VI du 2: Di^n nang dupe tai tu tram tang ap toi tram ha ap b5ng duong
A. 168 hp dan B 150 ho dan C 504 hp dan D 192 hp dan.
^hdn tich v>d hu&ng ddn gidi
G Q I cong suat di#n cua nha may la P, cong suat tieu thu cua m o i hp dan la Po, di#n tro d u o n g day tai la R va n la so ho dan dupe cung cap d i f n khi di?n ap truyen di la 4U
p2
Cong suat hao p h i tren duang truyen la : AP = — .R Theo bai ra ta c6:
p2 p2 p 2
P = 120.Po+-^-R 0 ) ; P = 1 4 4 . P o + ^ - R (2); P = n . P o + ^ ^ . R (3) Nhan (2) vai 4 t r u d i (1): 3P = 456Po => P = 152Po p2
(1) ^ - i ^ R = 32Po; (3) » 152P(, = nPf, + 2Po => n = 150
Chgn dap an B
Giai nhanh theo tarn suat
1 3 U len 2U => P hao p h i giam - => con lai - P
=^ So hp dan tang t u (144 - 120) = 24 hp dan
1 15
U len 4U => P hao p h i giam — => con lai — P => so hp dan tang them x? 16 16
Tarn suat: - P => Tang 24 hp dan
4 — P => Tang X hp dan — P => Tang X hp dan 16 ^ 1^.24 X = ^ = 30 n = 120 + 30 = 150 hp dan 3 4
Cau 7: Tai diem M c6 mpt may phat di^n xoay chieu mot pha, cong suat phat
di?n va hieu dien the hi^u dung a hai cue ciia may phat deu khong doi. N o i
hai cue ciia may phat voi mpt tram tang ap c6 h ^ so tang ap la k dat tai do. Tir may tang ap di?n nang dupe dua len day tai cung cap cho mpt xuong co khi each xa diem M . Xuong co khi co cac may tien cung loai cong suat khi hoat dpng la n h u nhau. K h i h f so k = 2 thi a xuong co khi co toi da 120 may ti?n
cung hoat dpng. K h i h$ so k = 3 thi a xuong co khi co toi da 125 may tien
cung hoat dpng. Do xay ra su co 6 tram tang ap nguoi ta phai noi true tiep day tai dien vao hai cue cua may phat di^n. K h i do 6 xuong eo khi co the cho toi da bao nhieu may tien cung hoat dpng. Coi rang chi co hao phi tren day tai dien la dang ke. D i ^ n ap va dong di^n tren day tai di^n luon cung pha. A. 93 B. 112 C.8 4 D. 108 422
'Phdn tich vd hit&ng dan gidi
Gpi: P la cong suat ciia may phat di^n va U la hi§u di?n the h i ^ u d u n g 6 hai cue may phat d i ^ n .
Po la cong suat cua mpt may ti^n. R la dien tro duong day tai di^n.
Theo gia thie't bai toan -j
K h i k = 2 t a c 6 : P = 120Pn + APi , , R
Cong suat hao p h i APi = P^ j vai Ui = 2U
^1 I . : ' . ' . • i
P = 120Po + APi= 120Po + P2 (*)
4 U
Tuong t u
Khi k = 3 ta co: P = 125Po + AP2= 125Po + P^ (**) 9U^
R
T u (*) va (**) P2 7 7 7 = 36Po =^ P = 120Po + 9Po = 129Po
Khi xay ra su co : P = NPo + AP= NPo {***) voi N la so may t i f n toi
da CO the hoat dpng
129P() = NPo + 36Po => N = 93.
Chpn dap an A
U 8: M p t khu tap the tieu thu mpt cong suat dien 14289 W, trong do cac dung cu dien 6 khu nay deu hoat dpng binh thuong 6 hi^u di?n t h e h i ^ u dung la 220 V. Dien tro ciia day tai dien t u noi cap dien den khu tap the la r. Khi khu tap the khong dung may bien ap ha the^ de cac d u n g cu di$n ciia khu nay hoat dpng binh thuong thi hieu d i f n the'hi^u d u n g 6 noi cap dien la 359 V, k h i do hieu dien the tuc thoi 6 2 dau day ciia k h u tap the nhanh
pha Ti/6 so voi dong dien tiic thoi chay trpng maeh. K h i khu tap the dung
may bien ap ha the'li tuong co ti so N 1 / N 2 = 15, de cac d u n g cu di$n ciia khu nay van hoat dpng binh thuong giong n h u khi khong dung may bien ap ha the thi hieu di?n the hieu dung 6 noi cap dien la (biet h§ so cong suat o maeh so cap ciia may bien ap ha thebang 1):