cung cẤp ĐiỆn
DESCRIPTION
Bài giảng được biện soạn theo đề cương môn học vật liệu điện: xác định phụ tải, chọn phương pháp cung cấp, chọn thiết bị, cũng như các biện pháp bảo vệ cho lưới.TRANSCRIPT
Chng 1
BGMH: CUNG CP IN
LI NI U
Bi ging c bin son theo cng mn hc Vt liu in cung cp nhng kin thc c bn v cung cp in nh: xc nh ph ti, chn phng n cung cp, chn thit b, cng nh cc bin php bo v cho li cho sinh vin ngnh in.
Bi ging gm mi chng ln lt trnh by cc vn :
Khi qut cung cp in c trnh by Chng 1.
Chng 2 v 3 trnh by v li in v tnh ton ph ti in.
Trm in c cp chng 4.
Tnh ton v li in v la chn thit b in ln lt trnh by chng 5, 6, v 7.
Chng 8 cp cc vn bo v h thng in v vic nng cao h s cng sut c trnh by chng 9.
Chng 10 trnh by v k thut chiu sng.
d dng tip cn cc vn trong bi ging: cc chng cn c c tun t t 1 n 10.
Bi ging c bin son nhm phc v cho sinh vin cao ng v trung hc chuyn nghip ng thi cn phc v cho nhng ngi quan tm n kin thc c bn trong cung cp in.
Do thi gian v trnh ngi bin son c hn nn khng trnh khi nhng thiu st. Tc gi rt mong nhng nhn xt, nh gi v gp ca bn c v ng nghip.
Mi kin xin gi v: [email protected]
Bnh dng, thng 9 nm 2008
Tc gi
MC LC
iLI NI U
iiMC LC
1Chng 1. GII THIU CHUNG V CUNG CP IN
11.1.Li in v li cung cp in:
21.2.Nhng yu cu chung v li cung cp in:
3Chng 2. CC LOI LI IN
32.1.Li in th:
32.2.Li in nng thn:
32.3.Li in x nghip:
32.4.Cc loi dy v cp in:
52.5.Cu trc ng dy ti in:
7Chng 3. TNH TON PH TI IN
73.1.Cc khi nim chung:
73.2.Xc nh ph ti in khu vc nng thn:
73.3.Xc nh ph ti in khu vc cng nghip:
83.4.Xc nh ph ti in khu vc th:
10Chng 4. TRM IN
104.1.Khi qut v phn loi trm in:
104.2.S ni dy trm bin p:
114.3.Cu trc trm:
124.4.La chn my bin p cho trm:
124.5.Ni t trm v ng dy ti in:
13Chng 5. TNH TON TN THT IN
135.1.S thay th li cung cp in:
175.2.Tnh ton tn tht in p:
185.3.Tnh ton tn tht cng sut:
205.4.Tnh ton tn tht in nng:
22Chng 6. TNH TON NGN MCH TRONG H THNG IN
226.1.Khi nim chung:
246.2.Cc phng tnh ton gn ng dng in ngn mch:
296.3.Khi qut v s dng my tnh trong tnh ton ngn mch:
296.4.Phng php tnh ngn mch trong mng in p thp n 1000V:
31Chng 7. LA CHN THIT B IN TRONG LI CUNG CP IN
317.1.Khi qut:
327.2.La chn my ct in:
337.3.La chn cu ch, dao cch ly:
337.4.La chn v kim tra s cch in:
337.5.La chn thanh dn:
347.6.La chn dy dn v cp:
347.7.La chn cc thit b khc:
35Chng 8. BO V H THNG IN
358.1.Khi qut:
358.2.Bo v relay:
368.3.Chng st v ni t:
39Chng 9. NNG CAO H S CNG SUT
399.1.H s cng sut v ngha vic nng h s cng sut:
399.2.Cc gii php b cos:
409.3.B cng sut cho li in x nghip:
41Chng 10. TNH TON CHIU SNG
4110.1.Khi nim chung:
4210.2.Ni dung thit k chiu sng:
4210.3.Thit k chiu sng dn dng:
4210.4.Thit k chiu sng cng nghip:
Chng 1. GII THIU CHUNG V CUNG CP IN
in nng ngy cng ph bin v d dng chuyn thnh cc dng nng lng khc nh: c, ha, nhit nng ; c sn xut ti cc trung tm in v c truyn ti n h tiu th vi hiu sut cao. Trong qu trnh sn xut v tiu th in nng c mt s c tnh:
in nng sn xut ra thng khng tch tr c, do phi c s cn bng gia sn xut v tiu th in.
Cc qu trnh v in xy ra rt nhanh v nguy him nu c s c xy ra, v vy thit b in c tnh t ng v i hi an ton v tin cy cao.
Hnh 1.1. H thng in
Nhng yu cu v ni dung ch yu khi thit k h thng cung cp in:
Muc tiu chnh ca thit k cung cp in l m bo cho h tiu th lun in nng vi cht lng trong phm vi cho php.
Mt phng n cung cp in (cho x nghip) c xem l hp l khi tha mn cc nhu cu sau:
Vn u t nh, ch tit kim ngoi t v vt t him.
m bo tin cy cung cp in ty theo tnh cht h tiu th.
Chi ph vn hnh hng nm thp.
m bo an ton cho ngi v thit b.
Thun tin cho vn hnh v sa cha
m bo cht lng in nng.
Ngoi ra, cn phi ch n cc iu kin khc nh: mi trng, s pht trin ca ph ti, thi gian xy dng
Mt s bc chnh thc hin mt phng n thit k cung cp in:
Xc nh ph ti tnh ton nh gi nhu cu v chn phng thc cung cp in.
Xc nh phng n v ngun in.
Xc nh cu trc mng.
Chn thit b.
Tnh ton chng st, ni t chng st v ni t an ton cho ngi v thit b.
Tnh ton cc ch tiu kinh t k thut.
Tip theo thit k k thut l bc thit k thi cng nh cc bn v lp t, nhng nguyn vt liu cn thit Cui cng l cng tc kim tra iu chnh v th nghim cc trang thit b, a vo vn hnh v bn giao.
1.1. Li in v li cung cp in:
1.1.1. Khi nim:
H thng in gm 3 khu: sn xut, truyn ti v tiu th in.
Ngun in l cc nh my in (nhit in, thy in, in nguyn t) v cc trm pht in (diesel, mt tri, gi)
Tiu th in gm tt c cc i tng s dng in trong cng, nng nghip v i sng
Li in truyn ti in t ngun n h tiu th, li gm ng dy truyn ti v cc trm bin p.
Li in Vit nam hin c cc cp in p: 0,4; 6; 10; 22; 35; 110; 220 v 500kV. Tng lai s ch cn cc cp: 0,4; 22; 110; 220 v 500kV.
1.1.2. Phn loi:
C nhiu cch phn loi li in:
Theo in p: siu cao p (500kV), cao p (220, 110kV), trung p (35, 22, 10, 6kV) v h p (0,4kV).
Theo nhim v: li cung cp (500, 220, 110kV) v li phn phi (35, 22, 10, 6 v 0,4kV).
Ngoi ra, c th chia theo khu vc, s pha, cng nghip, nng nghip
1.2. Nhng yu cu chung v li cung cp in:
1.2.1. tin cy cung cp in:
Ty theo tnh cht ca h dng in c th chia thnh 3 loi:
H loi 1: l nhng h rt quan trng, khng c mt in nh sn bay, hi cng, khu qun s, ngoi giao, cc khu cng nghip, bnh vin
H loi 2: l cc khu vc sn xut, nu mt in c th nh hng nhiu n kinh t
H loi 3: l nhng h khng quan trng cho php mt in tm thi.
Cch chia h nh vy ch l tm thi trong giai on nn kinh t cn thp km, ang hng n mc tiu cc h phi u l h loi 1 v c cp in lin tc.
1.2.2. Cht lng in:
Cht lng in c th hin qua hai thng s: tn s (f) v in p (U). Cc tr s ny phi nm trong phm vi cho php.
Trung tm iu quc gia v cc trm in c nhim v gi n nh cc thng s ny.
Tn s f c gi 50 0,5Hz.
in p yu cu lch |U|= U Um5%Um. Lu lch in p khc vi tn tht in p (hiu s in p gia u v cui ngun ca cng cp in p).
Hnh 1.2: lch v tn tht in p
1.2.3. Tnh kinh t:
Tnh kinh t ca mt phng n cung cp in th hin qua hai ch tiu: vn u t v chi ph vn hnh.
Vn u t mt cng trnh in bao gm tin mua vt t, thit b, tin vn chuyn, th nghim, th nghim, mua t ai, n b hoa mu, tin kho st thit k, lp t v nghim thu.
Ph tn vn hnh: bao gm cc khon tin phi chi ph trong qu trnh vn hnh cng trnh in: lng cho cn b qun l, k thut, vn hnh, chi ph bo dng v sa cha, chi ph cho th nghim th nghim, do tn tht in nng trn cng trnh in.
Thng thng hai loi chi ph ny mu thun nhau. Phng n cp in ti u l phng n dung ha hai chi ph trn, l phng n c chi ph tnh ton hng nm nh nht.
(
)
..min
vhtc
ZaaKcA
=++D
Trong :
vh
a
: h s vn hnh, vi ng dy trn khng ly 0,04; cp v trm bin p ly 0,1.
tc
a
: h s thu hi vn u t tiu chun
1
tc
T
=
, vi li cung cp in
5
tc
T
=
nm.
K: vn u t.
A
D
: tn tht in 1 nm.
c: gi tin tn tht in nng (/kWh).
1.2.4. Tnh an ton:
An ton thng c t ln hng u khi thit k, lp t v vn hnh cng trnh in. An ton cho cn b vn hnh, cho thit b, cng trnh, cho ngi dn v cc cng trnh xung quanh.
Ngi thit k v vn hnh cng trnh in phi tuyt i tun th cc quy nh an ton in.
1.2.5. Mt s k hiu thng dng:
Thit b
K hiu
Thit b
K hiu
My pht in hoc nh my in
ng c in
My bin p 2 cun dy
Khi ng t
My bin p 3 cun dy
My bin p iu chnh di ti
My ct in
Cu ch.
Cu dao cch ly
Aptmt
My ct ph ti
Cu ch t ri
T iu khin
T in b
T chiu sng cc b
T chiu sng lm vic
T phn phi
T phn phi ng lc
n si t
n hunh quang
cm in
Cng tc in
Khng in
My bin dng in
Dy cp in
Dy dn in
Thanh dn (thanh ci)
Dy dn tn s 50Hz
Dy dn mng hai dy
Dy dn mng 4 dy.
ng dy in p
U 36V.
ng dy mng ng lc 1 chiu
Chng st ng
Chng st van
Chng 2. CC LOI LI IN
2.1. Li in th:
Thng s dng cp in p trung p l 22 v 10kV.
tng tin cy cung cp in, li trung p thnh ph thng c cu trc mch vng kn vn hnh h.
m bo an ton v m quan th, thng s dng cp ngm cho mng trung v h p. Thng dng trm bin p kiu xy. Tuy nhin chi ph u t v vn hnh s cao hn nhiu.
thun li cho phn phi v t nh hng n giao thng cc trm bin p thng ch cung cp in cho mt bn ng v c t gc hay gia on ng.
Hnh 2.1. Trm bin p t gc ph.
2.2. Li in nng thn:
nng thn, mi huyn thng c cp in t 1 hay 2 trm bin p trung gian, hin nay thng s dng cp 10 v 35kV. Li phn phi c cu trc dng cy.
Tt c cc tuyn dy u l ng dy trn khng. Cc trm bin p thng dng kiu ct. d qun l v vn hnh trm bin p phn phi thng c t gia thn (lng).
2.3. Li in x nghip:
Cc x nghip cng nghip l nhng h tiu th in tp trung, cng sut ln, in nng cung cp cho cc x nghip c ly t cc trm bin p trung gian bng cc ng dy trung p.
S cung cp in cho x nghip c th phn thnh 2 phn: bn trong v bn ngoi.
S cung cp in bn ngoi: l phn cung cp in t h thng n trm bin p chnh hay trm phn phi trung tm ca x nghip. Bn di l mt s dng s ph bin: s a): khi cp in p s dng ca nh my trng vi in p cung cp t h thng; s b): cc trm bin p phn xng nhn in trc tip t h thnh v h xung 0,4kV s dng; s c): c trm bin p trung tm trc khi phn phi n cc trm bin p phn xng; v s d): khi x nghip c my pht in d phng.
Li trung p in x nghip c cu trc khc nhau ty vo quy m x nghip. i vi nhng x nghip c ti vi trm kVA, ch cn t 1 trm bin p. i vi nhng x nghip ln cn t nhiu trm bin p, mi trm cung cp cho mt hoc vi phn xng.
a)
b)c)
d)
Hnh 2.2: S cung cp in bn ngoi x nghip
S cung cp in bn trong: t trm phn phi trung tm n cc trm bin p phn xng. C 3 kiu s thng dng: s hnh tia, lin thng v s hn hp.
S. Hn hp
Hnh 2.3. S cp in bn trong
Li h p x nghip chnh l li in bn trong mi phn xng. cp in cho phn xng ngi ta t cc t phn phi nhn in h p t cc my bin p v cp cho cc t ng lc, t t ny cung cp in cho cc thit b.
2.4. Cc loi dy v cp in:
ti in ngi ta dng dy dn v cp. So vi dy dn ti in bng cp t tin hn nhng m quan hn, v th cp trung v h p thch hp cho li in th v x nghip. Ti in bng dy dn r tin, d sa cha v thay th thng c dng trn li trung p v khu vc nng thn.
2.4.1. Cc loi dy dn:
Dy dn gm hai loi: dy bc cch in v dy trn.
Dy bc cch in: thng dng trn li h p. Dy bc c nhiu loi: mt si, nhiu si, dy cng, mm, n, i Vt liu thng dng l ng v nhm.
Hnh 2.4: Cp v dy trn
K hiu: M(n, F), trong : M l dy ng; n l s dy; F l tit din dy.
Dy trn: dng cho mi cp in p. C cc loi nh: nhm, thp, ng v nhm li thp. Trong dy nhm v nhm li thp c dng ph bin cho ng dy trn khng, trong phn nhm lm nhim v dn in v phn thp tng bn c hc.
K hiu: Loi dy(A, AC) - F, trong : A l dy nhm; AC dy nhm li thp; F l tit din.
K hiu cho mng in: loi dy (n.F +1.Fo) vi n l s dy pha v Fo tit in dy trung tnh.
2.4.2. Cc loi cp:
a) Cu to cp:
Cp lc gm cc phn t chnh sau: li, cch in v lp v bo v.
Li (rut dn in):
Vt liu c bn dng lm rut dn in ca cp l ng hay nhm k thut in.
Rut cp c cc hnh dng trn, qut, hnh mnh. Rut c th gm mt hay nhiu si.
Lp cch in:
Lp vt liu cch in cch ly cc rut dn in vi nhau v cch ly vi lp bo v.
Hin nay cch in ca cp thng dng l nha tng hp, cc loi cao su, giy cch in, cc loi du v kh cch in.
Lp v bo v:
Lp v bo v bo v cch in ca cp trnh m t, trnh tc ng ca ha cht do du tm thot ra do h hng c hc cng nh trnh n mn, han g khi t trong t.
Lp v bo v dy dn l ai hay li bng thp, nhm hay ch. Ngoi cng l lp v cao su hoc nha tng hp.
b) Phn loi cp:
Cp c th phn loi theo nhiu cch:
Theo s li: mt, hai, ba hay bn li. Thng thng cp cao p ch c mt li.
Theo vt liu cch in: giy cch in (c tm hay khng tm), cch in cao su hay nha tng hp v cch in t hp.
Theo mc ch s dng: h, trung v cao p, ngoi ra cn c cp rado v cp thng tin.
Theo lnh vc s dng: cp dng cho hng hi, hng khng, du m, hm m, trong nc hay cho cc thit b di chuyn (cn cu, cn trc)
2.5. Cu trc ng dy ti in:
ng dy ti in trn khng k hiu l DK. ng dy ti in trn khng bao gm cc phn t: dy dn, s, x, ct, mng, cn c th c dy chng st, dy no v b chng rung.
2.5.1. Mt s nh ngha lin quan:
a) ng dy truyn ti in trn khng: cng trnh xy dng mang tnh cht k thut dng truyn ti in nng theo dy dn, c lp t ngoi tri. Dy dn c kp cht nh s, x ct v cc chi tit kt cu xy dng.
ng dy h p cn c thm mt dy trung tnh ly c in p pha v in p dy. Nu ph ti 3 pha i xng th ly dy trung tnh bng dy pha cn khi ph ti pha khng cn bng th tit din dy trung tnh ly bng tit din dy pha.
b) Khong cch tiu chun: gm cc khong cch ngn nht gia dy dn c cng v t, gia dy dn c cng v cng trnh xy dng, gia dy dn v ct, gia cc dy dn vi nhau.
c) vng trn dy: l khong cch theo chiu thng ng t ng thng ni 2 im treo dy trn ct ti im thp nht ca dy dn do tc dng ca khi lng dy.
d) Lc cng dy: l lc cng ko dy v kp cht c nh dy dn trn ct.
e) Ch lm vic bnh thng: l ch lm vic m dy dn khng b t.
f) Ch s c: l ch m dy dn b t d ch mt dy.
g) Khong vt trung gian ca ng dy: khong cch theo mt phng ngang gia 2 ct.
h) Khong no cht: l khong cch theo mt phng nm ngang gia 2 ct chu lc gn nhau. Cc ct chu lc bao gm cc ct u tuyn, cc ct cui tuyn v cc ct gc dy dn chuyn hng i.
2.5.2. Cu trc ng dy trn khng
a) Ct: li cung cp in trung p dng 2 loi ct: ct vung v ct ly tm, k hiu H v LT.
Ct vung (ct ch H): thng ch to c 7,5 v 8,5m. Ct H7,5 dng cho li h p v H8,5 dng cho li h p v li 10kV.
Ct ly tm (ct trn): cc ct c c di 10 v 12m, cc ct di 6, 8 v 10m. Ct v c ni vi nhau nh cc mng xng hay mt bch, t c th c cc ct 10, 12, 16, 20, 22m. Cc ct cn c phn loi thnh A, B, C, D theo kh nng chu lc (c tra cc bng).
b) X: dng dy dn v c nh khong cch gia cc dy, c lm bng st hoc b tng kch thc ty vo cp in p.
Trn x c khoan sn cc l bt s, khong cch gia hai l khoan (cng l khong cch gia hai dy) t 0,30,4m i vi ng dy h p, t 0,81,2m vi ng dy 10kV, t 1,52m vi ng dy 35kV.
c) S: s c tc dng va lm gi cho cc b phn mang in va lm vt cch in gia cc b phn vi t. V vy s phi bn, chu c dng ngn mch ng thi phi chu c in p ca mng k c lc qu in p.
S cch in thng c thit k v sn xut cho cp in p nht nh v c chia thnh hai dng chnh: s hay s treo dng hay treo thanh ci, dy dn v cc b phn mang in; s xuyn dng dn nhnh hay dn xuyn qua tng hoc nh.
S : thng dng cho ng dy c in p t 35kV tr xung, khi ng dy vt sng hay ng giao thng th c th dng s treo.
S treo: c th phn thnh s thanh v s a. S thanh c ch to c chiu di v chu c mt in p xc nh trc. Chui s c kt li t cc a v s lng c ghp vi nhau ty thuc in p ng dy. u im ca vic dng chui s cho ng dy cao th l in p lm vic c th tng bng cch thm cc a s vi chi ph nh.
SHAPE \* MERGEFORMAT SHAPE \* MERGEFORMAT
Hnh 2.5. Mt s dng s
Khi cn tng cng v lc ngi ta dng cc chui s ghp song song, khi tng cng cch in ngi ta tng thm s a. Vic kp dy dn vo s ng c thc hin bng cch qun dy hoc bng ghp kp dy chuyn dng. Vic kp dy vo s treo c thc hin bng kha kp dy chuyn dng.
S ng Hong lin sn c k hiu VHD-35. ng dy c in p 110kV tr ln dng s treo. Chui s treo gm cc a s tu theo cp in p m chui s c s a khc nhau.
in p (kV)
S a s
3-10
01
35
03
110
07
220
13
Ti s l chi tit c gn vo s ng bng cch vn ren v chn ximng, ct c dng lm tr kp cht s vi x trn ct in. Ti s c lm bng thp, c sn ph hay m chng g.
d) Mng ct: c nhim v chng lt ct. Trong vn hnh ct in chu lc ko ca dy v lc ca gi bo.
e) Dy no: ti cc ct no (ct u, cui v gc ng dy), tng cng chu lc ko cho cc ct ny cc dy no c t ngc hng lc ko dy.
f) B chng rung: chng rung cho dy dn do tc dng ca gi.
B chng rung gm 2 qu t bng gang ni vi nhau bng cp thp, on cp c kt vo ng dy nh kp.
Hnh 2.6: B chng rung v mng ct
Ngoi ra, trn ct v cc x cn c lp t cc tit b in phc v cho vic vn hnh v bo v hot ng ca li in nh: cc cu ch t ri, my ct ph ti, dao cch ly, thit b t ng li
Chng 3. TNH TON PH TI IN
3.1. Cc khi nim chung:
Nhim v u tin khi thit k cung cp in l xc nh nhu cu in ca cng trnh (gi l ph ti tnh ton). Nu ph ti tnh ton nh hn ph ti thc t s lm gim tui th thit b i khi c th gy chy n do qu ti thit b, ngc li th thit b c chn s qu ln gy lng ph vn u t.
3.1.1 Ph ti in:
Thng thng cng sut vn hnh khc vi cng sut thc t do nhiu yu t khc nhau v l mt hm theo thi gian. Nhng cn phi xc nh ph ti in cho vic tnh ton cung cp in. Cng sut tnh ton c gi l cng sut tnh ton (Ptt).
Nu Ptt < Pthc t: thit b mau gim tui th, c th chy n.
Nu Ptt > Pthc t: lng ph vn u t.
C nhiu phng php xc nh ph ti in, cng c nhiu thng tin cng la chn c phng php chnh xc. Thng thng c hai nhm phng php l phng php kinh nghim v phng php da trn xc xut thng k.
3.1.2 Cc c tnh chung ca ph ti in:
Mi ph ti c c trng ring, c 3 c trng m cc phng n cung cp phi xt n:
a) Cng sut nh mc: thng c ghi trn nhn ca thit b. i vi ng c, cng sut nh mc l cng sut trn trc ca ng c, cng sut in P =Pm/m.
Thng m =0,8 0,85; trng hp ng c nh c th xem P =Pm.
b) in p nh mc: in p lm vic ca thit b phi ph hp vi li in ni t thit b.
c) Tn s: tn s lm vic ca thit b khc nhau nhiu t 0Hz (in DC) n hng triu Hz thit b cao tn.
3.1.3 th ph ti:
th ph ti: c trng cho s tiu dng nng lng in ca cc thit b ring l, ca nhm thit b, ca phn xng hoc ca ton b x nghip.
a) Phn loi: c nhiu cch phn loi
Theo i lng o: th ph ti tc dng P(t), phn khng Q(t) v in nng A(t).
Theo thi gian kho st: th ph ti hng ngy, hng thng v hng nm.
b) Cc loi th ph ti thng dng:
th ph ti ngy: nh hnh a) c ghi bng my; b) c ghi v v li bi cc vn hnh vin v c) th hin dng bc thang thng s trung bnh trong mt khong thi gian.
b)a)c)
Hnh 3.1: th ph ti ngy
th ph ti hng ngy cho ta bit tnh trng lm vic ca thit b t sp xp li qui trnh vn hnh hp l nht, n cng lm cn c tnh chn thit b, tnh in nng tiu th
th ph ti ngy c 5 thng s c trng sau: ph ti cc i, h s cng sut cc i, in nng tc dng v phn khng ngy m, h s cng sut tng ng v h s in kin ca th ph ti.
th ph ti hng thng: c xy dng theo ph ti trung bnh ca tng thng ca x nghip trong mt nm lm vic.
th ph ti hng thng cho ta bit nhp sn xut ca x nghip. T c th ra lch vn hnh sa cha cc thit b in mt cch hp l nht, nhm p ng cc yu cu ca sn xut (VD: vo thng 3,4 sa cha va v ln, cn nhng thng cui nm ch sa cha nh v thay cc thit b).
Hnh 3.2: th ph ti thng
th ph ti nm: thng c xy dng dng bc thang, xy dng trn c s ca th ph ti ngy m in hnh (thng chn 1 ngy in hnh vo ma ng v vo ma h).
Hnh 3.3: th ph nm
th ph ti nm c cc thng s c trng nh: in nng tc dng v phn khng tiu th trong nm, thi gian s dng cng sut cc i Tmax, h s cng sut trung bnh v h s in kn ph ti.
3.2. Xc nh ph ti in khu vc nng thn:
i tng s sng in ph bin nng thn l: trm bm, trng hc v sinh hot.
3.2.1. Ph ti in trm bm:
Cc my bm nng nghip thng c cc thang cng sut: 14, 20, 33, 45, 55, 100, 200kW. Vi my bm cng sut nh (< 100kW) s dung in h p, my bm cng sut ln tr ln thng s dng in 6 hay 10kV.
Trm bm thng chia thnh hai loi: trm bm ti v trm bm tiu.
Ph ti trm bm tnh theo cng thc sau:
1
. v .
n
ttdttidmitttt
i
PKKPQPtg
j
=
==
(31)
Trong :
tt
P
,
tt
Q
: cng sut tc dng v phn khng tnh ton ca trm bm.
dt
K
: h s ng thi, ly theo thc t
dt
nlv
K
n
=
=s my lm vic/tng s my.
t
K
: h s ti ca my bm, ring i vi trm bm tiu ly bng 1.
3.2.2. Ph ti trng hc:
thit k cp in cho trng hc cn xc nh ph ti tng phng hc, tng tng, tng dy nh hc v ton trng hc.
c) Ph ti cho tng phng hc xc nh theo cng thc:
0
* v *
ppp
PPSQPtg
j
==
(32)
H s cng sut cho: n ng + qut cos(= 0,8; n si t + qut cos(= 0,9.
d) Ph ti tnh ton mt tng nh gm n phng:
1
n
Tdtpi
PKP
=
(33)
Vi:
dt
K
l h s ng thi.
e) Ph ti tnh ton cho mt ta nh gm m lu:
1
m
NdtTi
PKP
=
(34)
3.2.3. Ph ti chiu sng sinh hot
a) Ph ti tnh ton cho mt thn, xm hoc lng c xc nh:
00
* v *
tttt
PPHQQH
==
(35)
Trong H: s h dn trong lng, thn.
P0: sut ph ti tnh ton cho mt h.
b) Ph ti tnh ton cho x bao gm cc thn xm c xc nh.
22
11
; v
nn
XdtttiXdtttiXXX
PKPQKQSPQ
===+
(36)
3.3. Xc nh ph ti in khu vc cng nghip:
3.3.1. Trong giai on d n kh thi:
Thng tin thu nhn trong giai on ny thng khng chnh xc.
xc nh ph ti in cho vic thit k, xy dng ng dy cao p v trm bin p trung gian ngi ta da vo din tch hoc sn lng.
a) Xc nh ph ti in cho khu CN, ch xut cn c vo din tch:
0
*
tt
SSD
=
(37)
Trong : S0 sut ph ti trn n v din tch, ty ngnh CN m S0 chn 100400(kVA/ha).
D: din tch khu CN, ch xut (ha).
b) i vi x nghip, nu bit sn lng s sn xut, cng thc xc nh ph ti in nh sau:
max
.
tt
aM
P
T
=
(38)
Trong : a: sut in nng chi ph sn xut ra mt n v sn phm (kWH/sp).
M: sn lng.
Tmax: thi gian s dng cng sut cc i. Tmax v a thng c tra bng.
3.3.2. Trong giai on xy dng nh xng:
Thng tin nhn c trong giai on ny l cng sut t ca tng phn xng, din tch ca tng xng.
a) Ph ti in ng lc ca tng phn xng c xc nh theo cng thc:
. v .
ttncdtttt
PKPQPtg
j
==
(39)
Trong :
nc
K
: h s nhu cu (tra bng).
d
P
: cng sut t ca phn xng. Vi
.
ddm
PPn
=
dm
P
v n: cng sut nh mc ca ng c v s ng c.
b) Ph ti in chiu sng trong phn xng c xc nh theo din tch:
0
. v .
cscscs
PPDQPtg
j
==
(310)
Trong :
D
: din tch xng.
0
P
: sut chiu sng trn mt n v din tch (W/m2). Ty theo v tr, mc ich s dng chn
0
P
= 530 W/m2.
c) Ph ti in cho ton phn xng:
v
PXttcsPXttcs
PPPQQQ
=+=+
(311)
d) Ph ti in cho ton x nghip c n phn xng:
22
11
. ; . v
nn
XNdtXNiXNdtXNiXNXNXN
PKPQKQSPQ
===+
(312)
3.3.3. Trong giai on thit k chi tit:
y l cng on cui cng trong qu trnh thit k cp in cho x nghip cng nghip. giai on ny bit hu ht cc thng tin v i tng s dng in.
Ph ti tnh ton xc nh cho mt nhm my, c xc nh theo cng thc sau:
maxmax
1
.= ..
n
tttbsdtbi
PKPKKP
=
(313)
Trong :
tb
P
: cng sut trung bnh trong thi gian kho st.
max
,
sd
KK
: tra bng.
V d: tnh ton ph ti mt x nghip c s nh hnh v.
Nguyn tc tnh ton:
PttXN: phi c tnh t cc TB in ngc tr v pha ngun.
Phi k n tn tht trn ng dy v trong MBA.
Ph ti tnh ton XN cn phi k n d kin pht trin ca XN trong 5 - 10 nm ti.
Cc bc tnh ton c thc hin nh sau:
im 1: im trc tip cp in n cc thit b dng in, ti y cn xc nh ch lm vic ca tng thit b (xc nh Kt; ksd; cos).
im 2: Vi nhm thit b lm vic ch khc nhau Xc nh Ptt bng phng php s thit b hiu qu. Ptt = KM.Ptb v S2 =P2 + j.Q2
im 3: s bng ph ti im 2 cng thm phn tn tht ng dy h p: S3 =S2 + Sdd
im 4: im tng h p ca cc trm bin p phn xng. Tai y ph ti tnh ton c th tnh bng phng php h s nhu cu hoc tng hp cc ph ti ti cc im 4.
433
11
. + j
nn
dtii
SKPQ
=
im 5: S5 = S4 + SB2
im 6: S6 = S5 + Sdd
im 7:
766
11
. + j
nn
dtii
SKPQ
=
im 8: S8 = S7 + SB1
Ch : S8 cha phi l ph ti ca x nghip. V khi tnh ph ti x nghip cn phi k n s pht trin ca x nghip (5 - 10 nm) sau. SXN = S8 + SXN. xc nh c SXN phi d bo tng trng ph ti.
3.4. Xc nh ph ti in khu vc th:
3.4.1 Ph ti in cc h gia nh:
Cc h gia nh l i tng s dng in ln nht th.
a) Trong giai on xy dng c s h tng:
Thng tin nhn c l mt bng quy hoch ng ph, cng thc xc nh ph ti nh sau:
0
. v .
tttttt
PPLQPtg
j
==
(314)
Trong :L: chiu di on ph.
0
P
: cng sut ph ti trn mt mt chiu di.
b) Trong giai on thit k chi tit:
Thng tin nhn c tng i chnh xc, xc nh ph ti in c hai phng php tnh ton:
Phng php 1: Tnh ph ti t cn h ri n khu vc.
Phng php 2: Tnh ngc li t khu vc ri n cn h.
3.4.2 Ph ti in cc trng di hc, trung hc chuyn nghip:
i vi khu vc ging ng, hnh chnh vn phng, phng th nghim ph ti c xc nh theo cng thc:
0
*
p
PPS
=
vi
0
P
= 2040 W/m2. Sau c cng vi ph ti ca xng in, c kh, k tc xta c ph ti cho trng hc.
3.4.3 Cc loi ph ti khc:
Cc ph ti in khc nh: khu vn phng, khch sn siu th, nh hng cng vin c tnh ton tng t bng cch chn cng sut ph ti n v (
0
P
) ph hp.Chng 4. TRM IN
4.1. Khi qut v phn loi trm in:
Trm bin p dng bin i in nng t cp in p ny sang cp in p khc.
Theo nhim v, c th phn trm thnh hai loi:
Trm bin p trung gian hay cn gi l trm bin p chnh: trm ny nhn in 35220kV t h thng bin i thnh cp in p 10, 6 hay 0,4kV.
Trm bin p phn xng: nhn in t trm bin p trung gian bin i thnh cc cp in p thch hp phc v cho ph ti phn xng. Pha s cp thng l 35, 22, 15, 10, 6kV; cn pha h p c th l 660, 380/220 hay 220/127V.
Theo cu trc, cng c th chia thnh hai loi:
Trm bin p ngoi tri: trm ny, cc thit b cao p u c t ngoi tri, cn phn phn phi in p thp c t trong nh hoc trong cc t chuyn dng ch to sn.
Trm bin p trong nh: trm ny tt c cc thit b u c t trong nh. Chi ph xy dng trm trong nh thng cao hn trm ngoi tri nhiu.
4.2. S ni dy trm bin p:
S ni dy ca trm phi tha mn cc iu kin sau:
m bo lin tc cung cp in theo yu cu ph ti.
S ni dy r rng, thun tin trong vn hnh v lc x l s c.
An ton lc vn hnh v sa cha.
Cn bng gia cc ch tiu v kinh t v k thut.
Hnh 4.1: S trm h p trung gian v trm phn phi chnh
4.2.1. S ni dy trm h p trung gian:
S ni dy pha s cp ca trm loi ny ph thuc cc thng s: in p cung cp, s lng v cng sut my bin p, ch lm vic, tin cy yu cu, s pht trin trong tng lai Do vy c rt nhiu phng n gii quyt vn , tuy nhin rt t hoc khng c phng n no tha ht cc yu cu.
Sau y l mt s s ni dy trm bin p thng dng. Cc trm ny thng c thc hin theo dng sau:
Ni n h thng bng mt hoc hai l. Hai l n thng khng c thanh ci.
Pha in p th cp (in p phn phi) ngi ta dng s vi thanh ci n hay thanh ci kp.
4.2.2. Trm phn phi chnh:
Trm nm trong phm vi x nghip, thanh ci cao p ngoi ni vi h thng cn ni vi nh my in a phng hay t my pht in ring. Thanh ci c th l n hay kp vi my ct phn on. Do c ni vo ngun ln nn cc ph ti c th lp cc cun khng gim dng ngn mch nu c.
4.2.3. Trm phn phi trung gian:
i vi cc x nghip c nhiu phn xng nm ri rc v phn tn, th cn c cc trm bin p trung gian phn phi in nng t cc trm chnh n cc phn xng.
Vic kt ni gia trm trung gian v trm phn phi chnh nh cc l chnh.
4.2.4. Trm h p phn xng:
Trm h p phn xng thng c mt hay hai my bin p, khi trm c nhiu (> 3) my bin p th c th c thanh ci phn on.
a) Trm h p vi mt my bin p: trm ny thng phc v cho h loi 2, loi 3, tr trng hp lm ngun d phng cho h loi 1 c cng sut nh nh s dng t ng ng.
c im ca s trm h p mt my bin p phn xng l cch ni ca my bin p n ng dy cao p, thng thng c 3 cch ni sau:
Thng qua dao cch ly v my ct in: cch ny t s dng do my ct t tin, phi tnh ton n nh ng v n nh nhit khi c ngn mch.
Ni qua dao cch ly v cu ch: thng s dng, dao cch ly c nhim v ct dng khng ti. Nhc im l do bo v qu ti v ngn mch nh cu ch nn c nhy thp.
Ni qua dao cch ly v cu ch v my ct ph ti: s ny c dng my ct ph ti do ch thit k ct dng ph ti nn b phn dp tt h quang c cu to n gin, chi ph khng cao.
Hnh 4.2: Trm c mt v trm nhiu my bin p
b) Trm h p vi nhiu my bin p: phc v cho tt c cc loi h dng in. Ty theo s my bin p, s l cung cp, loi h c cung cp m c mt s dng s ph bin nh hnh.
c) Trm h p dng cc t ch to sn:
Cc t ch to sn thng c ch to thnh nhiu ngn. Mi ngn bao gm: my ct, dao cch ly, thit b o lng v bo v. Ty theo dng ph ti m my ct c th l my ct du, khng kh v i khi l my ct chn khng.
Hnh 4.3: Trm vi t ch to sn
4.3. Cu trc trm:
Khi thit k xy dng trm phi tit kim chi ph tuy nhin mt s ch tiu sau phi c m bo:
Chn ng trang thit b in, lp rp ng quy phm v tha cc iu kin vn hnh.
Tn trng khong cch gia cc phn dn in vi nhau v vi xung quanh.
Kh nng loi nhanh ha hon v cc s c khc.
Thun tin trong thao tc v cc hnh lang thi cng, sa cha.
Phi thc hin ni t bo v.
Phi s dng cc tn hiu cn thit.
4.3.1. Trm h p phn xng ngoi tri:
Thng p dng cho x nghip b, li in cung cp t ng dy trn khng. C hai dng ph bin l my bin p c treo trn ct v t ngay di chn ct.
Dng treo ct: khi cc my bin p ba pha hay mt pha (t 25240kVA) v cc trang b cng kh c in c tng trng lng nh (khong 3001800kg). Ton b trang b ca trm c treo trn cc gi mc vo mt, hai hay bn ct bng g hay xi mng ct thp.
Dng t di chn ct; i vi cc my bin p qu ln hay khng m bo c cn bng trng lng khi treo trn ct th my bin p c t trn mt nn g hay xi mng ngay di chn ct, xung quanh c ro li cao 2,5m ngn ngi hay vt n gn trm.
4.3.2. Trm h p phn xng trong nh:
i vi trm cng sut ln (hn 320MVA), khi c cc yu cu trong vn hnh, hoc trong iu kin c bit nh khng kh c hi trong qu trnh sn xut, khng gian b tr trm qu t th trm trong nh c chn xy dng; trm dng ny tt c cc thit b c t trong nh.
Trm ny thng c s ni dy n gin, ch s dng thanh ci khi c ph ti in p cao. Cc khi c phn cao p l cu ch ng, my ct ph ti vi cu ch, my ct du hay kh nn.
Trm c th c mt hay nhiu bung ty theo s lng my bin p. Cc bung phi c h thng thng gi vi chiu cao ph hp.
i vi cc thit b c cha du nh my bin p, mt ct c cha du phi c h thng gp du v b cha du phng khi c s c hay ha hon.
Vic ni dy gia cc my bin p v bung phn phi in p cao (nu c), cng nh vic ni dy n bng in p thp c th thc hin bng cc thanh dn hay cp.
4.3.3. Trm h p phn xng ch to sn thnh t:
Loi ny gm c: mt hay hai my bin p h p c t trong bung con bng kim loi hoc h nu my bin p c du. H thng phn phi in p cao (6 10kV) gm mt hay nhiu t con c gia cng v lp t sn theo mt s ni no . H thng phn phi in p thp cng gm cc t cu kin gia cng sn. ng dy ni gia cc my bin p v trang b in l cc thanh trn t bn trong cc khung bng kim loi ca t ny.
Hnh 4.4: T ch to sn
4.4. La chn my bin p cho trm:
La chn my bin p bao gm chn s lng v cng sut ca my bin p. Vic la chn ph hp vi loi h tiu th, ph hp vi ch tiu k thut v kinh t (ph u t v vn hnh).
4.5. Ni t trm v ng dy ti in:
Trong li cung cp ngi ta thc hin ni t vi nhiu mc ch khc nhau: ni t lm vic, an ton v chng st.
Trang b ni t bao gm cc in cc v dy dn ni t. Cc in cc ni t bao gm: in cc thng c ng su vo trong t v in cc ngang c chn ngm mt su nht nh. Cc dy ni t dng ni lin cc b phn c ni t vi cc in cc.
4.5.1. Ni t trm bin p:
H thng ni t trong trm bin p thc hin c ba chc nng: lm vic, an ton v chng st. Theo quy phm in tr ni t (R) ca h thng ni t phi t nh sau:
Vi trm bin p phn phi: R 4.
Vi trm bin p trung gian c Um 35kV: R 1.
Vi trm bin p trung gian c Um 110kV: R 0,5.
Kt cu h thng ni t ca trm thng dng mch vng gm cc cc di 2,5m ng ngp su 0,7m, cc cc cch nhau 2,5m v c hn ni vi nhau bng cc thanh thp to thnh mch vng.
i vi cc trm t h ph th phng n ni t hnh tia c thc hin.
4.5.2. Ni t ng dy ti in:
C hai loi ni t ng dy ti in:
a) Ni t chng st v an ton: cc DK trung p tr ln tt c cc ct u phi ni t, vi DK 0,4 kV phi ni t cc ct i qua khu vc ng dn.
Quy phm quy nh R ca mt ct nh sau:
Vng ng bng: R 10.
Vng trung du: R 15.
Vng ni: R 20.
Thng vi vng ng bng, in tr sut ca t nh, mi ct ch cn ni t 1 cc l t tr c cho php, vng trung du v vng ni phi tng s cc theo hnh tia n khi t tr s cho php.
b) Ni t trung tnh lp li: l hnh thc ni t ring cho DK 0,4kV d phng mt trung tnh ti trm bin p lm chy cc thit b dng in.
Theo quy phm, c khong 4 hay 5 ct phi thc hin ni t trung tnh lp li.
Lu : cn phn bit ni t trung tnh l ni t ng dy trung tnh xung cc ni t; ni t chng st v an ton l ni t x dy xung cc ni t.
Chng 5. TNH TON TN THT IN
Tnh ton v in l xc nh thng s ch ca li in.
Tnh ton v in bao gm tnh cc loi tn tht trong h thng nh tn tht in p, tn tht cng sut, tn tht in nng cng nh cc tnh ton v phn b cng sut, la chn tit din dy dn v cp, cc ch vn hnh
Tnh ton in phc v cho cng tc nh gi cc ch tiu k thut ca h thng cung cp in, xc nh tng ph ti, chn cc phn t ca mng in, xc nh phng n b cng sut phn khng
Ty mc ch s dng m chnh xc ca cc tnh ton i hi khc nhau. khi lng tnh ton gim bt c th s dng cc biu , bng tnh c sn trong cc sch tra cu.
Cc bc thc hin ln lt: x l cc d kin ban u (cp in p, loi dy dn, s mng), xy dng s thay th, thc hin tnh ton v x l kt qu.
5.1. S thay th li cung cp in:
5.1.1. Khi nim:
Thnh lp s thay th cho mt li in bt k gm c: la chn s tnh ton cho mi phn t ca li v tnh ton cc thng s ca chng, sau lp cc s thay th theo ng trnh t trong li, cui cng l quy i cc thng s trn s v cng cp in p.
S thay th ca ng dy v my bin p s c ln lt trnh by, y l hai thnh phn chnh ca li truyn ti v phn phi.
5.1.2. S thay th ng dy:
a) Cc thng s ca ng dy:
in dn G: l thng s phn nh hin tng tn tht cng sut tc dng trong s v in mi. Phn cng sut tn hao trong s ca ng dy trn khng mi cp in p rt b v c th b qua. Mt phn tn tht cng sut na l tn tht do vng quang, thng ch xy ra cp in p 110kV trong mt s iu kin nht nh. i vi dy cp c th b qua in dn.
Dung dn B: dung dn ng dy th hin in dung gia cc dy dn. Dung dn ny t l vi dng in chuyn dch (hay l dng in np ca ng dy), sinh ra cng sut phn khng trn ng dy. Dng in in dung ca cp thng ln hn ng dy trn khng, do vy i vi cp t 20kV tr ln phi xt n dung dn khi lp s thay th.
in tr R: in tr ng dy, ph thuc chiu di v thng c cho bi nh ch to.
in khng X: th hin hin tng tn t. Khi ti dng in xoay chiu ba pha s xut hin xung quanh cc dy dn mt t trng, to ra lc in ng trong mi dy dn v ph thuc khong cch tng h gia cc dy dn. i vi cc ng dy t 330kV tr ln, gim in khng ngi ta thng p dng k thut phn pha.
b) S thay th:
Cc thng s ca ng dy: in tr, in khng, in dn v dung dn hu nh phn b dc theo ng dy. d dng trong tnh ton, ty theo loi ng dy mt s thng s c th xem l tp trung hay b qua. Cc s thay th v trng hp p dng c tm tt trong bng bn di.
c) Tnh thng s ng dy:
(
)
...
oo
ZRjXrxl
=+=+
; ro v xo in tr v in cm khng trn n v chiu di (km).
(
)
...
oo
YGjBgbl
=+=+
; go v bo in dn v dung dn trn n v chiu di (km).
in dn G: c xc nh theo tn tht cng sut tc dng
2
U
vq
P
G
D
=
(51)
Trong
vq
P
D
l tn tht vng quang xc nh theo cng thc kinh nghim.
Bng 51. Cc s thay th ng dy
S
Trng hp p dng
U
1
I
1
, cos
1
I
2
, cos
2
U
2
R+jX
S ng dy.
2Gn2Bn2Gn2Bn
U
1
I
1
I
n
RnXn
Iy
Iy
I
2
U
2
S thay th hnh p dng cho ng dy trn khng 300km hay cp 50km.
Z= R + j.X
.
222
G
YB
j
=+
2Bn
U
1
I
1
I
n
RnXn
I
B
I
2
U
2
2Bn
I
B
S hnh b qua in dn, do:
in dn gy bi tn tht trong s v in mi rt b.
Tn tht vng quang thng ch xy ra ng dy trn khng > 200kV.
U
1
I
RnXnU
2
S thay th mng a phng b qua tng dn.
U
1
I
RnU
2
S thay th cho cp 610kV b qua tng dn
Dung dn bo:
6
10
7,58
1
.10
.
log.
o
tb
b
km
D
R
-
=
W
(52)
Trong :
tb
D
khong cch trung bnh hnh hc gia cc dy dn,
[
]
3
121323
..,
tb
DDDDmm
=
R l bn knh dy dn, [mm].
Nu ng dy c dy dn phn nh, th tr s R c thay th bng
1
.
n
n
dttb
RRa
-
=
Trong :Rt: bn knh ng tr ca cc dy dn trong mt pha.
n: s dy dn trong mt pha.
atb: khong cch trung bnh hnh hc gia cc dy dn trong mt pha.
R: bn knh thc ca mi dy phn nh.
in tr ro: thng c cho bi nh ch to hay tnh theo
(
)
20
120
t
rrt
a
=+-
(53)
Trong :rt: in tr nhit t.
r20: in tr nhit 20oC, c tra cc bng cho sn.
: h s nhit in tr, c tra cc bng cho sn, i vi ng, nhm, nhm li thp = 0,004.
in khng xo:
10
0,1445.log.0,0157,
tb
o
D
x
km
R
W
=+
(54)
Nu ng dy c dy dn phn nh, khi :
10
0,0157
0,1445.log.,
tb
o
dt
D
x
km
Rn
W
=+
5.1.3. S thay th my bin p:
a) Cc thng s ca my bin p:
Tng tr ca my bin p: l
.
TTT
ZRjX
=+
phn nh hin tng tn tht cng sut tc dng do hiu ng Joule v hin tng tn tht cng sut phn khng do tn t trong cc cun dy. Trong :
T
R
l in tr,
T
X
l in cm khng.
Tng dn ca my bin p:
.
TTT
YGjB
=+
phn nh hin tng tn tht cng sut trong li thp my bin p: tn hao do dng Foucault v tn hao t. Tn tht trong li thp hu nh khng ph thuc vo ti ca my bin p v bng lc khng ti. Vi:
T
G
l in dn,
T
B
l cm dn.
Cc thng s ca my bin p c th tnh theo cc s liu ca my bin p nh: tn tht ngn mch
k
P
D
, tn tht khng ti
o
P
D
, in p ngn mch
%
k
U
, dng in khng ti
%
o
I
. Cc s liu l kt qu ca th nghim ngn mch v th nghim khng ti.
b) S thay th v tnh cc thng s cho my bin p hai cun dy:
My bin p ba pha hai cun dy l loi c dng ph bin trong h thng cung cp in. Khi tnh ton dng s hnh nh hnh v.
TG
R
T
X
T
TB
R
T
X
T
TTTSPjQ
b)a)
Hnh 5.1. S thay th my bin p 2 cun dy
y:
'
12
T
RRR
=+
v
'
12
T
XXX
=+
(
''
22
v
RX
l in tr v cm khng ca cun dy th cp 2 quy i v cun dy s cp 1. Sau y s nu cc cng thc tnh thng s my bin p (
T
R
,
T
X
,
T
G
v
T
B
) thng qua cc s liu (
k
P
D
,
o
P
D
,
%
k
U
v
%
o
I
) ca n:
Tnh
T
R
: ta c
2
2
2
3..
dm
kdmTT
dm
S
PIRR
U
D==
, do
2
2
.
kdm
T
dm
PU
R
S
D
=
(55)
Tnh vi n v thng dng:
[
]
[
]
22
3
22
.
.10,
kdm
T
dm
PKWUKV
R
SKVA
D
=W
Tnh
T
X
: ta c
.
%.100
3
dmT
k
dm
IX
U
U
=
, do
[
]
[
]
22
%.
.10,
kdm
T
dm
UUKV
X
SKVA
=W
(56)
Tnh
T
G
: mt cch gn ng
0
2
T
dm
P
G
U
D
=
(57)
Tnh
T
B
: mt cch gn ng
0
2
T
dm
Q
B
U
D
=
(58)
Trong :
[
]
0
0
%.
,
100
dm
IS
QKVA
D
c) S thay th v tnh cc thng s cho my bin p ba cun dy v t ngu:
i vi my bin p ba cun dy v t ngu, nh ch to cho nhng s liu sau:
dm
S
: cng sut nh mc my bin p.
Cdm
U
,
Tdm
U
,
Hdm
U
hay
1
dm
U
,
2
dm
U
,
3
dm
U
: in p nh mc cc cun cao, trung v h.
%
o
I
: dng in khng ti tnh theo phn trm so vi dng in nh mc.
12
P
D
,
13
P
D
,
23
P
D
: tn tht ngn mch ng vi ba trng thi th nghim ngn mch.
12
%
U
,
13
%
U
,
23
%
U
: in p ngn mch ng vi ba trng thi th nghim ngn mch.
R
1
X
1
0S
1
I
1
U
1
R
2
X
2
2
I
2
U
2
R
3
X
3
3
I
3
U
3
1
2
3
2
1
3
a)
b)
c)
Hnh 5.2. a) My bin p ba cun dy; b) MBA t ngu; c) S thay th hnh sao
S thay th hnh sao c t lng tn hao trong thp:
0
.
FeFeFe
SSPjQ
D=D=D+D
(59)
Tn tht cng sut tc dng khi ngn mch v in p ngn mch ca my bin p ba cun dy v t ngu c tnh theo cc dng ngn mch sau:
1) Khi cun 2 b ngn mch, cun 3 h mch, cun 1 c t vo mt in p sao cho trong cun 1 v 2 c dng nh mc. Ngi ta o c
12
P
D
v
12
%
U
, vi:
1212
PPP
D=D+D
trong
1
P
D
v
2
P
D
l tn tht cng sut tc dng trong cun 1 v 2.
1212
%%%
UUU
=+
2) Cho h mch cun 2, ngn mch cun 3 v cun 1 c t vo mt in p sao cho trong cun 1 v 3 c dng nh mc ta thu c:
1313
PPP
D=D+D
v
1313
%%%
UUU
=+
.
3) Tng t khi cho cun 1 h mch, cun 3 ngn mch v t in p vo cun 2 sao cho trong cun 2 v 3 c dng nh mc ta c:
2323
PPP
D=D+D
v
2323
%%%
UUU
=+
.
Gii h cc phng trnh trn ta tnh c tn tht ngn mch v in p ngn mch i vi tng cun dy theo s liu cho:
(
)
1121323
2121
3131
1
2
PPPP
PPP
PPP
D=D+D-D
D=D-D
D=D-D
(510)
(
)
1121323
2121
31311
1
%%%%
2
%%%
%%%
UUUU
UUU
UUU
=+-
=-
=-
(511)
Sau p dng cng thc (5-5) v (5-6) tnh cc thng s ca my bin p.
5.2. Tnh ton tn tht in p:
Khi truyn ti in nng t ngun n h tiu th th mi phn t mng in do c tng tr nn u gy tn tht cng sut v in p.
Tn tht cng sut gy tnh trng thiu ht in nng ti ni tiu th, lm tng gi thnh truyn ti in v lm cho hiu qu kinh t km.
Tn tht in p lm cho in p ti cc h tiu th b gim thp, nh hng cht lng in.
Sau y ln lt gii thiu s lc phng php tnh ton tn tht in p, cng sut v in nng trn mng phn phi in.
5.2.1. Tn tht in p trn ng dy ba pha c ph ti tp trung:
Tn tht in p l i lng phc:
.
UUjU
d
D=D+
Gi thit mng lm vic ch i xng, do ch cn nghin cu mt pha.
Tng tr dy dn:
[
]
.
ZRjX
=+W
v ph ti tp trung cui ng dy
[
]
.
SPjQKVA
=+
.
Trn hnh v biu din vect in p ca ng dy:
Vect Oa: in p Up2 cui ng dy.
Vect Oc: in p Up1 u ng dy. Hnh 5.3. th vect tn tht in p
Tn tht in p c xc nh bng tam gic tn tht abc, trong :
Vect ab: l tn tht in p trn in tr, trng pha vi vect dng in I, ln = I.R.
Vect bc: l tn tht in p trn in khng, vung gc vi vect ab, c ln = I.X.
Vect ac: tn tht in p tng
12
.
ppp
UUjU
D=-
uuururur
c th phn tch thnh hai thnh phn:
Tn tht in p dc: on ad, l hnh chiu ca
U
D
ln trc.
Tn tht in p ngang
p
U
d
: on cd.
Lc ny tnh ton tn tht in p c th phn thnh hai trng hp:
Trng hp 1: i vi li c in p 35kV, thng rt b do c th b qua tn tht in p ngang.
Tn tht in p pha:
12
(xem )
p
Uadaffd
jjj
D==+==
..cos..sin
IRIX
jj
=+
Tn tht in p dy:
(
)
33..cos..sin
p
UUIRIX
jj
D=D=+
[
]
....
3
33
dm
dmdm
PRQXPRQX
V
U
UU
+
=+=
(512)
Tnh theo %:
2
..100
%.
1000
dm
PRQX
U
U
+
D=
, vi P[kW], Q[kVA], R v X[], Um[kV].
Trng hp 2: i vi li c in p > 35kV, phi xt n tn tht in p ngang
p
U
d
:
Tn tht in p ngang:
cossin
p
UcdcgdgcgbfIXIR
djj
==-=-=-
Tn tht in p ngang i vi in p dy:
(
)
33cossin
pp
UUIXIR
ddjj
==-
3
33
dm
dmdm
PXQRPXQR
U
UU
-
=-=
Do vy:
..
dmdm
PRQXPXQR
UUjUj
UU
d
+-
D=D+=+
(513)
5.2.2. Tn tht in p trn ng dy ba pha c nhiu ph ti tp trung:
Hnh 5.4. ng dy c hai ph ti tp trung
Trng hp ng dy c nhiu ph ti tp trung, gi tr tn tht in p l tng tn tht in p cc on dy, ta c cc cng thc sau:
(
)
(
)
2
11
1100
.. hay %..
1000.
dm
nn
iiiiiiii
ii
dm
UPrQxUPrQx
UU
==
D=+D=+
(514)
Trong :
,
ii
PQ
cng sut chy trn on th i, n v [kW], kVAR].
,
ii
rx
in tr v in khng ca on th i, n v [].
dm
U
in p dy nh mc, [kV].
(
)
(
)
2
11
1100
.. hay %..
1000.
dm
nn
iiiiiiii
ii
dm
UpRqXUpRqX
UU
==
D=+D=+
(515)
Trong :
,
ii
pq
cng sut ca ph ti ti im th i, n v [kW], kVAR].
,
ii
RX
in tr v in khng ca ng dy k t u ngun n im th i, []
dm
U
in p dy nh mc, [kV].
5.2.3. Tn tht in p trn ng dy ba pha c ph ti phn b u:
i vi ng dy c ph ti phn b u, ta c:
[
]
..
2.
dm
PRQX
UV
U
+
D=
(516)
Trong :
,
PQ
tng cng sut ca ph ti trn ng dy, n v [kW], kVAR].
,
RX
in tr v in khng ca ng dy, []
dm
U
in p dy nh mc, [kV].
5.2.4. Tn tht in p trong my bin p:
Tng t nh tnh tn tht in p trn ng dy c ph ti tp trung, tn tht in p trong my bin p l:
2
..100
%.
1000
dm
PRQX
U
U
+
D=
(517)
Trong :
,
PQ
cng sut do my bin p truyn ti, n v [kW], kVAR].
,
RX
in tr v in khng ca MBA quy i v cp in p tng ng, []
dm
U
in p nh mc, [kV].
5.3. Tnh ton tn tht cng sut:
5.3.1. Tn tht cng sut trn ng dy:
Tn tht cng sut trn ng dy l mt i lng phc:
.
SPjQ
D=D+D
, trong :
P
D
: tn tht cng sut tc dng do pht nng trn in tr ng dy.
Q
D
: tn tht cng sut phn khng do t ha ng dy.
xc nh tn tht cng sut trn ng dy, ta dng s thay th hnh .
Trng hp 1: xt mng in khu vc c in p t 110 220kV do c th b qua thng s in dn G (nh hnh a).
Hnh 5.5. S thay th tnh tn tht cng sut
Theo hnh v, d dng tnh c:
"""
222
.
c
SPjQPjQjQ
=+=+-
y:
22
2222
3..
22
ccdm
BB
QIUUU
==
Tn tht cng sut tc dng v phn khng khi c dng in ba pha chy qua
.
ZRjX
=+
:
2
2
2
2
2
2
3..
3..
S
PIRR
U
S
QIXX
U
D==
D==
hay
(
)
(
)
(
)
(
)
22
""
2
22
""
2
.
.
PQ
PR
U
PQ
QX
U
+
D=
+
D=
(518)
Vy:
(
)
(
)
'"""''
.
SSSPPjQQPjQ
=+D=+D++D=+
V:
'''
1111
cc
SSjQPjQjQPjQ
=-=+-=+
vi
22
1111
3..
22
ccdm
BB
QIUUU
==
Trng hp 2: i vi ng dy a phng ta c th b qua tng dn B, nh hnh b, khi tn tht cng sut c xc nh theo cng sut ti
22
PjQ
+
(
)
(
)
(
)
(
)
22
22
2
22
22
2
.
.
PQ
PR
U
PQ
QX
U
+
D=
+
D=
(519)
5.3.2. Tn tht cng sut trn ng dy c ph ti phn b u:
Nu ng dy phn phi c ph ti phn b u (nh ng dy chiu sng ngoi ng), c tng dng I v in tr R, th tn tht
2
PIR
D=
5.3.3. Tn tht cng sut trong my bin p:
Tn tht cng sut trong my bin p bao gm tn tht khng ti (tn tht trong li thp hay tn tht st) v tn tht c ti (tn tht trong dy qun hay tn tht ng).
a) Thnh phn tn tht khng ti:
Thnh phn tn tht trong li thp khng i khi ph ti thay i v bng tn tht khng ti:
000
.
SPjQ
D=D+D
(520)
Vi:
0
0
%.
100
dm
IS
Q
D=
ta c:
0
00
%.
.
100
dm
IS
SPj
D=D+
b) Tn tht c ti i vi my bin p hai cun dy:
i vi my bin p hai cun dy, tn tht cng sut tc dng trong cc cun dy khi ti nh mc bng tn tht cng sut ngn mch: Pcun dy nh mc = PK.
Tn tht cng sut phn khng trong cc cun dy, nu xem RT