- YJ =P2 =P1 LP= 1_LP =P
Can chuy rang khi dieu chTnh c6ng suat tac dt,mg P, do thay dBi nen c6ng suat
phan khang cung thay dBi theo.
b. TrU'c»ng hQ'p may phat di~n cong sucit tU'O'ng ti! lam vi~c song song.
Gia thll' c6 hai may phat di$n c6ng suat bang nhau lam Vi$C song song. 0 tmang hqp nay, trong dieu ki$n tai cua IU'6'i di$n kh6ng dBi, khi tang c6ng tac d1.,mg cua mot may ma kh6ng giam tU'ang Crng c6ng suat tac dt,mg cua may kia th1 tan so cua ll1'6'i di$n se thay dBi cho den khi c6 Sl,I' can bang m&i vakhien cho ho dung di~n phai lam Vi$C trong dieu ki~n tan so khac djnh mLPc. V1 Vf}.y, d§ giCI' cho f = canst khi tang c6ng suat tac dt,mg cua mot may th1 phai giam c6ng suat tac dt,mg cua may kia. Chfnh cung bang each d6 ma c6 th§ thay dBi Sl,I' phan phoi c6ng suat
tac dt,mg giCl'a hai may.
4.4.2.2. Oi~u chinh cong sucit phan khang cua may phat di~n d6ng bQ. khang cua may phat di~n d6ng bQ.
Ta hay xet Vi$C dieu chTnh c6ng suat phan khang cua may phat di$n d6ng bo lam vi$C trang IU'&i di~n v6 cung l&n (U, f = canst) khi c6ng suat tac dt,mg cua
may dU'Q'C giCI' khong dBi. 1
Gia thll' may c6 Cl,l'C an va d~ dO'n __,...._-t---\+-,--t-----::r---- ·/
gian, bo qua tBn hao tren day quan phan
2 I
LPng (r U'=O). Trang trU'ang hqp d6, d6 thi vecta s(,pc di$n dong c6 d9ng nhU' tren
hinh (4.11).
suat phan khang cua may phat di$n d6ng bo.
B 0
Hinh 4. 11 f)i§u chlnh c6ng su§t phan
V1 P= mUlcoscp = OA la kh6ng dBi, khang cua may phat ai~n a6ng b{).
va v&i dieu ki$n U= canst nen khi thay dBi Q, mut cua vecta I luon nam tren
dU'ang thang 1, thang g6c v&i U. V&i moi tri so cua I se c6 mot tri so cua coscp va ve d6 thi vectO' SU'C di$n dong tU'O'ng LPng se xac djnh dU'Q'C do 16'n cua vec ta E, tU' d6 suy ra dU'Q'C dong di$n khfch thfch it can thiet d§ sinh ra E cung can chu y rang
P = mEUsin~::::: P1 = const
Xd
Trang d6 U, xd kh6ng dBi nen va mut cua vecta E lu6n nam tren dU'ang thang 2 thang g6c v&i OB.
Ket qua phan tfch cho thay rang, muon dieu chTnh c6ng suat phan khang Q th1 phai thay dBi dong di$n khfch thfch it cua may phat di$n.
V&i moi tri s6 cua P = canst, thay dBi o va ve d6 thi vectO' SU'C di$n dong nhU' tren ta xac dinh dU'Q'C quan h$ gQi la d$c tfnh h1nh V cua may phat di$n d6ng bo. Thay dBi cac tri s6 cua P v&i phU'ang phap tren se thanh 12).p dU'Q'C mot hQ cac d$c tfnh h1nh V nhU' tren
hinh 4.12. Tren h1nh, dU'ang Am di qua cac di~m cl,l'c ti§u cua hQ d~c tfnh h1nh V tU'ang LPng v&i khi coscp =1. Khu Vl,l'C ben phai cua dU'ang Am (,png v&i tai c6 tf nh cam cp >O va che do lam Vi$C qua kfch thfch cua may phat di$n khu Vl,l'C 6' ben trai cua dU'ang d6 LPng v&i tai c6 tfnh dung (cp <O) va che dQ lam Vi$C thieu kfch thfch cua may. 8U'ang Bn LPng v&i gi&i hl;in am Vi$C Bn dinh v&i IU'6'i khi may phat di$n lam Vi$C 6' che do thieu kfch thfch.
a tren ta xet df>i VO'I may phat di$n Cl)'C ~n, nhLmg t§t ca nhCrng phan tfch do deu ap dt,mg dU'Q'C cho may phat di$n Cl)'C loi.
Trong trLI'ang hqp cong su§t cua ILI'&i di$n nho (thi dv chT c6 hai may phat di$n cong suat bang nhau lam Vi$C song song), neu tang dong di$n kich th f ch it cua mot may ma van giCr dong di$n kfch thfch cua may th(.p hai khong d6i, th1 do cong suat phan khang cua may mot tang, t6ng cong suat
'~.q~; P=i15Pt1m1 ,.,_.;:i.""" P=i15Pt1m1 ,.,_.;:i.""" • I .,,-e,,~ ... , ·-- ,,..,,. ',.i;J, iJJ,I, /~ V ~ .., ,... _ __..,._A ___ ··----"---- 0 ill] it
Hinh 4.12 HQ cac <1?c tfnh hinh V cua may ai~n aong bQ
phan khang se tang lam thay d6i di$n ap U cua IU'&i di$n, anh hU'&ng den trc;mg thai lam Vi$C b1nh thLI'ang cua ho dung di$n. NhU' v~t d§ duy tr1 trc;1ng thai lam Vi$C b1nh thU'ang cua ILI'&i di$n v&i U = const, khi tang dong di$n kich thich cua m9t may th1 phai giam tLI'O'ng Ll'ng dong di$n kich thich cua may th(.p hai. Bang phLI'O'ng d6 se thl)'c hi$n dLI'Q'C Sl)' phan phf>i lc;1i cong suat phan khang Q giCra hai may phat di~n.
Thi d1:1:
Hai may phat di$n gif>ng nhau lam vi$C song song c6 di$n tr& phan (.png r LI' = 2.18 0., di$n khang dong bo xdb = 62 0. cung cung cap di$n cho mot tai la 1830 kW v&i cos = 0,83 (ch~m sau). 8i$n ap dau Cl)'C cua tai la 13800 V. 8ieu chinh kfch tll' cua hai may sau cho mQt may c6 dong di$n phan khang la 40 A. Tf nh:
a) Dong di$n cua moi may phat di$n.
b) S(.pc di$n dong E cua moi may va g6c pha giCra cac SLl'C di$n dong d6. Giai.
Dong di$n t9i c6 tri s6:
I= P = 1380x103 = 92,3A
✓3U cos cp ✓3x13800 .0,83 ch~m sau di$n ap g6c va bi§u thi dU'&i dc;1ng ph(.pc s6 nhLI' sau:
Vi cong suat tac d1,mg phan phf>i deu cho hai may nen dong di$n tac dvng cua moi may la, hO'n nCra dong di$n phan khang cua may A la 40 A, do d6:
IA= 38,4-j40 va IB= I -IA= 38,4 -j11,4 A (.png dvng bi§u th(.pc (3-4) ta c6:
EA =U+IA(ru+jxab)=EAL0A = 13; 0 +(38,4-j40)(2,18+j62)=10720L12,22° V
Cung nhLI' v~y: Es = u + Is (ru + j.xab) = EsL0s = 9030L15.1° v
G6c 1$ch pha giCra hai s.d.d d6: 0A -0s =15,1° -12,22° =2,88°
4.5. May phat di~n d6ng bQ lam vi~c song song 4.5.1. Oi~u ki~n lam vi~c song song 4.5.1. Oi~u ki~n lam vi~c song song
Khi ghep mot may phat di$n dong bQ lam vi$C song song trong h$ thf>ng di$n ll)'c v&i mot may phat di$n dong bQ khac, d§ tranh dong di$n xung va cac Mdt
c6 tri s6 rat l&n c6 th§ gay ra Sl)' c6 hong may va cac thiet bi khac trong h$ thf>ng thi phai dam bao cac dieu ki$n sau:
- 0iE;m ap cua may phat phai trung pha v&i di$n ap cua IU'&i (cl)'c tfnh cua may phat phai can ghep song song phai giong Cl)'C tfnh cua ILI'&i): UF = UL
- Tan socac h$ thong ghep vao nhau phai bang nhau (quay cung toe dQ n): fF = fl - 0oi v&i may phat di$n ba pha can them dieu ki$n thLI' 3: Cung thLI' tl! pha.
Khi ghep song song Vi$C dieu chinh di$n ap UF cua may phat di$n dU'Q'C thl)'c hi$n bang each thay dBi dong di$n kfch thich cua may. Tan s6 fF cua may dU'Q'C dieu chfnh bang each thay dBi mornen ho$c t6c dQ quay cua d<)ng cO' sO' c§p keo may phat. SL! trung pha giCra di$n ap cua may phat di$n va cua ILI'&i di$n kiem tra bang den, von met chI khong ho$c dt,mg Cl) do d6ng bQ. ThU' tl)' pha cua may phat di$n d6ng bQ thLI'CYng chi dU'Q'C kiem tra mQt Ian sau khi lap rap may va hoa d6ng bQ voi IU'&i di$n Ian dau.
Vi$C ghep song song cac may phat di$n vao h$ thong di$n theo cac dieu ki$n tren gQi la hoa d6ng bQ chfnh xac may phat di$n. Trong mQt s6 trLI'CYng hqp c6
the dung phLI'O'ng phap hoa d6ng bQ khong chf nh xac nghTa la khong phai so sanh tan so, tri s6 g6c pha va cac di$n ap cua may phat di$n can dU'Q'C ghep song song va cua ILI'&f di$ri, phU'O'ng phap nay gQi la phU'O'ng phap tl! d6ng bQ.
4.5.2. Cac phLPO'ng phap hoa d6ng bQ chinh xac:
Dung bQ hoa d6ng bQ kieu anh sang den bQ hoa d6ng bQ kieu di$n tll' (c<)t d6ng bQ).