Phu Tai Dien(Cung Cao Dien)

TS. L MINH PHNG [CHNG III: TNH TON PH TI IN] CHNG III

TNH TON PH TI IN

1. Khi nim chung - Nhim v u tin ca ngi thit k cung cp in cho mt cng trnh l xc nh chnh xc nhu cu in ca cng trnh tc l xc nh ph ti ca cng trnh ng thi c tnh ton n n s pht trin ca ph ti trong tng lai. - Trn c s gi tr cng sut tnh ton m ta la chn ngun in v thit b nh MBA, dy dn, thit b phn phi, thit b bo v. - Vic xc nh khng chnh xc cng xut tnh ton ca nh my s dn n vic lng ph trong u t khi ph ti tnh ton ln hn ph ti thc t cng nh vic cung cp in khng m bo lm gim tui th cc thit b, c th gy chy n v qu ti khi ph ti tnh ton nh hn ph ti thc t. - Hin nay c nhiu phng php c s dng, tuy nhin thng dng nht vn l phng php Sp xp biu ph ti - hay phng php cng sut trung bnh v h s Kmax. - Cc phng php xc nh ph ti c chia lm hai nhm: Nhm th nht: da vo kinh nghim thit k v vn hnh tng kt v a ra h s tnh ton. Phng php ny thun tin, tn ton n gin nhng kt qu cho gn ng. Nhm th 2: da trn c s l thuyt xc xut v thng k, c tnh ton n cc yu t nh hng nn cho kt qu chnh xc hn. - Trong thc t ph thuc vo mc ch ca vic xc nh ph ti m ta la chn phng php tnh ton. 2. Nhng lu khi tnh ton thit k cung cp in - Tng cng sut tiu th ln nht thc t ca nhm thit b lun nh hn tng cng sut nh mc ca chng v khng phi lc no chng cng lm vic vi cng sut nh mc v thi im tiu th cng sut cc i cng khng phi lc no cng trng nhau. - Khi xc nh cng sut tnh ton ca nh my cn lu n tnh cht khng u ca ti theo gi, ngy, tun, thng, nm, tc l cn phi phn tch th ph ti. - Vic la chn s cung cp in v cc phn t trong h thng cung cp phi tin hnh da trn c s tnh ton kinh t - k thut la chn ra phng n ti u. - Phng n c la chn phi l phng n m bo cung cp in tin cy ng thi tit kim v mt kinh t (Chi ph u t, ph tn vn hnh hng nm, tn tht in nng ). - Nhng i lng chnh c cp n khi tnh ton ph ti: cng sut biu kin S(kVA), cng sut tc dng P(kW), cng sut phn khng (kVar), v dng in I (A). - H thng cung cp in c thit k phi m bo an ton cho ngi v thit b, thun tin cho ngi vn hnh, sa cha. 3. Cc bc chnh trong thit k h thng cung cp in cng nghip: a. Xc nh ph ti tnh ton ca tng phn xng v ca ton nh my. b. Xc nh phng n v ngun in c. Xc nh s cu trc mng in. d. Chn, kim tra dy dn v thit b bo v. e. Thit k h thng ni t an ton. f. Thit k h thng chng st. g. Xy dng bn v nguyn l v bn v thi cng Page1

BIGING MN CUNG CP IN

TS. L MINH PHNG [CHNG III: TNH TON PH TI IN]

4. th ph ti in - nh ngha: th ph ti in l ng cong biu din s thay i theo thi gian ca cng sut m ph ti tiu th. - Nhng i lng c bn dng biu th ph ti: dng in I(t), cng sut tc dng P(t), cng sut biu kin S(t), cng sut phn khng Q(t). Tuy nhin trong thc t ngi ta thng s dng th cng sut tc dng P(t). - quan st c s thay i ca ph ti theo thi gian ngi ta s dng dng c o v dng c t ghi ta thu c th dng tc thi. Theo kt qu thu c trong cc khong bng nhau ca cng t hay tnh gi tr trung bnh ta thu c th ph ti theo hnh bc thang. - Khi thit k, da vo th ph ti ta c th la chn c thit b, in nng tiu th. ng thi a ra c ch v hnh ti u ca cc thit b. - Mi nghnh cng nghip u c th ph ti ngy m v nm c trng ring c xc nh bi quy trnh cng ngh ca sn xut. Tuy nhin th ph ti ca x nghip ni chung l khng n nh m thay i ph thuc vo quy trnh cng ngh, s p dng cc tin b mi vo sn xut vic nng cao hiu sut s dng thit b c tnh n s y mnh v t ng ho qu trnh sn xut, s thay i sut tiu hao in nng cho n v sn phm a. Phn loi th ph ti - th ph ti ngy m: l th trong mt ngy m 24 gi. Trong thc t c th s dng dng c t ghi, hay nhn vin vn hnh v th. thun tin th c biu din di dng bc thang.

Hnh 3.1 th ngy m - th ph ti thng: l th trung bnh hng thng, theo th ny xc nh nhp lm vic, lch vn hnh, sa cha thit b hp l, p ng yu cu ca sn xut.

Hnh 3.2 th hng thng - th ph ti nm: t th ph ti hng ngy c th xy dng c th hng nm. Theo c th xc nh mc s dng in v tiu hao in nng. BIGING MN CUNG CP IN Page2


Hnh 3.3 th hng nm


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TS. L MINH PHNG [CHNG III: TNH TON PH TI IN] I. NHNG KHI NIM V I LNG C BN Thit b tiu th in: l thit b tiu th in nng: ng c in, l in, n in H tiu th in: l tp hp cc thit b in ca phn xng hay ca x nghip hoc ca khu vc. Ph ti in: l i lng c trng cho cng sut tiu th ca cc thit b hay cc h tiu th in. 1. Cng sut nh mc- Pm: l cng sut ca thit b hay cc h tiu th in nng c ghi trn tm bin ca thit b (do ni ch to cung cp) v l i lng c bn dng tnh ton ph ti in. a. Cng sut nh mc ca cc thit b. - i vi ng c in: Cng sut tc dng nh mc ca ng c in Pm l cng sut pht ca ng c trn trc ng c khi in p l nh mc, n c biu din bng (kW). V ng c khi lm vic c tn hao cng sut nn cng sut thc t phi cung cp cho ng c s ln hn v c tnh nh sau: P Pdm = ll

Pdm : cng sut ghi trn l lch ca ng c. : Hiu sut ca ng c. - i vi cc h tiu th khc nh l in tr, bng n : Cng sut tc dng nh mc Pm ca chng chnh l cng sut ghi trong l lch ca my hay bu n v bng cng sut tiu th t li khi in p l nh mc. - i vi thit b hay h tiu th lm vic ch ngn hn lp li : th cng sut nh mc ca chng c tnh bng cch quy i v cng sut nh mc di hn khi h s ng in a = 100% . H s ng in ph tuc vo quy trnh cng ngh v thng c gi tr tiu chun: 15; 25; 40;60;75. t lamviec t a% = 100% = lamviec 100% t lamviec + t nghi T i vi ng c in: p dm = pll a % i vi my bin p: s dd = sll a % Trong : pll ( KW ), sll (kVA) , l cc s liu v cng sut theo l lch v a - l thi gian ng in tng i ca h tiu th, tlamviec - thi gian m thit b c cp ngun lm vic.

Trong :

t nghi - thi gian ngh.

T - tng thi gian lm vic v ngh - i vi my bin p ca l in: cng sut nh mc c tnh: p dm = S11 cos 11 Trong S11 - Cng sut nh mc ca my bin p, kVA cos 11 - h s cng sut ca my bin p l in - i vi my bin p hn, cc kh c in v my bin p hn tay: cng sut tc dng nh mc l mt cng sut quy c no y quy i v T= 100% p dm = s11 cos 11 a % Trong cos 11 - h s cng sut nh mcca my bin p hnBIGING MN CUNG CP IN Page4

TS. L MINH PHNG [CHNG III: TNH TON PH TI IN] - Nu l my lin hp c truyn ng nhiu ng c: nn hiu l ton b my lin hp trong phn xng, cng sut nh mc ca n l tng cng sut nh mc (quy i theo a%= 100%) ca tt c cc ng c in ca my lin hp (t my). b. Xc nh thng s nh mc ca thit b v nhm thit b Thng s nh mc ca thit b 3 pha

q dm = p dm tg dm ; s dm =

p

2 dm

+q

2 dm

I dm _ TB =

s dm 3U dm

=

2 2 p dm + q dm

3U dm

Thng s nh mc nhm thit b ba pha: - Cng sut nh mc ca nhm l tng cng sut tc dng nh mc ca cc thit b tiu th hay h tiu th in nng ring bit quy i theo a%= 100%

Pdm = p dmi ; Qdm = q dmi , ; S dm = P + Qi =1 i =1

n

n

2 dm

2 dm

I dm =

S dm 3U dm

=

2 2 Pdm + Qdm

3U dm

Thng s nh mc ca thit b 1 pha

q dm = p dm tg dm ; s dm =

2 2 p dm + q dm I dm _ TB =

s dm = U dm

2 2 p dm + q dm

U dm

Thng s nh mc nhm thit b 1 pha - Nhng h tiu th mt pha c xem l phn b u theo cc pha khi tng cng sut nh mc ca cc thit b phn b khng u trn cc pha khng vt qu 15% ton b cng sut nh mc ca cc thit b ba pha v cc thit b mt pha phn b u trn cc pha ni vo nt - i vi nhng h tiu th in mt pha mc vo in p pha hoc in p dy c phn b u cho cc pha ca li in ba pha khi tnh ton c tnh nh h tiu th ba pha c cng sut bng tng cng sut nh mc ca nhng thit b mt pha . - Trng hp cc thit b mt pha phn b khng u ta s dng mt i lng c trng gi l cng * sut nh mc ba pha quy c ca cc thit b mt pha Pdm .* - Cng sut nh mc ba pha quy c ca cc thit b mt pha Pdm bng ba ln cng sut nh mc ca pha mang ti ln nht * Pdm = 3Pdm _ pha _ max

Trong : -

Pdm _ pha _ max : cng sut nh mc ca pha mang ti ln nht. Cng sut nh mc ca pha A, B, C c tnh nh sau: Pdm , A = Pdm , AB p ( AB ) B + Pdm , BC p ( BC ) B + Pdm , BN Pdm , B = Pdm , AB p ( AB ) B + Pdm, BC p ( BC ) B + Pdm , BN Pdm,C = Pdm , AC p ( AC ) C + Pdm , BC p( BC ) C + Pdm ,CN

Trong Pdm, AB - tng cng sut nh mc ca thit b mt pha lm vic in p dy A_B

Pdm , AC - tng cng sut nh mc ca thit b mt pha lm vic in p dy A_C Pdm , BC - tng cng sut nh mc ca thit b mt pha lm vic in p dy B_C Pdm, AN Pdm , BN Pdm,CN - Tng cng sut nh mc ca thit b mt pha lm vic in p pha A, B, C v trung tnh.BIGING MN CUNG CP IN Page5


p ( AB ) A, , p ( AC ) A, , q ( AB ) A, , q ( AC ) A, - h s quy i v pha A ca cc thit b ni vo in p dy AB v AC p ( AB ) B , , p ( BC ) B , q ( AB ) B , , q ( BC ) B , - h s quy i v pha B ca cc thit b ni vo in p dy AB v BC p ( AC ) C , , p ( BC )C , q ( AC ) C , , q ( BC )C , - h s quy i v pha B ca cc thit b ni vo in p dy AC v BC.K hiu H s cng sut 0.65 0.7 0.84 0.8 0.16 0.30 0.88 0.20 0.22 0.80

p ( AB ) A, p ( BC ) B p ( AC ) C , p ( AB ) B , p ( BC )C p ( AC ) A, q ( AB ) A, q ( BC ) B , q ( AC )C , q ( AB ) B , q ( BC )C , q ( AC ) A,

0.4 1.17 -0.17 0.86 1.44

0.5 1 0 0.58 1.16

0.6 0.89 0.11 0.38 0.96

0.8 0.72 0.28 0.09 0.67

0.9 0.64 0.36 -0.05 0.53

1 0.5 0.5 -0.29 0.29

Cng sut phn khng cng c tnh ton tng t Qdm, A = Qdm, AB q ( AB ) A + Qdm, AC q ( AC ) A + Qdm, AN

Qdm , B = Qdm , AB q ( AB ) B + Qdm , BC q ( BC ) B + Qdm , BN Qdm ,C = Qdm , AC q ( AC ) C + Qdm , BC q ( BC ) C + Qdm ,CN


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TS. L MINH PHNG [CHNG III: TNH TON PH TI IN] 2. PH TI TRUNG BNH - Ph ti trung bnh ca thit b hay nhm thit b l cng sut trung bnh ca thit b hay nhm thit b tiu th trong mt khong thi gian no . - i vi mt h tiu th: 1 t 1 t ptb = pdt qtb = qdt t 0 t 0 - i vi cc nhm h tiu th 1 T 1 T Ptb = Pdt Qtb = Qdt T 0 T 0 - Trong thc t ph ti thay i theo khng theo quy lut tuyn tnh nn kh ly tch phn v vy ta c th xc nh cng sut trung bnh thng qua in nng (c xc nh bng cng t)

ptb =

aQ t t 2 2 ptb + qtb itb 3U dm ap ; qtb = Aq T2 2 ; S tb = Ptb + Qtb

i vi nhm h tiu th : Ptb = Ap T ; Qtb =I tb ==

2 2 Ptb + Qtb

3U dm

Trong : - a p , a q , AP , AQ - in nng tc dng v phn khng tiu th ca mt h tiu th ring bt hoc ca

mt nhm h tiu th sau khong thi gian t (T) - Cng sut tc dng trung bnh (hay phn khng trung bnh) ca nhm cc h tiu th ring bit tham gia trong nhm ny :Ptb = ptb ,ii =1 n

; Qtb = qtb ,i

- Ph ti trung bnh theo cng sut trong mt ca c ti ln nht c k hiu tng t nh trn nhng thm ch s ph: Ptb ,max , Qtb ,max . Ph ti trung bnh cc i Ptb ,max , Qtb ,max l i lng c bn tnh ton ph ti nhm h tiu th v ca phn xng hay x nghip - Ca tiu th in nng ln nht ca cc nhm tiu th, phn xng hay x nghip trong mt ngy m in hnh gi l ca ti ln nht. Nhng ngy m c xem l in hnh nu trong thi gian in nng tiu th xp x bng gi tr in nng tiu th trung bnh cc i sau mi ngy lm vic trong thi gian ang kho st (tun l, thng,nm).


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TS. L MINH PHNG [CHNG III: TNH TON PH TI IN]3. PH TI TRUNG BNH BNH PHNG: dng xc nh tn hao cng sut trong dy dn Ph ti trung bnh bnh phng Ptb ,bp , Qtb ,bp , I tb ,bp sau khong thi gian bt k c xc nh theoPtbbp = 1 T

biu thc sau :

T

0

P 2 (T )dt ; Qtbbp =

1 T

T

0

Q 2 (T )dt ; I tbbp =

1 T

T

0

I 2 (T )dt

Trong T- khong thi gian kho st Hay:2 2 P12 t1 + P22 t 2 + ... + Pn2 t n Q12 t1 + Q2 t 2 + ... + Qn t n Ptbbp = Qtbbp = t1 + t 2 + ...t n t1 + t 2 + ...t n Nu t1=t2==tn =ti v T=t1+t2++tn =nti

Ptbbp =

P12 t1 + P22 t 2 + ... + Pn2 t n = t1 + t 2 + ...t n

nt i ( P12 t1 + P22 t 2 + ... + Pn2 t n ) = T

n ( A pi ) 2i =1

n

Tn ( Aqi ) 2n

2 2 2 2 nt i (Q12 t1 + Q2 t 2 + ... + Qn t n ) Q12 t1 + Q2 t 2 + ... + Qn t n i =1 = = t1 + t 2 + ...t n T T Trong Api, Aqi in nng tc dng v in nng phn khng tiu th trong khong thi gian ti - Cng sut phn khng trung bnh bnh phng Qtb ,bp c ngha quan trng nh gi hiu sut

Qtbbp =

gim tn tht in nng trong li in khi nng cao cos


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TS. L MINH PHNG [CHNG III: TNH TON PH TI IN]4. PH TI CC I. - Ph ti cc i chia lm hai loi a. Ph ti cc i Pmax: ph ti trung bnh ln nht trong khong thi gian no (10,30,60 pht). Thng thng ly thi gian 30 pht v gi l ph ti cc i na gi (P30, Q30, S30, I30). Theo gi tr ph ti ny la chn cc phn t ca h thng cung cp in theo iu kin pht nng v tnh tn hao cng sut cc i ca chng. b. Ph ti nh nhn Pn - ph ti cc i tc thi-ph ti nh: l ph ti cc i xut hin trong khong thi gian rt ngn 1-2 giy. Theo gi tr ph ti ny kim tra dao ng in p nh gi tn hao in p trong mng tip xc kim tra iu kin t khi ng ca ng c, chn dy chy cu ch, tnh dng in khi dng ca rle bo v dng in cc i. - Tn s xut hin ph ti nh nhn cng cao cng nh hng khng tt n ch lm vic ca cc thit b trong li in. khc phc tnh trng ny ngi ta p dng cc bin php gim dng in khi ng bng cc phng php khc nhau. 5. PH TI TNH TON - Ph ti tnh ton l ph ti gi thit khng i lu di ca cc phn t trong h thng cung cp in tng ng vi ph ti thc t theo iu kin tc dng nhit nng n nht. - Ph ti tnh ton c nh ngha l ph ti trung bnh cc i theo mt khong thi gian xc nh T, trong khong thi gian ny ph ti tnh ton lm dy dn nng ln ti nhit bng nhit ln nht do ph ti thc t gy ra. - Bng thc nghim ngi ta xc nh khong thi gian trung bnh ti u bng 3 ln thi gian nung nng dy dn . Trong khong thi gian gian trung bnh ti u ny pht nng ca dy dn t ti 95% tr s xc lp. Theo nghin cu thc t cho bit i vi dy dn va th =10 pht. V th thi gian tnh ph ti trung bnh cc i l 30 pht. Ptt = Ptb max_ 30

- Nh vy ph ti tnh ton Ptt dng la chn dy dn v thit b in theo iu kin pht nng c tnh bng ph ti cc i na gi.


Page9

TS. L MINH PHNG [CHNG III: TNH TON PH TI IN]II. CC CH TIU CA TH PH TI

- Cc ch tiu ca th ph ti l nhng h s khng th nguyn c trng ch lm vic ca cc h tiu th in nng theo cng sut hoc theo thi gian c dng kho st v tnh ton th ph ti in cc h s ca ph ti c xc nh cho th ring bit cng nh cho c th nhm ca cng sut phn khng, cng sut tc dng v cng sut biu kin hoc dng in Cc h s th ph ti c dng theo h thng k hiu sau - Tt c h s ca th ph ti ring bit, hay thit b v th ph ti nhm c k hiu tng ng bng ch k v K. - Loi h s c k hiu bng ch ci u tin tn gi n. - Tt c cc h s ca th ph ti cng sut tc dng P, p c k hiu khng c ch s ph , cn i vi cng sut phn khng Q,q v dng in I , i c k hiu theo ch s ph tng ng q v I na V d : K dt v K dtq l h s in kn th ph ti cng sut tc dng v cng sut phn khng.1. H s s dng: ksd, Ksd : H s s dng cng sut tc dng ca h tiu th k sd hoc ca nhm h tiu th K sd l t s gia cng sut tc dng trung bnh ca h tiu th (hay nhm h tiu th) vi cng sut nh mc ca n (quy v ch lm vic di hn): a. i vi mt thit b: p k sd = tb p dm - H s ny c xc nh bng phng php th nghim v c ghi vo cc bng theo cng thc cho cc thit b khc nhau: p1T1 + p 2T2 + ... + pi Ti A k sd = = sd p dm (T1 + T2 + ... + Ti + Tnghi ) Adm b. i vi nhm thit b:

K sd

P = tb = Pdm

ki =1 n 1

n

sdi

p dmidmi

p

; k sd =

Asd _ n hom P1T1 + P2T2 + ... + Pi Ti = Pdm (T1 + T2 + ... + Ti + Tnghi ) Adm _ n hom

Trong Asd, Asd_nhom in nng tiu th ca thit b hay ca nhm thit b trong thi gian kho st; Adm, Asd_nhom - in nng tiu th ca thit b hay ca nhm thit b trong thi gian kho st ch nh mc. Tng t , h s s dng cng sut phn khng k sd ,Q ; K sd ,Q v dng in k sd , I ; K sd , I c xc nh :k sd ,Q q = tb q dm

; K sd ,Q

Q = tb = Qdm

k1 n 1

n

sd ,Q

p dm

q

k1 n 1

n

sd ,Q

p dm

dm

pi

dm

k sd , I

i = tb idm

; K sd , I

I = tb I dm

k1 n 1

n

sd , I dm

i

dm


Page10

TS. L MINH PHNG [CHNG III: TNH TON PH TI IN]2. H s ng in cho h tiu th k l t s ca thi gian ng in cho h tiu th t lv vi thi gian ca c chu k kho st t ck . Thi gian ng in cho h tiu th t d trong mt chu k l tng thi gian lm vic t lv vi thi gian chy khng ti t kt , tc l : t t k = lv = lv tck tlv + tkt H s ng in cho nhm h tiu th hoc h s nhm K - i vi nhm ph ti: L gi tr trung bnh c trng s (theo cng sut tc dng nh mc) ca h s ng in cho tt c cc h tiu th tham gia trong nhm, tnh theo cng thc sau:

K = -

k1 n 1

n

i

pdmidmi

p

T th ph ti h s ng in c tnh bng biu thc sau: t + t + ... + tn k = 1 2 t1 + t2 + ... + tn + tkt 3. H s mang ti (h s ph ti) kpt, Kpt l t s gia cng sut tc dng thc t tiu th (tc l ph ti trung bnh trong thi gian ng ptb ,d thuc khong t ck ) vi cng sut nh mc ca n:pong p = k pt = thucte = pdm pdm 1 ttck

p(t )dt0

pdm

1 1 hay k pt = pdm t

tck

p(t )dt =0

A pm t

Mt khc ta bit A = ptb t ck v t = tlv nn ta c

k pt =-

ptb t ck k sd = pdm t k

Tng t nh h s ph ti theo cng sut phn khng v theo dng in bng k sd ,Q k sd , I k pt , I = k pt ,Q = kd kd H s ti theo cng sut tc dng ca c nhm K pt l t s ca h s s dng nhm K sd vi h sK pt =

-

ng nhm K d tc lK sd Kd - H s mang ti cng nh h s ng, c lin quan trc tip n quy trnh cng ngh v thay i theo ch lm vic ca h tiu th - Nu thit b lm vic lin tc trong sut qu trnh kho st th h s ph ti bng h s s dng v khi h s ng in bng 1 v h s ph ti bng h s s dng.


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TS. L MINH PHNG [CHNG III: TNH TON PH TI IN]4. H s hnh dng Khd : H s hnh dng th ph ti ca thit b ring bit k hd hoc ca th ph ti nhm K dh biu din s khng u ca th ph ti l t s gi tr gia cng sut trung bnh bnh phng vi cng sut trung bnh n trong thi gian kho st , tc l : ptb ,bp Ptb ,bp ; K hd = k hd = ptb Ptb - Tng t h s hnh dng ca mt h tiu th hoc ca nhm h tiu th tnh theo cng sut phn khng v dng in nh sau : qtb ,bp Qtb ,bp ; K hd ,Q = k hd ,Q = qtb Qtb i s I S k hd , I = tb ,bp = tb ,bp K hd , I = tb ,bp = tb ,bp itb stb I tb Stb - H s hnh dng c trng s khng ng u ca th ph ti theo thi gian, gi tr nh nht ca n ly bng 1, khi ph ti khng i theo thi gian. - Theo nghin cu thc nghim th h s hnh dng dao ng trong khong 1.02-1.15. - Nu xc nh bng cng t in thK hd = m( A pi ) 2i =1 n

Ap

Trong

Ap - in nng tc dng trong thi gian kho st T Api - in nng tc dng trong thi gian t i =

T n 5. H s cng sut tc dng cc i k max , K max L t s cng sut tc dng tnh ton ptt , Ptt vi cng sut trung bnh ptb , Ptb Trong thi gian kho st : p P k max = tt ; K max = tt ptb Ptb - Thi gian kho st ly bng thi gian ca ca mang ti ln nht. - Thng thng h s cc i c xt vi th ph ti nhm tc l xc nh K max v gi tr ca n ph thuc vo s thit b hiu qu ca nhm - Tng t h s cc i ca th ph ti tnh theo dng in dc xc nh nh sau : K max, I = I tt / I tbH s cc i K max l i lng tnh ph thuc vo s h tiu th hiu qu nhq v mt lot cc c trng cho ch tiu th in nng ca nhm h tiu th . H s cc i cng sut tc dng K max c th coi mt cch gn ng l hm s ca cc h tiu th hiu qu nhq v h s trung bnh Kmax=f(Ksd,nhd). - Trong tnh ton thc t quan h K max = f (nhq , K sd ) c biu din di dng cc ng cong tnh ton. C th xc nh Kmax bng cc cch sau: a. Xc nh bng cng thc: 1,5 K max = 1 + nhqBIGING MN CUNG CP IN

1 K sd K sdPage12


b.

Tra bng

c.

Xc nh theo ng cong.


Page13

TS. L MINH PHNG [CHNG III: TNH TON PH TI IN]6. H s nhu cu Knc: H s nhu cu cng sut tc dng l t s gia cng sut tc dng tnh ton (trong iu kin thit k) hoc cng sut tc dng tiu th (trong iu kin vn hnh) vi cng sut tcdng nh mc (cng sut t ca nhm h tiu th ) P P P P P P K nc= t ,thu K nc = tt = tt tb = tb tt = K sd K max hay Pm Pdm Pdm Ptb Pdm Ptb Tng t h s nhu cu i vi dng in ph ti tnh theo : I t ,th I K nc , I = K nc , I = tt hay I dd I dd - Gi tr h s nhu cu ca cc nhm h tiu th khc nhau ca nghnh cng nghip v cc x nghip khc nhau thng xc nh theo kinh nghim vn hnh v khi thit k ly t s tay tra cu t cc biu thc P P K nc = tt tb = K sd K max Pdd Ptb I K nc , I = tt = K sd , I K max, I I dd 7. H s in kn th ph ti cng sut tc dng K dk l t s gia cng sut trung bnh vi cng sut cc i trong thi gian kho st : P K dk = tb Pmax - Thi gian kho st ly bng thi gian ca ca ph ti ln nht. Nu coi rng Pmax thc cht l Ptt th h s in kn th ph ti l mt i lng nghch o ca h s cc i: P 1 K dk = tb == Pmax K max - H s in kn ca th ph ti c quan h vi th ph ti ca nhm nh h s cc i. Tng t xc nh c h s in kn th ph ti theo cng sut phn khng v theo dng in Q 1 K dk ,Q = tb = Qmax K max,Q

K dk , I =-

I tb 1 = I max K max, I

H s in kn th ph ti K dk , K dk ,Q , K dk , I ng vai tr quan trng trong vic nh gi th

ph ti ngy v m v th ph ti nm8. H s ng thi Kt - h s ng thi cc tr s cc i ca ph ti K dt : l t s gia cng sut tc dng tnh ton tng ti nt kho st ca h thng cung cp in vi tng cc cng sut tc dng tnh ton cc i ca cc nhm h tiu th ring bit ni vo nt : P ; K dt 1 K dt = n tt ptt ,i1

- H s ny cho ta bit cc kh nng ph ti cc i ca cc nhm thit b trong nt xy ra cng mt thi gian. Nu xy ra trong cng mt thi gian th Kt=1,BIGING MN CUNG CP IN Page14

TS. L MINH PHNG [CHNG III: TNH TON PH TI IN] - Gi tr K dt thay i theo thi gian ca nm, v cc i trong ngy thay i v tr s v theo thi gian Ptt , px - i vi phn xng: K dt , px = n ptt ,i1

-

-i vi nh my

K dt ,nm =

Ptt ,nm

P1

n

tt , px

Trong :

K dt , px - H s ng thi ca ph ti phn xng

p

n

tt ,i

- Tng ph ti tnh ton ca n nhm h tiu th ring bit trong phn xng

Ptt , px - Ph ti tnh ton tng ca phn xng K dt ,nm - H s ng thi ca nh my

P1

n

tt , px

- Tng ph ti tnh ton ca phn xng ring bit trong nh my

Ptt ,nm - Ph ti tnh ton tng ca nh myKhi thit k ta c th ly gi tr gn ng i vi ng dy cao p ca mng cung cp ni b nh my: K dt = 0,85 1,0 i vi thanh ci ca nh my, x nghip hay thanh ci ca trm phn phi chnh th K dt = 0,9 1,0 Lu : Phi la chn K dt sao cho ph ti tnh ton tng ca nt ang xt khng c nh hn ph ti trung bnh nt .

9. S thit b hiu qu nhq ca nhm thit b l s thit b quy i c cng sut nh mc, ch lm vic nh nhau v c tng cng sut tnh ton bng tng cng sut tiu th ca cc thit b thc t trong nhm. - Gi thit c mt nhm gm n h tiu th c cng sut nh mc v ch lm vic khc nhau. Ta gi nhq l s h tiu th hiu qu ca nhm , l mt s quy i gm nhq h tiu th c cng sut

nh mc v ch lm vic nh nhau, v c ph ti tnh ton bng ph ti tiu th thc bi n h tiu th trn ( Ptt _ ntbhq = Ptt _ ntb ). S h tiu th hiu qu c xc nh nh sau : n p dmi 1 = i =n 2 p dmii =1 2

n hq

Nu tt c cc thit b ca nhm u c cng sut nh mc nh nhau th nhq = n


Page15

TS. L MINH PHNG [CHNG III: TNH TON PH TI IN]III. XC NH PH TI CNG SUT TRUNG BNH CA NHM THIT B Nhm thit b ba pha Cng sut tc dng trung bnh ca ca ph ti ln nht Pca ca nhm thit b vi cng ch lm vic c xc nh bng cch nhn cng sut nh mc tng ca nhm h tiu th lm vic Pdm , quy i v cc h tiu th c ch lm vic ngn hn lp li v ch lm vic di hn (a = 100%) vi h s s dng nhm ca chng Pca = K sd Pdm - Cng sut phn khng trung bnh ca ca ph ti ln nht Qca nhm thit b vi ch lm vic ging nhau, c xc nh nh sau: Bng cch nhn cng sut phn khng nh mc tng ca nhm cc h tiu th lm vic Qdm quy i v ch lm vic di hn (a=100%) vi h s s dng nhm : Qca = K sd Qdm Bng cch nhn cng sut tc dng trung bnh Pca ca nhm vi tg tng ng vi h s cng sut trung bnh cos ca nhm Qca = Pca tg (4-52) Trong Ksd, cos l h s s dng v h s cng sut ca nhm

1. a. -

K sd =

ki =1 n i =1

n

sdi p i

pi

; cos =

cos pi =1 i

n

i

pi =1

n

i

Cng sut phn khng trung bnh ca nhm t in tnh c xc nh: U Qtb _ tu = Qll _ tu ( ) 2 U ll Trong : Qll _ tu - cng sut theo l lch ca nhm t ng vi in p U llU - in p thc t ca li. b. Nhm thit b mt pha: Cng sut trung bnh ca nhm thit b mt pha gn vo li 3 pha phn * b khng u c xc nh da trn ph ti trung bnh quy c Ptb ca nhm thit b mt pha:* Ptb = 3Ptb _ pha _ max* Qtb = 3Qtb _ pha _ max

Cng sut trung bnh ca tng pha c tnh ging nh cng sut nh mc Ptb , A = k sd _ AB p dm , AB p ( AB ) A + k sd _ AC p dm , AC p ( AC ) A + k sd _ AN p dm , ANPtb ,C = k sd _ BC p dm , BC p ( BC ) C + k sd _ AC p dm , AC p ( AC ) C + k sd _ CN p dm ,CN Ptb , B = k sd _ AB p dm , AB p ( AB ) B + k sd _ BC p dm , BC p ( BC ) B + k sd _ BN p dm , BN

Trong ksd_AB , ksd_BC , ksd_AC h s s dng cc thit b gn vo in p dy AB, BC, AC. ksd_AN , ksd_BN , ksd_AN h s s dng cc thit b gn vo in p dy AN, BN, CN


Page16


c. Trng hp ng qut: Cng sut trung bnh ti nt c c thit b ba pha v thit b mt pha phn b khng u trn in p pha v in p dy c tnh nh sau:* Ptb = Ptb + Ptbi * Qtb = Qtb + Qtbi i =1 i =1 n n

2. a.

XC NH PH TI NH: c trng cho ph ti nh thng thng l dng in

Mt thit b: Dng nh nhn ca thit b chnh l dng khi ng ca n I k = I mm = k mm I dm _ TB

b. Nhm thit b: Dng in nh ca nhm thit b in h p xc nh bng tng s ca dng in khi ng ln nht trong cc ng c trong nhm v dng in tnh ton ca cc thit b in cn li trong nhm tr dng in nh mc ca ng c c dng in khi ng ln nht trn (c xt n h s s dng ca n ) : I n _ n hom = I kd ,max + ( I tt k sd I dm ,max )

Trong I kd ,max - dng in khi ng thit b in c dng khi ng ln nht trong nhm.

I m,max - dng in nh mc quy i v T = 100% ca ng c c dng in khi ng ln nht k sd - h s s dng ca ng c c dng khi ng ln nht I tt - dng in tnh ton ph ti ca nhm h tiu th3U dm - Vi ng c in khng ng b roto lng sc v ng c in ng b kmm=3:5 - Vi ng c in mt chiu hoc ng c khng ng b roto dy qun dng in khi ng ly khng nh hn 2,5 ln dng in nh mc. - Dng in nh ca my bin p l in v my bin p khng nh hn 3 ln dng in nh mc (theo l lch my tc l khng quy i v T = 100% ) 3. XC NH DNG IN TNH TON a. Nu l 1 thit b th dng in tnh ton cc tnh bng cng thc pdm itt = idm = 3U dm cos b. Nu l nhm thit b th dng in tnh ton doc tnh bng cng thc S tt Ptt I tt = = 3U luoi 3U luoi cos

I tt =

S tt


Page17

TS. L MINH PHNG [CHNG III: TNH TON PH TI IN]IV. CC PHNG PHP XC NH PH TI TNH TON NH MY CNG NGHIP Trong thc t c nhiu phng php tnh ton ph ti chnh xc khc nhau nh: - Theo cng sut t v h s nhu cu. - Theo cng sut trung bnh v lch cng sut tnh ton vi cng sut trung bnh. - Theo cng sut trung bnh v h s hnh dng. - Theo cng sut trung bnh v h s cc i - Theo lng tiu th in nng trn mt n v sn phm. - Theo lng in nng trn mt dn v din tch. Vic la chn phng php tnh ton ph thuc vo chnh xc cho php cng nh d liu cho trc. Tuy nhin phng php c coi l chnh xc nht l phng php da trn d liu ca tng thit b ring l. 1. THEO SUT TIU HAO IN NNG TRN MT N V SN PHM - i vi h c th ph ti thc t khng thay i hoc thay i t ph ti tnh ton bng ph ti trung bnh v c xc nh theo sut tiu hao in nng trn mt n v sn phm khi cho trc tng sn phm sn xut trong mt khong thi gian. Nhng thit b ny thng l qut gi, bm, l in tr, xi nghip giy, x nghip ha cht h s ng in bng 1 cn h s ph ti thay i t: M a Ptt = Pca = ca Tca Trong : a - sut tiu hao in nng trn mt n v sn phm tnh bng kWh (ti liu tra cu) M ca - s lng sn phm sn sut trong mt ca Tca - thi gian lm vic ca ca mang ti ln nht. - Khi s liu ban u cho s lng sn phm hng nm ca phn xng hoc x nghip th Ma Ptt = Pca = Tmax Trong : a - sut tiu hao in nng trn mt n v sn phm tnh bng kWh (ti liu tra cu) M - s lng sn phm sn sut trong mt nm Tmax - thi gian s dng cng sut ln nht hng nm. 2. THEO SUT PH TI TRN MT N V DIN TCH. - Vi nhng phn xng sn xut c nhiu thit b phn b tng i ng u nh phn xng may, dt ta c th xc nh ph ti tnh ton nh sau : Ptt = p0 F Trong F - din tch b tr nhm h tiu th , m 2 p 0 - cng sut tnh ton trn mt m 2 din tch sn xut (tng t nh S 0 ) kW / m 2 - Nhn xt: Sut ph ti tnh ton p 0 ph thuc vo dng sn xut v c phn tch theo s lng thng k. Phng php ny l phng php gn ng v ch yu da vo kinh nghim


Page18

TS. L MINH PHNG [CHNG III: TNH TON PH TI IN]3. THEO CNG SUT T V H S NHU CU Pm, Knc - Ph ti tnh ton ca nhm h tiu th cng ch lm vic c tnh theo cng sut t ( Pm ) v h s nhu cu ( K nc )biu thc :

Ptt = K nc Pdm Qtt = Ptt tg2 S tt = Ptt2 + Qtt =

Ptt cos

Trong K nc - h s nhu cu ca nhm h tiu th c trng ly trong cc ti liu tra cu ; tg - tng ng vi cos c trng ca nhm h tiu th cho trong cc ti liu tra cu Gi tr K nc - ph thuc vo gi tr K sd - ly theo bng di y ng vi K d = 0,8 Pdm Cng sut t bit trc ca phn xng hay nhm thit b. 0.4 0.5 0.6 0.7 0.8 0.9 Ksd Knc 0.5 0.6 0.65-0.7 0.75-0.8 0.85-0.9 0.92-0.95

- Ph ti tnh ton im nt ca h thng cung cp in (phn xng, nh my, x nghip ) c xc nh bng tng ph ti tnh ton ca cc nhm h tiu th ni vo nt ny c k n h s ng thi, ngha l tnh theo biu thc sau :

n n S tt = K dt Ptt + Qtt 1 1 Trong

2

2

P

n

tt

- tng ph ti tc dng tnh ton ca cc nhm h tiu th, xc nh theo cng thc - tng ph ti phn khng tnh ton ca cc nhm h tiu th , xc nh theo cng thc

Q1

1 n

tt

K dt - h s ng thi. - H s nhu cu ng vi nhm thit c cng ch lm vic K nc khng i v bng K sd khi s thit b kh ln ( K max = 1 ) - Tr s K nc ch chnh xc khi la chn tit din dy dn (nh hn 25mm2). Nn i vi dy dn c tit din ln hn th nu dng tr s ny Ptt s ln hn cng sut tnh ton thc t. - Nhn xt: Xc nh ph ti tnh ton theo cng sut t v h s nhu cu l mt phng php gn ng s lc nh gi ph ti tnh ton v vy ch c th dng tnh ton s b ph ti cc im nt c nhiu h tiu th ni vo h thng cung cp in ca mt phn xng, mt to nh hoc mt nh my


Page19

TS. L MINH PHNG [CHNG III: TNH TON PH TI IN]4. THEO CNG SUT TRUNG BNH V H S HNH DNG - Ph ti ca nhm thit b c coi l cng sut trung bnh bnh phng v xc nh theo cng sut trung bnh v h s hnh dng th ph ti K hd dng cho nhm thit b c th ph ti thay i t xut, dao ng vi tn s cao. Qtt = K hdq Qtbca Ptt = K hd Ptbca

hoc

Qtt = Ptt tg2 S tt = Ptt2 + Qtt

- Theo phng php ny ph ti tnh ton c coi l bng ph ti trung bnh bnh phng, tc l Ptt = Ptbbp ; Qtt = Qtbbp - Nhn xt: Ni chung gi thit ph ti tnh ton bng ph ti trung bnh bnh phng l khng chnh xc , tuy nhin trong mt s trng hp ph ti trung bnh bnh phng c th s dng nh ph ti tnh ton , chng hn i vi cc nhm h tiu th vi ch lm vic lp li ngn hn.5. THEO CNG SUT TRUNG BNH V H S CC I Ptb, Kmax - Phng php ny gi l phng php sp xp biu ph ti hay l phng php xc nh ph ti tnh ton theo s thit b hiu qu, Theo phng php ny ph ti tnh ton l ph ti trung bnh cc i na gi. - Ph ti tc dng tnh ton ca nhm h tiu th c th ph ti bin i ( tt c cc bc ca li cung cp v phn phi, k c my bin bin p v ny bin i) c xc nh theo cng sut trung bnh v h s cc i nh sau. a. Khi cc thit b l 3 pha. Khi n3 th

Ptt = p dm ,i v Qtt = q dm ,i = p dm ,i tg dd ,i1 1 1

n

n

n

Trong pdmi cng sut nh mc ca tng thit b ( quy i) cosI - h s cng sut ca tng thit b. Khi s thit b trong nhm n>3 v nhq3 v nhq 4 nhq 200 Ptt = K max Ptb = K max K sd PdmBIGING MN CUNG CP IN Page20

TS. L MINH PHNG [CHNG III: TNH TON PH TI IN] Trong : K max = f (nhq ) - h s cc i c xc nh theo nhq v K sd theo ng cong hay theo cng thc: 1,5 1 K sd KM = 1+ K sd n hqPtb - Cng sut tc dng trung bnh ca nhm thit b trong ca c ph ti ln nht K sd - h s s dng ca nhm thit b. Pm cng sut t hay cng sut nh mc ca nhm thit b quy i v ch lm vic di hn (a=100%) nhq 10 Qtt = 1,1Qtb Khi

Khi Trong

nhq > 10

Qtt = Qtb

Qtb - cng sut phn khng trung bnh ca nhm thit b trong ca mang ti ln nht. Qtb = Ptb tg tb = Pm K sd tg tb tgtb - tang trung bnh ca nhm Nu s thit b hiu qu ca nhm nhq>200 th Ptt=Ptb2 S tt = Ptt2 + Qtt

I tt =

S tt3U m

=

2 Ptt2 + Qtt

3U m

b. Nu thit b l 1 pha: Ph ti tnh ton ca nhm thit b mt pha phn b u trn li 3 pha c cng ch lm vic c tnh nh thit b ba pha. - S thit b hiu qu ca nhm thit b mt pha c th tnh n gin nh sau:

nhq = Trong :

2 pmii =1

n

3 pm _ max

pm _ max - cng sut nh mc ca thit b mt pha ln nht

pi =1

n

mi

- tng cng sut ca n thit b mt pha ca nhm.

Ph ti tnh ton ca nhm thit b mt pha (n>3) phn b khng u trn li 3 pha c ch lm vic khc nhau c tnh thng qua ph ti tnh ton quy c Ptt* - S thit b hiu qu ca nhm thit b mt pha c th tnh n gin nh sau: nhq = 2 pmii =1 n

3 pm _ max

* Ptt* = Ptb K max


Page21

TS. L MINH PHNG [CHNG III: TNH TON PH TI IN] Khi Khi nhq 10 nhq > 10* Ptb = 3Ptb _ pha _ max * Qtb = 3Qtb _ pha _ max* * Qtt = 1,1Qtb

* * Qtt = Qtb

Ptb , A = k sd _ AB p dm , AB p ( AB ) A + k sd _ AC p dm , AC p ( AC ) A + k sd _ AN p dm , AN Ptb ,C = k sd _ BC p dm, BC p ( BC ) C + k sd _ AC p dm , AC p ( AC ) C + k sd _ CN p dm ,CN Ptb , B = k sd _ AB p dm , AB p ( AB ) B + k sd _ BC p dm , BC p ( BC ) B + k sd _ BN p dm , BN

Ph ti tnh ton ca nhm thit b mt pha phn b khng u trn li 3 pha c th ph ti khng i * Ptt* = Ptb* * Qtt = Qtb


Page22


V. XC NH PH TI TNH TON TI CC NT CA H THNG CUNG CP IN . - Thit k cung cp in cho cc x nghip gm hai giai on: giai on thit k s b v giai on thit k thi cng. Trong giai on on thit k s b ta ch cn tnh s b gn ng ph ti in da trn c s tng cng sut t ca cc thit b trong ton phn xng hay ton nh my. giai on thit k thi cng ta tin hnh tnh ton chnh xc ph ti in ti cc nt trong h thng. Xc nh ph ti t bc thp ln bc cao ca h thng.

- Ph ti tnh ton ti cc nt ring bit ca h thng cung cp in gm cc thit b khc nhau (ng c in c ch lm vic di hn, lm vic ngn hn lp li v lm vic ngn hn ca dng in ba pha v mt pha, in p n 1000V v cao hn) cc h tiu th chiu sng, c tin hnh theo cng sut trung bnh v h s cc i. - Phi xem xt ti h p v ti cao p ring bit. Ta phi tnh ton ph ti t di ln trn: 1. Xc nh ph ti tnh ton ca tng thit b in p di 1kV ta c th coi l cng sut nh mc ca thit b ny (nu thit b lm vic ch ngn mch lp li th phi quy i v ch lm vic di hn). Theo gi tr ti ny ta tnh dng in tnh ton ng thi la chn dy dn cng nh thit b bo v cho tng thit b: pm , im


Page23

TS. L MINH PHNG [CHNG III: TNH TON PH TI IN] 2. Ph ti tnh ton Ptt 2 ca mt nhm thit b ng lc xc nh theo mt trong cc phng php trnh by trn c tnh n ph ti chiu sng, ph ti sinh hot v thit b b cng sut phn khng lp t trn thanh ci (nu c)S tt 2 = ( Ptt 2 + Pcs 2 + Psh 2 ) 2 + (Qtt 2 + Qcs 2 + Qsh 2 Qbu 2 ) 2

Trong Ptt 2 , Pcs 2 , Psh 2 - cng sut tc dng tnh ton ca ti ng lc, ti chiu sng v ti sinh hot. Qtt 2 , Qcs 2 , Qsh 2 , Qbu 2 - Cng sut phn khng tnh ton ca ti ng lc, ti chiu sang, ti sinh hot v thit b b cng sut phn khng - Theo cng sut S tt 2 ta xc nh dng in tnh ton ng thi la chn dy dn cng nh thit b bo v. - Trong phn ny phi xc nh cng sut trung bnh ca nhm thit b ng lc Ptb _ nhm , Qtb _ nhm h s cng sut trung bnh cos tb _ nhm , h s s dng trung bnh nhm K sd _ nhm , h s cc i K max_ nhm . Sau xc nh cng sut tc dng tnh ton Ptt 2 3. Ph ti tnh ton ca thanh ci pha h p ca MBA lc c tnh bng tng cng sut tnh ton ca cc nhnh trc. Ph ti ny gm cc thit b cng sut ln, cc t phn phi cp cho cc t ng lc hay nhm thit b.Ptt 3 = Ptt 2 k + Pcs 2 j + Psh 2i + Pcs 3 zk =1 n j =1 i =1 z =1 n m l r

Qtt 3 = Qtt 2 k + Qcs 2 j + Qsh 2i + Qcs 3 z Qbu 2 Qbu 3k =1 j =1 i =1 z =1

m

l

r

S tt 3 = ( Ptt 2 + Pcs 2 + Psh 2 ) 2 + ( Qtt 2 + Qcs 2 + Qsh 2 Qbu 2 Qbu 3 ) 2 Nu tnh n h s ng thiPtt 3 = K t Ptt 2 k + Pcs 2 j + Psh 2i + Pcs 3 zk =1 n j =1 i =1 z =1 n m l r

Qtt 3 = K t Qtt 2 k + Qcs 2 j + Qsh 2i + Qcs 3 z Qbu 2 Qbu 3k =1 j =1 i =1 z =1

m

l

r

S tt 3 = ( K t Ptt 2 + Pcs 2 + Psh 2 ) + ( K t Qtt 2 + Qcs 2 + Qsh 2 Qbu 2 Qbu 3 ) 22

- Theo gi tr ti ny ta tnh dng in tnh ton ng thi la chn dy dn cng nh thit b bo v v la chn s lng v cng sut MBA lc. 4. Ph ti tnh ton pha cao p ca MBA lc 6-22kV ca trm bin pS tt 4 = ( Ptt 3 + PT ) 2 + (Qtt 3 + QT ) 2

Trong Ptb 3 , Qtb 3 cng sut tc dng v cng sut phn khng trung bnh ca pha h p MBA lc. PT , QT tn hao cng sut tc dng v cng sut phn khng ca MBA (Tra cu trong cc bng -trong trng hp khng r dng MBA th c th tnh cc gi tr ny nh sau: PT = 0.02 S tt 3 , QT = 0,1 S tt 3 , ) - Theo gi tr Stt 4 la chn tit din dy dn cp ngun cho trm bin p, thit b bo v tuyn ny.BIGING MN CUNG CP IN Page24

TS. L MINH PHNG [CHNG III: TNH TON PH TI IN] 5. Xc nh ph ti tnh ton trn thanh ci trm phn phi chnh. Ph ti tnh ton ny bao gm ph ti cc trm bin p phn xng v cc thit b lm vic vi in p cao th. la chn tit din thanh ci v tuyn dy ngun, thit b bo v trm h p chnh ta xc nh ph ti ca tng phn on. Cng sut tnh ton ny c xc nh theo cng sut phn khng v cng sut tc dng ca cc phn xng, c tnh n cng sut ca ph ti cao p, ph ti chiu sang nh my v cc thit b b cng sut phn khng2 Ptt 5 = K dt ( Ptt 4 ) + Pbu Qtt 5 = K dt ( Qtt 4 ) Qbu 5 S tt 5 = Ptt25 + Qtt 5

P

Trong : K dt - H s ng thittC 5

,

Q

ttC 5

- Tng cng sut tc dng v phn khng tnh ton ca cc thit b cao p c

cp ngun th thanh ci ca trm h p chnh. Pbu - Tn hao cng sut trong thit b b cao p. Qbu 5 - Cng sut phn khng ca thit b b cao p. Theo gi tr S tt 5 la chn tit din dy dn cho thit b bo v ng dy ngun. 6. Cng sut tnh ton trn thanh ci trm h p chnh xc nh theo cng sut tnh ton ca cc ng truyn ti c tnh n h s ng thi2 Ptt 6 = K t Ptt 5 ; Qtt 6 = ( K t Qtt 6 ) Qb _ 6 S tt 6 = Ptt26 + Qtt 6

- Theo gi tr S tt 6 la chn s lng my v cng sut my bin p trm h p chnh v thit b bo v trm h p chnh. 7. La chn tit din ng dy cp ngun cho trm h p chnh c da trn cng sut tnh ton S tt 7S tt 7 = ( Ptt 6 + PTC ) 2 + (Qtt 6 + QTC ) 2

Trong PTC , QTC - tn hao cng sut tc dng v phn khng trong MBA trm h p chnh.


Page25


VI. MT VI NT CHNH KHI TNH N MC TNG PH TI - Kinh nghim cho thy rng ph ti in ca x nghip tng ln khng ngng (hp l ho tiu th in nng, tng nng sut cc my chnh, tng dung lng nng lng thay hoc hon thin cc thit b cng ngh, xy lp thm cc thit b cng ngh . Nh ch r hp l ha s cung cp in v tt c cc phn t ca n ph thuc vo vic nh gi ng n ph ti in. Khng tnh n s pht trin ca ph ti s dn n ph hoi thng s ti u ca li. - Quan st cc x nghip thuc cc ngnh cng nghip khc nhau v s l s liu trn c s l thuyt xc sut v thng k ton hc ch ra rng hu ht cc trng hp s pht trin ph ti cc i c th m t kh chnh xc theo lut tuyn tnh : S (t ) = S 00 (1 + 1t ) Trong S 00 - cng sut tnh ton ca x nghip thi im khi ng S(t) cng sut tnh ton sau t nm 1 - h s pht trin hng nm ca ph ti

- Phn tch chi ph tnh ton ca cc ng dy v trm bin p cho thy thi gian tnh ton T ( thi gian thc t cng chi ph ) cn phi ly 25 -30 nm nhng khng ln hn thi hn phc v ca thit b chnh - Khi bit ph ti cho mt nm bt k trong khong thi gian tnh ton T c th bng phng php no la chon ng n cc thng s ca cc phn t ca h thng cung cp in x nghip cng nghip thi gian v dng hon thin tip theo khi thit k cho tng lai.


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