Thi Nghiem He Thong Dien

Bi 3

PTN H THNG IN 19

Bi 3 GC LCH PHA V ST P GIA U PHT V U THU CC THNG S NH HNG N CNG SUT TC DNG

V CNG SUT PHN KHNG

3.1. GC LCH PHA V ST P GIA U PHT - U THU 3.1.1. Mc ch

Kho st s iu chnh in p u nhn khi ngun pht khng i. Kho st gc lch pha gia in p u pht v u nhn trn ng dy truyn ti. Kho st s st p trn ng dy khi in p 2 u pht v nhn c cng ln.

3.1.2. Tm tt l thuyt

Trong th nghim trc, ta thy c s st p ln trn ng dy khi c ti (ti tr hay ti cm), iu ny khng th chp nhn trong thc t. Cc ng c, rle v cc bng n in ch c th lm vic trong iu kin in p n nh, xp x in p nh mc ca chng.Do , chng ta phi iu chnh in p ti u nhn ca ng dy truyn ti gn bng in p nh mc. Thng thng ta b bng t in. Cc t in tnh c bt/tt sut v gi tr ca n c iu chnh sao cho in p u nhn lch khng nhiu so vi nh mc.

Vi ti thun cm, t in pht ra cng sut phn khng bng vi cng sut phn

khng cun dy tiu th. iu ny sinh ra hin tng cng hng m trong cng sut phn khng m cun cm yu cu c t in cung cp ch khng phi do ng dy cung cp.

Vi ti tr, cng sut phn khng m t in cung cp iu chnh in p rt kh

tnh ton. Trong th nghim ny, chng ta s xc nh cng sut phn khng bng phng php gn ng, iu chnh cc t in cho n khi in p u nhn xp x bng u pht.

Trn ng dy trn ti ta c th tnh c st p trn ng dy khi bit c

in p ti u pht, in p u nhn v gc lch gia hai in p ny. Gi s khi ta bit c in p ti u pht l E1 v u nhn l E2, gc lch pha gia chng l , c biu din bng hnh sau:

st p gia E1 v E2 l E3 v E3 c th tnh bng s phc, c th tnh bng i s (xem li cch tnh).

Bi 3

PTN H THNG IN 20

Mt khc khi bit c cng sut tc dng v cng sut phn khng ti hai u pht v nhn th ta cng tnh c tn tht cng sut trn ng dy. Nu gi tn tht trn ng dy l S3 th dng in trn ng dy c xc nh l:

3

3

ESI =

Nu ng dy trn ti c tng tr l XL, th dng cn c tnh:

L

3

XEI =

V cng sut c th truyn trn ng dy:

= sinL

21

XEEP

Thit b cn thit

TN THIT B MODEL Resistive load 8311 Capactive load 8331 Three phase transmission line 8329 AC Voltmeter 8426 Three phase Wattmeter/Varmeter 8446 Phase meter 8451 Power Supply 8821 Connection leads (dy dn) 9128

3.1.3. Trnh t th nghim

Trong phn th nghim ny, chng ta kho st vic iu chnh in p ti u nhn sao cho bng in p u pht cung cp tt cho ti v kho st s st p trn ng dy truyn ti, gia tnh ton v thit b o ca chng ta c nh nhau khng.

CNH BO!

Nhng th nghim ny dng in p cao, khng ni mch khi ngun in ang m. 1. Mc mch nh hnh 3-1.

Hnh 3-1

Lu : E1 c chn lm chun.

Bi 3

PTN H THNG IN 21

Ti l ti tr ba pha cn bng, tng tr ca ng dy truyn ti l 200 . iu chnh in p ca Power Supply E1 = 300 V v gi in p ny khng i trong sut qu trnh th nghim. Ta ln lt thay i ti vi cc gi tr nh trong bng 3-1 (ch ti phi lun cn bng). Ghi li cc gi tr P1, Q1, E2, P2, Q2 v gc lch pha gia E1 v E2.

S n nh in p vi ti tr

R/pha E1 P1 Q1 E2 P2 Q2 V W Var V W Var o 300

4400 300 2200 300 1467 300 1100 300 880 300 733 300 629 300

Bng 3-1

V th ca E2 theo cng sut ti (P2) trong hnh 3-2. Trn th ny, hy xc nh

gc lch pha tng ng vi cc gi tr ca cng sut ti W2.

2. Mc mch nh hnh 3-1 nhng ti l ti tr song song vi ti dung. Tng ti tr nh cc gi tr trong bng 3-2 (lun gi ti cn bng), mi ln tng ti phi iu chnh gi tr ti dung (t in) sao cho in p ti E2 t gi tr gn 300 V nht (E1 = 300 V gi khng i trong sut th nghim). Ghi li kt qu vo bng 3-2.

S n nh in p vi ti tr

R/pha XC E1 P1 Q1 E2 P2 Q2 Gc V W Var V W Var o 300

4400 300

2200 300

1467 300

1100 300

880 300

733 300

629 300

Bng 3-2

Bi 3

PTN H THNG IN 22

Hnh 3-2

Hy biu din E2 theo P2 trn cng hnh 3-2. Trn ng biu din ny, hy xc nh

gc lch pha gia E1 v E2 cng nh cng sut phn khng Q2 m cc ti tr tiu th. 3. Mc mch nh hnh 3-3, vi in tr mi pha l 629 v vi E1 = 300 V, hy iu

chnh dung khng cho n khi in p ti E2 t gi tr cng gn 300 V cng tt. Ghi li gi tr E1, P1, Q1, E2, P2, Q2 v gc lch pha.

Hnh 3-3

E1 = _____________V E2 = _____________V E3 = _____________V P1 = _____________W P2 = _____________W Gc lch pha = _____0 Q1 = _____________Var Q2 = _____________Var

P2

50

100

150

200

250

300

E2 (V)

P

Bi 3

PTN H THNG IN 23

4. S dng kt qu trong bc 3 v p dng nhng hiu bit ca mnh, hy tnh st p v dng in trn ng dy. V biu pha ca in p ti u thu v ti u pht v so snh st in p vi gi tr o c (E3). 3.1.4. Cu hi

1. Mt ng dy truyn ti ba pha c tng tr 100 /pha cp cho ti tr ni sao. in p u pht l 110 kV v in p u nhn cng c lm cho n nh 110 kV bng cch mc song song cc t in tnh vi ti 50 MW. Hy tnh:

a) Cng sut phn khng do cc t in to ra: ............................................................................................................................................... ............................................................................................................................................... ............................................................................................................................................... b) Cng sut phn khng do ngun pht cp: ............................................................................................................................................... ............................................................................................................................................... ............................................................................................................................................... c) st in p mi pha trn ng dy: ............................................................................................................................................... ............................................................................................................................................... ............................................................................................................................................... d) Gc lch pha gia in p u pht v in p u nhn: ............................................................................................................................................... ............................................................................................................................................... ............................................................................................................................................... e) Cng sut biu kin do my pht cp: ............................................................................................................................................... ............................................................................................................................................... ...............................................................................................................................................

2. Nu ti tiu th 50 MW trong cu 1 t ngt khng c kt ni na, hy tnh in p u nhn (in p trn t in). Chng ta phi lm g phng hin tng ny?

...............................................................................................................................................

...............................................................................................................................................

...............................................................................................................................................

3. Nu ng dy truyn ti ch c ti thun tr, chng ta c th tng in p u pht v u nhn bng cch s dng cc t in tnh hay khng ?

C Khng Gii thch ............................................................................................................................................... ............................................................................................................................................... ...............................................................................................................................................

Bi 3

PTN H THNG IN 24

3.2. CC THNG S NH HNG N CNG SUT TC DNG V CNG SUT PHN KHNG 3.2.1. Mc ch Kho st ng truyn ca cng sut tc dng v cng sut phn khng trn ng dy truyn ti khi

in p u pht v u nhn c ln khng bng nhau nhng c cng pha. in p u pht v u nhn bng nhau v ln nhng khc pha. in p u pht v u nhn c ln khng bng nhau v cng khc pha.

3.2.2. Tm tt l thuyt

Nhng ng dy truyn ti c thit k v xy dng pht cng sut in. Cng sut truyn t my pht in (u pht) n ti (u nhn) tuy nhin trong nhng h thng kt ni bn trong phc tp, cc u pht v cc u thu c th o ngc ln nhau. Cng sut trong ng dy truyn ti ny c th truyn theo c hai hng ty thuc vo iu kin ti v ti ca ng dy thay i theo tng ngy. c tnh ca ti cng thay i tng gi, c ti v h s cng sut. Nh vy, bng cch no chng ta c th hiu v xc nh chiu truyn cng sut khi nhng iu kin v ti thay i phc tp nh th? V phc tp hn na khi o ngc ngun cp v t ti ti hai u ca ng dy?

Chng ta c th nhn c nhng cu tr li hon chnh nu quan tm n in p ti

hai u ca ng dy. Trong hnh 3-5, mt ng dy truyn ti c tng trX/pha () c in p u pht v u nhn ln lt l E1 v E2. Nu chng ta xc nh c ln cng nh lch pha ca in p 2 u pht v nhn th chng ta c th bit c chiu truyn ca cng sut.

Ta rt ra c cc qui lut truyn cng sut nh sau: - Hai cng sut ny c chiu truyn c lp nhau. - Cng sut phn khng truyn t ni c in p cao sang ni c in p thp. - Cng sut tc dng chiu t ni in p sm pha n in p tr pha.

Lu : Mt ng dy truyn ti c c in tr v in khng, tuy nhin in

khng rt ln so vi in tr, do ta c th b qua in tr. Nu ta bit gi tr ca E1 v E2 v gc lch pha ca chng, ta d dng tm c dng in I v in khng X ca ng dy. T , ta c th tnh c cng sut tc dng v cng sut phn khng c ngun in cp v cng sut tc dng v cng sut phn khng m ti nhn c. Ta xem v d sau: ng dy truyn ti c cc thng s sau:

Hnh 3-6

Bi 3

PTN H THNG IN 25

Nhng thng s trn, ta tnh c st p l 15 kV. Dng in trn ng dy c 150 A v tr pha so E3 vi mt gc 900. Ta cng bit c dng in sm pha so vi E1 mt gc 270

Hnh 3-7

Lu : Khi xc nh sin v cos ca gc gia in p v dng in, dng in lun

c chn lm chun. Do E1 c pha tr hn I mt gc 270, gc lch pha l m. Cng sut tc dng v cng sut phn khng - Cng sut tc dng u pht l:

150 A x 20 kV x cos (-270) = +2670 kW - Cng sut phn khng u pht l: 150 A x 20 kV x sin(-270) = -1360 kVar - Cng sut tc dng u nhn l:

150 A x 30 kV x cos (-53,50) = +2670 kW - Cng sut phn khng u nhn l: 150 A x 30 kV x sin(-53,50) = -3610 kVar

Ta c th biu din bng hnh v sau:

Hnh 3-8

Ta thy cng sut tc dng v cng sut phn khng c chiu truyn c lp nhau v

cng sut phn khng truyn t ni c in p cao sang ni c in p thp; cng sut tc dng chiu t ni in p sm pha n in p tr pha.

Bi 3

PTN H THNG IN 26

Thit b cn thit

TN THIT B MODEL Resistive load 8311 Inductive load 8321 Capactive load 8331 Three phase transmission line 8329 Three phase Regulating Autotransformer 8349 AC Voltmeter 8426 Three phase Wattmeter/Varmeter 8446 Phase meter 8451 Power Supply 8821 Connection leads (dy dn) 9128

Phn th nghim c chia thnh 3 phn kho st:

1. in p u pht v u nhn c ln khng bng nhau nhng c cng pha. 2. in p u pht v u nhn bng nhau v ln nhng khc pha. 3. in p u pht v u nhn c ln khng bng nhau v cng khc pha.

3.2.3. Trnh t th nghim

Lu ! Nhng th nghim ny dng in p cao, khng ni mch khi ngun in ang m.

in p u pht v u nhn c ln khng bng nhau nhng c cng pha

1. Mc mch nh hnh 3-9 vi tng tr ca ng dy truyn ti l 200 . Ch cch

mc ng h o pha (8451).

Hnh 3-9

2. Khi kha S m, iu chnh in p E1 v E2 ca hai ngun A v B bng nhau v bng

340 V v quan st thy rng gc lch pha gia 2 pha 4-5 ca ngun A v 2 pha 4-5 ca ngun B. Trn b hin thi gc pha (8451) gc lch phi bng 0. Nu khng th i 2 pha ca ngun cho thch hp.

Gc lch pha gia chng c bng 0 khng? C Khng

NGUN A NGUN B

Bi 3

PTN H THNG IN 27

3. Gi nguyn mch 3-15, o gc lch pha gia 4-5 ca ngun A v 2 pha 5-4 ca ngun B. Gc lch pha gia chng l bao nghiu? V E1 tr hay sm E2 (ly E1 lm chun)

..............................................................................................................................................

.............................................................................................................................................. Tr pha Sm pha

4. Gi nguyn mch 3-15, o gc lch pha gia 4-5 ca ngun A v 2 pha 5-6 ca ngun

B. Gc lch pha gia chng l bao nghiu? V E1 tr hay sm E2 (ly E1 lm chun) .............................................................................................................................................. ..............................................................................................................................................

Tr pha Sm 5. Gi nguyn mch 3-15, o gc lch pha gia 4-5 ca ngun A v 2 pha 6-4 ca ngun

B. Gc lch pha gia chng l bao nghiu? V E1 tr hay sm E2 (ly E1 lm chun) .............................................................................................................................................. ..............................................................................................................................................

Tr pha Sm pha 6. S dng ng h o pha, hy kim tra li hnh 3-10 c ng khng?

Hnh 3-10

C Khng Mc ch ca vic kim tra ny l g?

..............................................................................................................................................

..............................................................................................................................................

.............................................................................................................................................. 7. Chc chn gc lch pha ca 2 pha 4-5 ca ngun A v 4-5 ca ngun B l 0, ng

kho S iu chnhi E1 = E2 = 340 V, ghi li cc gi tr sau: P1 = W P2 = W Q1 = Var Q2 = Var

Bi 3

PTN H THNG IN 28

8. Tng in p ngun A ln 380 V v ghi li cc gi tr sau: P1 = W P2 = W Q1 = Var Q2 = Var

u l ngun pht? .............................................................................................................................................. .............................................................................................................................................. ..............................................................................................................................................

9. Gim in p ti ngun A xung 300 V v ghi li cc gi tr sau: P1 = W P2 = W Q1 = Var Q2 = Var

u l ngun pht? .............................................................................................................................................. .............................................................................................................................................. ..............................................................................................................................................

10. T cc bc th nghim trn, ta rt ra c qui lut truyn ca cng sut phn khng khng? V qui lut nh th no?

C Khng .............................................................................................................................................. .............................................................................................................................................. ..............................................................................................................................................

in p u pht v u nhn bng nhau v ln nhng khc pha

11. Mc mch nh hnh 3-11 vi tng tr ca ng dy l 400 . Trong th nghim ny ta kho st ng truyn ca cng sut khi in p 2 u pht v thu bng nhau nhng gia chng c s lch pha nhau. Gc lch pha gia 2 in p c iu chnh bng my bin p t ngu (8349). Ta tin hnh iu chnh gc lch in p 2 ngun A v B ln lt nh sau:

E1 cng pha vi E2 E1 sm pha vi E2 150 E1 tr pha vi E2 150

Ch : phi mc ng th t pha.

Ta iu chnh in p 2 ngun A v B bng nhau v bng 380 V. Ln lt lm cc th

nghim ng vi gc lch pha cho trong bng 3-3 v ghi cc gi tr cn li vo bng.

Bi 3

PTN H THNG IN 29

Hnh 3-11

V tr cng tc chuyn mch

E1 P1 Q1 E2 P2 Q2 0 V W Var V W Var 0

0 +15 -15

Bng 3-4

Qua th nghim ny, c chng minh c phi qui lut truyn cng sut tc dng trn

ng dy truyn ti truyn khng? C Khng

Qui lut nh th no? .............................................................................................................................................. .............................................................................................................................................. ..............................................................................................................................................

in p u pht v u nhn c ln khng bng nhau v cng khc pha

Mc ch ca th nghim ny l chng minh rng s lch pha gia in p ngun pht

v ngun nhn ch xut hin khi ti tiu th th cng sut. 12. Mc mch nh trn hnh 3-12, tng tr ca ng dy truyn ti l 200 , v ti l ti

tr cn bng 1100 /pha. iu chnh sao cho E1 = 380 V v c cc gi tr o c v ghi kt qu vo bng 3-4.

Hnh 3-12

Bi 3

PTN H THNG IN 30

15. Lp li thao tc bc 14 nhng ti l ti cm cn bng 1100 /pha. c cc gi tr o c v ghi kt qu vo bng 3-4.

16. Lp li thao tc bc 14 nhng ti l ti dung cn bng 1100 /pha. c cc gi tr o

c v ghi kt qu vo bng 3-4.

E1 P1 Q1 E2 P2 Q2 Gc lch pha Bc Ti V W Var V W Var 0

14 in tr 15 Cun cm 16 T in

Bng 3-5

Vi kt qu nh trn, hy cho nhn xt .............................................................................................................................................. .............................................................................................................................................. ..............................................................................................................................................

Cu hi

1. Mt ng dy truyn ti ba pha c tng tr 100 v ti nhng thi im khc nhau

trong ngy ngi ta ghi nhn cc gi tr bin v gc lch pha ca in p ngun pht v ngun thu nh trong bng 3-5.

Trong mi trng hp, hy tnh cng sut tc dng v cng sut phn khng ca ngun pht v ngun thu v xc nh chiu truyn ca cng sut. in p c cho l in p dy.

Ngun pht Ngun nhn ES ER P1 Q1 P2 Q2 kV kV

Gc pha MW MVar MW MVar

100 100 60o ES sm pha ER



120 120 30o ES tr pha ER

120 120 0o

Bng 3-5

2. Trong cu hi 1, ta xem rng ti mi thi im ES = ER = 100 kV nhng gc lch pha ca chng thay i tng bc mt gc 300 theo bng 3-6. Hy tnh gi tr ca cng sut tc dng v chiu truyn ca n trong mi trng hp, bit rng trong mi trng hp ER tr pha so vi ES.

Bi 3

PTN H THNG IN 31

Pht P

Nhn Q

o MW MW 0 30 60 90 120 150 180

Bng 3-6

V biu d biu din cng sut tc dng theo gc lch pha trn hnh 3-13. C gii hn v gi tr cng sut cc i m ng dy c th pht ra di nhng iu

kin in p tnh hay khng? C Khng

Hnh 3-13

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