, chi~u ~ai I = 5Ocm Uri giai :
b) M'!ch'RC n6i tiep:
3.7. NANG CAO HE: s6 C()NG SUAT COS",
Trang bi!u thuc cOng su~t Il1c dl,lng P = UIcos<p. cos<p dugc coi Ia M sO' cOng 8U4't.
H¢ sO' cOng sua:t ph\l thm)c vAo thOng sO' eua m<Jch di¢n. Trong nharm R.
L, C n6i tilp R cos<p = 7""",,~;;"==: JR2 + (XL _XC)2 ho~c P COSQ) = Jp2 + Q2
H¢ sO' cOng 5U4't III chi lieu ky thu~t quan tn;mg, c6 y nghta 11ft IOn v~ kinh
tl nhu sau:
- Nang cao h¢ sO' cOng su4't se t$o d\lDg t6t cOng 8U4't ngu6n (may pMt di¢n. m.ty biln "P •... ) cung c4'p cho tai. Vi dl,l mQt m.ty phil di¢n c6 cOng sua'"t
djnh muc Sdm = lOOOOkVA. olu h¢ sO' cOng suat eua lih COSQ) = D,S, cOng 8U4't
tac dvng cua m.ty pMt cho tai P = SdmCoS<P = 10000 . 0,5 = 5000kW. N(u
coscp = 0,9 tbi P = 10000 . 0,9 = 9000kW. Ro fang IA khi COScp cao may pMt ra nhi~u cOng sua'"t han.
- Khi c4n tru~n tAi mQt cOng 8u4'1 P nha't dinh t~n duang day. thi dbng di¢n chQY tren dutmg da.y IA:
1= P
Ucos<p
Nc!u CDS<p cao thi dbng di~n I sl!i giam. dAn d(n giiim tOn hao di¢n nang. giam di¢n "p rai tUn dUOng dAy vA e6 th~ ehQn dAy dAn ti(t di~n nho han.
cae rAi trong eOng nghi¢p vA sinh ho~ thUOng e6 dnh di¢n cam (cut;m dily dting cO' di¢n, m"y bi(n "P. ehan lw ... ) nen COSQ) th4"p. ~ nAng cao cosQ) ta thucrng dUng h,I di¢n n6i song song vOi tAi (hlnh 3.248).
I ---'--...,----., ---'--...,----., u I, I" ..L C T I I ...:...-_ _ --'- ___ ...I .) • b) Hlnh 3.24 65
Khi chua bu (chua c6 nhl1nh tl,l di¢n), dbng di¢n chn teen duang dAy bAng II> h¢ s6 cOng su~t cua ml'!-ch (cua tail la COS<PI
Khi c6 bu (c6 nhl1nh tl,l di¢n), dbng di¢n ch~y teen ducrng day II.ii.:
I~I, +Ic
Va h¢ s6 cOng sug:t cua m{lch IA cos<p. Tfr d6 thi hinh 3.24b ta tMy
I < II; <P < <PI va. Cos<p > COS<PI Nhu v4y M s6 cOng sug:t cos'" dil duqc nAng cao.
Di¢n dung C cc1n thitrt de nang h¢ s6 cOng sug:t tu COS<PI len cos", duqc tinh nhu sau:
Vl cOng su~t bic'dl,lng cua tai khOng dOi nen cOng sug:t phan khl1ng cua m{lch la:
Khi chua bu:
Q, ~ Ptgq>,
Khi c6 bu bAng tl,l dien (ty di¢n cung cg:p Qd
Q ~ Q, + Qc ~ Ptgq>, + Qc ~ Ptgq>
Tit d6 nit fa cOng su~t Qc cua ty di¢n l8.:
Qc ~ -p(tgq>, - tgq»
M~t kMc cOng sug:t Qc cua h,I di¢n dUQ'c dnh 18. :
Qc = -UcIc = -U.U.roC = -U2coC
(3-23)
(3-24) So sAnh (3-23) vA (3 - 24) ta tfnh d~gc di¢n dung C cu. bQ t~ di¢n lA:
p
C~--2 (tgq>,-tgq»
roU
Vi d~ 14: MQt tai g6m R = 6Il. XL = 8Il mAc n6"i titp. diu vilo ngu6n U = 220V (hlnh 3.25).
a) Hnh dong di~n II, cOng sulft P, Q, S vii COS<P1 cua tai.
b) Ngubi ta nAng h~ s6" cOng sulft cua m~ch di~n d~t
cos", = 0,93.
TCnh dl¢n dung C cua bQ tl,l di¢n da"u song song vm tai. 66
(3-25)
Hinh 3.25
I,
R
Lbi ghii; TOng lra tAi
D~ng di¢n tai II COng sulit P cua tai:
z=JR2+X[ =J62+S2 :100 R 6 COSqll =-;=10=0,6 U 220 II =-=-=22A Z 10 p= RI~ = it. 222 = 2904W C6 the tinh P = lJIlCOSlJI1 = 220 . 22 . 0,6 = 2904W Ctlng sulit Q cua tai.
C6 the tlnh: Q = UI1sinc:p1 = 220. 22 . 0,8 = 3872V Ar TfnhC COSIJII = 0,6 ; tg'Pl = 1,333 CO" = 0,93 ; tglJl = 0,395 B¢ t~ CbJ c6 di¢n dung JA C""~(tlqll-tlql) = 2904 2_(1,333-0,395)= 1,792.1O-4 P Olu 314.220
3.8. BI1!U mtN DONG IlI~N HtNH SIN BANG s6 PHUC
1. C'ch bl~u dlen .6 pbUc
Trong m~t phAng to~ dQ phuc, s6 phuc dugc bi~u di~n dum 2 d(Ulg sau (hinh 3.26).
a) D(Jng d(Ji 3d
.
C= a +jb
Trong d6 a l~ ph4n ,h\fC; jb l~ ph4n ao.
j = ~ 1~ dan vi ao (trong toin hQc don
vi aa kj hi¢u 1~ i, l:t dAy de khoi nhlim IAn voi dong di¢n i. ta kj hi¢u Ut j).
I I I I I ,
-J
Hinh 3.26
67
b) Dt;lngmil
c = celCl = CLa
Trong d6: C I~ mO dun (dO Ian)