT B B NGANG C IU KHIN (SVC)

III.1.Cc thit b b cng sut phn khng

III.1.1. B cng sut phn khng trong h thng in

Trong thc t ngi ta thit k v ch to ra cc thit b b chuyn dng khc

nhau nh cc thit b b ngang (cun khng b ngang, t in b dc, my b ng b

v cc b b bng t tnh in) nhm gii quyt cc vn nu ra trn.

III.1.1.a. Cun khng b ngang

Cun khng b ngang l loi cun khng c u t cc thanh ci u ng

dy xung t vi mc ch tiu th cng sut phn khng do ng dy sinh ra. Mi

on ng dy chiu di l lun sinh ra mt lng cng sut phn khng c th tnh

gn ng l:

QC = b.U2

(MVar)

Trong : B = bO.l (1/ )

U - in p lm vic trung bnh ca ng dy (kV).

bO - dung dn ng dy, tnh trn 1 km.

Thc t cng sut ny phn phi u dc theo chiu di ng dy. tuy nhin

trong tnh ton ngi ta thng coi nh phn b sang tp trung vo hai u ng dy.

trit tiu hon ton cng sut phn khng do ng dy sinh ra c th t hai

khng in ti hai u ng dy, tr s cng sut tng ng ca mi khng l:




41

QK = b.U2/ 2

(MVAr)

Tuy nhin cng sut phn khng pht ra ca ng dy (ngun cng sut phn

khng) rt c li nn trong tnh ton thit k thng ngi ta b khng hon ton

(khong 70%). Phn cn li c th cn bng vi mt phn cng sut phn khng tiu

th.

Cun khng b ngang thng c ch to c tr s c nh. Khi cn iu chnh

in p c th dng cun khng b ngang ng ct c theo tng cp, l bin php

kinh t nht tiu th bt cng sut phn khng v iu chnh c. a s cc cun

khng b ngang c dng cho cc ng dy trn khng siu cao p di. Chng cng

c dng cho cc ng cp ngm cao p v siu cao p trong khu vc thnh ph ln.

Cc cun khng b ngang c th ng m c, ni thanh ci siu cao p s phi

cnh tranh vi cc b b tnh c iu khin bng thyristor v cc tiu chun kinh t

k thut.

III1.1.2.b. T b dc.

Khi tin hnh b dc cho ng dy bng cc t b tnh, th cc thit b b cng

sut phn khng c tc dng rt tt n vic tng kh nng truyn ti in nng ca

ng dy. v cc ng dy di in khng XL rt ln, gc truyn ti =(U1-U2) c

tr s ng k. Do gii hn truyn ti gim i. Nu XL cng ln bao nhiu th tn

tht U cng ln v cng ln, P = (U1.U2.sin )/ XL cng b nu XL ln. Do khi b

dc (bng t in) th dao ng in p s gim i v lc ny in khng tng X =

(XL-XC) gim v nh

vy gim, U gim v tn tht in p gim, kh nng truyn ti ca ng dy tng

ln.




42

Vic dng t b dc nng cao kh nng gi n nh ca h thng do vic ta c

th lm thay i c gc truyn ti sao cho < 30O 35O th kh nng d tr n

nh ng rt cao. Khi c s thao tc no trong li: nh ct ra hoc ng vo mt

ph ti ln th trong li s c mt s dao ng cng sut, nhng nh c s tc ng

ca cc thit b b cng sut phn khng m dao ng cng sut ny nhanh chng b

dp tt.

III.1.1.c. T b tnh

T b tnh l mt n v hoc mt dy n v t ni vi nhau v ni song song

vi ph ti vi mc ch sn xut ra cng sut phn khng cung cp trc tip cho ph

ti. iu ny lm gim cng sut phn khng phi truyn ti trn ng dy. T b tnh

cng thng c ch to khng i (nhm gim gi thnh). Khi cn iu chnh in

p c th dng t in b tnh ng ct c theo cp, l bin php kinh t nht cho

vic sn xut ra cng sut phn khng. Cc t in b tnh c dng rng ri hiu

chnh h s cng sut trong cc h thng phn phi in nh: h thng phn phi in

cng nghip, thnh ph, khu ng dn c v nng thn. mt s cc t b tnh cng

c t cc trm truyn ti.

Tnh u vit ca cc t b tnh l chi ph thp c bit khng gy tn tht ph v

vic p dng rt linh hot, tuy nhin khuyt im ch yu ca chng l cung cp c

t cng sut phn khng khi c ri lon hoc thiu in, bi v dung lng ca cng

sut phn khng t l bnh phng vi in p. Tuy nhin nu dng chng kt hp

ngun cng sut phn khng khc th khng c tr ngi g ti vic dng rng ri cc t

b ngang.

III.1.1.d. My b ng b




43

My b ng b l mt my in ng b chy khng ti dng pht hoc tiu

th cng sut phn khng. My b ng b l phng php c truyn iu chnh

lin tc cng sut phn khng. Cc my b ng b thng c dng trong h thng

truyn ti, chng hn u vo cc ng dy ti in di, trong cc trm bin p quan

trng v trong cc trm bin i dng in mt chiu cao p.

Cc my b ng b ngy nay thng c trang b h thng kch thch t

nhanh, c b kch t chnh lu. C nhiu phng php khi ng khc nhau, mt

phng php hay dng l khi ng o chiu.

My b ng b c MVA lin tc cho vic pht cng sut phn khng. Trong

khi vn hnh pht cng sut phn khng th c kh nng qu ti ngn hn kh ln. Kh

nng tiu th cng sut phn khng 60% cng sut t. iu ny c ngha l phm vi

vn hnh thng l 160% cng sut t. Dung lng cng sut phn khng c iu

chnh mt cch lin tc. Mi cp iu chnh in p xy ra khong vi phn mi giy

v cao hn na ph thuc vo cc yu t khc nhau. Cc tn tht cng sut tc dng

ca cc my b ng b c lm mt bng hydrogen khong 10W/kVAr.

C th ni my b ng b l thit b b c th iu chnh trn duy nht trc

khi c k thut iu khin cng sut ln bng thyristor. u im ca loi ny l phm

vi iu chnh rng t pht n tiu th cng sut phn khng, iu chnh bng cch

thay i kch t. Nhc im ca loi ny l gi thnh cao v gy tn tht ph, tc

iu chnh chm.

III.1.2. Cc thit b b iu khin bng thyristor

Cc thit b b gii thiu trn khng c t ng iu chnh, hoc c iu chnh

nhng rt chm (nh my b ng b) hoc iu chnh tng nc. S pht trin vt

bc trong lnh vc iu khin t ng, c bit l k thut in t cng sut vi cc




44

thit b thyristor cng sut ln cho php thc hin cc thit b b iu chnh nhanh

(thng khng qu 1/4 chu k tn s cng nghip). Hin nay cc thit b b c iu

khin c xc nhn l rt tt khng nhng trong li cng nghip m c trong h

thng in truyn ti.

Cc thit b b iu chnh c hiu qu rt cao, m bo n nh c in p v

nng cao tnh n nh cho h thng in. i vi cc ng dy siu cao p cc thit b

b c iu khin i khi l thit b khng th thiu c. Chng lm nhim v chng

qu in p, gim dao ng cng sut v nng cao tnh n nh tnh v ng. Nhc

im ca cc thit b b c iu khin l gi thnh cao. la chn v lp t cc thit

b ny cn phi phn tch tnh ton t m v so snh phng n trn c s cc ch tiu

kinh t k thut. Cc thit b b tnh c iu khin bng thyristor l loi thit b b

ngang tnh (phn bit vi my b quay), cng sut phn khng c tiu th hoc pht

ra bi cc thit b ny c th thay i c bng vic ng m cc thyristor.

III.1.2.a. Thit b b b ngang c iu khin (SVC)

TCR Hnh 3.1a

TSR Hnh 3.1b

TSC Hnh 3.1c




45

Thit b b ngang c iu khin trong trng hp chung c cu to t ba

phn t c bn:

Thyristor Contronled Reactor (TCR) l cun khng c iu khin bng thyristor.

TCR c th iu chnh lin tc dung lng b bng cch thay i gc ng m ca

Thyristor mt cch lin tc t 90O 180O, hnh 3.1a.

Thyristor switched reactor (TSR) l cun khng ng ct t ng bng

thyristor. TSR ch c th ng hoc m dng thyristor, khi XK ch nhn mt trong

hai gi tr (XK= 0 hoc XK= XKmax), hnh 3.1b.

Thyristor switched capacitor (TSC) l t in ng ct bng thyristor,

in dung ca t ch c th thay i l 0 hoc XCmax, hnh 3.1c.

TSR v TSC thc cht l cc b khng v t in ng ct nhanh bng thyristor.

iu ng ch hn c l TCR, mt thit b khng c tham s c iu chnh trn

1

3 4

. . .

2

Hnh 3.2. 1- My bin p. 2- TCR. 3- Cc TSR. 4- cc TSC.

. . .




46

(t 0 n gi tr cc i). Khi t hp cc phn t ni trn, ni chung c th to

ra thit b b ngang thay i c lin tc thng s (in khng, cng sut) trong phm

vi gii hn bt k. V d nh s hnh 3.2.

C th gii thch nguyn l lm vic ca SVC trong trng hp ny nh sau: tn

hiu iu chnh gc m ly t pha in p cao qua bin in p TU, qua b t iu

chnh (TC) iu khin cc thyristor. u tin iu khin cc TSC v TSR iu

chnh th, sau iu chnh TCR li dng tnh cht

iu chnh lin tc ca n iu chnh CSPK qua SVC n tr s thch hp. Trong

phm vi thay i c ca CSPK, in p ti ni lp t SVC s c gi l hng s.

III.1.2.b. thit b b dc c iu khin (ASC - Advanced series compensator)

B dc c iu khin thng l phng tin dng ci to thng s ca ng

dy. nhng ng dy di, b hn ch v kh nng ti theo iu kin n nh hoc tn

tht in p s c ci thin ng k nh p dng b dc.

C

L

R

TCR

Hnh 3.3




47

Trong s hnh 3.3 th phn t chnh l t C ghp song song vi TCR, in tr

phi tuyn R c nhim v bo v qu in p cho t trong ch ngn mch. Hot ng

ca b dc c iu kin l nhm to ra in khng X thay i c, theo s hnh 3.3

ta tnh c: CL X

1

X

1

X

1c tnh thay i ca in khng tng ng X theo in

khng XL ca TCR c ch ra trn hnh 3.4.

thit b b dc c thng s iu chnh trn v n nh, thng chn phm vi

iu chnh ca TCR t XL = XL0 n XL = (vi XL0 > XC ; XL0 l in khng ca

TCR ng vi lc thyristor m hon ton; XL = l in khng ca TCR ng vi

thyristor ng hon ton).

Kt lun

XC

XL

XL0 +XC

- XC

- kXC

X

0

Hnh 3.4




48

Do c th thay i c thng s ca cc thit b in (b dc v b ngang) c

iu khin, m nng cao ng k hiu qu iu chnh cng sut phn khng trong h

thng in. Nu so vi my b ng b - l mt thit b b ph bin th SVC c qun

tnh nh, bn cao, khng gy tn tht v t phi chm sc bo qun khi vn hnh.

SVC khng ch lm nhim v iu chnh in p m n cn ng vai tr rt tch

cc trong vic gi n nh, nng cao cht lng vn hnh h thng.

Qua nhng phn gii thiu tng quan trn, trong ti ny ti tp trung

nghin cu v hiu qu ca thit b b c iu khin p dng trong h thng in ni

chung v li in cng nghip ni ring ti vn nng cao cht lng in p.

III.2.Hot ng ca thit b b ngang c iu khin SVC

III.2.1. c tnh iu chnh ca SVC

Nh bit phn t ng ch nht ca SVC l TCR. Nh c TCR tr s ca

SVC thay i c lin tc. Tc ng iu chnh cho TCR t vo cc iu khin ca

cc thyristor. Nh thay i gc m ca cc thyristor m dng in (thnh phn c bn)

qua khng c thay i lin tc t 0 n tr s cc i. iu ny tng ng vi s

thay i lin tc cng sut phn khng trn SVC.

c tnh iu chnh ca SVC c th xy dng c da vo nguyn l lm vic

ca thyristor. Trn hnh 3.5 m t n gin s v hot ng ca thyristor loi mt

thyristor v loi hai thyristor mc song song ngc.

Thyristor hot ng tng t nh chnh lu, tuy nhin ngoi iu kin in p

t ln bn thn thyristor thun chiu, cn yu cu thm mt xung in p t ln cc




49

iu khin. Xung ny c th khng cn ko di m thyristor vn m cho n khi iu

kin thun chiu in p khng cn na. Sang chu k mi, in p thun chiu nhng

mch cng ch m khi c xung a n cc iu khin. R rng, khi thay i thi im

pht xung mi chu k, ta c th thay i c dng ca ng cong dng in. Nu

coi thnh phn c bn ca dng in l thnh phn lm vic, th bin ca thnh phn

ny thay i theo gc m ca thyristor. Khi thyristor m hon ton (gc m = 900)

bin ca thnh phn c bn s ln nht (bng dng ban u), khi gc m = 180O

dng qua mch bng 0. Cn khi thay i t ngt gc m = 90O sang = 180O ta

nhn c trng thi ng ct ca hai phn t TSR hoc TSC.




50

thy r hn ta xt s c bn ca mt cun khng c iu khin bng

thyristor - gc pha thun tu (hnh 3.6a). mi nhnh ca ba pha bao gm mt cun dy

in cm L ni tip vi h thng hai thyristor mc song song ngc (TCR). Cc

thyristor T1, T2 s thay phin nhau lm vic ng vi mi chu k ca in p. Hnh

R1

UV R2

Ur

Uk

UV

R2

Ur

Uk

R1

t

UV

t

Uk

t

Ur

UV

Uk

t

t

t

Hnh 3.5: S v nguyn l hot ng ca thyristor




51

3.6b minh ho nguyn l vn hnh. Gc ct ca thyristor quyt nh bin ca thnh

phn dng in tn s c bn. Cc

thnh phn dng in bc cao ( bc 3, bc 5, bc 7 ) c tr s nh, c lm trit tiu

nh cc b lc ( hnh 3.6 a v b )

Khi thay i tr s gc ct 1, 2 ( 1 lun bng 2) s thay i c tr s hiu

dng ca dng in t ln khng in. Tng gc ct th bin ca thnh phn c

bn ca dng in s gim i.

c tnh iu chnh ca SVC c coi l quan h gia bin ca thnh phn

c bn ca dng in vi gc ct . c c ng c tnh ta phn tch dng in

ton phn thnh chui Fourier:

Theo l thuyt khai trin chui Fourier, nu hm tun hon f(t) vi chu k thi

gian l T, th chui Fourier ca n c dng:

1k

kk0 tkBtkA

2

Atf sincos)(

Trong : T

2;

A0 - thnh phn mt chiu (bc 0);

2

k

2

kk BAC - bin ca thnh phn bc k. Khi k=1 ta c thnh phn c

bn




52

uN

icb

t

t

udk udk1 udk2 udk2 udk1 udk1

t

t

i

udk udk1 udk2 udk2 udk1 udk1

t

t

i

t

i

a

b

c

d

e

g

h

090

090

090

const

Hnh 3.6a

u + -

L iL




53

i vi cc sng hi ca dng in sau khi khai trin ra chng ta quan tm ti

thnh phn c bn ca n (bc 1). Theo cng thc ton hc ta c:

,...,;.sin).(

,...,;.cos).(

).(

21kdttk

tf1

B

21kdttk

tf1

A

dttf1

A

k

k

0

p dng cho dng in chy qua TCR nh trn hnh 3.7a, vi dng in tn s

cng nghip f2T

2. Vi mc ch biu din hm f(t) qua gc ct ( y k

hiu l T0). Ly h trc to nh hnh 3.7b ta c:

Hnh 3.6b. th vc t dng in v in p; a - vc t

in p ngun (li); b - vc t dng in c bn (k = 1) khi gc

m 0 ; c,e - cc in p iu khin; d,g - vc t dng in c bn

(k = 1) khi gc m 0 ; h- vc t dng in c bn (k = 1) khi gc

m bt k.




54

4

T vi coscos

4

T

4

T

4

T0- vi coscos

)(

2

TtTT

T

2t

T

2K

TtTvoi0

TtTT

2t

T

2K

tf

000

00

000

(3-1)

Hm f(t) hay dng in ton phn sau khi khai trin Fourier trn on OABC c

dng:

k

0t

T

k2oscItitf )()(

I

UN

T

U,I

T UN

I90 I120

090

0120

T0 0 O A

C

Hnh 3.7a

B

Hnh 3.7b: th vect dng in v in p trn TCR




55

Thnh phn c bn ca dng in ng vi k = 1, ta c

tT

2II

TT

2

101

2

01

cos

cos

(3-2)

T biu thc (3-2) ta thy rng:

Khi 1 thi 10

0T

Khi )90 (hay 0

2

T

0 th 01

Tc l trong khong thay i lin tc ca gc ct T0 t 0 n 900 th

1 cng

thay i lin tc t 1 n 0. y cng chnh l quan h thay i bin ca thnh phn

c bn, bi v )(/0101

TII . iu ny c th c minh ho trn th hnh 3.8.

1

0 90

)( 01 T

0T

Hnh 3.8. c tnh iu chnh ca TCR




56

By gi ta xt quan h iu chnh thng s in khng v cng sut ca TCR.

Ta c

kminX

UI

0, y Xkmin c hiu l tr s in khng ca khng

in ng vi lc gc ct T0 = 0 ngha l ng vi tr s khng in khng iu

khin. Theo kt qu nhn c trn ta c th biu din c bin ca thnh phn

c bn theo gc ct T0.

1

k

1101

U

X

UII

X kminmin

(3-3)

Cch vit theo (3-3) cho php hiu TCR nh l cun khng c tr s thay i

c. C ngha l khi iu chnh SVC th hiu qu ca vic iu chnh tng ng

vi vic lm thay i tr s ca khng in n tr s 1k

X /Xkmin

(3-4).

T biu thc (3-4) thy rng khi 1 thay i t 1 ti 0 th Xk thay i t Xkmin

(tng ng vi gc ct bng khng) ti k

X ngha l loi b hon ton hiu ng

khng in (iu khin ht phm vi cho php - gc ct T0 = 900).

Trong thc t m rng phm vi iu chnh ca SVC thng dng s phi

hp vi TSR v TSC. Nh tr s in khng ng tr c th thay i trong 1 gii hn

rng t Xkmax ti Xkmin tu theo cu to ca tng loi SVC. y Xkmax tng ng

vi gc ct ln nht. Cng tu theo mc ch iu chnh m cc gi tr Xkmax v Xkmin

c th nhn du tu .

Bi ton t ra l nu xt theo tr s cng sut phn khng th liu ta c c

trng tng t nh trn xt hay khng, ta thy:




57

min

max

max

min

k

2

k

k

2

k

X

UQ

X

UQ

(3-5)

Tc l nu gi nguyn in p nt th CSPK cng thay i t Qmin n Qmax. V

vy, khi iu chnh SVC bng thyristor dng cng sut phn khng qua SVC cng thay

i. iu cho php n nh c h thng.

III.2.2. c tnh lm vic ca SVC

ch lm vic bnh thng ca h thng in, SVC lm nhim v t ng

iu chnh gi nguyn in p nt. Tn hiu iu khin l lch in p o c t

TU, tn hiu ny iu khin gc m ca cc thyristor lm thay i tr s ca thnh phn

c bn dng in i qua khng nh cng sut tiu th (cng sut phn khng) trn

SVC thay i. Khi in p tng tc dng iu chnh lm dng in tng, cng sut tiu

th bi SVC ln hn s h thp c in p nt. Khi in p b gim thp, dng in

qua khng gim, SVC gim cng sut tiu th (hoc pht cng sut phn khng ln h

thng khi in p ng tr c tnh dung). Nh tng cao c in p.

Trn hnh 3.9c l c tnh iu chnh theo in p ca SVC thun khng, ch

nhn cng sut phn khng; hnh 3.9d l c tnh tng i tng qut hn ca SVC.

SVC trong trng hp ny c th pht hoc nhn cng sut phn khng. Mt cch

tng t ta cng c ng c tnh ca in khng X k theo in p (hnh 3.9a, hnh

3.9c).




58

Trong phm vi thay i c ca cng sut (phm vi ca TCR) in p nt

c gi tr s t U0. Trong thc t, vi mc ch phi hp iu chnh, ngi ta ch

to SVC c c tnh iu chnh mm (c dc) nh trn hnh (3.10). Khi trong

phm vi iu chnh c ca cng sut, in p nt c php dao ng vi lch

U. nh c dc ca ng c tnh m trong phm vi iu chnh c c th phn

b cng sut cho cc SVC lm vic song song hoc lm vic vi cc thit b iu chnh

cng sut phn khng khc.

B

UC

BU

TC

UH

B

UC

BU

TC

UH

Hnh 3.9.




59

III.3. Mt s nh hng ph ca SVC

Da vo biu thc dng in qua SVC ta thy rng ng thi vi thnh phn c

bn, cc thnh phn bc l khc cng tn ti trong SVC. Cn c vo biu thc khai

trin ta cng c cc hm quan h )( 0k T biu din bin thin tr s tng i bin

ca cc thnh phn l bc k.

Qua phn tch thy rng bin ca cc thnh phn bc l ph thuc rt mnh

theo gc ct 0 (T0). c im ny dn n cc ch khi vn hnh khng cho dng li

U0

Q

U0

Q

U U

Xkmin

Hnh 3.9b Hnh 3.9d

U0

X

Hnh 3.9a

Xkmax

Xkmin U0

X

Hnh 3.9c

Xkmax

U U

maxkQ

minkQ

maxkQ

minkQ




60

lm vic cc gc ct nguy him (bin ca cc sng hi bc cao ch t bin cc

i ng vi 1 s gc ct T0 no ). Bi vy, trong SVC thng c thm b lc kh

cc thnh phn bc cao, c bit l thnh phn bc ba. Ni chung tr s ln nht ca

thnh phn bc ba cng khng vt qu 15% bin dng in cc i qua khng.

Ngoi ra, cn nhn thy rng cc hiu ng ph ca SVC c nh hng n cht

lng in nng:

Gy tn hao ph.

Gy dao ng tn s.

Nhiu thng tin.

Qmin

Qmax

Q

U0

U

U

Hnh 3.10




61

CHNG IV: NH GI HIU QU S DNG SVC TI KHU GANG THP

THI NGUYN


61

CHNG IV: NH GI HIU QU S DNG SVC TI KHU

GANG THP THI NGUYN

IV.1: M u:

L in h quang xoay chiu luyn thp l ph ti xung kch phi tuyn tnh c

bit.Khi l in h quang xoay chiu vn hnh, im pht h quang lun thay i theo

ph thp nng chy, theo chiu di h quang ca n cng lun bin i, ng thi

do sp liu, iu chnh in cc, thi xy... cc thao tc ny lm cho dng in bin i

nhanh v khng n nh. Thc tin v phn tch cho thy:

Dng in h quang trong l in xoay chiu cha ch yu phn lng dng

in sng hi bc hai n bc by, ng thi cn c phn lng thp tn s to ra dao

ng tc ln i vi in p ca li cp in v dn n bin i chp nhong,

ng thi l in ly cng sut hu cng v v cng t h thng cp in mt cch

bin ng rt ln s dn dn st in p v dao ng in p li; gim cng sut a

vo l in (v cng sut hu cng a vo l in t l thun vi bnh phng in

p) trc tip nh hng n sn lng thp ra l; ngoi ra s mt cn bng ca ba pha

in cc do thao tc v sp liu dn n ngn mch khng i xng gia ba pha in

cc, ngoi ra cn sinh ra dng th t m nghch sng c bn to ra ba pha mt cn

bng.

* Tc hi ca sng hi i vi thit b in th hin qua cc im sau:

1. Sng hi nh hng n s quay ca ng c: Sng hi nh hng n ng

c quay l do dn n tn tht ph, sau l sinh ra trn ng c gii, ting n v qu

p sng hi

2. Sng hi nh hng n bin th ca li cp in

3. nh hng ca sng hi i vi c cu i dng: S bin ng bt thng

ca in p li xoay chiu lm cho mch xung khng u ca gc iu khin b bin

dng, ng thi bng s phn hi dng s phng i bin i mo lch in p ca h

thng lm cho b bin dng lm vic khng n nh. Cn vi b nghch bin th c th


THI NGUYN


62

sinh ra tht bi i pha lin tc m khng th cng tc c thm ch hng thit b i

pha

4. nh hng ca sng hi n t b song song v cp in

5. Sng hi gy nhiu thng tin

6. nh hng ca sng hi n cng t in

7. Sng hi nh hng n r le bo v, h thng t ng v my tnh in t

* Sung kch v cng s dn n nhng nh hng xu sau:

1. Lm cho in p thanh ci cp in st p v dao ng, gim mc lm vic

ca thit b ng c

2. Khi in p thanh ci cp in dao ng s lm bin i m men quay ph

phi loi ng c d b, cng sut hu cng a vo ph ti cng v th m gim

xung, nh hng n lc ra ca thit b v sn xut

3. Xung kch v cng nhanh kiu l h quang in s dn n dao ng in p

thanh ci t bin, kch thch mt ngi, b nhiu hnh i vi ti vi v my tnh

* Biu hin tc hi ca th t m ch yu nh sau:

1. Di s tc ng ng thi ca sng hi v th t m lm cho rt nhiu bo

v v c cu t ng. Dng b lc th t m lm nguyn kin khi ng trong h

thng in lc sinh ra ng tc sai lch.

2. Do hng quay ca th t m sng c bn v th t dng sng c bn

ngc chiu nhau nn khi ua vo ng c ( d b v ng b ) sinh ra sc in ng

ph lm rung my v tn tht ph

L in xoay chiu sinh ra dng in sng hi cp cao ln, th t m, v in p

xung v cng dao ng v t bin nh hng nghim trng n bn thn h s dng

v s vn hnh an ton ca cc thit b trn li in, lm gim cht lng in ca

li. V vy cn phi cn c vo cc tiu chun ca cht lng in hn ch v c

gii php tng hp x l khc phc

IV.2: Cn c thit k h thng SVC


THI NGUYN


63

Ti liu c s ch yu thit k h thng SVC ny ly t cng ty Gang Thp

Thi Nguyn, tt c ti liu thit k u ly s liu mi nht.

S liu v h thng cp in:

IV.2.1: Cc thng s trm bin th Gia Sng v trm bin th cp in ca

Gang Thp:

* Trm bin p 110 kV ca li in quc gia dung lng on mch khi s

dng phng thc vn hnh ln nht v phng thc vn hnh nh nht l:

Smax = 943 MVA ; Smin = 719.4 MVA

* Trm bin th Thi Nguyn 110 kV n Gia Sng 110 kV; 50 MVA, dng hai

ng dy AC 120 dn, di 11 km, tr khng dy n 5.26

* My bin th cho khu l in 50 MVA i p c ti, in p 110/ 35/ 6 kV,

in p on mch cao trung: 9.5% ; cao thp: 17.43% ; trung thp: 6.53%, dng in

khng ti 0.23%

* Bin th 50 MVA bn 35 kV dn n thanh ci 35 kV l in, s dng dy

dn AC 240 n, di 4 km, tr khng 1.68

* L in mi vo sn xut; pha 6 kV ca bin th 50 MVA khng ti

IV.2.2: Cc thng s ca bin p l in nh sau:

L in h quang 12 tn, bin p 9000 kVA, in p on mch xem bng (1) sau:

in p th cp (V) 320 272 231

UK (%) 8.21 9.96 11.37

in p on mch ca l in 30 tn hin c xem bng (2). Tr s in p on

mch bin th 16000 kVA l 30 tn

in p th cp (V) 353 305 245 137

UK (%) 6.83 8.72 10.91 23.61

*L in 30 tn mi, bin p 25000 kVA, in p on mch 8%


THI NGUYN


64

* L tinh luyn 40 LF, bin p 7000 kVA, in p on mch 8%

IV.2.3: Tr khng v in khng hn dng ca mch ngn l in:

* L in xoay chiu 12 tn ( Bin th 9000 kVA ), tr khng mch ngn ca

in p th cp ln nht: 0.9 + j 2.7 ( m )

* L in xoay chiu 30 tn ( Bin th 16000 kVA ), tr khng mch ngn ca

in p th cp ln nht 0.8 + j 2.8 ( m )

* L in xoay chiu 30 tn mi ( Bin th 25000 kVA ), tr khng mch ngn

in p ln nht ca bn th cp 0.65 + j 2.65 ( m )

* L tinh luyn 40 tn LF ( Bin th 7000 kVA ), tr khng mch ngn ca in

p th cp ln nht 0.5 + j 2.5 ( m )

IV.2.4: Ch tiu k thut cn t c:

Yu cu cn t c l, cc ch tiu v cht lng in nng, theo tiu chun

k thut in v quy phm trang b in hin hnh

IV.2.4.1. Tr s cho php ca dng in sng hi:

Dng in sng hi cc cp trm Gia Sng a vo h thng 110 kV tho mn

c yu cu v sng hi trn li in theo tiu chun k thut in.

Trong tiu chun tr s cho php ca dng in sng hi cc cp, di dung

lng on mch c bn gi nh nh bng 3:

in p

tiu chun

110 kV

Dung lng

mch ngn

c bn

M.V.A

Tr s cho php dng in sng hi v s cp sng hi Ihp (A)

2 3 4 5 6 7

110 750 12 9.6 6.0 9.6 4.0 6.8

Do trong bng 3 dung lng mch ngn nh nht ca im kho st tnh ton

khng ging vi dung lng mch ngn nh nht tiu chun gi nh


THI NGUYN


65

( 750 MVA ).

Trong bng 3 theo tiu chun nh nc tr s dng in sng hi cho php trc

ht phi tnh i theo ph lc. Cng thc tnh i nh sau:

Ih = 2

1

k

k

S

S . Ihp (1)

Vi Sk1: Dung lng mch ngn nh nht ca im lin kt chung

Sk2: Dung lng mch ngn tiu chun MVA

Ihp: Tr s cho php ca dng in sng hi cp h trong bng 3

Ih: Tr s cho php ca dng in sng hi cp h khi dung lng mch ngn

l Sk1

Do dung lng mch ngn khi phng thc vn hnh nh nht ca trm 110kV

li in quc gia bit l: 719.4 MVA; qua tnh ton dung lng on mch di

phng thc vn hnh nh nht ca im kho st tnh ton trm Gia Sng 110kV l

629.3 MVA; Tr s dng in sng hi cho php nh nht tnh i nh bng 4:

Tr s cho php ca ca dng in sng hi cc cp trm 110 Gia Sng qua tnh

i dung lng on mch nh nht

Cp sng hi h 2 3 4 5 6 7

Tr s cho php sng hi

tnh i (A) 10.1 8.06 5.03 8.06 3.36 5.71

Theo yu cu ph lc quc gia, dng in sng hi cp thit cho php ti im

lin kt cn phi tnh i theo cng thc (2)

Ihi = Ih.

1

tS

iS (2)

Trong :

Ih: Tr s cho php dng in (A), sng hi cp h tnh i theo cng thc (1)


THI NGUYN


66

Si: Dung lng ca b i (ly 50 MVA) MVA

St; Dung lng thit b cp in ti im lin kt chung (ly 70 MVA)

: H s tng ca v tr pha ly theo bng 5

Bng 5: Tr s ly ca h s tng theo v tr pha

h 3 5 7 9 11 13

1.1 1.2 1.4 1.8 1.9 2.0

Tr s dng cho php sng hi trm 110kV Gia Sng tnh i theo cng thc (2)

nh sau:

Bng 6: Tr s cho php sng hi cc bc 110kV Trm Gia Sng im kho

st:

S cp sng hi 2 3 4 5 6 7

Tr s dng sng hi cho

php Ihi(A) 8.54 5.94 4.25 6.09 2.84 4.49

IV.2.4.2. Tr s cho php ca in p sng hi

Cn c vo qui nh Cht lng in Sng hi trn li chung ca Trung

Quc. Tr s hn nh in p sng hi ca cc cp in p trn h thng cung cp

in, nh bng 7 ( in p pha )

Tc tr s cho php t l lch mo sng hi ca thanh ci 110kV trm bin th

Gia Sng l 2%


THI NGUYN


67

Bng 7: Tr s in p sng hi cho php ca cc cp in p

in p li in

(kV)

T l bin lch

sng hi in p %

T l in p sng hi cc bc

Bc l Bc chn

35 3.0 2.4 1.2

110 2.0 1.6 0.8

IV.2.4.3. Dao ng in p v tr s t bin:

in p thanh ci 110kV trm bin th Gia Sng do cm l in sinh ra phi

tho mn theo yu cu Dao ng in p cho php v ca cht lng in theo tiu

chun k thut in bao gm:

* in p 110kV dao ng nh hn: 2%

* in p 110kV bin i t bin < 0.6%

IV.2.4.4. Tr s cho php in p th t nghch:

khng cn bng in p thanh ci 110kV, im o c ti trm bin th Gia

sng do cm l in gy ra p ng yu cu cn qui nh v khng cn bng in

p phi nh hn 1.3%.

IV.2.4.5: Yu cu h s cos ti im t cng t

H s cos cng sut bnh qun ti im o 110kV Gia Sng ln hn 0.92

IV.2.5: H thng cp in ca Cng ty Gang thp Thi Nguyn Vit Nam

Cng ty Gang thp Thi Nguyn hin nay c mt trm bin th 110 Gia sng do

ngun trm 110kV quc gia cung cp theo hai ng. Trm bin p Gia sng c hai

my bin th 110kV; mt my c dung lng 50 MVA, dn bng dy AC 120 kp, bc

trn cao, di 11 km. Mt my bin th dung lng 20 MVA, ly t trm bin p Thi

Nguyn, di 11 km, bng dy AC240 n. Trong my bin th 50MVA in p

110kV/35kV/6kV, hin my 50 MVA cp cho hai l in 35kV, 1 l 12 tn my bin


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68

th 9000kVA, mt l 30 tn my bin th 16.000 kVA, sn lng thp 30 tn/mt m.

Sp ti tng thm mt l in 30 tn cc cng sut my bin th 25.000 kVA, mt l

tinh luyn LF 40 tn, my bin th 7000 kVA v c cu h thng b v cng tnh

SVC, my bin th 20 MVA ch yu cung cp cho cm l in 6 kV v ph ti trong

nh my ( nh hng ca n i vi cht lng in rt nh c th b qua khng tnh ),

hai my bin th 110 kV, 6 kV vn hnh ring r khng nh hng g ti nhau, h

thng cp in v cc thng s nh mc ca thit b, vn hnh v s cp in nh

hnh 1:

35 kV

AC 120

11 km

110 kV

6 kV

B1

B4 9 MVA

8.2%

12 T

K

B3 25 MVA

8.0 %

30 T

Khng hot ng

Hnh 1:

B5 16 MVA

6.8%

30T

12 T

B2 7 MVA

8.0%

40 T

LF

35 kV

SVC

Mi

tng

110 kV

Trm Thi Nguyn

Trm Gia sng

12 %

110 kV


THI NGUYN


69

My bin p ba cun dy B1: 110 / 35 / 6 kV c UN CT% = 9.5 % ; UN CH % = 17.43

UN TH % = 6.53 % ; Sm = 50 MVA.

My bin p hai cun dy B2: 35 / 6 kV c UN = 8 % ; Sm = 7 MVA.

My bin p hai cun dy B3: 35 / 6 kV c UN = 8.0 % ; Sm = 25 MVA.



Cun khng c Xk % = 12 %

Ta c s ng tr nh hnh v ( tnh trong h n v c bn khng tn )

Chn Scb = 100 MVA ; Ucb = Utb

ng dy AC 120 ( l = 11 km ), tra ph lc 11 sch thit k nh my in

Bu Cong Suat SVC

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