D. Ba pha phiti co cilng dng t6'vd cilng do
l€ch pha giira diQn dp vd cwdng dp ddng diQn.
Hrtng ddn gi,rti. Ba cti6n 6p xoay chi6u lech
pha nhau 4. Ncu hiQu sd pha giira u vd i
ra
J
cira ba pha ld nhu nhau thi khi c6 cirng t6ng
tr0, ba cudng dQ ddng diQn cfing lech pha
.,*
nhau a. Vfly d6p 6n D dting. D
A .J L
J
DANG 2. Cac bai tQp dinh tLrqng.
Phucrng ph6p gifli. Phii nim vfrng c6c n6i
dung kiOn thric sau:
- Circc6ng thric cira mpch R, L, C mhcn& ti6p.
- Cdc c6ng thric cira m6y bitin 6p, cdng thric
tinh cong su6t cira mach diQn ba pha. C6c
biOu thric cira tliqn 6p hiQu dqng, cua cudng
dQ dong itiQn trong mach dien bu pt u.
- Phucrng ph6p giin t16 Fre-nen
*Thi dV 2. Cht;mg td riing trong cdch mdc hinh sao, ndu ba pha hoqt dQng nhu nhau thi
a) Ua =Ll oJ1.
b) Ddng diQn qua ddy trung hda bting kh6ng. Hudmg ddn gidi. C6 th6 gini bdi tpp ndy bing
phuong ph6p luqng gi6c hay phgcrng ph6p
giin d6 Fresnel. Sau ddy ta gi6i m6i cdu theo
mQt phuong ph6p.
a) Dilng phtrong phdp gidn di Fre-nen
Gi6 sti Ua li dien 6p hiQu dqng cira up, vfi
7,to=ttt-U2. TaC6
_L't- Hinh 5
Trong hinh 5, vecto (J'r21i ducrng ch6o ddi
.-)-)
cira hinh thoi c6 hai c4nh bdngUyU2 vit
Ydy Ur, =UrJl =ryr.fl vit
ur:(Jocos,t ; uz -uo.or(rr -+) ts6c nhon ld 1 s6c nhon ld 1 J TE (0 ,6=-. b) Dilng phmtng phdp bqng gidc
Khi ba pha hopt dQng nhu n\au tli ba cucrng
dQ ddng rli6n c6 bi6n d0 vir t6n sd blng nhau,
c6 pha ban diu lQch nhau *.r^ cudng ttQ
J
ddng diQn d6 ld
ir = I ocos(Dt i iz = Iocos( a, -*) ,
\ J,/i, = I^cos( \. at -1I).3i i, = I^cos( \. at -1I).3i
Ddng diQn qua dAy trung hda ld t6ng cira ba ddng diQn tr€n n6n .\ l=(21 *t3)+tz ( zr\( rro"4*r)=o.n =-locosl at-; - \. 3/\ ll 3 ) un =(J u2cos(att + g)
TORN HOC ..rt..rr.r.r......r..ar.r. ..c....o.....!*rrnor6rra.. oonnr* fi.fuw1ff2
chil da IMACH DAO DQNG MACH DAO DQNG
D{NG l. Cdc bdi tQp xdc dinh chu ki, tin s6,
di€n t{ch, ctdng dQ ddng diQn trong mqchdao dQng LC. dao dQng LC.
Phuong phdp gi6i. O5i vOi mach dao dQngkin, li tu*g, don gi6n ntr6t gOm m6t cu6n kin, li tu*g, don gi6n ntr6t gOm m6t cu6n
thudn chm c6.d0 t.o chm L vi mQt tp diQn c6
diQn dung C cdn 6p dlmg