ccd7 tinh ngan mach

7/26/2019 Ccd7 Tinh Ngan Mach

1/49

Chng7:TNH TON NGN MCH

7.1. KHI NIM CHUNG

7.2. CC DNG NGN MCH CHNH

7.3. CC GI THIT C BN

7.4. TNH TON IN KHNG CC PHN T7.5. TRNH T TIN HNH TNH TON NGN MCH

7.6. TNH NGN MCH MNG IN IN P CAO

7.7. TNH NGN MCH MNG IN IN P THP

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7.1. KHI NIM CHUNG

Ngn mchl tnhtrngs cnghimtrngvthngxuynxyratrongh thngcungcp in.

Do,ccphn ttrongh thngcungcp in phictnh ton vla chnsao chokhngnhnglm

vic tttrongtrngthi bnhthngm cn cth chung c trngthis ctronggii hnquynhchophp.

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7.1. KHI NIM CHUNG

la chn c ttccphn t ca h thngcungcp in phid on ccc tnhtrng ngn mchcth xyraviuquantrng hnltnh toncccs liu vtnhtrng ngn mch nhdngin ngnmch cc thi im khc nhau, cng sut ngn

mch...

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7.1. KHI NIM CHUNG

Cc s liu v tnh trng ngn mch l cn c quantrng gii quyt mt lot vn khcnhla chncc thit b in, thit k h thng bo v rle, nhphng thc vnhnh...

Tnh tonngn mchlmt phnkhngth thiu ckhithit kcungcp in.

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7.2. CC DNG NGN MCH CHNH7.2.1. nh ngha

Ngn mchlhin tngcc phachpnhau(i vimngtrung tnh cchin vi t) hoclhin tngcc phachpnhau vchm t(i vi mngtrung tnhtrung tnhtrc tip ni t).

Ngn mch lhin tngmch in b ni tt liquamt tng tr rt nhcthxemnh bngkhng.

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7.2. CC DNG NGN MCH CHNH7.2.1. nh ngha

Lcngn mch tng tr h thng b gim xung v tytheovtrim ngn mchxa haygn nguncungcpmtng tr h thng gim xungt haynhiu.

Khingn mch,trongmch xut hinqu trnh qunghal dnginvinputhayi,dngintnglnrt nhiusovilc lmvicbnhthng,cninp trongmng inthgim xung.

Thigianinpgim xungxcnh bng thigiantcng ca bo v rlev myct in t gn imngn mch nht.

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7.2. CC DNG NGN MCH CHNH7.2.2. Cc dng ngn mch

7K hiu v xc sut xy ra i vi tng dng ngn mch

Dng ngn mch S nguyn lK hiu Xc xut

xy ra [%]

Ngn mch ba pha N(3) 5

Ngn mch hai pha N(2) 10

Ngn mch mt pha N(1) 65

Ngn mch hai phachm t

N(1-1) 20

A


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7.2. CC DNG NGN MCH CHNH7.2.2. Cc dng ngn mch

Cnnghincungn mchba phav:- Tuytxyranhng vnckh nng xyra.

- C lc nquyt nhtnhtrnglmvic ca h thngin chng hnkhixyrangn mchtrnngdy

linlc giacch thng in vi nhau haygiaccnh myin vi h thng.

- T ngn mch ba pha c th dng phng phpthnhphn i xng tnh dnginvinpca

ccdng ngn mchkhc(nh ngn mchhai pha,mtpha, hai phachm t)...

- Trong tnh tonchnmyct inv cc khc in,cn kim tra n nh lc in ngca chng xutphttdngngn mchba pha.

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7.2. CC DNG NGN MCH CHNH7.2.3. Nguyn nhn ca ngn mch

Do cch in b hng:

- Dovnhnh lu ngycchin bgi ham khngphthin kp thi bngccth nghim nh k.

-Do stnhvo ccngdyti intrn khnghoc stnh trc tipvothit b phnphingoitri hocdo quinpni b.

-Do nguyn nhnc hckhcnh ct in b ,khio t chm phiccngdy cp.

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7.2. CC DNG NGN MCH CHNH7.2.3. Nguyn nhn ca ngn mch

Ngn mch xyraikhi cn do thao tcnhm lncanhn vin vn hnh hoc do cc nguyn nhn ngunhin khcnhchim bay hayng vt chm phiccphn dn in trn.

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7.2. CC DNG NGN MCH CHNH7.2.4. Hu qu ca ngn mch

- Khingn mch,dngin tnglnrt nhiugytnngcc b ccb phn c dng in ngn mch iqua dthigiantn ti ngn mch rt ngn.

-Toralc in ng lncthphhngcc khc

in, s hoclmuncong thanhdn...

-inpmng b tt xungcthlm chong c inngngquay,sn xut b ngng tr hoc ng cquaychm liv lmh hng sn phm.

-Phhoi slmvic ng bcacc my phtintrongh thng mt n nhv tan r.

-Lm ginonviccungcp incho cchtiuth.11


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7.2. CC DNG NGN MCH CHNH7.2.5. Mc ch tnh ngn mch

-La chnccthit b inv khc innhmyctin,dao cch ly,scchin,thanhdn...

-La chnccbinphphn chdngngn mch.

-Tnh tonthit k bo v rle.

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7.2. CC DNG NGN MCH CHNH7.2.6. Ni dung tnh ton ngn mch

- I: dngngn mchsiu qu,l gitrbanu cathnhphnchuk cadngngn mch. Nclmcn c tnh ton ccs liukhcnh ixk, Ixk.

- ixk: dngngn mchxung kchtc thil gitr tc

thi cc i cadngngn mchtonphn. N dng kimtra ccthit b in,thanh ci,s ... vkhnng n nh lc in ng.

- Ixk: dngngn mchxung kchhiu dng.

- I0,2: dngngn mchsauthigian 0,2 giy, dngkimtrakh nng ct camyct.

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7.2. CC DNG NGN MCH CHNH7.2.6. Ni dung tnh ton ngn mch

- I: dngngn mch thigiann nht = dngkim tra kh nng n nh nhit ca cc thit b inthanh gp,s ...

- S0,2: cngsut ngn mchlc 0,2 giy, dng kim

trakh nng ct camy.

- tN:thigianxyrangn mch.Thigian nyctnhbng tng thigian tcng ca thit b bo vvthigian tcng camyct. tN= tbv+ tMC

- tgt:thigiangi thit(cngilthigian quyi)lkhong thigiancn thit dngngn mch cthpht ramt nhit lng ng bng nhit lngdo dngngn mch thc tpht ra trongthigian tN.

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Tnh chnh xcdng in ngn mch trong h thnginphc tplmt iukhkhn, bnthn dnginngn mch ph thucvonhiu yu t.

n ginhavictnh tonsgi thit:

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- Cc my pht in khng c dao ng cng sut,nghal gclchphagia sc in ng cacc myphtinkhng thayitrongthigianngn mch.

-Tnhgn ng ph ti, thayph ti bng mt tng tr

c nh tptrungti mt imnt chung.Vi ng c in c ln,khingn mch gn cc cachng,ti thi imbanucthxemnhmy phtincungcpdng choim ngn mch.

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-Bquain trqu ni ngn mch.

-Khng tnhn sbo hatcacch thng t.

-Bqua dngin thacamybinp.

-Bqua dungdn ca ngdy(tr trng hp inp cao U220kV vngdy di).

-H thng inba pha li xng.

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7.4. TNH TON IN KHNG CC PHN T

Tnh tonngn mchtrongmng inp cao U>1000Vchxtn nhng yu tcinkhngnh hng lnn dng ngn mch nh my pht in, cun inkhng,ngdy trn khng, mybinp

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7.4. TNH TON IN KHNG CC PHN T7.4.1.in khng my pht in

XF= X

d

[]

trong:

- Um = Utb :inp trung bnhnh mc camy pht [kV].- SmF: dunglng nh mc camy pht [MVA].

- XF:inkhng my phtin[].

- Xd:inkhng siu qu dc trc camy phtin[],

tra bng.

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7.4. TNH TON IN KHNG CC PHN T7.4.1. in khng my pht in

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in khng siu qu dc trc ca my pht in

Cp in p

nh mc [kV] 500 220 110 35 15 10 6 3 0,38

in p trung bnhnh mc [kV]

500 230 115 37 15,75 10,5 6,3 3,15 0,4

in p trung bnh nh mc ca cc cp

Thit b in Xd[]

-My pht in tucbin nc khng c cun cm-My pht in tucbin nc c cun cm-My pht in tucbin hi

-My b ng b-ng c in ng b

0,3 0,38

0,14 0,3

0,125

0,15 0,20,18 0,38


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7.4. TNH TON IN KHNG CC PHN T7.4.2. in khng my bin p

XBA

=%

00

[]

trong:

- Un% :inpngn mch phn trm camybinp chotrnnhnmyhoctra trongstayk thut.

- Um= Utb:inp trung bnh phath cp camybinp[kV].

- SmBA: dunglng nh mc camybinp [MVA].

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7.4. TNH TON IN KHNG CC PHN T7.4.3. in khng ng dy cp v ng dy trn khng

Xd = xo.l []trong :

- l: chiu di ng dy [km].

- Scb: dung lng c bn t chn [MVA].

- xo: in khng trn mt n v chiu di dy dn[/km].

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in khng trn mt n v chiu di dy dn

Loi ng dy x0 [/km]

ng dy trn khng U = 6220kVng dy trn khng U 1000VCp ba li U = 35kV

Cp ba li U = 310KVCp h p U 1000V

0,40,3

0,12

0,070,080,060,07


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7.5. TRNH T TIN HNH TNH TON NGN MCH7.5.1. Trnh t tnh ton ngn mch

Xc nh im ngn mch.Xc nh in khng cc phn t trong mch in ngnmch. Sau dng php bin i a v mt s ng tr c mt in khng tng. Mt u l sc in

ng v u kia l im ngn mch.

ng dng nh lut Ohm xc nh dng in ngnmch. Nh vy xc nh in khng l mt bc quantrng trong tnh ton ngn mch.

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S tnh tonngn mch


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7.5. TRNH T TIN HNH TNH TON NGN MCH7.5.2. Chn im ngn mch

chn thit b in, phi kimtraiu kinn nh lcin ngvn nh nhit.

Khi cn gi thit rng ngn mch ti mt imnomdngin ngn mch chyquathit blln nht.

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Xts mng in tnhngn mch chn thit bin.

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Mun chnmyctMC1, tnhngn mch tiN-1.ChnMC2, tnh ngn mch N-2. Chn MC3 tnh, ngnmch N-3.

Nh thc qunhiu im ngn mch phitnh.Thcras nych cntnhmt imhaiim ngn mchm thi.

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Cthtnhim ngn mchN-4t imN-1 v N-2 vim ngn mch N-1 v N-2 so vi im N-4 rt gnnhau(chqua thanh gp,inkhng khngng k).

Nu thit b ca2 mybinp hon tontng tthcthtnhmt imv suy ra IN-4= 2IN-1= 2IN-2.

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Cni viMC3chn lygitrdngngn mchnotrong 2 dng IN-1v IN-2lln nht.

Vchn imc dngngn mch ln nhtnn khi tnh,gi thitmyctMC3ng li.

Nh vykhi tnh toncnnghincu k s sao choch chn mtviim ngn mchl cthtnhcchovic la chn hu htccthit btrongmch .

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7.5. TRNH T TIN HNH TNH TON NGN MCH7.5.3. Thnh lp s thay th

Muntnh dngin ngn mch,trc tinphithnhlps thayth.

yl s ntuyn,trongmi phn t ca hthng in c thaybng mt inkhng tngng,vimy phtin c thaybng mt in khng vmt sc in ng.

Trong s thayth, mi phn t ca mch in c

biu din bng mtphns, t sghis th t ca caphn tcnmu sghitr s inkhngca phn t.

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7.5. TRNH T TIN HNH TNH TON NGN MCH7.5.3. Thnh lp s thay th

Xtmt phn t bt k ca h thng inba pha c ccthng s nh mc: in p nh mc Um [kV], dngin nhmc Im[kA], cngsut nhmcSm[kVA],inkhngnhmcxm[].

Chng linh vinhaubicciu kin:

Sm= 3 Um Im

xm=

Um Im

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7.5. TRNH T TIN HNH TNH TON NGN MCH7.5.4. Xc nh tng tr khng

Nutrongs cnhiu cp inp khc nhau,inkhngccphn t trongs phi c quyi vcngmt cp inpc bn.

Cp inpc bnny lcp inp tnhtrm ngnmch, tclim ngn mch cp inp no th Ucbc lylinp trung bnhnh mc ca cp inp.

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Cngthcquyi inkhng:XUcb= XUtb

trong:

- XUcb :inkhng quyv inpc bntnh ton []

- XUtb :inkhngng vi cp inp trung bnhca phnt inkhng []

Khi ccgitr inkhng ccphn tquyvcngcp inpc bntnh ton, tnhcinkhngtng

t ngun n im ngn mch.

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Xt s mng in tnh in khng cc phn t

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Cp inpc bntnh ton lUcb= U4Gitr inkhng ccphn tquyi v cp inpcbntnh tonnhsau:

- My phtin: X1q= X1

= X1

4

- Mybinp 1: X2q= X2

= X2

4

-ngdy 1: X3q

= X3

= X3

4

- Mybinp 2: X4q= X4

= X4

4

-ngdy 2: X5q= X5

= X5

4

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7.5. TRNH T TIN HNH TNH TON NGN MCH7.5.5. Bin i s thay th v dng n gin

Sau khi thnhlp s thaythv tnhinkhngcaccphn t, cn phi tin hnhcc php bin i a s v dng n gin nht.

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7.5. TRNH T TIN HNH TNH TON NGN MCH7.5.5. Bin i s thay th v dng n gin7.5.5.1. Ghp song song cc nhnh c ngun

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Ghp song song

cc nhnh c ngun

S thay thS

ng tr

Et

Xt

Ch TNH TON NGN MCH


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7.5. TRNH T TIN HNH TNH TON NGN MCH7.5.5. Bin i s thay th v dng n gin7.5.5.2. Bin i tng ng cc nhnh khng c ngun

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S o ban au S o tng ng Cong thc bien oi

n

i iXX 1

11

n

i

iXX

1

231312

1323

3

231312

2312

2

231312

1312

1

XXX

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1

32

3223

2

31

3113

3

21

2112

X

XXXXX

X

XXXXX

X

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1

1

1

1

2

1

1

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11

11

11

n

i i

nnK

n

i i

nII

n

i i

nI

XXXX

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X2

X1

X3

Xn

S1

S1 X

S1 X S1 XX X

S1 X12

X13 X23

S2

S3 S3

S1 S2

X1 X2

X3

S1 X12

X13 X23

S2

S3

S3

S1 S2

X1 X2

X3

S1

S2

X1

X2

Xn+1

Xn

XI

XII

Sn

Xn

Sn

S1

S2

Ch TNH TON NGN MCH


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7.6. TNH NGN MCH MNG IN IN P CAO7.6.1. Ngn mch ba pha trong mng in n gin

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Dng in ngn mch

Ch TNH TON NGN MCH


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Thnhvchothydngin ngn mch t tr s lnnhtsaunabn chuk(t = 0,01sec). Nbng tng trs tc thidnginchukv khng chukvgildngin ngn mchxung kch.

ixk= ick(t = 0,01) + ikck(t = 0,01)

Hay: ixk= Ickm+ Ickm.

0,0 = (1+

0,0 ) Ickm

ixk= kxk.

Ickm= kxk. 2

Ick

trong :

kxk= 1+

0,0 l h s xung kch ca dng in ngn mch.

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Ch 7 TNH TON NGN MCH


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-Nu mch inthun cm(x = 0) th Ta=v Kxk= 2,nghaldnginkhng chukkhngtt dn.

-Nu mch inthun tr(r = 0) th Ta= 0 v Kxk= 1,nghalthnhphnkhng chukkhngxut hin.

Nh vy: 1Kxk 2

H skxkcthtractheongcong kxk= f(Ta),

Kxk

= f

hoctrabng stayk thut.

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Ch 7 TNH TON NGN MCH


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7.6. TNH NGN MCH MNG IN IN P CAO7.6.2. Tr s hiu dng ca dng in ngn mch ton phn

Dngin ngn mchtonphntrong qu trnh qukhngphi lngcong hnh sin v c stham giacadnginkhng chuk.

Nh vy tr s hiu dng cadngin ngn mchtonphn ti thi imt l IN(t)cthtnhgn ng nhgitrtrung bnh bnh phngtrong bn chuk(0,02sec)mthi imtnm gia.

iN(t)= I2

ck(t) I2

kck(t)

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Ch ng 7 TNH TON NGN MCH


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7.6. TNH NGN MCH MNG IN IN P CAO7.6.2. Tr s hiu dng ca dng in ngn mch ton phn

Tr s hiu dng ca dng in xung kch Ixk ti thiimt =

= 0,01sec vvi iu kin Ikck(0)= Ickm (trc

lcngn mchl khngti)

Ikck(t)= ixk Ickm= kxk.Ickm Ickm= (kxk1)Ickm

Ikck(t)= 2(kxk1) Ick(t)

Cuicng tnhc:

iN(t)= I2ck(t)2(kxk 1) I2ck(t)

iN(t)= 1 2(kxk 1)2 Ick(t)

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Chng 7 TNH TON NGN MCH


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7.7. TNH NGN MCH MNG IN IN P THP7.7.1. Cc gi thit

Vphn ln cc mybinpphn xng u ccngsutbhn nhiusovicngsut ngun cungcp. Vvy trong tnh ton c thxem cng sut canguncungcpl v cngln. Do,thnhphnchu

k skhngitrongsut thigianngn mchvbngIck= I

in trcaccphn ttrongmng in,mybinp,ngdy,in tr tipxccacc myct in...cnh hng ln n tr s ngn mchnn khngthbquac.

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Chng 7: TNH TON NGN MCH


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Vin tr tng i lnnnthnhphn tt dn tt rtnhanh, cth bquakhng tnh nthnhphnny.Tnh ton chothy rng i vi mybinp c dunglng S=1000kVA th dng in tt dn s tt nhanh

theothigianvit = 0,3sec.Tng trmybinp v ccphn t nibnth cpmybinp l khng ln,dokhingn mchbnth cpmybinp th cthxeminp bns cp

l khng thayi.

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inkhngtng i ca ngun ti mng in inpthpkhngnh hn tr s x*tt> 0,43.

x*HTm= x*Fm+ x*BAm+ x*dd+ x*BIm

= 0,125 + 0,105 + 0,105 + 0,105 = 0,43

Khi tnh ton trongmng inpthp thngdnghn vc tn U[V], I[A], R[m], x[m], S[kVA].

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7.7. TNH NGN MCH MNG IN IN P THP7.7.2. Tnh cng sut ca h thng in

Trng hp h thngcungcp in c uvo myct in, bit ccngsut ct camyct,lc lycngsut ngn mch ca h thng bngcngsut ctcamyct SNHT= Sct.

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7.7. TNH NGN MCH MNG IN IN P THP7.7.3. Tnh dng in ngn mch

Tnh dngin ngn mch3 phad c dy trung tnhhay khngcngdng cngthc:

IN=

.

+

. 103 [kA]

trong:

- Utb :inp trung bnhnh mc ng vi im ngn mch[V]

- R, X:in tr tng, inkhngtng t ngun n imngn mch[m]

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Tr s tc thi cadngngn mchxung kch:ixk= kxk. 2.IN

Tr s hiu dng cadngngn mchxung kch:

Ixk=

IN 1 2kxk 1

2

viKxklh sxung kch

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V tr ca im ngn mch H s kxk

Trn thanh ci my bin p

- S = (500 1000)kVA , Un% = 5,5

- S = (100 320)kVA , Un% = 5,5

xa my bin p

1,3

1,2

1,0



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Trongtrng hp ngn mch ngayu cc ca ngckhngng bthng cny cth trthnh myphtin, cungcpdnginctr s tc thi khong6,5lndngnh mc ca ng c.

Dodnginxung kch tnh:

ixk= Kxk. 2.IN + 6,5mC

ccd7 tinh ngan mach

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