VI du 2: Di^n nang dupe tai tu tram tang ap toi tram ha ap b5ng duong
Phan tich va hicang ddn gid
Ta co: P = cong suat co + cong suat n h i ^ t = Pco + PR
Cty TNHH MTV DWH Khang Vi$t
. Pco + PR = lUcoscp 20P - 200.0,891 + 320 = 0 . 20P - 1781 + 320 = 0 => lOP - 891 + 160 = 0.
G i a i p h u o n g t r i n h tren ta co hai nghi^m: I i = 6,4 ( A ) va h = 2,5 ( A )
LU'U y : a vi du 1 ta chpn ngay nghiem ma khong can luang lu gi dung khong cdc
ban! Tat nhien la chiing ta phdi lam nhu the, vi phuang trinh bac hai theo I chi co mot nghiem (nghiem kep). Trong vi du nay ta cUng gidi phuong trinh bac hai theo I nhung Iqi co hai nghiem I phan biet deu dumg. Vqy ta chon nghiem ndo? Sau day la cdc gidi quyei van detren:
N e u I = I i = 6,4 ( A ) t h i cong suat toa n h i f t Pj = R I j = 20.6,4^ = 819,2W cong suat nay q u a I o n so v o i cong sua't co. N e n loai t r u o n g h p p nay.
N e u I = h = 2,5 ( A ) t h i cong suat toa n h i ^ t Pj = R I i =20.2,5^ = 1 2 5 W c 6 n g
suat nay n h o h o n cong suat ciia d p n g co Pco d o do ta chpn nghiem I = 2,5A. C h p n dap an C
V i d g 5 : (Trich de thi t h u S u ph^m H a N p i Ian 1 nam 2013)
M p t d o a n m a c h g o m m p t d p n g co d i ^ n mac n o i tiep v o i m p t c u p n d a y v a mac vao n g u o n d i ^ n xoay chieu. D p n g co d i ^ n tieu t h u m p t cong suat P = 9 , 5 3 k W , d o n g d i ^ n qua d p n g co co c u o n g d p h i ^ u d u n g b a n g 40y4 va cham pha m p t goc cpj = — so v o i d i f n ap giiJa h a i d a u d p n g co. D i f n ap
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g i i i a hai d a u c u p n day co gia trj h i | u d u n g la 1 2 0 y va s o m p h a m p t goc
(Pj = — so v o i d o n g d i | n chay q u a no. D i ^ n ap h i ^ u d y n g g i i i a h a i d a u
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d o a n m a c h la: