Chn Icu Ics Ir Isd In Im Icw Isc cho ACB, MCCB, CB
Chn Icu Ics Ir Isd In Im Icw Isc cho ACB, MCCB, CB
Glossary:
EDW: ElectroDynamic Withstand SCPD: Short circuit protection
device IEC: International Electrotechnical Commission BS: British
Standard CT: Current transformers CU: control Unit MSB: Main
Switchboard BBT: Busbar Trunking MV: Medium Voltage (1kV to 36kV)
Isc: Short-circuit current Isc(D1): Short-circuit current at the
point D1 is installed Usc: Short-circuit voltage MCCB: Moulded case
circuit-breaker BC: Breaking Capacity Icu(*): Ultimate Breaking
Capacity IcuD1(*): Ultimate Breaking Capacity of D1 Ue: Rated
operational voltage Ui: Rated insulation voltage Uimp: Rated
impulse withstand voltage In: Rated operational current Ith:
Conventional free air thermal current Ithe: Conventional enclosed
thermal current Iu: Rated uninterrupted current Icm: Rated
short-circuit making capacity Icu: Rated ultimate short-circuit
breaking capacity Ics: Rated service breaking capacity Icw: Rated
short time withstand current Ir: Adjustable overload setting
current 1.05 x Ir: Conventional non-tripping current
Tm hiu thm mt s sau:
Mnh lm vic vi MCB v MCCB kh nhiu nn xin tr li cho bn thc mc ny.
Mt CB bt k (MCB, MCCB, ACB,...) th c cc thng s c bn sau y: - Dng nh
mc In: 2, 3, 6, 10, 16, 20, 25, ... Vi cc dng nh mc ln ca cc CB ln
nh MCCB hay ACB, dng ny s i km vi cc my bin p in lc c cng sut tng
ng. V d: trm 200kVA - 315A, trm 250kVA - 400A, trm 315kVA - 500A,
... - Thng s s bn th hai l characteristic cuver hay cn gi l ng cong
chn lc ca CB. y chnh l thng s quan trong nht cho vic chn CB nm v tr
no cho h thng in. Bn nn xem k li cc ti liu ni v ng cong chn lc ny.
- Thng s th ba l Icu hay cn gi l ultimated current l kh nng chu ng
dng in ln nht ca tip im CB trong thi gian 1 giy. V d Icu = 10kA th
tip im CB s chu ng c dng in 10kA trong thi gian 1 giy/ Thng s ny
cho bit bn tip im ca CB. Ngoi thng s ny thng s Ics cng c tnh cht
tng t. - Thng s th t l thng s ln ng ngt. V d bn ngt CB ri bt CB ln
li th gi l 1 ln ng ngt. CB thng thng cng quy nh s ln ny. Cc MCB c
quy nh l t 7500 n 10000 ln, MCCB th hn 10000 ln. ACB th khng 8000
ln ty theo hng. Ngoi ra cn rt nhiu thng s khc na p dng cho CB. Tuy
nhin trong cc thit k ngi ta thng dng thng s In v Icu. Theo ti hai
thng s ny khng quy nh v chng loi CB. Thng s th hai chnh l thng s
quan trong nht ca CB. y chnh l ch s ID chnh thc ca cc CB.
******************************
+ Ultimate breaking capacity(kA), Icu : kh nng chu c dng cc i
khi xy ra s c ca thit b. + Service breaking capacity(%Icu), Ics :
kh nng ct thc t khi xy ra s c ca thit b , iu ny ph thuc vo tng nh
sn xut. VD, cng l hng LS(LG cu) co hai loai MCCB, loai co
Ics=50%Icu, nhng cng c loi Ics=100%Icu, l do cng ngh ca tng hng c
th lm c n u.
***********************
Lu nay ti vn mun trnh by cc bn th no l Icu v th no l Ics m cha c
dp. Trong mt s ch , ti c trnh by v Characteristic cuver rt nhiu. Cn
Icu v Ics th cha c dp no c. Xin trnh by mt s nh sau: - Nu bn v Icu
th thy rt nhiu hng ghi nhng con s khc nhau. y xin ni v Icu theo nh
ngha ca hng Siemens. Bn dlhm2008 nh ngha chnh xc tn ting Anh ca
Icu. y ti xin ni v bn cht ca Icu. Icu l mt dng in cc i i qua tip im
ca CB trong vng 1 giy m khng lm hng tip im ny. V d mt dng Icu =
50kA, ta thy tip im CB chu ng dng ny v c th nh gi rng CB ny rt tt.
Ni nh th tc l gi thnh CB s ph thuc vo Icu ny. iu ny hon ton ng. -
Ics cng c bn dlhm2008 nh ngha hon ton ng. y ti cng xin ni v bn cht
ca Ics. Theo Siemens th Ics chnh l dng in ln nht ti qua tip im CB 3
ln vi chu di thi gian mi ln l 1 giy m CB khng b h hng. C hng khc
cng nh ngha l Ics l dng in ln nht ti qua tip im CB trong thi gian 3
giy m CB khng b h hng. Hai cch nh ngha trn theo ti iu c ngha ging
nhau. By gi xin ni v gi tr thc tin ca Icu v Ics. Trn thc t, vic tnh
ton thit k cho mt mng li bt k u tnh vi thi gian s c l 1 giy. Nh th
Icu s l thng s chn CB ng ng ch trong mng li in. Ti v d mt bin th
22/0.4kV - 1600kVA, duk = 6%, dng ngn mch hiu dng pha h th l:
1600/(duk*0.4*sqrt(3)) = 40.4kA. Dng ngn mch cc i ty theo ti s c
nhn thm h s hiu chnh th 1.02 n 2 ln dng hiu dng. Tuy nhin thng thng
tnh n CB tng u tin s bng khong 1.4 n 1.5 dng hiu dng. Khi dng ngn
mch ti CB tng s tnh t khng t 57 - 61kA. Vi mc tnh ny, r rng cc MCCB
hay ACB c dng Icu t 65kA l CB phi chn. By gi ch cn gi tr Ics, ngha
ca gi tr ny nh th no. Mong cc bn gp thm chng ta hiu thm v gi tr
ny!
********************
duk: l in p ngn mch ca bin p. Mnh nh ch denta Hy lp khng c! Tt
nhin vic tnh ton cho cc nhnh phi c chiu di dy dn, t bn tnh c Xnm v
Rnm. Khi s tnh c dng ngn mch hiu dng h s ngn mch cc i. T ta c dng
ngn mch cc i ca nhnh v sau s tnh c nn chn my ct nh th no!
Icu, v Ics th cc bc ni r ri, nhng trong MCCB cn c dng (A,Ir)
Adjustabli current l dng g ko?
******************************
Ir l dng chnh nh . Bn c CB 100A m ti ca ban ch cn 65A vy bn phi
chnh Cb xung cho ph hp vi ti
nh vy dng chnh nh Ir=(h s)xIn (h s e thy t 0.8-1)or(0.5-1). e
hieu rui, cm n bc!
********************************
Ah` c ai bit Isd ko?Trn ACB ca Schneider . Isd=heso(1-2)xIr.
**************************
Icu (Ultimate breaking capacity(kA)) : l dng ngn mch ti a, n c
kh nng chu c dng cc i khi xy ra s c ca thit b. Ics (Service
breaking capacity(%Icu)) : l dng ngn mch thc...
********************************
Ni n Atomat ngi ta ch quan tm n thng s k thut ( s cc, dng nh mc,
dng ch nh, dng ngn mch) v biu Thi gian - Dng ca n. Cu to rt n gin n
gm c tay gt, cu trc c kh, relay, bung dp h quang, cc u ni dy....
Ngoi ra n cn c thm cc phu kin : AL (cng tc cnh bo), AX ( cng tc
ph), SHT (thit b ct t xa), UVT (tb ct in p thp), EAL (cnh bo r in),
TBM (nt kim tra), MG (cng tc cch in), PAL ( tin cnh bo), OAL (cnh
bo ct qu dng)...
Bng tra thng s ng c v thit b in Mitsubishi, LS, ...
HNG DN LA CHN DY CP IN TRONG XY DNG NH Tnh ton la chn dy dn in
cho nh l mt vic cn thit v quan trng, th nht l vn an tan cho ngi v
ti sn, th hai l tit kim (v c th trnh c vic phi tho ra lm li khi thy
khng ph hp). Hng dn ny trnh by mt cch ngn gn v vn ny, ng hu gip cho
ngi dng t tin v d dng hn trong vic la chn dy dn in cho nh . Trong
hng dn ny, cu trc v tn gi ca cc loi dy lp t trong nh (xem 3.3) c
tham kho theo tiu chun TCVN 2103; cc loi cp ngoi tri v cp in k (xem
3.1 v 3.2) c tham kho theo tiu chun ca ngnh in lc cng nh cc nh sn
xut cp uy tn Vit nam hin nay.
Hng dn gm cc mc nh sau:
- Cc ngun in s dng cho nh - Mt s cch i dy v loi dy tng ng, thng
dng- Cc loi dy dn thch hp cho nh - Cng sut chu ti ca cc loi dy cp
in thng s dng cho nh - Cch tnh ton v la chn dy dn- Cc lu cho h thng
in nh - Nhng tc hi khi dng dy & cp in km cht lng- Nhng kinh
nghim la chn dy in cho nh
1. Cc ngun in s dng cho nh 1.1 Ngun in 1pha 2dy (thng dng
nht)Ngun 1pha 2dy gm c 1 dy pha v 1 dy trung tnh (cn c gi l 1 dy
nng v 1 dy ngui). y l ngun in cho nh thng dng nht ti Vit Nam hin
nay.
1.2 Ngun in 1pha 3dyNgun in 1pha 3dy gm c 1 dy pha 1 dy trung
tnh v 1 dy ni t (cn c gi l 1 dy nng, 1 dy ngui v 1 dy bo v). Vit
Nam hin nay ngun in ny bt u p dng cc ta nh cao tng, bit th,
building, khch sn, cc ni c s dng cc my mc thit b quan trng hoc cc
nh cao cp hn.
1.3 Ngun in 3pha 4dy (t gp)Ngun in 3pha 4dy gm c 3 dy pha v 1 dy
trung tnh (cn c gi l 3 dy nng, 1 dy ngui). Vit Nam hin nay ngun in
ny t gp trong nh , tr khi ch nh c nh s dng thit b in 3pha.
1.4 Ngun in 3pha 5dy (rt t gp)Ngun in 3pha 5dy gm c 3 dy pha 1
dy trung tnh v 1 dy ni t bo v (cn c gi l 3 dy nng, 1 dy ngui v 1 dy
bo v). Vit Nam hin nay ngun in ny rt t gp trong nh , tr khi ch nh c
nh s dng thit b in 3pha v c yu cu thm v dy bo v.
2. Mt s cch i dy v loi dy tng ng, thng dng2.1 i dy ni: Dy &
cp in c lun trong cc ng nha hoc np nha v c c nh trn tng, trn nh. S
lng dy trong ng cn xem xt sao cho ng qu cht c th rt dy, lun dy khi
cn thit sa cha thay th. Cc loi dy nh VCm, VCmd, VC l thch hp cho
cch i dy ni.
2.2 i dy m tng, m trn, m sn: Dy & cp in c lun trong cc ng
nha (ng trn khi i thng, ng rut g khi chuyn hng) t m trong tng, trn
hoc sn nh. S lng dy trong ng cn xem xt sao cho ng qu cht c th rt
dy, lun dy khi cn thit sa cha thay th. Cc loi dy nh VC, CV, CVV l
thch hp cho cch i dy m.
2.3 i dy ngm: i vi cc cng trnh ngoi vi, khng dnh lin vi nh, dy
& cp in c lun trong cc ng nha cng hoc ng thp chu lc, khng thm
nc v chn ngm di t su khang 0,7mt. Cc loi cp c o gip thp hoc c bc
kim loi th c th chn trc tip trong t m khng cn lun trong ng. Cn thit
phi chn cc loi dy/ cp c kh nng chng thm nc, chng cn trng cho ng dy
i ngm.
3. Cc loi dy dn thch hp cho nh Theo thng l ca ngnh in lc cng nh
thc t hin nay Vit Nam, hng dn ny chn ngun in 1 pha 2 dy trnh by cho
mc ch nh . Hng dn ny chia h thng dy cho nh ra lm 3 phn v tng ng vi
mi phn hng dn ny a ra cc ngh v cc loi dy dn c th c dng nh sau:
3.1 on dy ngoi ng vo u nh (on dy ngoi tri)on dy ny l dy ni t li
in a phng vo n nh, thng thng on dy ny nm han tan ngoi tri (ngoi tr
mt s rt t nh s dng cp ngm th on dy ny c chn di t). on dy ngoi tri
ny c ngh s dng mt trong cc loi dy/cp sau y:
Cp Duplex rut ng, cch in PVC (Duplex Du-CV)Cp Duplex Du-CV c 2
rut dn bng ng, rut dn l 1 si ng c hoc 7 si ng c xon li vi nhau, mi
rut dn c bc cch in PVC sau xon vi nhau. Cp in p ca cp l 450/750V
hoc 0,6/1kV.
Cp Duplex rut ng, cch in XLPE (Duplex Du-CX)Cp Duplex Du-CX c 2
rut dn bng ng, rut dn l 1 si ng c hoc 7 si ng c xon li vi nhau, mi
rut dn c bc cch in XLPE mu en sau xon vi nhau, mt trong hai li c gn
ni phn bit pha. Cp in p ca cp l 0,6/1kV.
3.2 on dy t u nh vo in k (on cp in k)on dy ny l dy ni t u cui on
dy ngoi tri (c ni mc 3.1) n in k (ng h o in nng tiu th). Thng thng
on dy ny nm mt na dc theo tng, mt na trong nh (v thng thng in k c t
trong nh). on dy ny c ngh s dng mt trong cc loi dy/cp sau y:
Cp in k rut ng, cch in PVC (K-CVV)Cp in k rut ng cch in PVC cn
gi l cp Muller rut ng cch in PVC, cp c 2 hoc nhiu hn 2 rut dn, rut
dn l 1 si ng c hoc 7 si c xon li vi nhau, mi rut dn c bc cch in bng
vt liu PVC, mt lp bc lt PVC, mt lp bng nhm ( chng trm in) v lp v bc
PVC bo v bn ngoi, cp in p ca cp l 450/750V hoc 0,6/1kV.
Cp in k rut ng, cch in XLPE (K-CXV)Cp in k rut ng cch in XLPE cn
gi l cp Muller rut ng cch in XLPE, cp c 2 hoc nhiu hn 2 rut dn, rut
dn l 1 si ng c hoc 7 si c xon li vi nhau, mi rut dn c bc cch in bng
vt liu XLPE mu trng-trong (mu t nhin), mt trong hai li c bng mu hoc
sc mu phn bit pha, mt lp bc lt PVC, mt lp bng nhm ( chng trm in) v
lp v bc PVC bo v bn ngoi, cp in p ca cp l 0,6/1kV.
3.3 Dy dn t in k n cc thit b tiu th in (dy dn trong nh) Vit Nam,
hu nh 2 on dy cp mc 3.1 v 3.2 u do ngnh in lc t la chn v lp t nu ch
nh khng c yu cu g ring. Cn cc dy dn t in k n cc thit b tiu th in,
hu ht l do ch nh t quyt nh lo liu, y l cng vic m hng dn ny cho l ch
nh cn thit phi quan tm. Cc dy dn ny c ngh s dng mt trong cc loi sau
y.
3.3.1 Dy n cng (VC)Dy n cng (VC) l dy c rut dn l 1 si ng, bc cch
in PVC. Cp in p ca dy l 600V.Ngoi ra, cn c Dy n cng khng ch
(LF-VC), khng tc hi cho con ngi v mi trng bng cch s dng vt liu PVC
khng ch (LF-PVC), ph hp quy nh RoHS (Restriction of Hazardous
Substances) ca chu u.
3.3.2 Dy n mm (VCm)Dy n mm (VCm) l dy c rut dn gm nhiu si ng c
xon vi nhau, bc cch in bng vt liu PVC. Cp in p ca dy l 250V.Ngoi
ra, cn c Dy n mm khng ch (LF-VCm), khng tc hi cho con ngi v mi trng
bng cch s dng vt liu PVC khng ch (LF-PVC).
3.3.3 Dy i mm dt (VCmd)Dy i mm dt (VCmd) l dy c 2 rut dn, mi rut
dn gm nhiu si ng xon li vi nhau, 2 rut dn ny c bc cch in PVC v phn
cch in ca 2 rut dn dnh vi nhau to ra mt dy dt c 2 rut dn cch in
song song vi nhau. Cp in p ca dy l 250V.Ngoi ra, cn c Dy i mm dt
khng ch (LF-VCmd), khng tc hi cho con ngi v mi trng bng cch s dng
vt liu PVC khng ch (LF-PVC).
3.3.4 Dy i mm xon (VCmx)Dy i mm xon (VCmx) l dy c xon li t 2 dy
n mm (VCm) ring bit. Cp in p ca dy l 250V.Ngoi ra, cn c Dy i mm xon
khng ch (LF-VCmx), khng tc hi cho con ngi v mi trng bng cch s dng
vt liu PVC khng ch (LF-PVC).
3.3.5 Dy i mm trn (VCmt)Dy i mm xon trn (VCmt) l dy gm 2 dy n mm
(VCm) ring bit c xon li hoc t song song ri bc bn ngoi mt lp v bo v
bng PVC. Dy ny cng c gi l cp CVVm. Cp in p ca dy l 250V.Ngoi ra, cn
c Dy i mm trn khng ch (LF-VCmt), khng tc hi cho con ngi v mi trng
bng cch s dng vt liu PVC khng ch (LF-PVC).
3.3.6 Dy i mm van (VCmo)Dy i mm van (VCmo) l dy gm 2 dy n mm
(VCm) ring bit c xon li hoc t song song ri bc bn ngoi mt lp v bo v
bng PVC. Dy ny cng c gi l cp CVVm van. Cp in p ca dy l 250V.Ngoi
ra, cn c Dy i mm van khng ch (LF-VCmo), khng tc hi cho con ngi v mi
trng bng cch s dng vt liu PVC khng ch (LF-PVC).
3.3.7 Dy n cng, rut nhm (VA)Dy n cng, rut nhm (VA) l dy c rut dn
l 1 si nhm, bc cch in PVC. Cp in p ca dy l 600V.Ngoi ra, cn c Dy n
cng rut nhm khng ch (LF-VA), khng tc hi cho con ngi v mi trng bng
cch s dng vt liu PVC khng ch (LF-PVC).
3.3.8 Dy in lc rut ng, cch in PVC (CV)Dy in lc rut ng, cch in
PVC (CV) l dy c rut dn gm 7 (hoc 19) si ng xon ng tm, bc mt lp cch
in PVC. Cp in p ca dy l 450/750V hoc 0,6/1kV.Ngoi ra, cn c Dy in lc
rut ng, cch in PVC khng ch (LF-CV), khng tc hi cho con ngi v mi
trng bng cch s dng vt liu PVC khng ch (LF-PVC).
3.3.9 Cp in lc rut ng, cch in PVC, v bo v PVC (CVV)Cp in lc rut
ng, cch in PVC, v bo v PVC (CVV) l cp c 1 hoc nhiu li cp, mi li cp
c rut dn gm 7 (hoc 19) si ng xon ng tm v bc mt lp cch in PVC. Cp
CVV c mt lp v bo v PVC bn ngoi. Cp in p ca cp l 450/750V hoc
0,6/1kV.Ngoi ra, cn c Cp in lc rut ng, cch in PVC khng ch, v bo v
PVC khng ch (LF-CVV), khng tc hi cho con ngi v mi trng bng cch s
dng vt liu PVC khng ch (LF-PVC) cho cch in v v bc.
4. Cng sut chu ti ca cc loi dy cp in thng s dng cho nh Mi c dy/
cp (tit din rut dn) v mi loi dy/cp c mc chu ti khc nhau. i vi mc ch
nh , hng dn ny a ra cc bng m t cng sut chu ti ca cc loi dy/cp nh di
y. Cng sut chu ti nu trong cc bng ny l ph hp vi nhit mi trng n 40 C
v cng xem xt n vn st p nhm m bo cht lng in sinh hot cho nh .
Bng 1: Cng sut chu ti ca cp Duplex Du-CV, Duplex Du-CXTit din
rut dnCng sut chu tiChiu di ng dyTit din rut dnCng sut chu tiChiu
di ng dy
3 mm2 5,5 kW 30 m10 mm2 12,1 kW 45 m
4 mm2 6,8 kW 30 m11 mm2 12,9 kW 45 m
5 mm2 7,8 kW 35 m14 mm2 15,0 kW 50 m
5.5 mm2 8,3 kW 35 m16 mm2 16,2 kW 50 m
6 mm2 8,7 kW 35 m22 mm2 20,0 kW 60 m
7 mm2 9,5 kW 40 m25 mm2 21,2 kW 60 m
8 mm2 10,6 kW 40 m35 mm2 26,2 kW 70 m
Chiu di ng dy ngh s dng bng ny c tnh tan theo st p khng qu 5% iu
kin y ti.i vi ngun 1pha 2dy, 220V, sau khi chn c tit din rut dn ph
hp vi cng sut nhng cha ph hp vi chiu di ng dy mong mun th ch vic
tng tit din ln mt cp (v d tng t 3mm2 ln 4mm2) v kim tra li theo cng
thc di y, nu tha mn th tit din dy va tng ln l ph hp, nu cha tha mn
th tng tit din rut dn ln mt cp na v kim tra li nh trn cho n khi tha
mn.
Trong P = Cng sut tnh tan chn dy, kW L = Chiu di ng dy mong mun,
m S = Tit din rut dn ca dy, mm2Bng 2: Cng sut chu ti ca cp in k
K-CVV, K-CXVTit din rut dnCng sut chu tiTit din rut dnCng sut chu
ti
Cch in PVC(K-CVV)Cch in XLPE(K-CXV)Cch in PVC(K-CVV)Cch in
XLPE(K-CXV)
3 mm2 6,4 kW 8,2 kW10 mm2 13,4 kW 17,0 kW
4 mm2 7,6 kW 9,8 kW11 mm2 14,2 kW 18,1 kW
5 mm2 8,8 kW 11,2 kW14 mm2 16,6 kW 20,7 kW
5,5 mm2 9,4 kW 11,9 kW16 mm2 17,8 kW 22,0 kW
6 mm2 9,8 kW 12,4 kW22 mm2 22,0 kW 27,2 kW
7 mm2 10,8 kW 13,8 kW25 mm2 23,6 kW 29,2 kW
8 mm2 11,8 kW 15,0 kW35 mm2 29,0 kW 36,0 kW
Thng thng chiu di s dng Cp in k kh ngn nn khng cn quan tm n st
p.Bng 3: Cng sut chu ti ca dy VC, CV, CVVTit din rut dnCng sut chu
tiTit din rut dnCng sut chu ti
0,5 mm20,8 kW3 mm2 5,6 kW
0,75 mm2 1,3 kW4 mm2 7,3 kW
1,0 mm21,8 kW5 mm28,7 kW
1,25 mm22,1 kW6 mm2 10,3 kW
1,5 mm2 2,6 kW7 mm2 11,4 kW
2,0 mm2 3,6 kW8 mm212,5 kW
2,5 mm24,4 kW10 mm214,3 kW
Cng sut nu trong bng trn ph hp cho chiu di dy n 30m, vi st p
khng qu 5% iu kin y tiBng 4: Cng sut chu ti ca dy i mm VCm, VCmd,
VCmx, VCmt, VCmoTit din rut dnCng sut chu tiTit din rut dnCng sut
chu ti
0,5 mm2 0,8 kW2,5 mm24,0 kW
0,75 mm21,2 kW3,5 mm25,7 kW
1,0 mm21,7 kW4 mm26,2 kW
1,25 mm2 2,1 kW5,5 mm2 8,8 kW
1,5 mm22,4 kW6 mm2 9,6 kW
2,0 mm23,3 kW--
Cng sut nu trong bng trn ph hp cho chiu di dy n 30m, vi st p
khng qu 5% iu kin y tiBng 5: Cng sut chu ti ca dy VATit din rut
dnCng sut chu tiTit din rut dnCng sut chu ti
1,0 mm21,0 kW5 mm2 5,5 kW
1,5 mm21,5 kW6 mm26,2 kW
2,0 mm22,1 kW7 mm27,3 kW
2,5 mm22,6 kW8 mm2 8,5 kW
3 mm23,4 kW10 mm2 11,4 kW
4 mm24,2 kW12 mm213,2 kW
Cng sut nu trong bng trn ph hp cho chiu di dy n 30m, vi st p
khng qu 5% iu kin y ti5. Cch tnh ton v la chn dy dnTnh ton v la chn
dy dn cn phi thc hin theo cc bc sau y.
- Xc nh ngun in s dng- Tnh tng cng sut thit b tiu th in- La chn
dy dn cho tng phn ca nh , bao gm ba bc nh:+ La chn an dy ngoi tri+
La chn an cp in k+ La chn dy cho tng nhnh v dy n tng thit b tiu th
in.
5.1 Xc nh ngun in s dngCn c vo thit b in trong nh m ngi dng s
dng l thit b 1 pha hay 3 pha, ng thi cng phi cn c vo ngun cung cp
ca in lc a phng mnh c nhng loi ngun in no. Hu ht ngun in dng cho nh
hin nay Vit Nam l ngun 1 pha 2dy.Bc ny thng b ph thuc vo ngun cung
cp tng a phng, nu ngi dng ch xi thit b in 1 pha v ngun a phng ca in
lc ch c 2 dy (1 nng, 1 ngui) hoc 4 dy (3 nng, 1 ngui) th ch c ngun
1pha 2dy (nh nu mc 1.1) l p dng c. Trong trng hp ny vn c th chn
ngun 1pha 3dy (nh nu mc 1.2) dng, nhng phi thit k thm h thng ni t
cho h thng in trong nh, pha sau ng h o in.
5.2 Tnh tng cng sut thit b tiu th inThit b tiu th in l nhng thit
b hat ng bng nng lng in. Cc thit b tiu th in trong nh c th k ra nh:
n in, qut in, ni cm in, bn i, t lnh, my git, l nng vi sng, my iu ha
nhit , my bm nc Trn mi thit b tiu th in, hu ht u c ghi tr s cng
sut, c n v l W (Woat) hoc kW (Kil-Woat) hoc HP (Horse Power- Sc
nga). Mt cch gn ng, c th xem tt c cc tr s cng sut ghi trn cc thit b
l cng sut tiu th in. Tnh tng cng sut thit b tiu th in l lit k v cng
li tt c tr s cng sut ca cc thit b tiu th in trong nh nhm xc nh cng
sut tiu th in tng ca c ngi nh.
Khi gp cc n v cng sut khc nhau th quy i sang cng mt n v nh
sau:
1kW = 1.000W1HP = 750W
5.3 La chn dy dn cho tng phn ca nh y l buc cui cng tm ra cc c dy
cn phi dng. Ty theo cng sut chu ti ca tng nhnh trong s in, ngi dng
c th chn nhiu loi dy, c dy khc nhau.
* V d: Tnh tan la chn dy dn cho mt nh c th. bi:Cn tnh tan chn la
dy dn cho h thng in ca mt ngi nh 1 trt 1 lu, i dy m tng, khang cch
t nh n li in a phng l 30m, tt c thit b in trong nh s dng in 1pha
220V, v c cng sut c nu trong bng sau.
Tng trtTng lu
Tn thit b/ Cng sutS lngTng cng sutTn thit b/ Cng sutS lngTng cng
sut
Bng n hynh quang 1,2m/ 40W840 x 8 = 320WBng n hynh quang 1,2m/
40W540 x5 = 200W
n trang tr/ 20W520 x 5 = 100Wn trang tr/ 20W320 x 3 = 60W
Qut in/ 100W4100 x 4 = 400WQut in/ 100W3100 x 3 = 300W
Ni cm in/ 600W1600 x 1 = 600WMy iu ha/ 1,5HP11,5 x 750 x 1 =
1125W
Tivi/ 150W1150 x 1 = 150WTivi/ 150W1150 x 1 = 150W
u my + ampli/ 150W150 x 1 = 150WB my vi tnh/ 500W1500 x 1 =
500W
L nng vi sng/ 1000W11000 x 1 = 1000WMy sy tc/ 1000W11000 x 1 =
1000W
Bn i/ 1000W11000 x 1 = 1000W---
My iu ha/ 1,5HP21,5 x 750 x 2 = 2250W---
My git 7kg/ 750W1750 x 2 = 1500W---
M-t bm nc/ 750W1750 x 1 = 750W---
Bi gii:Bc 1: Xc nh loi ngun in s dng: V tt c thit b in trong nh
s dng in 1pha, 220V nn ta chn ngun in thng dng nht l ngun 1pha 2
dy.
Bc 2: Tnh tng cng sut thit b tiu th in: Cng tt c cng sut ca cc
thit b ca tng trt, tng lu v cng sut tng ca c nh ta c s liu sau.
Tng cng sut tng trt: 7.470WTng cng sut tng lu: 3.335WTng cng sut
c nh: 10.805W
Bc 3: La chn dy dn cho tng phn ca nh La chn an dy ngoi trion dy
ngoi tri l an dy dn in vo nh nn n phi chu c tng cng sut c nh l
10.805W. Tuy nhin, hu nh khng c thi im no m tt c cc thit b in trong
nh hat ng ng thi cng mt lc, cho nn ngi ta c th gim cng sut tnh tan
xung cn khang 80% cng sut tnh tan ri mi chn la dy dn theo cng sut c
gim. Khi gim xung 80% nh vy ngi ta c cch gi khc l chn h s ng thi
(kt) = 0,8. Trong v d ny hng dn ny cng chn kt = 0,8 v cng sut sau
khi gim l:
P = 10.805 x 0,8 = 8644W = 8,644kW
on dy ngoi tri thng thng c s dng l loi dy Duplex rut ng, cch in
PVC (Du-CV). Cn c vo cng sut 8,644kW ta tra bng tm c (tit din rut
dn) cp cho thch hp. Tra bng 1 (cp Du-CV v Du-CX), chn gi tr ln hn
gn nht ta thy cp tit din rut dn 6mm2 c cng sut chu ti ph hp. Chiu
di lp t ca cp c tit din rut dn 6mm2 cho trong bng 1 cng tha mn vi
chiu di lp t m u bi yu cu l 30m, v vy ta c th chn on cp ngoi tri l
cp Du-CV 2x6mm2 hoc Du-CX 2x6mm2
La chn an cp in kon cp in k ni t an dy ngoi tri vo n nh nn n cng
phi c cng sut chu ti ln hn hoc bng 8,644kW. Tra bng 2 ta thy cp
K-CVV tit din rut dn 5mm2 hoc cp K-CXV tit din rut dn 4mm2 l ph hp.
on cp in k thng kh ngn (< 10m) nn khng cn quan tm n in p ri theo
chiu di. Nh vy, ngi dng c th s dng K-CVV 2 x 5mm2 hoc K-CXV 2 x
4mm2.
La chn dy cho tng nhnh v dy dn n tng thit b inNgi nh c tng trt v
1 tng lu, hai tng c cng sut tiu th khc nhau nhiu, do tit kim ngi
dng c th phn lm 2 nhnh. ng dy cho 2 nhnh ny ngi dng nn chn loi dy n
cng (VC).
Nhnh 1 cho tng trt:Tng trt c cng sut tng l 7.470W = 7,47kW. Tng
t nh cp trn, hu nh cc thit b khng hat ng ng thi nn c th chn h s ng
thi kt = 0,8, lc cng sut chn dy dn l 7,47 x 0,8 = 5,976kW. Tra bng
3 ta thy dy VC tit din rut dn 4mm2 l ph hp, nh vy ngi dng c th chn
dy VC 4mm2 cho nhnh 1 (tng trt).
Nhnh 2 cho tng lu:Tng lu c cng sut tng l 3.335W = 3,335kW. Tng t
nh cp trn, hu nh cc thit b khng hat ng ng thi nn c th chn h s ng
thi kt = 0,8, lc cng sut chn dy dn l 3,335 x 0,8 = 2,668kW. Tra bng
3 ta thy dy VC tit din rut dn 2mm2 l ph hp, nh vy ngi dng c th chn
dy VC 2mm2 cho nhnh 2 (tng lu).
Dy cho tng thit b:Theo l thuyt th mi thit b c cng sut khc nhau s
cn mt c dy khc nhau. Vic chn tng c dy ring cho tng thit b nh vy c u
im l tit kim c chi ph dy dn, nhng li rt phc tp cho vic mua dy cng
nh i dy, s phc tp ny nhiu khi cng rt tn km. V vy, khi trong nh khng
c thit b no c cng sut ln c bit th ngi dng c th chn mt c dy v dng
chung cho tt c cc thit b.Cng sut s dng cc cm thng khng c nh, khng
bit trc chc chn, v i khi c hai hay nhiu thit b s dng chung mt cm,
do , bm bo, ngi dng nn chn dy cho cm hn mt cp so vi c dy d nh dng
chung cho tt c cc thit b.Ty theo cch lp t, ngi dng c th chn loi dy
n cng hoc dy i mm, ngi nh trong v d ny c yu cu i dy m tng nn ta chn
dy n VC cho tt c cc thit b. Nhn vo bng cng sut ta thy cng sut ca my
iu ha nhit 1,5HP (1,125kW) l ln nht, tra bng 3 ta thy cp VC tit din
rut dn 0,75mm2 l ph hp, tuy nhin cn chn dy cho cm hn mt cp cho nn
ngi dng c th chn dy VC 1,0mm2 cho tt c cc thit b v cm.
Tm li: Cc loi dy, c dy c tnh ton la chn cho ngi nh trn nh
sau:
- on dy ngoi tri: cp Duplex Du-CV 2x6mm2 hoc Duplex Du-CX
2x6mm2- on cp in k: cp K-CVV 2 x 5mm2 hoc K-CXV 2 x 4mm2- Dy cho
nhnh tng trt: dy VC 4mm2- Dy cho nhnh tng lu: dy VC 2mm2- Dy cho cc
thit b in v cm: dy VC 1,0mm2
Ghi ch: Ngi dng c th la chn lp t cc loi dy & cp khng ch vi
tit din rut dn ging nh la chn trn.6. Cc lu cho h thng in nh - Nn
chia ng in phn phi trong nh thnh nhiu nhnh thun tin cho vic ngt in
khi cn sa cha, thay th.- Cc dy pha (dy nng) c cng mu v tt nht l mu
, mu cam hoc mu vng. Khi c nhiu nhnh i chung mt tuyn m kch c ging
nhau th mu ca tng nhnh nn khc nhau d phn bit.- Dy cho h thng ni t
nn c mu ring bit vi tt c cc dy khc v nn chn dy mu xanh- sc- vng hoc
vng- sc- xanh.- Khi lun dy trong ng hoc trong np, phi chn kch thc
ng, np rng sao cho d lun, d rt m khng h hi n dy dn.- Khng nn i dy
ni m thp hoc qu gn cc ngun nhit, ha cht.- Mi ni dy phi cht, tip xc
tt khng gy ra m-ve nc la khi mang ti.- Khng c ni trc tip rut dn ng
v nhm vi nhau.- on dy i trong ng khng nn c mi ni.- Khng nn i dy m
trong nn ca tng trt nu nn khng m bo c nh vi tng khi nn b ln.- Khng
nn s dng dy c tit din nh hn 0.5mm2.
7. Nhng tc hi khi dng dy & cp in km cht lngKhi rut ng km cht
lng hoc khng tit din c th gy ra cc tc hi sau- Dn in km, gy st p trn
ng dy lm cho thit b hat ng khng hiu qu, tui th thit b gim nhanh.-
Pht nng qu mc trn ng dy, gy h hi lp cch in, gy chm chp chy n.- Rut
ng km cht lng rt d gy, kh ni, kh lp vo cc ph kin in khc.
Khi lp cch in km cht lng c th gy ra cc tc hi sau- Nt cch in, h
rut dn, gy in git cho ngi.- Rn nt cch in sau mt thi gian ngn, gy r
in, tn tht in nng, chm chp chy n.- Khng chu c nhit cho php ca rut
dn, chy nho gy ra chm chp chy n.- Khng t tt khi b pht chy bi tc nhn
bn ngoi.- Mt mu sau mt thi gian ngn, gy nhm ln cc dy vi nhau khi sa
cha, thay th.
8. Nhng kinh nghim la chn dy din cho nh Nhng kinh nghim c nu y
ch yu hng ti cc loi dy dng trong nh (nh mc 3.1 cp).Vi rt nhiu cc
loi dy in trn th trng hin nay, tt c, xu c, tht c, gi c, thm ch c
khi gp dy chng c nhn mc, tn nh sn xut g c. V vy, mt ngi khng chuyn
th vic la chn dy no, nhn hiu no m c th tin cy c l mt vic khng d dng
g. Bng mt vi kinh nghim ca ngi bin son, hng dn ny a ra mt s khuyn
ngh v nhng ch du hy vng rng ngi dng c th trnh c cc sn phm dy/ cp in
km cht lng.
- Khng nn chn dy khng c nhn mc trn bao b, khng c tn nh sn xut,
khng a ch r rng.- Khng nn chn dy m trn dy khng c cc thng tin c bn
nh: nhn hiu, tn loi dy, tit din, cu trc rut dn (s si v ng knh mi
si), tiu chun sn xut.- Dy tt thng c b ngoi ca v nha bng, lng.- Lp
nha cch in ca dy tt rt do, khi tut ra khi rut dn, c th ko gin gp i,
gp ba chiu di ban u m cha b t. Dy c th b gp nhiu ln hoc xon gt nhng
b mt cch in khng b rng nt.- C th kim tra rut dn, bng cch m s si nh
bn trong so vi s si c ghi bn ngoi. ng knh ca cc si nh bn trong rt
kh kim tra, v phi c thc chuyn dng mi o c. Tuy nhin, vi mt thng hiu
uy tn, trn dy c ghi c th cu trc rut dn (s si v ng knh mi si) th c
th tin tng c.- Dy tt th c rut dn sng, bng, nu l dy ng th rut dn rt
mm do. i vi dy rut dn ng c nhiu si nh th c th dng hai ngn tay xon
rut dn d dng m cc si nh khng bung, khng gy, khng m vo tay. i vi dy
rut dn c mt si th c th b gp rut ng n vi chc ln m khng gy.- Thng
thng, dy tt c gi cao hn dy dm vi cng c loi.
TP.HCM, thng 3/2009Ng Hu onCu hi trc tin ca nhng ngi ln u sm my
lnh l mua my lnh cng sut nh th no cho ph hp vi din tch nh, th tch
phng. K mi n vic chn my lnh hiu g, c thm nhng tnh nng no... i vi cc
h gia nh nh, c th dng loi hai cc (Spilit type) hoc mt cc tu theo cu
trc nh. Phng c din tch t 9 n 15m2 c th gn my cng sut 9.000 BTU/h
(mt nga), din tch t 15 n 20m2 gn my 12.000 BTU/h (1,5 nga), din tch
t 20 n 30 m2 gn my 24.000 BTU/h (2.5 nga). 30000 BTU/h (3 nga).
36000 BTU/h (4 nga). 48000 BTU/h (5 nga) Bn cnh , vic la chn cng
sut cn ph thuc vo s ngi thng xuyn c trong phng (v thn nhit ngi s lm
gim lnh), che ph nh sng mt tri, cch nhit ca phng, v tr v ln ca ca
s... y l nhng yu t c th lm gim lnh. Tha th sao, thiu th sao? Nu chn
my lnh cng sut, bn s m bo rng khon tin u t ph hp, lng in tiu hao
cng ph hp. ng bao gi chn my lnh thiu cng sut so vi th tch, nhu cu s
dng ca cn phng. Nhit khng lnh s buc my phi lm vic lin tc, dn ti hao
in, nng my v bn ca my gim. Khi mua my nn chn cng sut d ra mt t. S
tin u t ban u c th nhiu hn chn my ng cng sut nhng c li l my mnh,
thi gian t lnh nhanh hn v khi my t lnh th s t ngng hot ng. Vi loi
my d cng sut so vi nhu cu th my s c nhiu thi gian "ngh", gip cho bn
ca my c ko di. Cng c ngi lo dng my tha cng sut s tn in nhiu hn, iu
ny ng nu nh so snh gia hai my c cng sut ln v nh cng hot ng lin tc.
Trong trng hp dng cho mt cn phng c th tch bng nhau th c khi loi my
cng sut ln li t hao in hn v chng ch chy trong mt thi gian ngn l
phng t lnh v t ngt. Trong khi , my c cng sut va hoc thiu s buc phi
chy lin tc v nh vy s phi tiu th in nng lin tc. Cng sut lnh: 1HP
--> 9000 BTU --> 2.63764 KW Cng sut in: 2.63764 KW / 2.4 =
1.09 KW ---------------------- Cng sut lnh: 2HP --> 18000 BTU
--> 5.275279 KW Cng sut in: 5.275279 KW / 2.4 (2.4 low -->
2.7 high) = 2.19 KW --------------------------- Cng sut lnh: 3HP
--> 30000 BTU --> 8.792132 KW Cng sut in: 8.792132 KW / 2.4
(2.4 low --> 2.7 high) = 3.66 KW
------------------------------------------------------------------------------------
How do you convert BTU (British Thermal Units) to KW? BTUs and
kilowatts measure different types of quantities. A BTU (British
Thermal Unit) measures heat (energy), while a kilowatt (1000 watts)
measures power (energy per unit time). 1 BTU equals 0.0002928
kilowatt-hour 1 BTU/minute equals 0.01757 kilowatt. To convert a
watt to BTUs, the factor is 1 kilowatt of power = 3412.1416 BTU/hr
3.412 BTUs equal a watt. 1 kW = 3412.1416 BTU/hour with appropriate
significant figures 3*103 BUT per hour To convert BTU to kW simply
multiply by 0.000293. To convert kW to BTU simply multiply by
3414.
Tham
