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CHNG 3
VN HNH MY PHT IN
3.1 C IM V PHN LOI
3.1.1 c im
Thit b in chim v tr quan trng nht trong cc nh my in (NM) l my pht in (MP). Cc my pht in c nhim v bin i cc dng c nng thnh in nng. l khu chnh ca qu trnh sn xut in nng. Hin nay cc MP dng trong NM ch yu vn l cc MP ng b ba pha. Chng c cng sut t vi kW n hng nghn MW, in p nh mc t 380V n 25kV. Khi lm vic trong NM, cc MP khng th tch ri cc thit b ph nh: h thng kch t, h thng bi trn, h thng lm mt...
Mt MP ch c th pht ra in nng (c trng bi S, f, U, I) khi c cc iu kin sau:
- Phi c dng in kch thch a vo cun dy rto ca MP to ra t thng chnh 0 . Dng kch thch ny do my pht kch thch mt chiu cung cp.
- Phi c cng sut c to ra m men c M1 lm quay rto ca MP. Cng sut c do cc ng c s cp cung cp (tua bin hi, tua bin nc,...)
Cc yu t lm vic ca mt MP c m t nh hnh 3.1.
Cng sut c M1 ch yu iu chnh c tn s f v cng sut tc dng PF .
Dng in kch thch to ra t trng chnh 0 , ch yu iu chnh in p U (sc in ng E) v cng sut phn khng QF .
Tuy nhin s iu chnh cng sut c M1 cng lm thay i c in p U, s iu chnh dng kch thch cng lm thay i c tn s f, nhng s ph thuc t hn.
R rng l mun iu chnh c tn s f v cng sut tc dng PF th phi iu chnh cng sut c M1 tc l iu chnh lng hi vo tua bin hi (i vi MP tua bin hi) hay iu chnh lng nc vo tua bin nc (i vi MP tua bin nc). Mun iu chnh in p u cc my pht U v cng sut phn khng QF th phi iu chnh dng in kch thch Ikt .
Nh vy, nu cht lng in nng c c trng bi U v f th M1 v 0 quyt nh nhiu n cht lng in nng.
Nguyn l lm vic chung ca my pht in ng b da trn s chuyn ng tng i ca phn cm (cn gi l phn kch t) v phn ng (pht ra in xoay chiu). Khi rto chuyn ng quay u vi vn tc , dng in mt chiu chy trong cun dy kch t ca rto s sinh ra t trng quay c t thng khp mch qua cun dy ca phn ng stato v sinh ra
ng c s cp (tua bin hi, tua bin nc)
My pht kch thch mt chiu
M1
MP E , I , f , SF , PF , QF , cos F
Hnh 3.1 : S nguyn l cc yu t lm vic ca MP
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sc in ng cm ng Eo bin i theo chu k hnh sin c tn s f = 50Hz hoc f = 60Hz. Chuyn ng tng i ca phn cm v phn ng cho php phn cm quay phn ng ng yn hoc phn ng quay phn cm ng yn. Mch kch t v cun dy kch t dng in p mt chiu thp, c cu to cc t n gin hn cc t ca phn ng.Cc cun dy phn ng thng c nhiu vng chu in p cao, c cu to mch t v cch u ni dy dn phc tp. Do nhng c im trn nn my pht in ng b thng ch to vi phn cm quay gi l rto, phn ng ng yn gi l stato.
My pht in ng b hot ng c l nh c h thng tuabin, tua bin ca my pht c vai tr truyn lc v truyn m men quay M1 vo lm quay trc my pht, nng lng c dng quay cnh tua bin l sc nc, kh ga, hi nc, ty theo vic x dng ngun nng lng no m c tua bin c tn gi khc nhau:
- Tua bin dng nng lng nc c gi l tua bin nc. Vi cc nh my thy in cng sut ln c tc quay ca tua bin thp khong 100 150 vng/ pht, cc my pht in tua bin nc c tc thp thng dng kiu cc li. Vi cc nh my thy in c thit k c mc chnh p nc ln thng c tc quay tua bin cao khong 1000 1500 vng/ pht.
- Cc my pht in tua bin kh v tua bin hi dng cc ngun nng lng nh kh ga (nh my tua bin kh) hoc hi (nh my nhit in). My pht in tua bin kh hoc tua bin hi thng c 2 hoc 4 cc c thit k ch to lm vic tc cao khong 1500 3600 v/ pht.
- Cc my pht in c ko trc tip bng ng c Diesel hoc bng ng c xng khng dng tua bin thng c tc khong 100 1000 v/ pht. Hin nay my pht in Diesel khng dng trong li in m ch l ngun pht in c lp, v cng sut v hiu sut thp, gi thnh sn xut in nng cao,chi ph nhin liu v chi ph cho sa cha cao.
3.1.2 Phn loi
1) My pht tuabin hi
My pht in tua bin hi (my pht nhit in) c tnh ton ch to vi tc quay ln (vi tn s 50 Hz, quay 3000 vg/ph), v vy rto c lm theo kiu cc n bng c mt khi thp hp kim rn c cht lng cao v tnh cht v c kh cao. Dng hnh tr di, trc quay c b tr nm ngang. My pht in tua bin hi lm vic c tc ln th cc tua bin hi s c hiu sut cao, kch thc gim i ng k.
Mt u trc rto ca MP c ni trc tip vi trc ca tua bin hi (thng ni cng), u cn li ni vi rto ca my kch thch (nu c).
Mi quan h gia tn s v tc quay c th hin bi biu thc
n
fp
60 (3.1)
trong : p - s lng cp cc ;
n - tc quay, vng/pht;
f - tn s.
Nh vy ng vi tn s 50Hz, nu my pht tuabin hi c mt cp cc th tc quay s l 3000 vg/ph. V rotor ca cc my pht tuabin hi quay nhanh nn ng knh rt nh, kt cu cc n m bo bn c hc cao. Mch t ca stator v rotor my pht in ni chung c cc lm bng thp c t dn ln v bn c hc cao c th hn ch c tn hao do dng in xoy. S kt cu ca my pht c th hin trn hnh 3.2. c im kt cu ca my pht c th tm tt nh sau:
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a) V stator c ch to lin khi khng thm kh, c bn c hc stator c th khng b hng bi s bin dng khi c s c n, v c t trc tip ln b my v bt cht bng bulng.
b) Li stator c cu to t cc l thp k thut, trn b mt cc l thp ny c qut lp sn cch in v dc theo trc c cc rnh thng gi.
Cun dy ca stator c cu to kiu 3 pha 2 lp, cch in gia cc cun dy thng dng l cch in loi B s ni hnh sao kp gm 9 u ra.
c) Rotor c rn lin khi bng thp c bit m bo rotor c bn c hc trong mi ch lm vic ca my pht. Cun dy ca rotor c cch in loi B, li c khoan xuyn tm t cc dy ni cc cun rotor n chi than, cc vng dy rotor qun trn cc g rnh, cc rnh ny to nn cc khe thng gi. Mt u trc rotor c ni trc tip vi trc tuabin hi, u cn li ni vi my kch t. Cc thuc loi trt c bi trn bng du p lc cao.
d) B chn trc dng gi kh H2 khng thot ra ngoi theo dc trc c kt cu m bo nn cht bc vo g trc nh p lc du chn, du nn v m bo t ng dch chuyn dc khi c s di trc.
e) B lm mt c b tr bao bc phn trn v dc theo thn my pht.
f) Thng gi cho my pht in c thc hin theo chu trnh tun hon kn cng vi vic lm mt kh H2 bng cc b lm mt t trong v stator, cn c vo yu cu lm mt kh H2, nh ch to t 2 qut 2 u trc ca rotor my pht.
Kiu trc ngang l kiu m trc r to my pht nm song song vi mt t, kiu trc ngang thng dng cho cc my pht in c cng sut thp (hnh 3.2)
u im:
- Trang b h thng bi trn n gin hn so vi kiu trc ng.
- Thun li trong vic sa cha v bo dng nh k.
- Gi thnh xy lp, ch to r.
Nhc im:
- Gian my yu cu phi c din tch mt bng ln, chiu cao gian my thp
- My pht in c t cng cao tua bin nn gp kh khn trong vic gii quyt cao ca gian t my trn mc nc l.
- Hiu sut khai thc ct nc km hiu qu so vi kiu trc ng.
- Bt li trong vic gii quyt vng ca trc r to, chiu di ca trc my pht b hn ch bi vng.
Hnh 3.2 M t my pht in trc ngang
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2) My pht in tuabin nc
My pht in tua bin nc (my pht thu in) c ch to vi tc quay thp v nm trong phm vi 100750 vg/ph. V vy, rto ca my pht thu in l loi c nhiu cc li.
Rto MP thu in c ng knh ln hn nhiu so vi chiu di ca n, v vy rto ca MP thu in thng c b tr cho trc quay thng ng. Nh th s tit kim c chiu cao ca gian my. Trc quay nm ngang ch p dng i vi my c cng sut nh, tc quay nhanh.
My pht in tuabin nc ( cc nh my thu in) c ch to vi tc quay chm hn nhiu so vi my pht tuabin hi. Hn na, tc quay ca my pht cc nh my thu in khc nhau thng cng khng ging nhau. l v m bo hiu sut cao, tuabin nc cn c cng sut nh mc v tc quay ph hp vi tham s ca ngun nc (chiu cao hiu dng ct nc, lu lng dng nc...). Khi ct nc nh (nhng lu lng nc ln) tuabin nc c th c tc quay thp n 100 vg/ph.
Do tc quay thp, s cp cc ca my pht tuabin nc rt ln, do ng knh ca rotor phi ln hn nhiu so vi ng knh ca rotor my pht tuabin hi. Thng th ng knh ca rotor my pht tuabin nc ln hn nhiu so vi chiu di ca n, kt cu c dng bnh xe rng (hnh 3.3). Do ng knh ln, chiu di ngn, rotor ca my pht thu in thng c b tr cho trc quay thng ng, iu cho php tit kim c chiu cao ca my. i vi my c cng sut nh, tc quay nhanh, trc quay c b tr nm ngang. Vnh bnh xe c ni vi trc quay bi cc trc thp, mt ngoi gn cc cc t c cun dy.
C hai kt cu cho my pht thu in trc ng l kiu treo v kiu . i vi my pht kiu treo, chnh c b tr pha trn rotor, cn trong kiu - pha di. u im ca kiu treo l n nh, t chu nh hng tc ng ca cc phn ph, cn u im ca kiu l gim c kch thc theo chiu cao v do gim c kch thc chung ca my. Kiu thng p dng cho cc my c cng sut ln. My pht v tuabin nc thng c chung trc v , do chu lc dc trc ln ca ton b trng lng cc rotor cng nh lc hng trc ca dng nc. V th ca cc my pht tuabin nc phi c kt cu rt c bit.
My pht in thng dng 2 loi: Kiu trc ng v kiu trc ngang.
Kiu trc ng ph hp vi cc my pht in cng sut ln, trc ca r to my pht c phng vung gc vi mt t (hnh 3.3)
u im:
- Gian my khng yu cu c din tch mt bng ln.
- My pht in c t cao hn tua bin nn rt thun li trong vic gii quyt cao ca gian t my trn mc nc l.
- Hiu sut khai thc ct nc rt hiu qu.
- Khung ca stato c ch to thnh nhiu phn nn rt thun li cho vic thi cng lp t ph hp vi loi my pht in c cng sut ln, tc thp.
- Trc my khng c vng.
- Chiu di ca trc khng hn ch.
Nhc im:
- Gi thnh xy lp, ch to cao.
- Do khng t c bnh nn bnh ca my pht phi dng nh rto.
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- Trang b h thng bi trn kh phc tp.
- Khng thun li trong vic sa cha bo v dng nh k, trn gian my phi c trang b cu chuyn dng loi ln.
Kiu trc ngang cc my pht in cng sut nh, trc ca r to my pht c phng song song vi mt t (hnh 3.5)
3.2. CC THNG S C BN V H THNG KCH T
3.2.1 Cc thng s
My pht lc l mt ng c s cp (Tuc bin nc hoc hi) lm quay rto ca my pht
in vi tc n bng tc t trng quay n1: p
fn
.60 , trong p l s i cc ca my
pht in.
Khi thay i cng sut c M1 th tn s v cng sut tc dng pht ra ca my pht cng thay i theo.
Hnh 3.4 Hnh nh bn ngoi
my pht trc ng Hnh 3.5 Hnh nh bn ngoi
my pht trc ngang
Hnh 3.3 M t my pht in trc ng
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m nhn c s iu chnh ch yu i vi f v PF th my pht lc c hai yu cu chnh sau:
- c tnh tc quay: n = f(l).
c tnh tc phi nhy, phm vi iu chnh phi rng, v phi thay i c thch ng vi mi s thay i ca cng sut. Mun m bo c cc yu cu trn, cc my pht lc phi c b iu chnh tc tt, tc l iu chnh nhy v phm vi iu chnh rng. B iu tc lm nhim v thay i lng hi nc vo tuc bin gi cho tc quay ca my pht n nh.
- c tnh tc gc: = f(t).
Cc my pht lc yu cu phi c tr s tc gc u: = const.
s
rad
t.
hay
60
22 n
P
f
c trng cho n nh ca tc gc ta s dng mt h s gi l h s iu ho, k hiu i:
tb
i
minmax
trong : max- L tc gc cc i.
min- L tc gc cc tiu.
tb- L tc gc trung bnh.
Tr s i cng nh c tnh tc gc cng tt, d n nh cho tn s pht, to iu kin ho d dng.
H s iu ho i ph thuc vo kiu v c im ca my pht lc: My pht tuc bin hi, nc c i 0, my pht i den c i ln.
- Cng sut nh mc
Cng sut ca my pht in b gii hn bi nhit ca cc b phn trn my pht. Cng sut nh mc ca my pht in c quy nh theo cng sut biu kin S [kVA] vi cc iu kin tiu chun v in p, dng in, tn s. Cc tn tht st trn li thp v tn tht ng trn cun dy my pht c xc nh bi in tr v dng in ch khng quy nh theo cng sut tc dng.
- in p nh mc:
in p nh mc trn cc my pht quyt nh bi s cun dy ni tip ca cng mt pha v cng t thng ct qua cc cun dy stato. Nh vy mun c my pht c in p cao hn cn phi ch to s lng thanh dn nhiu hn, stato c nhiu rnh hn, iu ny ng ngha vi vic ch to mch t ca stato ln hn, cch in ca cc bi dy dn in phi tt hn v phi m bo c iu kin thng gi cho my pht. y l nguyn nhn lm cho gi thnh ch to ca my pht tng ln.
- H s cng sut ca my pht:
H s cng sut ca my pht in thng t 0,8 n 0,98. Khi cn tng cng kh nng truyn ti cng sut ln nht th my pht c ch to vi h s cng sut l 1,0.
- Tc quay nh mc:
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Tc quay nh mc ph thuc vo tc quay ca tuabin. Ngoi ra cn ph thuc vo s i cc ca my pht. Nu tc quay l n, s i cc l p, tn s ca h thng l f = 50Hz (60) th tc quay ng b l:
phtvngp
fn /
60
S i cc thay i ty theo cu to ca tng loi my pht, s i cc p thng l (1, 2, 3, 4, 5, 6, ). Tc quay ca cc my pht phi m bo t c tc ng b ca h thng in.
3.2.2 H thng kch t
H thng kch t (hay kch t) c nhim v cung cp dng in mt chiu cho cc cun dy kch t nhm gi in p khng i khi ph ti bin i v nng cao gii hn cng sut truyn ti t nh my in vo h thng m bo n nh tnh v n nh ng. Trong ch lm vic bnh thng b t ng iu chnh kch t (TK) s iu chnh in p trn u cc my pht, thay i lng cng sut phn khng ng thi nng cao n nh tnh v n nh ng ca h thng. Trong ch s c (ngn mch) ch c b phn kch t cng bc lm vic, n cho php duy tr in p ca li n nh. Hiu qu thc hin nhim v trn ph thuc vo c trng v thng s ca h thng kch t cng nh kt cu ca b phn TK.
m bo ch lm vic cht lng v tin cy, dng mt chiu cung cp cho cun dy kch t ca MP ng b phi ln. Thng thng i hi cng sut nh mc ca h thng kch t bng (0,20,6)% cng sut nh mc ca MP. Vic to ra h thng kch t c cng sut ln nh vy thng gp rt nhiu kh khn. l v cng sut ch to ca cc my pht in mt chiu b hn ch bi iu kin lm vic ca b phn i chiu. Khi cng sut ln, do tia la pht sinh mnh, nn b phn lm vic km tin cy v mau hng. Bi vy, i vi cc MP cng sut ln, thay v s dng h thng kch t mt chiu, ngi ta thng p dng h thng kch t dng MP xoay chiu kt hp vi b chnh lu. Ngoi cng sut nh mc v in p nh mc, h thng kch t cn c c trng bng hai thng s quan trng khc l in p kch t gii hn Ufgh v hng s thi gian Te.
in p kch t gii hn l in p kch t ln nht to ra dng in ca h thng kch t. in p ny cng ln th phm vi tc ng iu chnh dng kch t cng rng v cng c kh nng iu chnh nhanh. i vi MP tuabin hi thng c gi tr ln hn hoc bng in p nh mc my pht (Ufgh UnF), cn MP thu in th Ufgh 1,5UnF. Trong nhiu trng hp, p ng yu cu m bo n nh ca h thng ngi ta p dng in p gii hn ln hn (Ufgh=34)UnF . Tuy nhin Ufgh cng ln i hi cch in ca h thng kch t cng phi cao.
Hng s thi gian Te c trng cho tc thay i dng kch t, n c xc nh bi qun tnh in t ca cc cun dy in cm. Hng s thi gian c tr s cng nh th tc iu chnh kch t cng nhanh. Tnh tc ng nhanh ca h thng kch t c c trng bi tc tng in p kch t trong trng hp kch t cng bc:
1
632,0tU
UUv
nF
nFfgh (3.2)
trong : Ufgh - in p khch t gii hn;
UnF - in p nh mc;
t1 - thi gian tng in p kch t t tr s nh mc UnF n tr
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s UnF +0,632(Ufgh -UnF).
y chnh l tc trung bnh tng in p giai on u ca qu trnh kch t cng bc. a s cc trng hp c th coi in p kch t cng bc tng theo quy lut hm m:
Uf(t)= Ufgh - (Ufgh - UnF)e-t/Te, (3.3)
Cng thc (3.3) cho thy, tc tng in p kch t cng nhanh khi Ugh cng ln v hng s thi gian Te cng nh. Cc tham s ny ph thuc vo kt cu v nguyn l lm vic ca h thng kch t c th.
H thng kch t c th c ch to theo 3 loi sau:
- H thng kch t dng my pht in mt chiu;
- H thng kch t dng my pht in xoay chiu chnh lu;
- H thng kch t dng chnh lu c iu khin
1) H thng kch t dng my pht in mt chiu
quay MP mt chi ngi ta s dng nng lng ca chnh trc quay ca MP ng b. i khi cng c th s dng mt ng c in xoay chiu ring cho mc ch ny. ng c xoay chiu c cung cp t li in t dng ca nh my qua my bin p hoc t mt MP ng b ring ghp cng trc vi MP chnh nhng c cng sut nh.
Trng hp u c u im l n gin, tin cy , gi thnh h, tc quay n nh khng ph thuc vo in p ca li in t dng. Tuy nhin, c nhc im l khi cn sa cha my kch t nht thit khi ngng my pht in ng b, khng thay th c bng ngun kch t d phng. Ngoi ra, tc quay qu ln ca tuabin hi khng thch hp vi MP mt chiu, do phng php ny c s dng ch cc MP cng sut nh. i vi MP thu in, tc trc quay li qu nh cng hn ch cng sut ch to MP kch t. Nhc im ca phng n dng ng c in xoay chiu l vn hnh phc tp, gi thnh cao, chu nh hng ca vic thay i tn s v in p li nht l trong ch s c. V mt ny phng n cung cp cho ng c t my pht in xoay chiu, ni cng trc vi my pht in chnh, t ra c u im hn.
Nhc im chung ca h thng kch t dng MP mt chiu l hng s thi gian Te ln (0,3 0,6s) v gii hn iu chnh khng cao. Ngoi ra do c vnh gp v chi in,cng sut ch to b hn ch. V vy h thng kch t t loi ny thng ch c p dng cc MP nh v trung bnh.
2) H thng kch t my pht in xoay chiu v chnh lu
C hai loi chnh: dng my pht in xoay chiu tn s cao v dng my pht in xoay chiu khng vnh trt .
My pht in xoay chiu vi tn s cao c ch to theo kiu cm ng: rotor khng c cun dy, cun kch t cng t phn tnh. T thng thay i c nh vo kt cu thay rng rnh ca rotor. Cun kch t chnh ca MP kch t thng c ni trc tip vi ti ca n. Cc cun kch t ph c cung cp v iu chnh qua thit b TK vi nhn in nng t pha u cc ca MP ng b (qua cc my bin i p v dng BU v BI). Tn s ca dng in trong MP kch t tn s cao l 500Hz( khi quay cng trc vi MP ng b tuabin hi 3000vg/ph). Dng in ny c chnh lu ba pha bin i thnh dng in mt chiu.
Dng MP xoay chiu tn s cao, h thng kch t c th p dng cho cc MP ng b cng sut ln (200300) MW. Hn ch cng sut trong trng hp ny ch yu vn l do tn ti vnh trt v chi in cung cp dng in kch t cho rotor ca my pht in ng b.
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Hng s thi gian Te v in p kch t gii hn Ufgh trong trng hp ny gn nh h thng kch t dng MP mt chiu (Te ln, Ufgh nh).
tng cng sut kch t ln hn na ngi ta p dng h thng kch t khng vnh trt. Trong h thng kch t ny ngi ta dng MP xoay chiu ba pha quay ng trc vi MP chnh lm ngun cung cp. My pht xoay chiu c kt cu c bit: cun kch t t stator, cn cun dy ba pha li t rotor. Dng in xoay chiu ba pha to ra my pht kch t c chnh lu thnh dng in mt chiu nh b chnh lu cng sut ln cng gn ngay trn trc rotor ca cc my pht. Nh vy cun dy kch t ca MP chnh c th nhn ngay c dng in chnh lu khng qua vnh trt v chi in.
cung cp cho cun dy kch t ca my pht kch t ( t stato) ngi ta dng mt b chnh lu khc (thng l chnh lu c iu khin) m ngun cung cp ca n c th l MP xoay chiu tn s cao hoc ngun xoay chiu bt k khc. Ngoi u im c cng sut ln, hng s thi gian kch t Te ca h thng kch t loi ny cng qu nh (0,1 0,5)s, in p kch t gii hn ln hn.
3) H thng kch t dng chnh lu c iu khin
Vic p dng h thng kch t vi cc loi chnh lu c iu khin cng sut ln (cc chnh lu thu ngn c cc iu khin, cc b thyristor) cho php gim hng s thi gian Te. Ngun in xoay chiu ba pha cung cp cho cun dy kch t ca my pht ng b qua b chnh lu c iu khin l mt my pht in xoay chiu ba pha tn s (50 500)Hz, hoc my bin p t dng
Khc vi chnh lu bnh thng, trong chnh lu c iu khin, ngoi iu kin thun chiu ca in p trn chnh lu, cn i hi c mt tn hiu (dng in) xut hin trn cc iu khin mi c dng in chy qua. Tc iu chnh ca h thng kch t dng chnh lu c iu khin rt nhanh, c th coi nh tc ng tc thi vo in p kch t. Hng s thi gian ch cn khong (0,020,04)s Do u im ca h thng kch t ny , chng c p dng rng ri trong cc MP cng sut ln, c yu cu iu chnh cao.
Yu cu c bn i vi h thng kch thch l:
- C kh nng iu chnh dng kch thch trong gii hn cn thit.
- C kh nng tng cng kch thch trong ch s c ( v ln v tc tng kch thch). Khi c qu ti t nhin hoc ngn mch t nhin trn mng in m my ct cha kp tc ng lm cho in p u cc my pht gim rt thp. trnh gy ri lon cho h thng cn tng cng kch thch ln tht ln trong thi gian rt nhanh.
- Phi m bo dp tt t trng nhanh. Khi c ngn mch gia cc vng dy hoc gia cc pha th my pht c ct khi li ng thi phi dp tt t trng nhanh ca cun kch thch hn ch s ph hoi ca dng kch thch i vi dy qun stato.
- Phi m bo tin cy.
3.3. LM MT CHO MY PHT IN
3.3.1 Khi qut chung
Ph thuc vo cng sut s lm mt my pht in c thc hin vi mi cht l nc, du, khng kh hoc kh hydro. Cc my pht in cng sut nh thng c lm mt bng khng kh, cn cc my pht cng sut ln vic lm mt c thc hin bi mi cht l kh hydro. S thay th khng bng kh hydro cho php gim ma st v tng hiu sut ca my pht. Kh hydro c u im l c dn nhit cao gp 7 ln v tc nhn nhit gp gn 1,5
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ln so vi khng kh cng p sut, thm vo mt kh hydro thp hn nhiu nn gim c ma st v cng sut bm. Nhng nhc im ca kh hydro l c th gy n nu trong my c ln kh xy, do my c lm mt bng kh hydro cn c bn cao v cu trc c bit kn. tng cng hiu qu lm mt, mi cht c thi qua cc rnh c ch to sn trc, stator v rotor. Qu trnh lm mt c thc hin theo hai phng php: gin tip v trc tip.
3.3.2 Lm mt gin tip b mt
1)Lm mt b mt bng khng kh:
a) Lm mt gin tip c thc hin bng cch thi mi cht lm mt (khng kh hoc kh hydro) qua cc khe h gia stator v rotor v cc khe h c ch to vi mc ch lm mt. C th thc hin theo hai phng thc
1. Lm mt bng khng kh tun hon t nhin.
Cc cnh qut c gn vo hai u trc rotor, khi rotor quay s to thnh lung gi tun hon t nhin thi mt my theo hng trc hoc hng knh. Phng thc ny tuy n gin nhng c nhc im l hiu sut lm mt thp; Khng kh lm mt cn nhiu bi bn lm h hi cch in. Vi nhng nhc im nh vy phng thc ny ch c p dng cho cc loi my pht c cng sut nh mc di 3 MW.
2. Lm mt bng khng kh tun hon cng bc.
- Phng php lm mt thng dng nht l dng khng kh thi t nhin hoc bng qut gi thi khng kh tun hon cng bc qua b mt my pht. Khng kh dng lm mt my pht c ly t bn ngoi gian my thi qua my pht ri thi ra ngoi.
- Phng php lm mt bng kh thi cn c thc hin trong mt h thng bm tun hon v ng ng dn khng kh theo mt chu trnh kn kt hp vi b lc bi v h thng lm lnh bng dn phun nc. u im ca bin php ny l cun dy ca my pht t b bn, hiu sut cao, t chu tc ng ca nhit mi trng bn ngoi.
H thng lm mt bng khng kh thi tun hon cng bc c m t trn hnh 3.6
Khng kh c lu thng tun hon trong ng ng kn, t bung lnh lm sch khng kh s c nhit < 200 khng mang theo hi m vo my pht c cc qut gi ht v thi vo hai u my pht. Gi lnh sau khi i qua my pht s hp th nhit ca my pht tr thnh gi nng li quay v bung lnh lm sch. Bung lnh c dn ng kim loi khoan nhiu l nh, nc xi mnh ra qua dn ng c nhit 0 < 200 300. Sau khi c h nhit v c lc bi khng kh s quay tr li i vo hai u ca my pht. Phng php lm mt tun hon khng kh c hiu sut cao v c kh nng iu chnh c nhit lm mt.
Hnh 3.6 H thng lm mt bng khng kh thi tun hon cng bc
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Ngoi ra h thng lm mt khi cn cn c kh nng dp la cho my pht nu xy ra ha hon. Phng php ny c ng dng cho cc my pht c cng sut > 3MW.
2)Lm mt b mt bng kh H2
Lm mt b mt bng kh hyr H2 c thc hin ging nh lm mt bng khng kh tun hon cng bc. H2 c sn xut v duy tr vi tinh khit n 99,9%. Kh H2 thuc vo dng kh tr c kh nng cch in cao khng tc dng trc tip vi kh xy O2.
p sut 0,5at th:
- Mt ca hn hp kh H2 thp hn khong 8 ln so vi khng kh.
- H s truyn nhit t b mt lm mt ti H2 ln hn 1,35 ln so vi khng kh.
- dn nhit ln hn khong 5 ln so vi khng kh.
- H s dn nhit ca cch in tng ln c 1,3 ln.
Phng php lm mt bng kh H2 c nhiu u im vt tri so vi phng php lm mt bng khng kh:
- Tn hao ma st v tn hao thng gi ca rto ti kh lm mt gim i khong 8 ln, hiu sut lm mt tng ln rt nhiu.
Th d: cc my pht in c cng sut t 25 100MW khi lm mt bng khng kh, cc tn hao ny cng li khong 25 50% ca cc tn hao. Khi lm mt bng kh H2 th mc tn hao ny ch cn 3 6% ca cc tn hao.
- dn nhit ca kh H2 ln hn dn nhit ca khng kh rt nhiu to ra kh nng tn nhit nhanh ca cc phn t truyn nhit trong my pht. Nu duy tr c ch lm mt bng kh H2, gi n nh nhit cu my pht th c th nng c cng sut ca my pht ln 1,2 ln.
- H thng lm mt bng H2 ngn chn bi bn v hi m chui vo my pht nn chng c lo ha cho cc vt liu cch in trong my pht.
- Thit b lm mt bng H2 c kch thc nh gn.
- Kh H2 khng duy tr s chy.
Tuy vy phng php lm mt bng kh H2 cng cn mt s yu cu k thut c bit:
- sch ca kh H2 trong ng ng dn cn phi t trn 99,9%,
- Trong ng ng cn phi c p lc kh H2 nh nht l 0,035 0,05at. Nu khng c p lc kh H2 bn trong khng kh d xm nhp vo ng ng qua cc khe h ti cc m du hoc qua l thng khuyt tt ca ng ng a hi m vo trong cun dy my pht.
- Khi c kch n bng ngn la H2 s gy n to ra p lc ln. p lc tc dng khi xy ra n khng qu 3,5at do ng dn kh v v my pht cn c bn cao chu c p lc tnh ton n 6at.
- Phi trang b h thng sn xut v bnh kh nn d tr H2.
Tuy nhin vic lm mt b mt bng kh H2 cha gim s chnh lch nhit t cun dy ti kh lm mt. S tng p lc kh H2 ch yu gim nhit t b mt rnh nhng li khng gy c nh hng n s chnh lch nhit cn li. Bng cch tng p lc kh trn ng ng s gim c nhit trn cun dy v nng cao c cng sut cho my pht trong khi kch thc ca my pht vn gi nguyn. Nu p lc kh H2 trong h thng ng ng lm mt n 2at th cng sut gii hn c th t c n 200MW.
3.3.3 Lm mt trc tip
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Lm mt trc tip l phng php cho kh H2, gi, tun hon trc tip bn trong ng dy dn in hay i qua h thng ng ng dn c tip xc vi dy dn in. Phng php ny c hiu sut lm mt cao hn phng php lm mt b mt v lm gim c chnh lch nhit t cun dy n kh lm mt. Phng php ny thng p dng cho cc my pht in tua bin hi cho php gim c kch thc tc dng, nng cao c cng sut ti hn, nng cao c hiu qu kinh t do gim c gi thnh xy dng, tng hiu sut v gim c chi ph vn hnh. Nu m bo c ch tiu qu nhit tng t nh lm mt b mt th cho php tng cng sut gii hn n 2,4 ln. Nu tng p lc kh trong ng ng dn kh H2 lm mt th hiu qu lm mt cng tng ln
Nc ct tinh khit cng dng lm mt trc tip cho my pht. Lm mt bng nc t hiu qu cao hn so vi vic dng kh H2 rt nhiu nc c kh nng tn nhit tt hn. Lm mt trc tip bng nc ct tinh khit c ng dng trong nhng my pht in tua bin kh c cng sut ln v cc my pht in thy lc ln c tc thp (khong 500v/pht).
Hnh 3.7 m t h thng lm mt trc tip bng nc. Dy dn in stato lm bng ng ng rng c th dng lm ng dn nc c lin h vi ng dn nc lm mt bng mt on ng dn nc cch in bng silicn mm do. on ng dn nc cch in c hnh dng bn ngoi ging nh mt qu s xuyn nhiu tn, c chiu di dng r cho php 2,5cm/ 1kV. Nc tinh khit c chng ct v kh b cc thnh phn kim loi do khng dn in. Bung h nhit l mt h thng dn phun nc lm mt, nc trong ng sau khi i qua bung h nhit s tun hon tr li lm mt cho my pht nh mt my bm nc t trn ng ng. Cc u cc stato thng c in p t 6,6 kV n 21kV c u qua s trung gian bng thanh dn mm c lm bng cc l ng ghp li. ng dn nc lm mt c ni vo h thng tip a an ton c Rt 4. Vi nhng my pht in c cng sut nh th dy dn stato thng c tit din nh do khng ng dng phng php lm mt bng nc trc tip qua dy dn.
Hnh 3.8 gii thiu cc kiu lm mt cho my pht in trc ngang, c th tm tt nh sau:
Kiu lm mt bng gi t nhin: c u ht v u thi c t pha trong ca gian my, nhit bn trong gian my tng ln, pht ra ting n ln, phn bn ngoi my khng lp v nm cun dy d b nhim bn, din tch mt bng t my nh, ch c p dng cho cc my nh, gi thnh thp.
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Kiu thng gi bng ng li ra: ht bn trong v thi bn ngoi nhit bn trong khng tng, c ting n kh nh, y l loi trung gian gia loi m v loi ng hon ton cun dy cng d b nhim bn.
Kiu thng gi bng ng li ra v li vo: c u ht v u thi t bn ngoi nhit phn bn trong khng tng ting n nh cun dy v ng dn d b nhim bn phn bn ngoi ln nn c bao bc bng v chim din tch mt bng ln thng p dng cho cc my nh hn 20MVA gi thnh sn xut cao cn trang b chng rung
Kiu trao i nhit lm mt bng nc: khng kh c s dng li trong qu trnh lm mt vic lm mt khng b nh hng ngay c khi phn bn trong c nhit cao v khng kh m cao, ting n nh, cun dy v ng dn khng b nhim bn, phn bn ngoi ln v phc tp, chim din tch mt bng ln thng p dng cho cc my cng sut ln gi thnh sn xut cao.
3.4. KHI NG, HA NG B V NGNG MY PHT IN
3.4.1 Kim tra chun b trc khi khi ng my
- Thu hi cc phiu cng tc v gii tr cc bin php an ton my pht in v cc thit b lin quan n my pht in.
- Kim tra ton din cc thit b sau khi sa cha (i tiu tu, bao gm cc mch nht th v nh th), kim tra vnh trt rto, c gp my kch thch, p lc chi than phi tt, c gp, vnh trt phi sch s.
- Kim tra my pht in v cc thit b ph thuc phi sch s.
- Kim tra u dy nht th.
- Kim tra u dy ca my bin dng in, bin p o lng phi tt v sch s.
- Kim tra h thng lm mt v khng kh lm mt nh qut, ng ng, nhit nc lm mt v khng kh lm mt.
- Kim tra in tr cch in ca mch stato v mch rto.
Hnh 3.8 Lm mt cho my pht in trc ngang
Kiu lm mt bng gi t nhin
Kiu thng gi bng ng li ra
Kiu thng gi bng ng li ra v li vo
Kiu trao i nhit lm mt bng nc
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- Th tn hiu lin lc in v tuc bin v ngc li, th ng c iu tc phi ng chiu tng, gim tt.
- Th ng ct p t mt my kch thch, my ct my pht in, th lin ng gia my ct u cc my pht v p t mt mch kch thch.
3.4.2 Khi ng my pht
Trng ca nh my in, khi nhn c bo co ca trng kp in rng my pht in sn sng khi ng, s ra lnh khi ng my. Khi my pht in bt u nng tc quay ln n 100300 vng/pht th c my pht v mi thit b lin quan ca n u c coi l c in p. T lc ny nghim cm lm bt c vic g my tr nhng vic m quy phm an ton cho php.
1) iu kin khi ng my pht thy lc
Trc khi khi ng cn phi khng nh khng c vt l trong tt c cc khu vc my pht. Ch c php khi ng khi:
a. H thng phanh khng c p lc v cc guc phanh h xung.
b. Mc du trong cc thng v hng bnh thng.
c. Nhit du trong cc thng khng thp di 1000C.
d. C nc tun hon trong tt c cc b lm mt du v kh.
2) iu kin khi ng my pht nhit in
Khi tng tc vng quay ca my pht in th phi ch n vng quay ti hn 1500 vng/pht, lc ny c th xut hin s rung nguy him cho my. Cho nn cn thit phi vt qua tr s vng quay ny cng nhanh cng tt. Khi quay xung ng tuabin v tng vng quay ca n n tr s nh mc, nhn vin trc chnh cn phi theo di:
a. Xem c ting ku g c bit khng? khi thy my c hin tng khng bnh thng ni trn cn nhanh chng ngng my li sa cha khc phc.
b. S lm vic ca h thng bi trn, cc gi v cc du chn lu lng phi va , chnh p lc ca du, kh H2 trong my pht in phi trong gii hn 0,50,7kG/cm2 v phi c t ng duy tr do b iu chnh chnh p lc.
c. S lm vic ti u ca cc b lm mt kh, nhit ca nc u vo v ca H2 cn phi duy tr trong gii hn.
d. rung ca gi khng c ln hn 0,03mm.
e. Khng c s d r H2 t my pht ra.
Sau khi my pht t c tc quay nh mc v sau khi nhn c tn hiu sn sng ho vo li th cn phi iu chnh s khi v cc s cc my bin in p theo phng thc vn hnh quy nh. Tin hnh nng kch t nng cao in p my pht n tr s cho php ho in ri ho in theo qui trnh. a b t ng iu chnh in p (TA) vo lm vic. Tin hnh phn phi cng sut cho my. Tc tng ph ti hu cng phi t t v da vo iu kin vn hnh ca tuabin, tc tng ca ph ti v cng khng b hn ch.
C cu t ng iu chnh kch t (TCKT) phi lun lun trng thi sn sng. Khi ct dng in ngn mch, nu khng s dng cc bin php c bit th s phc hi t thng din ra s kh chm v c th dn n s mt ng b nu momen c ca ng c s cp ln hn mmen in t. Chc nng c bn ca c cu t ng iu chnh kch t l nhanh chng khi phc sut in ng ca my pht nhm tng mmen in t v to ra cng sut phn khng
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ngn chn s suy gim in p. Chnh v l m c cu TCKT cn phi lun c mc trong mng c th nhanh chng khc phc s c.
Vi mc ch nng cao tin cy ca nh my nhit in v duy tr qu trnh cng ngh sn xut in nng trong trng hp c cu kch t b ngng hot ng do s c, cc my pht lun c lp thm h thng kch t d phng. Nhim v ca c cu kch t d phng l thay th c cu kch t chnh khi cn thit, thng n ch c thit k lm vic tm thi, bi vy my pht ch c khi ng vi c cu kch t chnh.
3.4.3 Ho my pht vo li
Khi ng my pht vo lm vic song song vi mng in hoc vi cc my pht khc thng c th xut hin dng in cn bng c th gy h hng cho my, ng thi lm gim in p trong mng, lm tng tn tht. Bi vy qu trnh ho ng b my pht phi c thc hin sao cho nh hng ca dng in ny nh nht n mc c th, qu trnh din ra cng nhanh cng tt.
1) Phng php ho ng b
Trong thc t hin nay c hai phng php ho ng b c p dng l phng php ng b chnh xc v phng php t ng b.
a) Phng php ng b chnh xc
Theo phng php ny my pht c kch t v tng tc quay gn bng tc ng b. Thi im ng ng b vo mng c chn bi nhn vin vn hnh hoc do thit b t ng theo cc iu kin:
- Vn tc gc 1 ca my pht bng vn tc 2 ca h thng;
- in p ca my pht bng in p h thng;
- Th t cc pha trng nhau.
Nu cc iu kin trn tho mn th dng cn bng s khng xut hin. Tuy nhin vic thc hin chnh xc cc iu kin trn l rt kh khn, bi vy thng lc ng my pht vo h thng vn c dng cn bng xut hin.
b) Phng php t ng b
Trc ht ta cn ng vo mch rotor my pht mt in tr dp tt v chun b a c cu t ng iu chnh kch t vo lm vic. Trng hp khng c n th bin tr trong mch kch t c t ng vi v tr khng ti. Sau vi s tr gip ca ng c s cp, my pht c quay khng c kch t, khi tc quay t gi tr 9698% tc ng b, th ng my pht vo lm vic song song v lin sau l ng kch t. My pht t mnh ho vo ng b. S ng c th tin hnh trt 510%.
u im ca phng php t ng b l:
- Thao tc n gin;
- Qu trnh din ra t ng;
- Loi tr kh nng ng nhm;
- Qu trnh ng din ra rt nhanh (35 s) so vi phng php ng b chnh xc(510 pht).
2) Ho my pht vo li
Ho vo li in do trng kp tin hnh theo lnh ca trng ca v nng in p, ly ng b v ho vo li. Trc lc nng in p ca my pht trng kp in phi chun b s
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kch t theo qui trnh vn hnh cc my kch t lm vic d phng. Tc nng in p ca my pht in khng hn ch d l khi ng t trng thi lnh hay trng thi nng.
Cc Ampermt t stator dng kim tra sai st c th trong s in ca my pht in, trong qu trnh nng in p, nu c sai st (th d cc thit b ng vo my pht b chp mch), trong trng hp ny phi ct kch t v kim tra li s in ca my pht in. Ch s Ampermt ca rotor v kilovonmt ca stator khi my pht c kch t cn phi tng ln u n.
Nghim cm tng dng in ca rotor cao hn mc cho php trong khi my chy khng ti v tc quay ca tuabin tr s nh mc. Khi nng in p ca my pht in ln tr s nh mc, trng kp in cn phi kim tra:
+ S lm vic ca chi than.
+ Nhit ca nc lm mt v kh H2.
+ Tt c cc thit b u ni vo thanh ci ca my pht in.
+ Loi tr cc h hng trong h thng kch t, kim tra cch in ca mch kch t bng vn k kim tra.
Sau khi my pht c ho vo h thng, cn phi bo co cho trng ca bit my c ng vo lm vic song song vi li. Bng cch iu chnh kch t v iu chnh tc tuabin, xc lp ch cng sut tc dng v phn khng theo biu do trng ca quy nh, ph ti phn khng cn phi c tng theo ph ti tc dng. Trong trng hp s c, cn a b t ng iu chnh kch t (TK) v cng hnh kch t vo lm vic. Trong qu trnh ny cn phi theo di cht ch ch s ca cc ng h tc dng, khng cho php my pht in chuyn ch khi non kch t.
3.4.4 Theo di vn hnh
1) Ni dung ca cng tc theo di.
Khi my lm vic cn b qun l vn hnh phi thc hin cng vic sau:
- Theo di ch lm vic bnh thng ca my pht in. Ch lm vic bnh thng l ch m cc i lng c trng nh PF, QF, UF, cosF, fF v nhit kh lm mt lm u tr s nh mc theo qui chun vn hnh.
- c v theo di cc s ch ca cc ng h, cc s ch ca cc ng h phi tr s nh mc (vch ng h).
- Ghi chp s liu : c sau na gi phi theo di v c chnh xc cc ng h mt ln, sau mt gi phi ghi vo s nht k vn hnh mt ln.
- iu chnh v s l khi vn hnh: khi cc s ch ca cc ng h sai lch tr s bnh thng th phi tin hnh iu chnh v bo co vi trng ca. Phi iu chnh c kt qu duy tr cc tham s ca my pht nh U, I, f v lm tr s nh mc. Chng hn, x l in p thp nh sau: Lc vn hnh bnh thng ca my pht in phi duy tr in p trng thi nh mc v cho php bin trong phm vi 5%Um. Khi in p my pht b hn nh mc (5%Um) th phi lp tc iu chnh kch thch khi phc in p n phm vi qui nh sau bo co vi iu vin Trung ng. Nu iu chnh kch thch ht c trng thi nh mc m in p my pht vn thp th c th gim cng sut hu cng nng dn U ln. Khi h thng b s c in p gim thp, kch thch cng hnh tc ng, trong lc ny ta khng c iu chnh. Khi h thng n nh m mch kch thch cng hnh vn cn lm vic th ta ct ngay mch kch thch cng hnh ra v bo phn xng cho ngi kim tra s l. Dng bin tr iu chnh iu chnh in p.
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2) Nhn xt
Phn ny do trc chnh thc hin ghi vo s nht k vn hnh nhm nh gi v nhn xt v tnh trng lm vic ca my sau mt ca vn hnh, lm s liu theo di cho ca sau khi giao ca vn hnh.
Ni dung chnh :
- Ghi r rng, chnh xc ca ngi trc vn hnh v tnh trng lm vic ca my.
- Nhng cng vic chnh lm trong ca.
- Nhng lu v ngh.
- K tn, ghi r h tn, ngy thng, gi ghi nht k.
3.4.5 Ngng my pht in
Vic dng t my c th l do s c hoc theo quy trnh vn hnh (sa cha trung, i tu vv.) Vic dng bnh thng c tin hnh theo lnh ca ngi iu h thng hoc theo lnh ca k s trc. Dng s c c thc hin khi c hng hc hoc khi thit b bo v tc ng.
Trong iu kin vn hnh c th c trng hp s tho ti xy ra do cc nguyn nhn khng c lin quan g n t my hoc khi c, v d nh s c h hng mng in bn ngoi. my khng b ngt trong trng hp ny, cn phi c kho lin ng gi cho my pht lm vic ch khng ti, iu cho php ng li ti nhanh chng sau khi s c c khc phc.
Vic dng t my pht v l do bo dng nh k c thc hin theo k hoch nh trc. cc nh my nhit in qu trnh lm vic v dng cc t my phi c thc hin theo ch th ca h thng iu quc gia, vo ma kh do s gim cng sut pht cc nh my thu in, nh my nhit in phi lm vic y ti, v vy m hu nh tt c t my u a vo vn hnh, cn khi sang ma ma vic cung cp in li u tin nh my thu in, nn trong thi gian ny nh my nhit in c th dng mt s t my tin hnh cc cng vic sa cha trung v i tu. Lch sa cha i tu t my l 4 nm 1 ln v thi gian thc hin l 3 thng, cn sa cha trung tu th 2 nm 1 ln vi thi gian thc hin l 1 thng. Nh vy c 2 ln trung tu th s c mt ln i tu.
Trnh t ngng my pht in :
Sau khi nhn c lnh ca trng ca, trng kp in bo cho cc nhn vin trong kp bit v cc phn xng hu quan, ng thi phn cng vic chun b ngng my pht in. Qu trnh ngng my pht c tin hnh theo cc bc sau:
- T t chuyn hoc gim ph ti tc dng v phn khng ca my sp ngng v gn khng, ch gi cho cos phm vi quy nh. Tc gim ti ca my pht in theo yu cu ca tuabin.
- Ct b t ng iu chnh in p (theo quy trnh) dng bin tr iu chnh Rc iu chnh in p my pht UF.
- Ct my ct u cc my pht in.
- a Rc v tr s cc i, ct my ct kch thch.
- Pht tn hiu sang tuabin my pht ct.
Sau khi my pht in ngng hn phi tin hnh:
- o in tr cch in ca stator v rotorr my pht in v my kch t.
- p dng cc bin php an ton theo yu cu ca phiu cng tc.
- Nu ngng my v khng sa cha g th tin hnh sy my pht in sn sng vn hnh khi cn thit.
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3.5 CC CH LM VIC CA MY PHT IN
3.5.1 Ch lm vic bnh thng
Ch lm vic bnh thng ca my pht in (MF) l ch lm vic n nh, p ng c yu cu cng sut ca ph ti, duy tr c thi gian cung cp in lin tc vi tn s v in p u cc ca my pht t tr s nh mc cho php.
Ch lm vic nh mc l ch lm vic bnh thng ca my pht in, cc thng s k thut nh in p u cc UF, dng in IF, tn s fF, cng sut pht SF, h s cng sut cosF nm trong gii hn nh mc.
1) Biu vc t v c tnh cng sut ca my pht in
a) Biu vc t
Biu vc t my pht th hin trn hnh 3.9. V in tr ca MF qu nh so vi in khng ca n nn trn biu ch th hin in khng. Mt khc in khng c phn thnh dc xd v ngang xq theo roto, khi my pht cc n (MF tuc bin hi) xd = xq v my pht cc li (MF thy lc) th xd xq. Hnh 3.9a l biu vc t MF cc n, cn hnh 3.9b l biu MF cc li.
Cc k hiu trn biu vc t l nh sau :
xd, xq - in khng thnh phn dc v ngang ;
I - dng in stator ;
U - in p u cc MF ;
Eq - sut in ng MF ;
- gc lch gia sut in ng v in p ;
-gc lch gia U v I.
b)c tnh cng sut
Trc ht xt c tnh cng sut MF cc n.
Ti u mt vc t U, im C dng h ta vung gc xCy (hnh 3.9a). T u mt vc t
Eq, im A h ng vung gc AB xung trc y. Ta c cc gc DOCCAB do gc c
cnh tng ng vung gc ( ODACOCAB , ).
y
P x
A B U
Eq
C
I
jIxd
D
y A B
U
Eq
C
I
Ixq
Ixd
a) b)
Hnh 3.9 Biu vc t my pht in a) Cc n; b) Cc li
O O
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66
Trong dxIACABABC .cos: , cn trong sinsin: qEOAABAOB , suy ra
sin.sincos.sincos.. UExPUExUIExI qdqdqd . Vy ta c :
sin..
d
q
x
UEP (3.4a)
Cng trong ABC c sin.sin dxIACCB ;
Mt khc UEOCOBCB q cos ,
suy ra UUExQUUExIU qdqd .cos..cossin. . Vy ta c :
dd
q
x
U
x
UEQ
2
cos. (3.4b)
Cng thc (3.4a) v(3.4b) l c tnh cng sut tc dng v cg sut phn khng ca MF cc n.
c tnh cng sut MF cc li
Vic xy dng c tnh cng sut MF cc li c tin hnh tng t nh trn, kt qu c th hin bng cng thc (3.5a) v (3.5b) nh sau :
2sin.2
sin2
qd
qd
d
q
xx
xxU
x
UEP
(3.5a)
qd
qd
qd
qd
d
q
xx
xxU
xx
xxU
x
UEQ
.
22cos.
2cos
22
(3.5b)
Nu p trn cc MF thay i th chn mt nt trong h thng in c U=const, im cch cc MF mt in khng xng (hnh 3.10) th c tnh P,Q vn c dng nh nu trn ch c khc l xd c thay bng xd+xng v ),( UEf q i U l p ca nt cch cc MF mt in
khng xng.
c) S th hin P,Q trn th (xt hnh 3.9a)
Gi thit U = const, ta c U
xP
U
xUI
U
UxIAB ddd ..cos.cos.. ; Do const
U
xd nn
PAB , c ngha l trc ta Cx trn hnh 3.9a l trc cng sut tc dng P. Khi I = 0 th A v B tr v C, ng vi P = 0, vy C l gc ca trc P ( do U = const nn im O v C c nh, nn C c ly l gc). T ta c P l ng Cx v v P lun dng nn P ch nm v mt pha, t im A h vung gc xung Cx s xc nh c P.
Ta li c U
xQ
U
xUI
U
UxICB ddd ..sin.sin. . Do const
U
xd nn QCB , c ngha l trc
ta Cy trn hnh 3.9a l trc cng sut phn khng Q. Khi I = 0 th A v B tr v C, ng vi
U=const
xng
Hnh 3.10 S h thng in vi nt U=const
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67
Q = 0, vy C l gc ca trc Q ( do U = const nn im O v C c nh, nn C c ly l gc). T ta c Q l ng Cy, t im A h vung gc xung Cy s xc nh c Q. Gi tr Q c th dng v cng c th m, c th l :
- Vi ti cm khng th B trn C, ta c QCB >0, MF pht cng sut phn khng ;
- Vi ti dung khng th B di C, ta c QCB
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68
b) Ch Eq=var (c iu chnh kch t), P=const
V P = const, nn im A nm trn ng thng Ao-A-A*-Agh (hnh 3.11b).
- im Ao ng vi sut in ng c gi tr gii hn Eqgh, gc t gi tr min
UE
xP
qgh
d
.
.arcsinmin ;
- im A ng vi ch lm vic nh mc (cc thng s u t ga tr dm) ;
- im A* ng ch cng sut phn khng i du, chuyn t ch pht Q sang ch tiu th Q ;
- im Agh ng ch Eq t gi tr cc tiu, cng sut phn khng tiu th cc i, ta c :
o
d
dqq
x
UQQ
U
xPEE 90;;
. 2
maxmin
c) Ch khi tt c cc thng s thay i
Gi s trn hnh 3.9a cc thng s u c gi tr nh mc :
dmdmdmdmdmqdmqdm IISSQQPPEEUU coscos;;;;;;
Phn tch ch khi cc thng s u tha i (hnh 3.12)
Ly O lm tm v cung trn (1) bn knh qdmEOA .Min trong cung(1) l min lm vic cho
php theo pht nng cho php ca phn quay roto.
Hnh 3.12 Vng lm vic ca MF khi cc thng s thay i
y
P x
A B
Eq
C
I
D
O
(1)
(2)
(3)
E
F
H J
K
G
maxP minP
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69
Ly C lm tm v cung trn (2) bn knh dmSCA .Min trong cung(2) l min lm vic cho
php theo pht nng cho php ca ton b MF. Cng sut MF b hn ch bi s tng nhit ca chng. S tng nhit l do tn st t v tn tht trong cun dy. Tn tht st t l do c t thng khp mch qua li thp, m li thp c t tr v dng in xoy (dng fuc) lm cho nhit ca li thp tng ln.
Ni chung MF khng c qu ti v P, tc l phi vn hnh vi maxPP ,tc l min lm
vic b gii hn bi ng thng Pmax (pha phi ng thng Pmax). Vi MF cc n (MF tuc bin hi) th phi vn hnh vi minPP ,tc l min lm vic b gii hn bi ng thng Pmin
(pha tri ng thng Pmin).
MF c th lm vic vi U=0,95Udm , khi m bo pht c cng sut nh mc Sdm th dng in s l :
dm
dm
dm IU
SI 05,1
95,0.3
, c ngha l p gim 5% th dng c php tng ln 5%. th hin iu ny
ly O lm tm v cung trn (3) bn knh 0,95Udm.Min trn cung(3) l min lm vic cho php theo iu kin in p h thp.
Nh phn tch trn, vng lm vic ca MF c th hin trn hnh 3.12, l bn trong vng EFHKGJA. Vng lm vic ny c 3 vng nh, m mi vng c nhng c im c th nh sau :
- Vng trn EFA l vng c dmdm QQpP ; . Vng ny t s dng v khng tn dng c
pht cng sut tc dng P, c ngha l cng cng sut biu kin S, lung pht cng sut P khng nhiu.
- Vng gia FHJA l vng c dmdm QQPPP 0;min . Vng ny thng s dng v cho
pht cng sut P v Q hp l.
- Vng di HKGJ l vng c 0;min QPPP dm . Vng ny cng t dng v MF lm vic
khng n nh, Eq nh m li tiu th cng sut phn khng Q.
Tm li trong ch lm vic bnh thng MF nn iu chnh cc thng s im lm vic A trong vng FHJA.
Trong vn hnh cc thng s thay i, m bo im lm vic trong vng mong mun tt yu phi thc hin cc iu chnh nh b AVR (T ng iu chnh in p), b PSS (b n nh h thng in). Yu cu ca iu chnh l nh sau :
1.V in p :
- in p u cc gim th dng stato tng dn n tnh trng cun dy v mch t pht nng, lm suy gim cch in, ng thi lm nh hng n ph ti. Do vy cn khng ch mc mc h thp in p khng c di 0,95Udm.
- Nu in p tng cao U >1,065 Udm th t thng chnh trong li thp tng ln gy nng mch t lm nguy hi cho cch in ca cun dy v lm suy gim dn kh nng dn t ca li thp. Nu U >1,1Udm th cun dy my pht d b chc thng cch in, ph hng my pht. Khi in p tng cao qa nh mc s dn n h hng cc thit b in.
2. V tn s :
-Tn s f(Hz) ca my pht in l mt ch tiu quyt nh vic cho php my pht ha vo h thng in. Tn s c quy chun f = 50Hz trn ton b h thng in quc gia ( mt s
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70
nc tn s ly quy chun f = 60Hz). Cc my pht in hot ng khng cng tn s s khng cho php ha vo h thng in. Trong ch lm vic bnh thng tn s f = 50Hz hoc dao ng trong phm vi cho php:
fcf = 0,2Hz hoc fcf = 0,4% fm.
Nh vy trong ch lm vic bnh thng tn s ca my pht c php dao ng trong phm vi f = 49,8Hz n f = 50,2Hz.
- Nu tn s ca my pht tng vt qu gii hn cho php f > 50,2Hz th rto ca my pht v tuabin chy vt tc lm mn hng cc gi trc.Tn s tng ln dn n s lch pha in p ca my pht in v in p ca h thng in.
(UF, Uht) l gc lch pha in p ca my pht in v in p ca h thng in, cf l gc lch pha gii hn cho php. Nu (UF, Uht) > cf th my pht in s ri vo tnh trng mt n nh.
3. V h s cos:
Trong ch lm vic bnh thng h s cos c quy nh nm trong mt gii hn m bo ch tiu vn hnh kinh t nht cho MF (cosdm=0,8 0,95)
- Khi cosF < cosdm, cng sut tc dng pht ra gim i, sin tng ln, cng sut phn khng tng ln, dng in phn khng tng ln lm cho phn ng kh t tng ln dn n in p u cc gim i. Mun gi n nh in p phi tng dng in kch t ln hn dng kch t nh mc: Ikt > Iktdm. Nhng khi dng in kch t tng ln qu nh mc s li gy ra pht nng cho cun dy rto.
- Khi cosF > cosdm: cosF tng th cng sut phn khng) gim i, dng in phn khng Ipk gim i lm cho phn ng kh t gim dn n in p u cc tng ln. Mun gi n nh in p phi gim dng in kch t. Khi gim dng kch t th nhit ca my pht gim i, cng sut tc dng pht ra ca my pht s c php tng ln. Nu nh PF > PFdm th ng c s cp ca my pht in li ri vo tnh trng qu ti, bt li cho my pht. Khi ha vo li in quc gia nu cosF > 0,95 th my pht s pht huy ti a cng sut, hiu sut lm vic ca my pht c tng ln nhng my pht s hot ng mt n nh.
3.5.2 c tnh in p ca MF
Xt c tnh in p ca MF khi chng vn hnh trong ch khng ti, ch ngn mch duy tr, ch mang ti nh mc.
1) ng cong bo ha khng ti
ng cong bo ha khng ti OM trn hnh 3.13 m t quan h ca in p trn cc u cc MF v dng in kch thch. Khi MF chy khng ti vi tc quay ca r to l nh mc v c dng in kch thch If tng dn ln t tr s khng, in p u cc tng ln theo. Khi in p vng c tr s thp th Uo v If c quan h gn nh tuyn tnh, cn khi bo ha ng c tnh OM gn nh i ngang, in p Uo khng tng mc d If tip tc tng .
th hin mc bo ha trong MF, ngi ta a ra mt khi nim gi l h s bo ha kbh m vic xc nh n c tin hnh nh sau (hnh 3.13):
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71
- Trn ng cong OM ly im c tng ng vi in p U = 1,2 Um, dng sang ngang ct trc tung ti im b. - T O k ng tip tuyn vi ng OM ct ng thng cb ti c. - Tnh h s bo ha bng biu thc:
'
'
bc
cckbh
2)ng cong ngn mch 3 pha
Dng ngn mch 3 pha c th hin trn hnh 3.14. Dng ngn mch 3 pha ny xy ra khi MF c tc quay ca r to l nh mc, 3 u cc cun dy phn ng c ni tt (ni ngn mch), dng in kch thch tng dn t tr s 0. Ta gi y l dng ngn mch duy tr hoc ngn mch lu di. Dng in ngn mch 3 pha ph thuc vo tng tr ca cun dy phn ng. Do cun dy phn ng c in tr nh hn nhiu in khng nn dng in ngn mch ti thi im ny l dng in t tr vi h s cng sut cos 0. Phn ng phn ng c tc dng kh t, lc ny t thng tn ti rt nh v vy ng cong ngn mch coi nh c dng tuyn tnh, khng bo ha.
3)T s ngn mch v tng tr ng b
a) T s ngn mch
T s ngn mch Ks l mt trong cc hng s c trng ca my in ng b.
Hnh 3.15 biu din 3 ng cong c tnh: ng cong bo ha khng ti M, ng cong ngn mch 3 pha S, ng cong tng tr ng b k. Vi tc ca MF l nh mc ta c dng in kch thch If (on od) tng ng vi in p nh mc khng ti Uo (on cd), v dng in If (on oe) tng ng vi dng in lm vic lu di IS (on fd), dng in nh mc Idm (on ge),.
Hnh 3.14 Th nghim c tnh ngn mch 3 pha a) S th nghim ngn mch 3 pha b) ng cong ngn mch 3 pha
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72
T s ngn mch c xc nh nh sau:
dmf
f
I
Is
ge
fd
I
I
Oe
OdKs
''
'
T y ta c: Is = Ks . Idm
trong : Is l dng in ngn mch lu di.
Idm l dng in nh mc.
Ks l t s ngn mch.
Trong trng hp sc in ng khng ti bng in p nh mc khng ti Udm v MF in b ngn mch 3 pha th dng in ngn mch lu di Is bng Ks ln dng in nh mc Idm.
Gi tr t s ngn mch i vi cc loi MF l:
- Vi my pht in tua bin nc Ks = 0,9 1,2
- Vi cc my in khc Ks = 0,6 1,0
b) Tng tr ng b ZS
Zs c tnh bng t s ca sc in ng cm ng mt pha Eo v dng in ngn mch Is
vi cng mt dng in kch thch Is
EoZs
Trn hnh 3.15 ng cong tng tr ng b jhk cho thy Zs khng phi l hng s m thay i ph thuc vo tnh trng bo ha ca mch t theo dng in kch thch If . Vi cc MF ni chung tng tr ng b thng c tnh bng t s gia in p pha nh mc (vi s u dy ca phn ng my pht u hnh Y). Dng in ngn mch 3 pha Is tng ng vi dng in kch thch yu cu cm ng ra Edm
dhdf
dc
Is
EZs
UoE dmdm
3;3
Trong h n v tng i th tng tr ngn mch c tnh : Ks
Zs1
Tng tr ng b bng nghch o ca h s ngn mch. Nu nhn vi 100 th c gi l tng tr ng b phn trm.
Hnh 3.15 ng cong bo ha khng ti, ng cong ngn mch 3 pha, ng cong tng tr ng b v t s ngn mch
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73
c)Mi quan h gia t s ngn mch vi cc thng s khc
Theo biu thc nu trn, nu t s ngn mch Ks nh th tng tr ng b Zs ln dn n phn ng phn ng ln ng ngha vi cc khe h t nh. Ch to MF vi phng thc ny s tit kim c vt liu ng v st. Ngc li nu my pht in c Ks ln th khi ch to s tn km vt liu hn nhng b li my pht s c kh nng d phng ln, iu chnh in p tt hn v c kh nng chu qu ti tt hn ph hp cho cc ng dy truyn ti in cng sut ln v c khong cch chuyn ti xa. Trong trng hp cn n yu cu iu chnh in p tt, cn c kh nng truyn ti ln cho ng dy th dng my pht loi ny, t s ngn mch Ks thng ln : Ks = 1,5 1,8.
Vi my pht in c Ks nh, c sc in ng ln theo dng in phn ng s c gi tn l my in ng. Vi my pht in c Ks ln, c t thng ln, x dng nhiu vt liu st s c gi tn l my in st.
4) ng cong bo ha ti
Trong vn hnh MF in chu nh hng ca h s cng sut ti. Nu ln lt thay i cc loi ti c h s cng sut khc nhau, gi vn tc ca my pht khng i, thay i dng in kch thch nu h s cos ca ti cng thp, tr cng ln th in p ca my pht cng kh tng ln. Nguyn nhn l do dng in chy vo phn ng cng ln th s kh t do tc ng dc trc cng tng ln, t thng nm gip ranh khu vc khe h t c khuynh hng b kh.
Khi my pht mang ti c h s cng sut khng i, vn tc khng i v dng in khng i ta c ng cong bo ha ti, l ng cong biu din mi quan h gia in p u cc v dng in kch thch. Nu cng vi h s cng sut khng i nhng dng in ph ti l nh mc th ng cong bo ha ti c gi l ng cong bo ha ti l tng. Trong vn hnh my pht thng xuyn cn phi thay i h s cng sut, ng cong bo ha ti s cho dng in kch thch cn thit duy tr c in p nh mc. Hnh 3.16 th hin ng cong bo ha ph thuc vo dng kch t v h s cos
5) ng cong c tnh ngoi
ng cong c tnh ngoi biu th quan h gia in p u cc my pht vi dng in ph ti khi h s cos thay i trong qu trnh vn hnh. Dng in kch thch c xc nh duy tr in p nh mc trn MF khi chng lm vic tc nh mc, dng in nh mc vi mt h s cng sut nht nh. Trn hnh 3.17 biu din ng cong c tnh ngoi ca my pht gm 3 ng cong in hnh vi h s cng sut cos = 1,0, h s cng sut tr (mang c tnh in cm) h s cng sut sm (mang c tnh in dung).
Hnh 3.16 ng cong bo ha ti N l ng cong bo ha khng ti. Lb l ng cong bo ha ti vi h
s cng sut cos = 1. Lc l ng cong bo ha ti vi h
s cng sut cos = 0,8. Lc l ng cong bo ha ti vi h
s cng sut cos = 0.
Hnh 3.17 ng cong c tnh ngoi ng 1: ng vi trng hp h s cng sut tr (cm khng), dng in ph ti tng in p u cc gim. ng 2: ng vi trng hp h s cng sut bng 1,0 (tr), dng in ph ti tng in p u cc gim. ng 3: ng vi trng hp h s cng sut sm (dung khng), dng in ph ti tng in p u cc tng.
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74
3.5.3 Ch lm vic khng bnh thng
Ch lm vic khng bnh thng l ch lm vic mt n nh ca my pht in, khng p ng c yu cu cng sut ca ph ti, khng duy tr c thi gian cung cp in lin tc vi tn s v in p t nh mc cho php.
Ch lm vic khng bnh thng hay xy ra trong mt khong thi gian ngn. Nu tnh trng khng bnh thng c nguy c ph hng my pht th phi cho ngng hot ng my pht.
Ngy nay cc my pht in c trang b cc thit b t ng c kh nng kim sot tnh trng hot ng ca my pht thng qua cc thit b o lng, tn hiu. Trong : H thng iu khin t ng c kh nng duy tr n nh in p, tn s; H thng rle t ng ct in khi c s c: ngn mch, chm t mt pha trong cun dy stato hoc chm t mch in kch thch, mt ng b khi gim dng in kch thch hoc mt in cun dy kch thch my pht.
Sau y ta im qua mt s ch khng bnh thng ca my pht.
1) Ch qu ti my pht
Ch qu ti l dng in xoay chiu i qua cun dy stato hay dng in mt chiu i qua cun dy r to tng ln qu tr s nh mc
Khi b qu dng, dn n:
- Qu dng lm cho nhit my pht tng ln cao qu mc quy nh lm gi ci cch in ca my pht.
- Sinh lc gia cc vng dy, lm cho chng chng b hng.
C hai trng thi qu ti:
- Qu ti bnh thng xy ra khi my pht b tng cao cng sut trong khi h thng vn hnh bnh thng. Trong vn hnh bnh thng khng cho php qu ti.
- Qu ti s c xy ra khi c mt trong cc t my pht t xut phi tch ra khi li. Cc my pht cn li phi duy tr vic cung cp in cho ph ti ca h thng dn n qu ti ta gi l qu ti s c.
Mt s quy nh v qu ti cho php nh sau:
-Theo quy nh ca nh ch to, my pht trong tnh trng s c cho php qu ti ngn hn theo dng in stato l 50% trong 2 pht. Trong tt c cc ch hot ng bt thng ca my pht, qu ti ngn hn cho php theo dng stato vi bi s ca dng in so vi tr s nh mc ca dng in stato nhng phi tng ng vi cc tr s quy nh ca tng nh my pht in, ng thi s ln qu ti ngn hn khng c nhiu hn hai ln trong mt nm.
- My pht khi c cng hnh kch thch cho php tng gp i dng kch thch nh mc trong khong thi gian 50s. Cng hnh kch thch l trng thi chp tt cc vng dy ca cun dy kch thch rto tng tc thi dng in kch thch nhm chng suy gim in p u cc my pht khi dng in stato tng t bin. Thi gian qu ti ngn hn cho php cn c quy nh theo bi s qu ti ca dng in dng in kch thch so vi dng in nh mc.
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75
tham kho trn bng 3.1, bng 3.2 gii thiu qu ti cho php ngn hn ca hai nh my thy in ca Vit nam.
Bng 31 Qu ti ngn hn cho php theo dng stato
Bi s qu ti 2,0 1,5 1,4 1,3 1,3 1,1
Thi gian qa ti (pht)
Nh my in Tr An 2 3 4 6 60
Nh my in Ha Bnh 50s 2 3 4 6 60
Bng 3.2 Thi gian qu ti ngn hn cho php theo dng in kch thch
Nh my in Tr An
Bi s qu ti 1,4 1,25 1,2 1,15 1,10 Thi gian qu ti 2 3 4 6 60
Nh my in Ha Bnh
Bi s qu ti 2,0 1,5 Thi gian qu ti 50s 2 3 4 6,50 Lu
di
2) Ch vn hnh khng i xng (KX)
Ch vn hnh khng i xng l ch p v dng in ba pha khng cn bng nhau: hoc m un khc nhau hoc gc lch cc pha khng cn l 1200 na hoc c ha .
Nguyn nhn ca KX l:
- do chnh ti KX: ti mt pha hay bn thn ti 3 pha KX;
- do ng dy di khng hon v hoc hon v khng hon ton. Trn thc t i vi ng dy di c khong sau vi trm km th cc pha phi c hon v: pha A thnh B, B thnh C v C thnh A;
- s dng mt s ch lm vic c bit nh ch lm vic khng ton pha, ch ng dy ch lm vic trn 2 hoc 1 pha, ch 2 pha t;
- do ngn mch KX:*** Trn cc pha xut hin dng in th t thun I1 v th t nghch I2. Dng in I2 cm ng trn cun dy sta to t thng nghch 2 c vn tc quay nhanh gp 2 ln tc ng b, t thng 2 li cm ng trn cun dy rto v trn mch t rto mt dng in I2 c tn s f2 = 100Hz, gp i tn s f1 = 50Hz. Dng in I2 gy ra tn hao ph lm cho thn rto v cun dy rto b pht nng cc b. Ngoi ra tc dng tng h ca dng in I2 v t thng 2 l sinh ra m men cn M2 c chiu ngc vi chiu ca m men ng b M1 gy rung ng my pht in.
Trong vn hnh bnh thng cng c lc xy ra s mt i xng khng phi do s c gy ra, gii hn mt i xng cho php c quy nh theo s chnh lch ca dng in gia cc pha ca stato vi dng in nh mc.
Khi my pht mang ti nh mc: Vi my pht in tua b hi dng in chnh lch trong mt pha khng qu 10% so vi dng in nh mc my pht ImF. Vi my pht in tua b nc dng in chnh lch trong mt pha khng qu 20% so vi dng in nh mc my pht ImF so vi dng in nh mc.
Khi my pht mang ti nh hn nh mc: Mc mt i xng cho php ln hn quy nh trn nhng mc lch dng in phi c xc nh bng thc nghim. Theo bn nhit ca r to, cc my pht ch cho php c hot ng ngn hn trong cc ch khng i xng trong mt khong thi gian. Thi gian cho php hot ng ngn hn trong cc ch
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76
i xng s c quy nh khc nhau cho tng cc nh my pht in, c th tham kho bng
3.6. Thi gian cho php c tnh nh sau: sI 40%.t2
Trong : I2% l dng in th t nghch tnh theo phn trm (%) ca dng in nh mc stato Is, t l thi gian khng i xng tnh bng giy.
Bng 3.6 Thi gian cho php hot ng ngn hn trong cc ch khng i xng
Tr An
I2% 0,1 0,5 1,0 2,0 3,0
t(sec) 4000 160 40 10 4,4
Ha Bnh
I2% 1,0 1,5 2,0 3,0 4,0
t(sec) 40 18 10 4 2
Khi li in xy ra s c chm t mt pha gy ra mt i xng ta gi l mt i xng do s c: Vi li in Ud = 110kV trung tnh ni t khi xy ra chm t mt pha dng in chm t rt ln c gi l dng in ngn mch mt pha, quy nh khng cho php vn hnh, phi ct in tch my pht ra khi li. Vi li in Ud 35kV trung tnh cch in khi xy ra chm t mt pha dng in chm t rt nh, quy nh cho php duy tr vn hnh vi thi gin cho php: Khng qu 1 gi vi mng in c in p Ud = 10,5 35kV, khng qu 2 gi vi mng in c in p Ud = 6,3kV nhng nu dng in chm t mt pha I(1)N ln hn 5A th phi ct in tch my pht ra khi li.
3.3 Ch khng ng b
Trong h thng in cc my pht in s hot ng bnh thng ch ng b. Trng hp xy ra mt ng b l khi in p v tn s ca my pht no b dao ng khng ph hp vi h thng. Nguyn nhn mt ng b l do dng in kch thch t nhin gim hoc b mt kch thch, do ngn mch ni b my pht in, do s c trong h thng tua bin v mt vi nguyn nhn khc.
Ch khng ng b xy ra ngay c khi bt u ha ng b my pht in vo li in. Yu cu khi ha ng b my pht l phi c cng tn s, cng in p, cng th t pha. Khi h thng t ng ha ng b hot ng sai th my pht in khng ha c vi h thng, nu h thng relais chng ha sai lm vic khng tt s dn n tnh trng mt ng b ngay ti thi im ha.
Khi xy ra mt ng b dng in stato ca my pht t nhin tng ln rt ln, in p h thng b dao ng, my pht in c ting r mnh, cc ng h b dao ng mnh ngay lp tc h thng relais bo v khi ng i ct my pht ra khi h thng.
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3.6. CC DNG S C V THAO TC LOI TR S C MY PHT IN
Ch khc l ch lm vic ca my pht khng bnh thng do s c gy ra. Khi c xy ra th cn phi pht hin kp thi, tm nguyn nhn v x l xong mi cho my pht tip tc hot ng.
1. Khi nhit my pht tng qu tr s cho php
My pht in ang lm vic bnh thng, cng sut nm trong nh mc th pht hin thy:
- Nhit k ch nhit ca cun dy stato v rto tng.
- Nhit k ch nhit ca mch t tng cao.
- Nhit k ch nhit h thng lm mt vt qu 300C.
Nguyn nhn do cng sut ti tng t bin, do ng thng gi hot ng km hiu qu, do c h hng h thng bm nc tun hon lm mtcn phi kim tra tm ra nguyn nhn, nu khng pht hin ra v gii quyt c phi cho ngng hot ng my pht.
2. Khi c chm t 1 pha cun dy stato
Thng thng my pht in u Y cun dy stato, trung im 3 cun dy c ni t, cc my pht u c trang b relais bo v chm t. Khi xy ra chm t relais bo v chm t s khi ng i ct in my pht. Nu bo v relais khng tc ng phi gim ti ngay v tch my pht ra khi li.
3. Khi c chm t 1 pha cun dy rto
My pht vn hnh n nh c hay khng l do iu chnh dc dng in kch thch duy tr in p u cc my pht t nh mc cho php. Cun dy kch thch hoc mch in kch thch b chm t s t bin thay i dng in kch thch, chnh v vy khng cho php chm t trong mch kch thch, phi gim ti ngay v tch my pht ra khi li.
4. Khi c ngn mch u cc my pht in
Ngn mch u cc l trng thi nguy him nht i vi my pht in v:
Xut hin lc in ng tc dng ln cun dy phn ng lm x lch cun dy.
Gy ra qu nhit ph hng cch in my pht.
Mi pha ca my pht c th chu c dng in ngn mch duy tr Is khi dng in kch thch If tng dn (t 0 Ifcf ), dng in Is chy qua phn ng, mi quan h ca If v Is
l tuyn tnh nh biu thc sau: If
EoIs
Khi ngn mch th dng in i qua cun dy my pht b tng t bin sau vi giy ri mi gim dn n tr s dng in ngn mch duy tr. Ti thi im xy ra ngn mch ch c in khng r phn ng cn tr dng in ngn mch. Sau mt thi gian dng in qu mi gim ti tr s dng in ngn mch duy tr, n c xc nh theo in khng ng b Zs. (hnh 3.20)
c tuyn trn hnh 3.20 c thnh phn mt chiu IDC gim dn theo hng s thi gian Ta. Thnh phn dng in xoay chiu IAC t tr s ln nht khi ngn mch, sau dng in ny gim dn v chuyn sang trng thi ngn mch duy tr c c tuyn hnh sin v c bin khng i. Dng in mt chiu sinh ra trong qu trnh qu xy ra ngn mch. Khi ngn mch dng in phn ng tng ln gy ra s gim t thng ca dng in khch thch v dn n gim rt nhanh in p ca my pht. V t thng sinh ra trn cun cn c chiu ngc
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78
chiu t thng chnh nn hn ch c s suy gim t thng chnh, do trong thi gian qu t 9 n 10 chu k u tin in p vn c duy tr.
Thi gian qu c tnh t thi im c ngn mch n thi im c dng in mt chiu gim bng khng. Qu trnh qu ny ko di t 9 n 10 chu k u tin, mi chu k l 0,02sec.
Thi gian siu qu c tnh trong 3 chu k u tin, dng in ngn mch siu qu tng t bin c th n 40 ln dng in nh mc. Trong khong thi gian siu qu lc in ng tng rt ln c th b cong trc, lm bung cc bi dy stato my pht
Sau 0,2 sec tng ng vi 9 n 10 chu k u tin l thi gian ngn mch duy tr, dng in ngn mch duy tr c th tng ln t 7 n 10 ln dng in nh mc. Trong thi gian ngn mch duy tr nhit ca my pht in b tng ln qa gii hn cho php gy ph hng cch in.
Do thi gian ngn mch qu rt ngn nn cc trang b bo v r le v my ct in khng kp tc ng, chnh v vy phi tnh ton chnh nh relay bo v theo dng in ngn mch duy tr.
5. My pht in b mt kch thch
Hnh 3.20 c tuyn dng in ngn mch ca my pht
Hnh 3.21 c tuyn ngn mch xoay chiu duy tr
Hnh 3.22 S nguyn l mch
kch thch ca my pht in
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79
Mt kch thch l tnh trng h hng mch kch thch dn n mt in cun dy kch thch (hnh 2.22).
Nguyn nhn:
Do t mch cun dy kch thch,
Do chm t cun dy kch thch ti hai im lm cho cun dy kch thch b ni tt hon ton,
Do h hng my pht in kch thch (do t mch cun dy kch thch ca my pht in kch thch thch, chi than ca in tr iu chnh tip xc km)
Trong trng hp h hng mch kch thch tua bin ca my pht in vn quay cp cng sut c M1, my pht khng pht ra in m li nhn in p t h thng. Lc ny h thng in li cung cp cho my pht in mt lng cng sut v cng QF lm cho in p ca h thng b suy gim. Ngoi ra h thng in cn phi cung cp cho my pht mt dng in kch thch ph trn cun dy kch thch my pht pht ra cng sut tc dng PF lm cho dng in trn stato b tng ln.
Loi tr trng hp mt kch thch do t mch cun dy kch thch CKF, cc trng hp cn li cun dy kch thch vn l mt mch kn trong khi rto vn quay vi vn tc n lm cho cng sut PF b gim t ngt v m men cn in t b gim t ngt so vi m men s cp MCt < M1 dn n tc ca rto b tng ln, my pht xut hin h s trt s, lc ny
my pht ri vo trng thi khng ng b.n
nnS
1
Khi ri vo tnh trng khng ng b s xut hin m men cn in t khng ng b Mckb lm cho tc ca rto li gim xung, lc ny s ch trn cc ng h o in p, o dng in, o tn s, o cng sut b dao ng, my pht in c hin tng chn ng.
Nu my ct kch thch MCKT nhy m my ct u cc my pht cha nhy v in p kch thch vn bnh thng th lp tc ng in tr li MCKT nng in p kch thch ln. Nu in p kch thch bnh thng m dng in trn mch kch thch bng khng th chc chn mch kch thch rto b t, cn thay th my kch thch chnh bng mt my kch thch d phng. Trong mi iu kin khng cho php my pht lm vic trong ch mt kch thich.
6. My pht tr thnh ng c in
My pht ang vn hnh ch bnh thng t nhin chuyn sang ch ng c, lc ny m men quay trn trc my pht khng cn na dn n tnh trng cng sut c truyn t h thng tua bin sang trc my pht b mt, my pht chuyn thnh ng c in. Khi my pht s nhn mt cng sut PF t h thng in dng thng lc ma st trn trc my pht v ko tua bin quay. Lc ny ng h o cng sut hu cng ch tr s m, ng h o cng sut v cng ch tng ln, in p v tn s gim xung, c tn hiu chung v n bo sp van chnh hoc bo s c tua bin my nguy him. Rto ca my pht in vn quay vi vn tc n = n1, dng in kch thch trong rto vn tn ti nn my pht s pht ra cng sut v cng QF ln li in.
Thc t cho thy: PF < PF ; QF > QF Gp trng hp ny khng cn thit dng ngay my pht m phi tm cch phc hi li hi
tua bin, nhanh chng a hi vo tua bin my pht tr li trng thi bnh thng sau iu chnh nng cng sut hu cng ca my pht ln, iu chnh in p v tn s v tr s quy nh. Nu khng gi li c van hi chnh ca tua bin v khng c cch no khc phc c th mi tch my pht ra khi li in.
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80
7. Khng nng c in p my pht
Khi khi ng my pht u tin phi nng dn tc ca rto ln dn n tr s nh mc, sau iu chnh dng in kch thch bng bin tr iu chnh nng dn in p my pht nhng c khi in p khng nng ln c.
Trng hp ny xy ra khi:
Mch u dy ca my kch thch b u ngc cc tnh.
My pht c th b mt t d cn phi np li t d.
Tip xc ca chi than khng tt do lc p ca l so chi than km.
C gp vnh trt b bn gy ra tip xc khng tt.
Mch u dy cha tt hoc qun cha u ni.
3.7. CNG TC KIM TRA, TH NGHIM, BO DNG MY PHT IN
1. Mc ch v ngha
a, Mc ch
Qua s liu th nghim ta nh gi c cht lng k thut ca qu trnh ch to cng nh qu trnh sa cha i vi mi my in
Qua s liu th nghim ta nh gi c kh nng lm vic ca my tt hay xu sau mt thi gian vn hnh.
b, ngha
Qua th nghim m ta pht hin v loi tr c phn ln nhng h hng cng nh tnh trng khng bnh thng ca my, do m ko di c tui th cho my
Nng cao c kh nng lm vic an ton v lin tc cho thit b.
Nng cao c tnh lin tc cung cp in v gim nh c s ngng cung cp in do h hng gy ra.
2. Cc hnh thc th nghim- nghim thu
a, Hnh thc th nghim xut xng ( OTK )
Hnh thc ny c tin hnh sau khi ch to xong i vi mi my in, n c tin hnh vi y cc ni dung v hng mc . Nh c th nghim xut xng m lp c l lch ca my da trn c s cc s liu v c tnh th nghim. y l hnh thc th nghim y nht, quan trng nht, do nh my ch to thc hin.
b, Hnh thc th nghim nh k
Hnh thc ny c tin hnh nh k theo thi gian k t khi a my vo vn hnh. Hnh thc ny nhm kim tra nh gi cht lng k thut ca my sau mt thi gian vn hnh. Hnh thc ny do b phn th nghim ca c quan qun l thc hin.
c, Hnh thc th nghim sa cha
Hnh thc ny nhm nh gi cht lng sa cha, ng thi hiu chnh li s liu c thay i trong l lch ca my. Hnh thc ny c tin hnh sau khi sa cha xong, hoc c th tin hnh song song vi qu trnh sa cha tng b phn
3- Cc ni dung th nghim my pht in
Xt vi hnh thc th nghim xut xng
- o in tr tc dng, in khng pha ca cun dy stato my pht in.
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81
- o in tr cch in cun dy.
- Lp cc ng c tnh khng ti, ngn mch 3 pha, ph ti 3 pha i xng.
Trn c s cc s liu v c tnh k thut, tin hnh lp h s l lch my v nh gi cht lng xut xng.
4. Xc nh in tr tc dng, in khng pha my pht in
a. S th nghim
in p ngun U1 = 220V hoc 380V
in p th cp U2 = 12 - 60V.
Nu khng c bin p BA th c th dng ngay in p li.
Cc thng s mch Rto ta khng xt.
b. Cch xc nh in tr, in khng pha ca cun dy stato
Cn c vo cc s liu o c ta xc nh c cc tham s nh sau:
Tng tr cc pha: AB
ABA
I
UZ
2 ;
BC
BCB
I
UZ
2 ;
AC
ACC
I
UZ
2
in tr cc pha: 22 AB
ABA
I
PR ;
22 BC
BCB
I
PR ;
22 AC
ACC
I
PR
in khng cc pha: 22 AAA RZX ; 22BBB RZX ;
22CCc RZX
Gi tr trung bnh: 3
CBAtb
ZZZZ
( )
3
CBAtb
RRRR
( )
3
CBAtb
XXXX
( )
5. o in tr cun dy my pht in
in tr cch in ch yu ca my pht in ng bl cch in gia cun dy stato v cun dy roto vi t ( mch t ).
o in tr ngi ta dng Mgmmt, k hiu nh sau:
MG Trong M v G l cc cc o.
M G
V W A U2
BI
A
Sta
to
B
C
U1~
BA
Hnh 324
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82
a. o in tr cch in cun dy Stato:
Dng M gm mt -2500V
Cc cun dy pha c ni tt hai u vi nhau nh hnh 3.25. Pha cn o, u ni tt c u vo cc M ca M gm mt, cn cc G ca M gm mt u vo v ca stato. Quay M gm mt vi tc quay nh mc ri c tr s sau 60 giy. Cc pha khc cng tin hnh tng t.
b. o in tr cch in cun Rto
Cun rto cng c ni tt, u ni tt c u vo cc M ca M gm mt, cn cc G ca m gm mt u vo trc ca rto nh hnh 3-26. Quay M gm mt vi tc quay nh mc ri c tr s sau 60 giy.
c. Bng tiu chun in tr cch in
Cc hng mc th nghim
in p MG (V) Tr s Rc qui nh (M )
Cun dy stato in p n 1000v.
2500
0.5 khi nhit o t 10-300C
Cun dy rto in p n 1000v.
1000 hoc 500
2000 khi o 750c 2000 khi o 200c
Mch kch thch my pht v nhng thit b ph thuc mch kch thch.
1000 hoc 500
1000
Cun kch thch ca my pht kch thch.
1000
0.5 khi nhit o t 10-300c
Gi trc my pht pha my kch thch.
1000
0.3 vi my pht Thu 1.0 vi my pht Nhit
6. Xc nh k hiu u dy v th t pha ca cun dy stato my pht in
a. Xc nh k hiu u dy ca cun dy stato my pht in
Sau khi gia cng ch to hoc xa cha xong b dy stato ca my pht in (MF) cn phi kim tra xc nh li k hiu cc u dy ra ca n. Nu xc nh k hiu u dy khng ng dn n u nhm cc u dy v th t pha, kt qu l nu a my pht vo vn hnh gy nn s c mt i xng ca h thng sc in ng, in p v dng in p 3 pha( mt i xng c v tr s bin ln gc pha). C hai phng php xc nh k hiu u dy, l phng php dng dng in mt chiu v phng php dng dng in xoay chiu.
M G
Hnh 325
B
C A
Trc
M G
Vnh gp
CKF
Hnh 326
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83
- Phng php xc nh k hiu u dy bng dng in mt chiu
Ni ngun mt chiu vo mt cun dy thng qua cng tc K nh hnh 3-27, in k mt chiu ni vo mt trong hai cun dy cn li. nh du u cun dy ni vi cc(+) ca in k ( v d: C3 ), nh du u ni vi cc(-) ca in k (v d: C03 ). ng cng tc K, trong qu trnh qu ca t thng bin thin kim ca in k b lch i mt gc, ta ghi nh chiu quay ca kim in k.
Chuyn in k sang cun dy cn li v cng nh du vi cc dng (v d: C2 ), u ni vi cc m ca in k( v d:C02 ). Ln ny cng vy ng ng tc K, trong qu trnh qu ca t thng bin thin kim ca in k cng lch i mt gc. Nu chiu quay ca kim in k ln sau trng vi chiu quay ln trc th cc u ni vi cc dong ca in k c cng cc tnh ( C2 ,C3 cng cc tnh-tc cng l u u hoc u cui).Cn nu chiu quay ca kim in k ngc vi ln trc th C2 v C3 khc cc tnh.
Chuyn ngun mt chiu sang cun dy pha khc v thc hin kim tra tng t nh trn ta s xc nh c cc u cng cc tnh ca cun dy.
- Phng php xc nh k hiu u dy bng dng in xoay chiu
- Th ln 1; Gi s xc nh c 1, 2 cng pha 3, 4 cng pha v 5, 6 cng pha. Ni mch th nh hnh 3.26a vn mt thang o 6V hoc 10V. t ngun mt chiu in p thp (khong 20 - 30%Um ca ng c) vo hai u dy 1, 4 ri quan st vn mt. Nu kim ca in k khng ln hoc ch nhch ra khi v tr 0 mt t th cc u dy 2 v 3 cng cc tnh (cng l u hoc cng l cui ). Nu kim in k ca vn mt ch vi vn th 2 v 3 khc cc tnh (mt u l u mt u l cui). Gi s ln ny kim in k ca vn mt ch vi vn ngha l 2 v 3 khc cc tnh.
Th ln 2: Ni mch th nh hnh 3.26b. Gi s ln th ny kim ca vn mt khng ln, ngha l 4, 5 cng cc tnh.
Qua cc ln th ta xc nh c 1, 3, 6 cng cc tnh v 2, 4, 6 cng cc tnh.
b. Xc nh th t pha
Vic xc nh th t pha ca my pht in ng b c ngha c bit quan trng khi cc my pht lm vic song song vi nhau. V vy vi mi my pht cn phi xc nh chnh xc th t pha khi th nghim.
C02 C01 C03
K C2 C1 C3
+
E
+
+ G -
Hnh 327; E=12 60V ; G l in k mt chiu.
V
2
1 3
4 6
5
110V
Hnh 3.26a
V V
1
2
3
4 6
5
110
Hnh 3.26b
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- Phng php xc nh th t pha theo mu sn
Khi gia cng ch to b dy ca my pht in ngi ta thc hin nh du cc thanh dn v rnh thuc mi pha theo mu sn theo qui nh ca Quc gia: Mu vng ch pha A, mu xanh ch pha B, mu ch pha C. Nh vy cun dy cn mu sn th vic xc nh pha hon ton n gin. Nu nh mt mu sn ta c th xc nh th t pha theo phng php khc.
- Phng php xc nh th t pha bng t trng ca dng in mt chiu
Hnh 327. Xc nh th t pha bng dng in mt chiu
a ngun in mt chiu vo cun dy rto thng qua chi than, cc u cui ca cun dy stato u li vi nhau. ng cng tc K trong cun dy rto sinh ra t trng, t trng ny c gi tr ln c th cm ng ra trong cc cun dy stato nhng sc in ng cm ng. Ko rto quay vi tc 15003000 vng/pht, khi trong cun dy stato s sinh ra sc in ng cm ng do t trng ca cun rto cm ng sang, kt qu l cc kim in k b lch khi v tr 0. Khi trc t ca rto trng vi trc ca cun dy no th kim in k ni vo pha quay phi (s... cm ng pha c cc tnh m), cn cc kim in k khc quay tri (s... cm ng pha c cc tnh dng).
Theo nh hnh v trn, khi trc t ca rto trng vi trc ca cun dy mt pha - coi l pha C- th kim in k ni vo pha C lch v bn phi (pha C c cc tnh m), cn cc kim in k khc lch nhau v bn tri ( cc pha khc c cc tnh dng ).
Khi rto quay c 1200 ri 2400 ta cng c cc kt qu nh trn (Xem hnh 328).
Kt qu th nghim ta lp thnh bng, nu bng lun tun theo bng sau th cho php ta xc nh pha ng ca my pht in.
CK
G + -
G + -
G + -
C1
C2 + C3 +
E +
nr
C01
C02 C03
K
C
B A
-
+ +
nr
C
B A
+
- +
+
B A
+
+ -
Khi gc lch bng 0o Khi gc lch bng120o Khi gc lch bng 240o
Hnh 3.28. V tr cc cc t Rto so vi trc cun dy stato.
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85
Gc thay i ca Rto so vi trc ca cun dy stato
Pha
in A B C 0 + - - 120 - + + 240 + - +
7. Th nghim khng ti v ngn mch my pht in
a. S th nghim
.
Hnh 329 S th nghim c tnh khng ti Hnh 330 S th nghim c tnh ngn mch
MCF
A
A
MF
ARRc
CK
M
A
A
Rdc
CKkt
MF
DCL1 MCdc DCL2
cc
MFkkt
V
V
V
b. Mc ch v trnh t th nghim Th nghim khng ti l lp mi
quan h bng ng c tnh gia in p stato v dng kch t roto khi my pht lm vic khng ti: E0=f(Ikt), trn c s ta xc nh c cc tham s khng ti ca my pht in nh Emax v Ed.
Trnh t th nghim: - M CL1, ng CL2, nng tc quay
ca roto ti nh mc: n = nm - iu chnh Rc tng dn dng kch t
Ikt t gi tr 0 n gi tr nh mc Iktm. Khi dng kch t tng th dng kch t ca my pht E0 cng tng, ng vi mi gi tr ca Ikt ta v c ng c tnh c dng nh ng s 1 trn hnh v 329. Ti im A, khi Ikt = Iktm ta xc nh c Emax bin cc i. Thng th Emax= (1,3 1,5)UmF. - iu chnh gim dn ikt t gi tr Iktm v 0, ng vi mi gi tr ca Ikt ta c gi tr ca E0. Qu trnh iu chnh Ikt ta v c ng c tnh s 2 trn hnh v.
Th nghim ngn mch l lp mi quan h bng ng c tnh gia dng ngn mch 3 pha stato vi dng kch t rto: INS = f(Ikt) trn c s ta xc nh cc tham s ngn mch ca my pht in nh IktN (dng kch t ng vi dng ngn mch stato bng nh mc: INS = ImS ). So snh c tnh xy dng c vi c tnh cho ca nh my ch to, nu c s sai khc th tm nguyn nhn ca s sai khc v khc phc. Qu trnh th nghim 3 pha A, B, C c ni tt (ni tt u cc MCF). trnh MCF ct th ta phi ct ngun iu khin a vo cun ct ca my ct. Trnh t th nghim: - M my ct u cc my pht, nng tc quay rto n 10001500 vng/pht, a ton b kch t vo mch rto (Ikt = Iktm), cho my pht chy khng ti trong thi gian 1-2 ting ng h. Trong thi gian ta tin hnh kim tra s phn phi dng in trong mch stato v mch kch thch, sau gim Ikt v v tr 0.
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c. Xc nh Xq v Xd
Cn phi xc nh in khng ng b dc trc xd v in khng ng b ngang trc xq ca my pht in ch vn hnh.
xc nh xd v xq ca my pht in ng b c th da vo c tnh khng ti v c tnh ngn mch ba pha. Cch xc nh nh sau:
Trn cng mt h trc to , ta v ng c tnh khng ti E0 = f(Ikt) ng 1 trn hnh 3-31, v ng c tnh ngn mch INS = f(Ikt)- ng 2, v ng thng tip tuyn vi ng c tnh khng ti k t gc to (gi l ng c tnh gii hn)- ng s 3
T ng c tnh s 1 v 2 ta thy, ng vi mi sc in ng ca stato c hai gi tr ca dng kch t, nguyn nhn ca s sai lch ny l do tn hao trong mch t gy ra (do t tr) Th nghim c tin hnh khng qu 5 pht.
- ng MCF c ni tt, tng t t dng kch t kim tra c dng stato ca my pht. Vic tng Ikt phi m bo sao cho dng ngn mch stato INS khng vt qu dng nh mc ImS. - Nng tc quay ca rto ti tr s nh mc ri tin hnh ly c tnh ngn mch ba pha. Nh bin tr iu chnh Rc ta c gi tr ca INS. Ly 4-5 cp tr s ri tin hnh v c tnh. c tnh ngn mch l mt ng c thng i qua gc to (hnh 330). Tr s gii hn ca INS l ImS, ng vi tr s ta c IktN.
ng c tnh xy dng c phi ging nh ng c tnh cho ca nh my ch to. Nu thp hn chng t cun CKF hoc cun CKkt b ni tt mt s vng.
Sau khi ly c tnh xong ngng my pht theo trnh t sau: Ct my ct u cc my pht MCF, gim kch t hon ton ri ngng quay rto.
Ch : lp c ng c tnh ngn mch 3 pha, qu trnh th nghim nhiu khi phi dng kch thch ngoi hoc kch thch hn hp (thit b com pun) c c cc tr s mong mun.
B
Ikt
IktN
Ims
INS B
0
E0 EMax
Ed
0 I ktm Ikt
1
2
A
ng c tnh khng ti MF
ng c tnh ngn mch MF
T mt gi tr bt k ca Ikt (gi s ti im C) ta k mt ng thng song song vi trc tung ct ng c tnh ngn mch ti E v ct ng kch t ti hn ti F. Ta
c: EC
FCxd .
im F trn ng kch t ti hn xc nh s.. dc trc Ed , tng ng vi dng ngn mch ba pha xc nh bi EC khi c cng mt gi tr ca dng kch t OC. in khng ng b ngang trc c xc nh theo xd : xq = xd khi my pht in l cc n (MF tuc bin hi). xq = 0.6 xd khi my pht in l cc li (MF tuc bin nc).
Emax
B
1
E0 INS
IdmS
0 C IktN Iktdm Ikt
3 A
K
E 2
F
Hnh331. Xc nh Xq v Xd
-
87
3.7. SY MY PHT IN
1. Nguyn tc chung
Theo quy trnh vn hnh my in, cc my pht in v my b ng b in p di 15 kV c th ng vo mng khng cn sy nu tho mn 3 iu kin sau :
- in tr cch in ca cc cun dy stator (quy v nhit 750C) sau 60s k t khi cp in p khng thp hn gi tr R60, xc nh theo biu thc
n
n
P
UR
01,0100060
, M ;
Trong
Un v Pn in p v cng sut nh mc ca my pht, (V) v (kW);
- H s hp ph khng khp nh hn 1,2; "15
"60
R
Rkhp
R15- in tr tng ng 15 giy k t khi cp in p.
- H s phi tuyn (t s gia in tr cch in ng vi in p chnh lu 0,5Un trn in tr cch in ng vi in p chnh lu 2,5Un) khng ln hn 1,3.
Ngoi cc trng hp trn, tt c cc my in khi a vo vn hnh t trng thi d phng hoc sau sa cha i tu, cn phi c kim tra cch in v sy. Qu trnh sy my in c th c thc hin theo cc phng php: t sy, tn tht trong li thp ca stator, phng php t nng bng dng in mt chiu hoc phng php t nng bng dng ngn mch 3 pha (i vi my pht thu in). Cc loi my in cng sut ln thng c sy bng phng php tn tht trong li thp v phng php dng in mt chiu, phng php dng in ngn mch 3 pha thng c p dng trong iu kin vn hnh, khi cch in b m khng nhiu.
Vic ui khng kh m ra khi my trong qu trnh sy c th thc hin vi s tr gip ca cc my qut. Nhit cc i trong qu trnh cn c iu chnh trong phm vi gn gii hn nhit cho php ng vi loi cch in s dng trong cc cun dy, nhn chung khng thp hn 800C. Tc tng nhit khng qu 50C/gi.
u tin gi tr in gim do s mm ho cch in, sau s tng dn n gi tr xc lp. Trong qu trnh sy cn tin hnh kim tra in tr cch in R60 khong 2 gi mt ln, i vi my ln kim tra 2-3 ln mi ngy. Qu trnh sy s kt thc nu in tr cch in khng thay i trong vng 5 gi ng vi nhit xc lp.
2. Phng php dng t sy
My pht c t trong l hoc t sy,pha di l c ca dn kh vo, pha trn l gc i din c ca thot kh ra (hnh 3.32). Thnh l sy c lm bng vt liu chu la nh kim loi hoc xi mng aming. Nhit nng cung cp cho t sy c th l hi nc hoc dng in. Kh nng trong t c lu thng vi s tr gip ca cc my qut.
Nhit trong t c th kim tra bng nhit k hoc thit b o t xa. Nhit ca khng kh nng ca vo phi c kim tra thng xuyn khng c qu 900C. Sau mi gi phi o in tr cch in mt ln. Phng php sy ny c u im l n gin v tin cy nhng tiu tn nhiu nng lng v thi gian sy di.
3. Sy bng dng in
Qu trnh sy bng dng in c thc hin bng cch cp cho cun dy dng in p thp,khi chy trong cun dy dng in sinh ra mt lng nhit lm tng nhit v sy cun
-
88
dy. Theo phng php ny in nng tiu th s khng nhiu do s t nng trc tip cun dy lm hi nc thot ra mnh. Nhit t nng c th thay i bng cch iu chnh cng dng in trong cun dy. Nu dng dng in mt chiu th ch cun dy c in c t nng, cn nu dng dng in xoay chiu th nhit nng s c to ra tt c cc cun dy c mch khp kn. S mch in sy my in c th hin trn hnh 3.33.
Qu trnh sy my pht bng dng ngn mch 3 pha c thc hin khi my ang quay vi tc nh mc. Dng in sy c ly t ngun khc, cc cun dy ca rotor c ni ngn mch. S iu chnh nhit c thc hin bng cch iu chnh cng dng in kch t, tng dn n gi tr cn thit. in tr ca cun dy stator khi sy bng phng php dng in khng c nh hn 0,05 M, cn in tr ca cun dy rotor khng nh hn 2 M. Dng in sy c th ly bng 1,5In nu sy trong khong thi gian 1 gi v bng dng nh mc nu sy trong vng 2 gi.
4. Sy bng phng php cm ng
a. Phng php tn tht trong li thp ca stator
Phng php ny s dng ngun nhit to ra bi dng in xoy trong li thp ca stator. S sy c th hin trn hnh 3.34. Cun dy sy, cn gi l cun t ho, c lng trong rnh stator, khi c cp ngun, mt t thng s sinh ra dng in xoy t nng li thp. Thng thng qu trnh sy c thc hin khng c rotor, bi v s c mt ca rotor s gy cn tr cho vic lp t cun dy t ho v gy phc tp cho qu trnh sy v c sau mi 30 pht li phi quay rotor i 1800 trnh s un rotor. Trc khi sy cn phi kim tra cn thn v nu c vt th kim loi nm trong rnh stator th s dn n ngn mch v lm hng li thp. Do cun dy t ho lm vic trong mi trng nhit cao nn ph ti ch ly bng 60% gii hn cho php ng vi tit din dy dn la chn.
Hnh 3.34. S sy my pht theo phng php tn tht trong li thp stator 1 cun dy sy; 2 stator my pht
2
1
V A W
U
Hnh 3.33. S sy bng dng
in
1 my bin p hn;
2 cun khng in;
3 stator my in sy
2
3
V
A
1
C1 C2 C3
C4 C5 C6
Kh nng
Hnh 3.32 Sy my in bng l
-
89
S vng ca cun dy t ho c tnh theo cng thc sau:
BS
U
.
.45 vng, trong :
U in p t vo cun dy t ho (V)
S tit din gng t li thp stato (cm2)
S = l1.hg1.
l1 chiu di ca gng (cm).
hg1 - chiu cao ca gng t (cm).
B cm ng t trong li thp stator, tesla (T)
b. Phng php tn tht trong v my
Phng php sy cm ng c th thc hin bng cch qun trn v my mt s vng dy v cp cho n ngun in xoay chiu in p thp (hnh 3.35). Lc ny v ca my in c chc nng nh cun dy th cp c ni ngn mch ca my bin p kh (cun s cp chnh l cc vng dy qun quanh v). V ca my s c nung nng bi dng in cm ng sinh ra trong n. tng cng s i lu khng kh, my in khi sy nn trng thi quay.
Sut in ng ca cun dy t ho xc nh theo biu thc :E = keU
Trong
U in p cp cho cun dy t ho, V;
ke h s tnh n ri in p trong cun dy, c th ly gi tr trong bng 7.2 sau
Bng 3.7. Gi tr cc h s ph thuc vo vt liu lm v my
H s v bng gang v nhm khng v
ke 0,7 0,8 0,8 0,9 1,1 1,15
cos 0,2 0,4 0,1 0,2 0,1 0,2
(Gi tr ln c ly ng vi my c cng sut cao)
S vng dy cn thit ca cun t ho :ca FB
E
222
10. 8
Trong
Ba- gi tr thc t ca cm ng t :s
ak
BB
ks h s t tn c gi tr trong khong 1,151,3 (gi tr ln ng vi cng sut nh).
B cm ng t c gi tr 1200020000 (gi tr ln ng vi my cng sut thp) ;
Fc din tch mch t : Fc = kc(L-b.n)ha
kc h s lp y li thp;
L chiu di dc trc ca stator, cm ;
b b rng ca rnh thot kh , cm ;
n s lng rnh ;
ha chiu cao hiu dng ca stator, cm ;
rtrn
a hDD
h
2
A
CD
Hnh 3.35 S sy my pht theo phng php tn tht trong v my
-
90
Dn, Dtr - ng knh ngoi v ng knh trong ca li thp sattor, cm ;
hr chiu cao rng stator, cm.
Lc t ho
F = H.ltb
Cng t trng H c xc nh theo biu hnh 3.36 hoc tra bng 3.8 ph thuc vo gi tr ca cm ng t Ba
ltb chiu di trung bnh ca ng sc : ltb = (Dn-ha)
Dng t ho ca cun dy :F
I , A
Cng sut t ho : S = U.I.10-3, kVA ; P = S.cos, kW
H s cos c gi tr trong khong 0,20,4 (bng 3.7)
Tit din dy dn t ho : j
IF , mm2
j mt dng in (A/mm2) ly gi tr trong khong 3,55 i vi dy ng v 23 i vi dy nhm.
Bng 3.8. Cng t trng H ph thuc vo Ba, (A/cm)
Ba, Tesla 0 100 200 300 400 500 600 700 800 900 12000 8,43 8,66 8,91 9,18 9,46 9,76 10,1 10,4 10,7 11 13000 11,4 11,8 12,2 12,6 13,0 13,4 13,8 14,3 14,8 15,3 14000 15,8 16,4 17,1 17,8 18,6 19,5 20,5 21,5 22,6 23,8 15000 25,0 26,4 27,9 29,5 31,1 32,8 34,6 36,6 38,8 41,2 16000 43,7 46,3 49,1 52,2 55,3 58,8 62,3 66,0 69,8 73,3 17000 77,6 82,0 86,3 90,7 96,3 101 106 111 116 122 18000 128 134 142 146 152 159 166 173 180 188 19000 197 206 216 226 236 246 256 268 282 296
v d B=13000 th H=11,4; B=13100 th H=11,8 ; B=13200 th H=12,2 vv.
Hnh 3.36. ng cong ph thuc ca cng t trng H =f(Ba)
0
50
100
150
200
250
300
12000 13000 14000 15000 16000 17000 18000 19000
B, Tesla
H, A/cm
