VI du 2: Di^n nang dupe tai tu tram tang ap toi tram ha ap b5ng duong
n uw AO 480kW.h
Cong suat hao phi AP = = 20 kW ^ ^ 24.h
P-AP 200 - 20
Hi?u suat ciia qua trinh tai dien H = = = 0,90 = 90%. ^ ^ P 200
Chpn dap an C
V« d u 4 : Dien nang tu mot nha may dugc dua den noi tieu thu nho cac day dan, tai noi tieu thu can mot cong suat khong doi. Ban dau hi^u sua't tai difn la 90%. Muon hi^u suat tai di^n la 96% can giam cuong dp dong dien tren day tai di
A.40,2% B.36,8 % C.42,2 % D.38,8%
'Phdn tich vd hucmg dan gidi
Gpi cong suat noi tieu thu la P, di^n tro day dan la R, hao phi khi chua thay do! I la AP| sau khi thay doi la APj
Taco: H : = — = 0,9 i:^ AP: = i p ^ I?R = i p (1)
P + AP, 9 1 9 ^ ' H 2 = —-— = 0 , 9 6 A P 2 = —P= > l 2 R = — P (2) P + A P 2 24 2 24 ^ ' T u ( l ) v a (2) taco: 4 = — ^ ^ = 1 - 1 — = 0,388 l2 24 I , ^ I, ^ h Do do can giam di 38,8% Chgn dap an D ^
Vi d u 5 : Trong qua trinh truyen tai di^n nang di xa, dp giam di^n ap tren
duong day tai dien mot pha bang n Ian (n < 1) dien ap con lai 6 cuo'
duong day nay. Coi rang dong dien luon cung pha voi di^n ap. De con^ 414
suat hao phi tren duong day giam m Ian (m > 1) nhung van dam bao cong suat den noi tieu thy nhan dupe khong doi. Can phai tang di^n ap dua vao truyen tai
n + Vm n n + m n + m A. r B. — 7 ^ C. 7 : T - D .
Vi^(n + 1) • m(n + l ) ' (n + l ) ' ^(^n + l)
'Phdn tich vd hit&ng dan gidi
Gpi P la cong suat noi tieu thu, R di| n tro duong day. P i , P2 la cong suat 6 noi phat, A P i , AP2 la cong suat hao phi khi chua tang di^n ap va khi tang d i? n ap, U i , U 2 la difn ap 6 noi phat liic dau va sau khi tang di^n ap, U ' j ,
U ' 2 la di^n ap 0 noi tieu th\ liic dau va sau khi tang di$n ap .
Tinhli N Di^n ap a noi thieu thy liic ban dau: U ' j = U i - A U i ' ;
Theo dau bai A U i = n ( U i - A U i ) => A U i = = L .R => L = "^^ '
n + l ^ 1 ( n + l)R . T ' AR L^R ^ L n U i Tinh I2: ta c6 — ^ = — = m => I , = = -f= i AP2 V m V m. ( n + 1).R Tinh U 2 : ta c6 Ptt = P2 - A P 2 = P i - A P i = U2.I2 - h^.R = U i . I i - Ii^.R U 2 I2
Thay I,,. I2 ta dupe U 2 = _ H i = (HLIHL
Vm.(n + 1) U j Vm.(n + 1) Chpn dap an D
Vi d u 6 : (Trich de thi tuyen sinh vao dai hpc nam 2012)
Tu mot tram phat di^n xoay chieu mpt pha dat t^i vi tri M , dif n nang
dupe truyen tai den noi tieu thy N , each M 180 km. Biet duong day c6 J di^n tro tong cpng 80Q (coi day tai di?n la dong chat, c6 di?n tro ti I?
i thuan voi chieu dai ciia day). Do sy co, duong day bj ro di^n tai diem Q I (hai day tai di?n bi noi tat boi mpt vat c6 di?n tro c6 gia trj xac dinh R). I De xac dinh vj tri Q, trudc tien nguoi ta ngat duong day khoi may phat
[ va tai tieu thu, sau do dung nguon difn khong doi 12V, di§n tro trong