V D CHN DY DN KT HP VI CBV d 1: Chn dy dn cho ng c 3 pha cng
sut10 kW, in p380 V , cos = 0,8, i cng 4 cp 3 pha dy di 25ma/ Phi
hp chn dy vi CBb/ Phi hp chn dy vi cu chBi gii:a/ Phi hp chn dy vi
CBDng lm vic ca ng c l: Chn CB c dng nh mc In tha iu kin sau:In
IbChn dng nh mc CB = 25 A( dy dng nh mc CB ca cc hng nh LG,
Schneider, ABB, Siemens ch to tra cataloge trang 146 289 sch s tay
la chn v tra cu thit b in t 0,4 n 500 kV ca NG HNG QUANG )Chn dng
pht nng cho php Icp ca dy /cp m CB c th bo vIcp = In = 25AT iu kin
lp t thc t ca dy/ cp ta tm c h s hiu chnh KV dy khng chn trong t nn
ta c:K=K1K2K 3 = 0,7 x 0,75 x 0,93 = 0,488Xc nh dng pht nng cho php
tnh ton Icptt :
Chn loi dy/cp v tit dip ph hp vi dng pht nng nh mc Icpdm tha iu
kin:Icpdm Icptt tra bng cataloge dy dn cp in lc 4 rut dng cho ng c
3 pha ta chn dy dn c tit din = 28 mm2 c Icpdm = 55A ,in p ri = 4,8
V/A/km(trang 102 sch CUNG CP IN ca thy PGS.TS QUYN HUY NH)b/ Phi hp
chn dy vi cu ch :Ib = 19A chn dng tc ng ca dy chy cu ch Idc tha iu
kin:Idc Ib nn ta chn dng nh mc cu ch Idc = 20 A ( chn theo cataloge
cu ch ca hng ABB sn xut trang 105 sch la chn v tra cu thit b in ca
NG HNG QUANG)Chn dng pht nng cho php Icp ca dy/cp m cu ch c kh nng
bo v l:Icp = 1,21 x Idc = 1,21 x 20 = 24,2 AXc nh h s K tng t nh cu
a nn ta c: K = 0,488Xc nh dng pht nng cho php tnh ton Icptt :
Icpdm Icptt tra bng cataloge dy dn cp in lc 4 rut dng cho ng c 3
pha ta chn dy dn c tit din = 28 mm2 c Icpdm = 55A ,in p ri = 4,8
V/A/kmKim tra st p cho phpU = Vd x I x L = 4,8 x 19 x 0,025 = 2,28
V
V vy cn tng tit din dy dn =222 mm2 c dng nh mc = 102 A in p
riVd= 1,8V/A/kmU = Vd x I x L = 1,8 x 19 x 0,025 = 0,0855 V
V d 2: Chn dy theo iu kin n tht in p cho php
Ucp % = 5 %, = 53 m/mm2, xo= 0,25/kmBi gii :
Ul thnh phn tn tht in p do cng sut tc dng v in tr ng dy gy nn.
Ul thnh phn tn tht in p do cng sut phn khng v in khng ng dy gy nn.
x0, r0 ln lt l in tr v in khng trn mt n v chiu di ng dy (/km)
tit din dy dn
( Tra bng cataloge cp in lc dng trong mng phn phi khu vc cch in
PVC trang 102 sch cung cp in ca thy PGS.TS QUYN HUY NH)Ta chn dy c
tit din = 14 mm2 , dng nh mc 88 A, in p ri Vd = 2,5 V/A/km.
