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Cable Calculation

The document determines the current rating of a 132 KV cable. It provides details of a 400 mm squared stranded copper cable, including dimensions and material properties. It then outlines the calculation to determine current rating based on ambient temperature, voltage rating, short time current rating, and thermal resistances between cable components using an equation that considers temperature rise and losses. The calculated current rating of the circuit is 713 amps.

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arunmozhi
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277 views4 pages

Cable Calculation

The document determines the current rating of a 132 KV cable. It provides details of a 400 mm squared stranded copper cable, including dimensions and material properties. It then outlines the calculation to determine current rating based on ambient temperature, voltage rating, short time current rating, and thermal resistances between cable components using an equation that considers temperature rise and losses. The calculated current rating of the circuit is 713 amps.

Uploaded by

arunmozhi
Copyright
© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
Available Formats
Download as PDF, TXT or read online on Scribd
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Determination of current rating for 132 KV cable

single core cable


trefoil arrangement
single point bonding
laid in trench (air)

ambient temperature 45
voltage rating in KV 132 76.210236
current rating of circuit 437
starting size of cable
short time current rating in KA 40
maximum conductor temperature 90

  Wd 0.5T1  n T2  T3  T4  
I
RT1  nR 1  1  T2  nR 1  1   2 T3  T4 

where
I=current in one conductor
=conductor temperature rise above ambient temp
R=AC Resistance
Wd=dielectric loss of insulation surrounding the conductor
T1=thermal resistance between one conductor and sheath
T2=thermal resistance between sheath and armour
T3= thermal resistance of external serving
T4=thermal resistance between cable surface and surrounding
n= number of conductor in cable
ratio of losses in metal sheath to total losses in all conductor
ratio of losses in armour to total losses in all conductor

details of 400 mm sqr stranded copper cable


mm m
area in mmsqr 400 4.00E-04
conductor dia 23.2 0.0232
screen thickness 1.5 0.0015
insulation thckness 18 0.018
ins screen thickness 1.2 0.0012
al sheath 1.9 0.0019
outer sheath 3.6 0.0036
total= 75.6 0.0756

 90-45= 45

AC resistance
Ys=SKIN EFFECT FACTOR
R=R'(1+YS+YP) Yp=PROXIMITY EFFECT FACTOR
R'=DC RESISTANCE
DC resistance

R'=Ro[1+a20(O-20) Ro=DC RESISTANCE AT 20 DEGREE


a20=MASS TEMP COIFFICIENT 3.93E-03
O=MAX TEMP
Ro=rl/A

r=RESISTIVITY 1.72E-08

Ro= 4.30E-05

R'= 5.48E-05

X s4
Ys 
192  0.8 X s 4

8 f 7
X s2  10 ks
R'

= 2.29E+00

Ys= 2.67E-02

Yp=PROXIMITY EFFECT FACTOR

X p4 2 dc=dia of conductor
 dc 
Yp   2.9
192  0.8 X p  s 
4 
s= distance between the conductor

8 f 7
X p2  10 k p
R'

Yp= 1.01E-02

R= 5.68E-05
DIELECTRIC LOSS Wd

Wd  CU o2 tan 


C 10 9
 Di 
18 ln  
 Dc 

Di external dia of insulator in mm= 62.2


Dc dia of conductor including screen= 26.2

c= 1.92768E-10

Wd= 1.7480851

loss factor

l1=l1'+l1"
l1"=0

Rs 1
11  2
R R 
1  s 
X 

Rs resistance of the sheath per unit length


X is the reactance=2we-7ln(2s/d)
w=2pif
s is distance between the conductor axis
d is the mean sheath dia

x= 5.16124E-05
Di= 64.6 4173.16
Area = pi/4*(Do^2/Di^2) Do= 68.4 4678.56

A 396.739 mmsqr 505.4

Rs'= 7.15836E-05 Rs= 9.17773E-05

l1= 0.387890718 w/m


Thermal resistivity T1
t  2t1 
T1  ln 1  
2  dc 
t  thermalresistivity

dc=dia of conductor 23.2


t1=thickness b/w conductor and sheath 18

T1= 0.52208478

T2= 0

t  2t3 
T3  ln 1  
2  Da 

T3= 0.055778998

T4= 0.6476 not calculated

I= sqrt(num/dem)

num= 43.31410934

den= 8.51767E-05

I= 713.106237

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