Vn 1:VIT BIU THC CNG DNG IN HIU IN THXC NH R, L, C MCH MC NI
TIPTm tt l thuyt Phng php gii ton:1. Tnh tng tr Z.a. Tnh in tr thun
R.b. Tnh cm khng ZL.c. Tnh dung khng ZC.d. Tnh tng tr: Cng thcGhp
ni tip Ghp song songin trlRS R= R1 + R2 + Rn1 21 1 1 1...nR R R R +
+T cmZL=L.1 2...nL L L LZ Z Z Z + +1 21 1 1 1...nL L L LZ Z Z Z + +
+in dung1.CCZZ 1 2...nC C C CZ Z Z Z + + +1 21 1 1 1...nC C C CZ Z
Z Z + + +Tng tr:2 2Z= R (Z Z )L C+ 2. Tnh I hoc U bng nh lut m
:UIZT tnh: I0= I. 2 ; U0=U. 23. Tnh lch pha : tanL CZ ZR4. Vit biu
thc:Nui = Io cos (t + i) u = Uo cos (t + i + )Nu u = Uo cos (t + u
)i = Io cos (t + u )Ch 1: on mchZ R ZLZCtan 0 Gin vecton mchZ2 2R
ZL+2 2R ZC+Z ZL Ctan ZRL- ZRCtGin vecton mchZ2 2Z= R (Z Z )L C+
tanZ ZRL
C0URr0Ir0ULr0Ir0UCr0Ur0ULr0Ir0URr0Ir0URr0Ur0UCr0Ir0UCr0ULr0Ur20Ir0ULrGin
vect30URr 0Ir0UCr0UrCh 2:- Dng in xoay chiu qua on mch ch c in tr
thun R:+ Hiu in th u hai u on mch v cng dng in i bin thin cng pha,
cng tn s.u=U0costi=I0costU0=I0.R; U0=U 2 ; I0=I 2 ; U=I.R.+ Cng thc
tnh R theo in tr sut , chiu di l v tit din S ca dy dn:lR=SBng n c
dy tc nng sng, bp in, dy nung, bn l (bn i) thng c coi l in tr thun
khi mc vo mch in xoay chiu.- Dng in xoay chiu qua on mch ch c cun
dy thun cm:+ Hiu in th u hai u on mch v cng dng in i bin thin cng
tn s, nhng nhanh pha hn cng dng in i mt gc 2.u=U0cost. i=I0cos(t -
2)hoc i=I0costu=U0 cos(t + 2)U0=I0.ZL; U0=U 2 ; I0=I 2 ; U=I.ZL.+
Cm khng: ZL=L. = L2f.- Dng in xoay chiu qua on mch ch c t in:+ Hiu
in th u hai u on mch v cng dng in i bin thin cng tn s nhng chm pha
hn cng dng in i mt gc2.u=U0cost. i=I0cos(t + 2)hoc i=I0costu=U0
cos(t - 2)U0=I0.ZC; U0=U 2 ; I0=I 2 ; U=I.ZC.+ Dung khng: ZC=1C. =
1C.2 f .+ Hiu in th nh nht m lp cht in mi ca t in chu c (khng b nh
thng):Umin= U 2 =U04* Cng sut P ca dng in xoay chiu:P = UI cos P =
RI2 = URIcos : h s cng sut, ch c R tiu th in nng.* H s cng sut:cos
= PU.I=U RU ZR* Nhit lng ta ra trn mch (trn R):Q = RI2t* Cng hng
in: Imax = minU UZ RZL = ZC
L.C.2= 1 = 0 (hiu in th hai u mch cng pha vi cng dng in)cos = 1:
h s cng sut cc i.5Bi mu:Mt mch in gm in tr thun R = 75 mc ni tip
cun cm c t cm L = 54 H v vi t in c in dung C = 3105F. Dng in xoay
chiu chy trong mch c biu thc:i = 2 cos 100t (A)a) Tnh cm khng, dung
khng, tng tr ca on mch.b) Vit biu thc hiu in th tc thi gia hai u in
tr, gia hai u cun cm, gia hai u t in.c) Tnh lch pha ca hiu in th v
cng dng in.d) Vit biu thc tc thi ca hiu in th gia hai u on
mch.Giia) Cm khng, dung khng, tng tr ca mch:Cm khng: ZL = L.5100
1254 Dung khng: ZC = 31 15010 C..1005 Tng tr: Z = 2 2 2 2R (Z Z )
75 (125 50) 75 2 106L C+ + b) uR , uL , uC :-Biu thc hiu in th gia
hai u in tr uR cng pha vi i v U0R = I0R.R = 2.75 = 150 V . Nn uR =
150 cos 100t (V)- Biu thc hiu in th gia hai u cun cm nhanh pha hn i
2radV U0L = I0.ZL = 2.125 = 250 VNn: uL = 250 cos (100t + 2)
(V)-Biu thc hiu in th gia hai u t in uC chm pha hn i2radV U0C =
I0ZC = 2.50 = 100 VNn uC = 100 cos (100t - 2) (V)c) lch pha :Ta c:
tanL CZ ZR=125 50175.Suy ra: = 4radd) Biu thc hiu in th u:Vi U0 =
I0Z = 2.75. 2 =150 2(V)Nn: u = 150 2 cos (100t + 4)6Mot mach ien
xoay chieu ABDEF gom cac linh kien sau ay mac noi tiep (xem hnh
ve)- Mot cuon day co he so t cam L, va khong co ien tr.- Hai ien tr
giong nhau, moi cai co gia tr R.- Mot tu ien co ien dung C.at gia
hai au A, F cua mach ien mot hieu ien the xoay chieu co gia tr hieu
dung UAF = 50V va co tan so f = 50Hz. Hieu ien the gia hai au cac
oan mach AD va BE o c la UAD = 40V va UBE = 30VCng o dong ien hieu
dung trong mach la I = 1Aa) Tnh cac gia tr R, L va Cb) Tnh he so
cong suat cua mach ien c) Tnh o lech pha gia cac hieu ien the UAD
va UDF.H Tai chnh Ke toan - 1999ABD E F LRC RGiia) Tng tr Z=2 2U
50(2R) (Z Z ) 50I 1AFL C+ 2 24R (Z Z ) 2500L C + (1)Li c ZAD=2 2U
40R Z 40I 1ADL+ 2 2R Z 1600L + (2)ZBE=2 2U 30R Z 30I 1BEC+ 2 2R Z
900C + (3)T (2) v (3): 4R2 + 22 2Z 2Z 5000L C+ (4)T (1): 4R2 + 2 2Z
Z 2Z Z 2500L C L C+ (5)Ly (4) tr (5): 2 2 2Z Z 2Z Z (Z Z ) 2500L C
L C L C+ + + Z Z 50L C + ( loi nghim Z Z 50 0)L C+ = .1000=200V2.
Cng sut nhn c cun th cp:=H = . =9600WCng hiu dng trong mch th cp: =
=> = = =60A3. in tr ca mch th cp: ==> R = 83,74.3. Mt my pht
in c cng sut 100kW. Hiu in th hai cc my pht 1kV. truyn n ni tiu th,
ngi ta dng mt ng dy ti in c in tr tng cng l 6.1. Tnh hiu sut ca s
ti in ny.2. Tnh hiu in th hai u dy ni tiu th.433. tng hiu sut ti in
, ngi ta dng mt my bin th t ni my pht phi c t s gia vng dy cun s cp
v th cp l 10. Tnh cng sut hao ph trn dy v hiu sut ti in lc ny. B
qua hao ph trong my bin th4. ni tiu th cn dng in c hiu in th 200V
th phi dng mt binth c t s vng dy gia hai cun s v th lbao nhiu?Gii1.
Gi P l cng sut hao ph: P= RI2=R= 60kWHiu sut ca vic ti in ny l: H=
= .100=40%2. gim th trn ng dy l:=RI=R=600VHiu in th ni tiu th l: U=
U -= 1000-600=400V3. Hiu in th hai u cun th cp v ni pht l :=10
=>= 10U = 10kW = 104WDo b qua hao ph trong my bin th nn cng dng
in trn dy lc ny l:I2== = 10ACng sut hao ph lc ny l:P = R
=6.(10)2=600WHiu sut ti in l:H= = .100= 99,4%4. gim th trn ng dy:
=RI2=6.10=60VHiu in th cui ng dy: U1= - = 104-60 =9940VT s vng dy
gia hai cun s v th l:= 49,74.4. Mt my pht in xoay chiu c 4 cp cc,
cung cp mt hiu in th xoay chiu c tr s hiu dng 100V, tn s 50Hz . B
qua in tr trong ca my pht.1. Tnh vn tc quay ca Roto2. Nu vn tc quay
tng ln gp i th tn s v hiu in th hiu dng l bao nhiu?Gii1.Vn tc quay
ca Roto: f = p => n = = 750 vng/giy2. Hiu in th hiu dng l: f =
2f = 100HzVy: U = 2U=200(V)444.5. Mt my pht in phn cm c 12 cp cc
quay vi vn tc 300vng/pht. T thng cc i qua cun dy lc i ngang qua u
cc l 0,2Wb v mi cun c nm vng dy(s cun dy bng s cc t)1. Tnh tn s dng
in xoay chiu pht ra.2. Vit biu thc sut in ng theo thi gian.3. Tnh
cng sut trung bnh ca my khi c mc ti cv h s cng sut l 0,8 v cng hiu
dng qua ti l 2Ap n: 1. f=60Hz2. e = 9034cos120t(V)3. P=10250W4.6.
Mt my pht in xoay chiu ba phac cc cun dy phn ng mc theo kiu hnh
sao, c hiu in thpha l 220V .Mc cc ti ging nhau vo mi pha . Mi ti c
in tr R = 60 ni tip vi cun thun cm c t cm L = H . Tn s dng in l
50Hz. Tnh:1. Hiu in th dy ca mng in.2. Cng dng in qua mi ti.3. Cng
sut ca dng in ba phap n:1Ud = 380V2. I =2,2A3. P = 871,2W4.7. T mng
in c hiu in th 220V cn truyn mt cng sut 1kW n ni tiu th cch mng in
2km (bng hai dy dn). gim hiu in th trn dy khng qu 10%.1. in tr ca
dy dn c th ln nht bng bao nhiu?2. Tnh tit din nh nht ca dy ng dng
lm ng dy . Bit in tr sut ca dy ng l 1,7 mp n:1. R = 4,482. S
14mm245TRC NGHIM VT L V DNG IN XOAY CHIUI. mch R_L_C ni tip1. Mc ni
tip R vi cun cm L c R0 ri mc vo ngun xoay chiu. Dng vnk c RVrt ln o
U hai u cun cm, in trv c on mch ta c cc gi tr tng ng l 100V, 100V,
173,2V. Suy ra h s cng sut ca cun cm l:A. 0,5B. 0,707C. 0,866D.
0,62. Chn pht biu ng khi ni v cng hiu dngA. Gi tr ca cng hiu dng c
tnh bi cng thc I=I0. 2B.Cng hiu dng ca dng in xoay chiu bng cng dng
in khng i.C. Cng hiu dng khng o c bng ampe kD. Gi tr ca cng hiu dng
o c bng ampe k.3. Dng in xoay chiu l dng in c tnh cht no sau y?A.
Chiu dng in thay i tun hon theo thi gian.B. Cng bin i tun hon theo
thi gian.C. Chiu thay i tun hon v cng bin thin iu ho theo thi
gian.D. Chiu v cng thay i u n theo thi gian.4. Hai cun dy (R1, L1)
v (R2, L2) mc ni tip nhau v t vo mt hiu in th xoay chiu c gi tr hiu
dng U. Gi U1 v U2 l hiu in th hiu dng tng ng gia hai cun(R1, L1) v
(R2, L2) . iu kin U=U1+U2 l:A. 1 21 2L LR RB. 1 22 1L LR RC.
L1.L2=R1.R2D. L1+L2=R1+R25. Trong mch in xoay chiu gm R, L, C mc ni
tip. Bit cc gi tr R=25, ZL=16, ZC=9ng vitn sf. Thay i f n khi tn sc
gi tr bng f0th trong mch xy ra cng hng in. Ta c:A. f0>f46B. f0my
pht in xoay chiu- my bin th v s truyn ti in nng31.Trong thc t s dng
my bin thngi ta thng mc cun s cp lin tc vi ngun m khng cn tho ra k
c khi khng cn dng my bin th l vA. Dng in trong cun s cp rt nh v cm
khng rt ln khi khng c tiB. Cng sut v h s cng sut ca cun th cp lun
bng nhauC. Tng tr ca bin th nhD. Cun dy s cp c in tr thun rt ln nn
dng s cp rt nh, khng ng k32.Mtmy pht in xoay chiu mt phapht rasut
in nge=1000 2 cos100 t . Nu roto quay vi vn tc 600 vng/pht th s cp
cc l:A. 8.B. 5.C. 10.D. 4.33. Trong vic truyn ti in nng, gim cng
sut tiu hao trn ng dy k ln th phi:52A. Gim hiu in th k ln.B. Tng
hiu in thk ln.C. Gim hiu in th k2 ln.D. Tng tit din ca dy dn v hiu
in th k ln.34. Nguyn nhn ch yu gy ra s hao ph nng lng trong my bin
th l do:A. Hao ph nng lng di dng nhit nng to ra cc cun s cp v th cp
ca my bin th.B. Li st c t tr v gy dng Fuc.C. C s tht thot nng lng
di dng bc x sng in t.D. C A, B, C u ng.35.Mt my bin thc s vng dy ca
cun s cpl 1000 vng, ca cun th cpl 100 vng.Hiu in thv cng hiu dng
mch th cp l 24V v 10A. Hiu in th v cng hiu dng mch s cp l:A. 240V;
100AB. 240V; 1AC. 2,4V; 100AD. 2,4V; 1A36. Cng mt cng sut inc ti i
trn cng mt dy dn. Cng sut hao ph khi dng hiu in th 400 kV so vi khi
dng hiu in th 200 kV l:A. Ln hn 2 ln.B. Ln hn 4 ln.C. Nh hn 2 ln.D.
Nh hn 4 ln.37. Mt ng c khng ng ba pha c hiu in th nh mc mi pha l
220 V. Bit rng cng sut ca ng c 10,56 kW v h s cng sut bng 0,8. Cng
dng in hiu dng qua mi cun dy ca ng c l:A. 2 AB. 6 AC. 20 AD. 60
A38. u im ca dng xoay chiu ba pha so vi dng xoay chiu mt pha:A. Dng
xoay chiu ba pha tng ng vi dng xoay chiu mt pha.B. Tit kim c dy dn,
gim hao ph trn ng truyn ti.D. C A, B, C u ng.39. Mt my pht in xoay
chiu c 8 cp cc, phn ng gm 22 cun dy mc ni tip.T thngcc i o phn
cmsinh ra i qua mi cun dy c gi tr cc i 53110Wb. Rtoquay vi vn tc375
vng/pht. Sut in ngcc i do my c th pht ra l:A. 110 VB. 110 2 VC. 220
VD. 220 2 V40. Ta cn truyn mt cng sut in 1MW n ni tiu th bng ng dy
1 pha, hiu in th hiu dng 10kV. Mch in c h s cng sut :. Mun cho t l
nng lng mt mt trn ng dy khng qu 5% cng sut truyn th in tr phi c gi
tr :A. R3,61B. R361C. R0,361D. R36,141. Cho dng in xoay chiu 3 pha
tn s 50Hz chy qua 3 cun dy ca stato ca ng c khng ng b ba pha. ng c
hot ng bnh thng. Tc quay ca Roto khng th ln hn :A. 50 rad/sB. 100
rad/sC. 60 rad/sD. 314 rad/s42.Mt my bin thc s vng cun s cpl 2200
vng. Mc cun s cpvo mng in xoay chiu 220V - 50Hz, khi hiu in th gia
hai u cun th cp h l 6V. S vng dy ca cun th cp l :A. 80 vngB. 40
vngC. 60 vngD. 30 vng43.Mt trm pht in xoay chiu c cng sut khng i c
truyn i vi hiu in th hiu dng hai u dy ti ni truyn i l 2kV, hiu sut
truyn ti in l 80%. Mun hiu sut truyn ti in t 95% th ta phi :A. Tng
hiu in th ln n 4kVB. Tng hiu in th ln n 6kVC. Gim hiu in th xung cn
1kVD. Tng hiu in th ln n 8kV5444. Mt my pht in xoay chiu 1 pha c
phn cm l roto gm 10 cp cc, quay vi vn tc khng i 300 vng/pht. Phn ng
l stato, gm 10 cp cun dy mc ni tip, mi cun dy c 10 vng. T thng cc i
qua mi vng dy l 19,8 mWb. Sut in ng t cm hiu dng ca my l :A. 220 2
vB. 220VC. 110VD. 110 2 v45. Mt my bin th c s vng cun th cp gp i s
vng cun s cp. Cun s cp c t cm L=10H v in tr trong r=1000.Ni cun s
cp vi ngun c tn s 50Hzv hiu in th hiu dng U.Cho rng t thng khng b
tht thot ra ngoi li. Tnh hiu in th hai u cun th cp h :A. UB. 42 UC.
2UD.2 U46. Cun s cp ca mt my bin th c 800 vng, c mc vo mng in xoay
chiu c hiu in th hiu dng 120V , hai u cun th cp c ni vi mt mch gm
10 bng n loi 6V-3W mc song song vi nhau, tt c cc bng u sng bnh
thng. B qua in tr dy ni. S vng ca cun th cp v cng hiu dng ca dng in
trong mch s cp l :A. 40 vng v 0,25AB. 50 vng v 0,12AC. 50 vng v
0,25AD. 40 vng v 0,12A47. Mt my pht in 3 pha mc hnh sao c hiu in th
pha 127 V, tn s 50Hz. Ngi ta a dng in 3 pha vo 3 ti nh nhau mc hnh
tam gic, mi ti c in tr thun 12 v t cm 51mH. Cng dng in qua cc ti
l:A. 7,86AB. 6,35AC. 11AD. 7,1A48. Mt my pht in c phn cm gm hai cp
cc v phn ng gm hai cp cun dy mc ni tip. Sut in nghiu dng ca my l
220V v tn s50Hz. Cho bit t thngcc i qua mi vng dy l 4mWb. Tnh s vng
dy ca mi cun trong phn ng.A. 175 vng55B. 62 vngC. 248 vngD. 44
vng49. T trm pht in ngi ta mun truyn i mt cng sut 500kW trn mt ng
dy c in tr 25. in nng hao ph khng vt qu 10kW th hiu in th trm phi c
gi tr nh th no :A. U25kVB. U12kVC. U20kVD. Kt qu khc50. T trm pht
in ngi ta mun truyn i mt cng sut 500kW trn mt ng dy c in tr 40 m.
cng sut hao ph khng vt qu 2% th hiu in th trm phi tha mn iu kin no
sau y :A. U
