, chi~u ~ai I = 5Ocm Uri giai :
b) TCnh dbng di¢n dAy l.J eua ngueSn cung elp eho 2 till lIen Lbi gial : a) Set deS m{lCh di¢n 3 pha ve tren hlnh 4
Lbi gial : a) Set deS m{lCh di¢n 3 pha ve tren hlnh 4 - 10
COng sulft bil'!:ll kiln t!i 1 r---cc
SI: Jp,2+Q,2 :: J62 +42", 7,211kVA. COng snlft bil'!:u kii!n [Ai 2
S:z== Jpi+Q,2== Jr
,2O;-+-2'2==8.246kVA.
Theo cong thllt (4 - 14). dbng di¢n dAy cua [ii ItA
1= S, =~=IO.956A
I JjUd J).380
89
dong di~n dAy cUa tii 2 I A • 12=~ J3ud ::: 8246 = 12,528A ./3.380
De tfnh dong di~n I.! eua nguOn eung c!p cho [ai, [a elin tfuh cOng su/ft cua ngudn.
COng suit lac dyng nguon cung c/fp cho 2 uii
P= Pr + P2 = 6 + 8 = 14kW : 'J" • ~80 . I, T'11 P1,Ql Hinh 4.10
COng suit phan khang nguOn cung c/fp eho 2 [ai Q = Qr + Q2 = 4 + 2 = 6kVAr
COng su/ft bieu ki6n ngudn
s= ~p2 +<1' = J14' +6' = 15.231kVA<
~
T.612
1\ ,Qa
Ap dyng cOng thllt: (4 - 14) ta c6 dong di~n dAy nguOn cung c!p cho 2 tlii
I = S '" 15231 '" 23,14A
• :nUd $.380
4.5. CACH GlAI M~CH I>I~N BA PHA 061 XU'NG
D6i val m""ch di¢n ba pha d6i xd:ng, d~ng di~n (di~n ap) cac pha c6 tei s(
hi¢u dl:mg bAng nhau, vA l~ch pba nhau mQt g6c. Vi v~y khi m~ch d6i xllng, t1
tach ra mQt pha de tfnh, khi bi.!t duqc d~ng di¢n cua mQt pha, ta c6 the suy r; d~ng di¢n d.c pha c~n l~.
Khi tai n6i vAo ngu6n c6 di~n ap dAy Ud , be, qua t6ng tra duang day, n.!l hi.!t t6ng trlt tai, cac buOc tfnh toan thl!C hi¢n nhu sau:
90
- Buac 1 : Xac dinh cach n6i dAy cua tM (hlnh sao hay hinh tam giac). - BuOc 2 : Xac djnh di¢n ap pha Up cua tM
N~u tiii n6i hlnh sao
u,
U, = ..fj
N~u lai n6i bloh tam gi~c
Up= Ud
- BlIac J : Xac dinh t60g tn; pha Zp va M 86 cOng sua't ella tai T6ng tra pha eila taL
z" = JrR-;;-' p-+-X~'-p
R Rp
He 86 cOng su6t cos <p = ---I. = -,=-;;6=ee-
• zp 'R 2 +X 2
'I p p
trong d6 Rp , x,. tuang llng l~ di~n tn; pha, di~n khang pha cua m6i pha cua tai.
- Bu6c 4: TCnh dbng di~n pba Ip eua tai
u
Ip = ..::f. 'p
TIl dbng di~n pba Ip , trob dbng di¢n day I.J cUa tid.
N~u lSi n6i hlnh sao
J., = Ip
Ntu tAi n6i hlnh tam gi4c I, = ,fj I,
- Ouoe 5 : Tinh cOng su6t tii tieu th1,1
P = 3 RpI.,2 ho~c 3U~p coscp ho~c J3 UdId CDS<p.
Q = 3 X,I,' ho~c 3U,Ip sin~ ho~c ,fj U,J., sin~.
S = 3z.,Ip2 lJ,04c 3UpIp ho4c J3 UdId .
V, dl,l 6 : MQl tAi 3 pha c6 di¢n tnJ pha Rp == 20 n, di~ khang pha Xp = 15 n,
noi hlnh tam gi4c, d4"u v10 m~g di¢n c6 di~ lip day Ud = 220 V (hlnh 4.11 a). Tfrill dbng d..i¢n pha Ip , dbng di¢n da.y Id• cOng su4"t tAi titu thy va ve d6 thi vectC1 di¢n lip dAy va dbog di¢n ~a tAi.
Ltd giai : Thco sa d6 noi day m{lch di¢n, tiii n6i lam gilic. Di¢n lip pha cUa tiii
T6ng trO pha ella tiii
zp "" JrR~,';-+-Xp-'2-= J202 + 152 = 25.0
91
D6ng di¢n pha cua tii
Up 220
Ip= - = -=8,8A
zp 25
Vi tai n6i tam gilk. d6ng di¢n dAy cua uii: I, = ,flIp = .fj. 8,8 = I5,24A COng l'u!!t tai tieu thl,!
P = 3 Rp I~ = 3. 20. 8.82 = 4646, 4W Q = 3 Xp I~ = 3. 15.8,82
", 3484,8VAr S = .fj U,I" = .fj. 380. [5,24 = [OO30,35VA. H¢ s6 COng sua't cua tai
cos '9 = Rp =20 ",0,8
Zp 25
'9 = 36,87°
D6ng di¢n pha ch~ sau di~n lip pha mQt g6c '9 = 36,87° . D6 thl vecta d6ng di¢n va di¢n lip pha v! (Ten hlnh 4.11.
I, A A U,'22OV C IE • 36,870 U~ Too T~ B C u" .) b) Hlnh 4.11
Vi d\l 7: MQt tai 3 pha g6m 'ba cUQn dAy d!!u vlo m~g di¢n ba pha c6 di¢n lip dAy li\ 380V. CuQn day duqc thitt ke cho lam vi~c vOi di~n lip dtnh mlk 220V. CUQn
dAy c6 di¢n tra R = 20 ; di~n khling X =80.
a) XI1.c dtnh clich n6i clic cUQn day thAnh tii ba pha.