tÍnh toÁn ngẮn mẠch phẦn ii - voer.pdf
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Ngy 27 thng 9 nm 2014 TNH TON NGN MCH PHN II - VOER
https://voer.edu.vn/m/tinh-toan-ngan-mach-phan-ii/dcae3a08 1/12
TNH TON NGN MCH PHN II
KHOA HC V CNG NGH
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Ngn mch 1 pha chm t.
Ma trn tng dn ngn mch 1 pha chm t pha a thu c t bng 7.1.
Dng ngn mch v in p nt thu c bng cch thay th
t phng trnh (7.24) vo trong (7.16), (7.18) v (7.20). Dng ngn mch ti nt p l:
TI LIU
0Thch 0Chia s
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Ngy 27 thng 9 nm 2014 TNH TON NGN MCH PHN II - VOER
https://voer.edu.vn/m/tinh-toan-ngan-mach-phan-ii/dcae3a08 2/12
Bin i n gin ta c:
Thnh phn pha ca dng ngn mch ti nt p c th thu c bng cch nhn c hai v ca phng trnh
(7.25) bi T . Dng thu c l:
in p ngn mch ti nt p l:
Bin i n gin ta c:
Thnh phn pha ca in p ngn mch.
s
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Ngy 27 thng 9 nm 2014 TNH TON NGN MCH PHN II - VOER
https://voer.edu.vn/m/tinh-toan-ngan-mach-phan-ii/dcae3a08 3/12
in p ti cc nt khc nt p l:
Bin i n gin ta c:
Cc thnh phn pha l:
Cc cng thc thu c trong cc mc trn tng kt trong bng 7.3. in p ca mt pha i vi t xem nh
mt n v so vi gc qui chiu. Cng thc trong bng 7.2 bao gm in p mt pha i vi t, n c th xem
nh mt n v. Dng lc ngn mch trong cc nhnh ca mng in c th tnh ton t cng thc (7.21).
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Ngy 27 thng 9 nm 2014 TNH TON NGN MCH PHN II - VOER
https://voer.edu.vn/m/tinh-toan-ngan-mach-phan-ii/dcae3a08 4/12
7.4. TNH TON NGN MCH BNG CCH DNG Z VNG
Dng v p lc ngn mch c th tnh ton bng cch dng ma trn tng tr vng cho h thng n gin trnh
by trong hnh 7.2. Dng in vng ca h thng in n gin l bng 0 trc lc ngn mch khng ch
n tt c cc dng nt. l cn thit v vy kt qu tnh ton dng in vng trong tng dng ngn mch
xc nh dng v p ngn mch. Tnh ton ngn mch c th thc hin c bng cch tnh theo h thng 3
pha hoc l tnh theo cc thnh phn i xng. Phng php sau y s biu din bng cch dng h thng 3
pha.
S nhnh ca h thng 3 pha n gin bng s nhnh ca mng in cng vi s my pht tng ng. S nt
bng s nt n cng vi t, ngha l bng n+1. S nhnh cy hay s vng c bn ca h thng n gin l:
l = (e + e ) - (n + 1) + 1
Hay
l = e + e + n
Vi e l s nhnh ca h thng 3 pha v e l s my pht tng ng 3 pha.
Ngn mch ti nt p tng ng vi cng thm mt nhnh cy t nt n t.
Dng din t h thng trong hnh 7.3, in p lc ngn mch l:
n q
n q
q
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Ngy 27 thng 9 nm 2014 TNH TON NGN MCH PHN II - VOER
https://voer.edu.vn/m/tinh-toan-ngan-mach-phan-ii/dcae3a08 5/12
(7.26)
Trong vect
biu din thay i trong in p nt thu c t in p nt ngun
lc ngn mch.
Phng trnh t tnh ca mng in trong dng vng nh sau.
Cho h thng ngn mch trnh by trong hnh 7.3, vect in p vng bit l:
Kch thc ca ma trn tng tr vng, n bao gm c vng ngn mch l 3(l + 1) x 3(l + 1). Vevt dng in
vng cha bit trong ngn mch l:
Trong
l dng in lin kt vi vng ngn mch. Dng in vng c th tnh ton t.
Dng in trong tt c cc nhnh ca mng in lc ngn mch c th tnh nh sau:
(7.27)
Vi C l ma trn vng hng c bn trn 3 pha. Vect dng c th phn chia nh sau:
n n
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Ngy 27 thng 9 nm 2014 TNH TON NGN MCH PHN II - VOER
https://voer.edu.vn/m/tinh-toan-ngan-mach-phan-ii/dcae3a08 6/12
Vi
: L vect dng in trong nhnh b cy
: L vect dng in trong nhnh cy
Do vect in p thay i l:
Vi K l ma trn ng dn - nhnh b cy c bn trn 3 pha.
: L ma trn tng tr gc i vi nhnh b cy
in p nt lc ngn mch thu c bng cch cng thm in p thay i vi in p trc lc ngn mch.
Phng trnh (7.26) tr thnh.
(7.28)
Dng ti nt ngn mch l ging nh dng trong vng ph l
. Phng php c th l mt cng vic biu din tnh ton ngn mch ti nhiu v tr trong h thng bng cch cng thm
cc nhnh cy, ti mi thi im, gia nt ngn mch vi t. Yu cu hnh thnh v nghch o ma trn tng tr vng
cho mi v tr ngn mch khc nhau. Php ton ma trn cn thit i hi cung cp d liu ngn mch cho mt s ln v tr
v vy n tn rt nhiu thi gian.
Phng php tng bc, mi nhnh cy ng thi c cng thm vo gia mi nt v t, yu cu hnh
thnh ma trn tng tr vng n v ch nghch o mt ma trn con. Trong phng php ny, dng in trong
vng ph l thay i ng vi tng v tr ngn mch khc nhau. Dng in pha c xem nh l lin kt trong
vng ph vi nt ngn mch p n ph thuc vo dng ngn mch. Xem dng in pha l mt n v, dng in
trong vng ph th p l:
i vi ngn mch 3 pha.
i vi ngn mch 1 pha chm t (trn pha a).
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Ngy 27 thng 9 nm 2014 TNH TON NGN MCH PHN II - VOER
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i vi ngn mch hai pha (gia pha b v pha c).
Dng trong tt c cc vng ph khc l xem nh bng 0.
Vect in p, dng in v ma trn tng tr vng trong phng trnh biu din cho ton mng in, bao gm
vng ph c th phn chia nh sau:
Trong phng trnh (7.29) vect
v
c xem nh l cc vect dng in v in p vng trong h thng n gin v
v
c xem nh l cc vect dng in v in p vng ph.
Vect
c th tnh ton cho ngn mch ti nt p t phng trnh (7.29) bng cch xem dng in trong vng ph l:
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Ngy 27 thng 9 nm 2014 TNH TON NGN MCH PHN II - VOER
https://voer.edu.vn/m/tinh-toan-ngan-mach-phan-ii/dcae3a08 8/12
Trong
c xem nh vect dng 3 pha ca vng ph th p. T phng trnh (7.29) ta c.
(7.31)
T
phng trnh (7.31) tr thnh.
i vi h thng n gin dng in vng tm c l:
(7.32)
in p vng ph t phng trnh (7.29) l:
Th
vo trong phng trnh t (7.32) ta c .
(7.33)
Phng trnh (7.33) xc nh ngun in p vng ph, t dng in vng ph tnh bi phng trnh (7.30).
Thc t xc nh dng ngn mch vi ngun in p trong vng ph th p
phi bng in p nt th p trc ngn mch. Tnh ton ngun in p ca vng ph th p
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Ngy 27 thng 9 nm 2014 TNH TON NGN MCH PHN II - VOER
https://voer.edu.vn/m/tinh-toan-ngan-mach-phan-ii/dcae3a08 9/12
thu c t phng trnh (7.33) dng tng ng tnh ton dng in. Dng ngn mch thc t ti nt p l:
i vi pha a:
(thc t) =
(tng ng)
i vi pha b:
(thc t) =
(tng ng)
................ ................
Dng in vng
ca h thng n gin c th thu c t phng trnh (7.32) dng dng in vng hin ti. Dng nhnh b cy c th
tnh ton t phng trnh (7.27) v in p nt, sau c th xc nh t phng trnh (7.28).
Trong phng trnh (7.33) xem dng in vng ph
trong cc nhnh cy ph kt ni cc nt ca mng in vi t v v vy n c xem l dng nt. in p vng ph
l in p nt thu c t dng in hin ti. Trong phng trnh (7.33).
V vy trong phng php ma trn tng tr vng dng xc nh ma trn tng tr nt cho tnh ton ngn
mch.
7.5. CHNG TRNH M T TNH TON NGN MCH
Phn ln nghin cu ngn mch l ch cn tnh cho ngn mch 3 pha v 1 pha chm t. Tnh ngn mch
trong h thng in l nhm mc ch tnh ton nhng s c, dng ma trn tng tr nt th t thun v th t
khng biu din nh mc 7.3 v h thng in n gin trnh by trong mc 7.2.
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Ngy 27 thng 9 nm 2014 TNH TON NGN MCH PHN II - VOER
https://voer.edu.vn/m/tinh-toan-ngan-mach-phan-ii/dcae3a08 10/12
D liu nhp vo din t h thng l thuyt thnh lp ngun nng lng v cc bin i trung gian. D liu
cho my pht, b t, s im ni v in khng th t thun th t khng. V l thuyt 1 pha gm 2 thnh
phn, thnh phn th nht l cho mi mt im ni dc theo chiu di ng dy l mt in khng ng
dy, thnh phn th hai ca ng dy l in khng tng h i hi gia hai dy vi nhau. My bin p v
l thuyt c xem nh mt im ni ti mi trm vi s cun dy, s kt ni v in khng th t thun th t
khng ca n.
Chng trnh tnh ton u tin gn cho mt dy s nt v sp xp h thng d liu cho thun li, hnh thnh
cc ma trn tng tr nt th t thun, th t khng. Kim tra v biu din d liu trong mi pha. Tip theo,
thit lp cc ma trn tng tr nt th t thun, th t khng. Ma trn c lu tr tm thi trong vng nh ph
cung cp cho chng trnh tnh tip theo. Sau cc ma trn tng tr nt th t thun v th t khng
c gi ra dng trong tnh ton ngn mch. T ma trn i xng ch lu tr cc thnh phn trn ng
cho. Chng trnh tnh ngn mch th t tng bc c trnh by trong hnh 7.6.
S thut ton tnh ton ngn mch trong h thng in:
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