example calculating 300 mm

7/25/2019 Example Calculating 300 mm

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Calculation example for 300 mm2

Parameters used for current carrying capacity as per IEC 287-1-1 and 287-2-1

Operating Frequency 60 Hz

Operating Voltage LL 13,80 kV

Operating Voltage LN 7,97 kV

Ambient Temp. Air 50 C

Ambient Temp. Ground 40 C

cable maximum operating temp. 90 C

Thermal resitivity earth 2 K.m/W

Thermal resitivity concrete 1 K.m/W

Thermal resitivity XLPE 3,5 K.m/W

Thermal resitivity PVC 6 K.m/W

Duct outer diameter 160 mm

Duct inner diameter 150 mm

Duct material PVC

RAC at 90C 0,08 /km

Conductor diameter 20,8 mm

Thickness of XLPE 4,5 mm

Thickness of screen 2,5 mm

Thickness of PVC 2,1 mm

Overall diameter 39 mm

Diameter of trefoil 84 mm

Rdc20

70 mm.sq. 0,2680 0,3420 ohm/km 9,90 mm 4,5 mm 2,25 mm






tanfor Wd 0,004

for Wd 2,5

cond. DiameterRac at 90Cconductor cross-sectional area

Cable type: copper conductor single-core unarmoured in trefoil configuration (Saudi Cable Catalouge for RACat 90C and Geometry)

Thickness of XLPE Thickness of screen


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Ductbank geometry

Ductbank X (width) 730 mm

Ductbank Y (height) 730 mm

L 1500 mm 8th cable/duct center distance to ground

LG 1290 mm distance from ground to ductbank center

3

4 6

7 8 9


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Calculation Procedure

= 90 40 = 50 (difference betwen maximum operating temperature of the conductor and ambient

temperature)

Wdis neglected for voltage levels less than 60 kV as per table 3 in IEC 287-1-1

R is RAC= 0.00008 /m (AC resistance at maximum operating temperature of 90C)

= 0.08 (assupmtion as not all parameters are available and it accounts for range of sheath losses)

n = 3 (number of single-core cables within a duct for T4)

n = 1 (number of single-core cables under jacket for T3)

T2is equal zero since the cable is unarmoured

T1= 0,200

T3= 0,109

T4 = 4,586

I = 202,9 A cable capacity is 4850 MVA

1.4.1.1 from IEC 287-1-1


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T= 3,5 thermal resistivity of insulation (XLPE)

t1= 4,5 thickness of insulation

dc= 20,8 diameter of conductor

T1= 0,200

T= 6 thermal resistivity of cable jacket (PVC)

t3= 2,1 thickness of jacket

Da= 34 ,8 diameter of cable under jacket

T3= 0,109

2.1.1.1 from IEC 287-2-1

2.1.3 from IEC 287-1-1


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U = 1,87 constant as per table 4 IEC 287-2-1

V = 0,312 constant as per table 4 IEC 287-2-1

Y = 0,0037 constant as per table 4 IEC 287-2-1

m= 50 temperature of medium filling the duct

De= 84 diameter of trefoil configuration

T4= 0,361

T= 6 thermal resistivity of duct materia l (PVC)

Do= 160 outer diameter of duct

Dd= 150 inner diameter of duct

T4= 0,062

2.2.7.1 from IEC 287-2-1

2.2.7.2 from IEC 287-2-1


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N = 6 number of ducts with loaded cables

e= 2 thermal resistivity of earth

c= 1 thermal resistivity of concrete

u = LG/rb = 3,215

LG = 1290 distance from surface to center of ductbank

rb = 401 equivalent radius of concrete ductbank

part 1 of T4= 1,753

2.2.7.3 from IEC 287-2-1

algerbic correction for T'''4 for cables in ducts

N: number of loaded cables!

2.2.3.2 from IEC 287-2-1

Tc for multiple cables in duct not touching


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c= 1 thermal resistivity of concrete

u = 2 x L/De = 18,750

L = 1500 distance from surface to center of cable to be calcualted (position 8)

De = 160 outer diameter of duct

d83/d83 = 5,51 d83 distance to cable 3 in mirror position, d83 distance to to cable 3

d84/d84 = 9,42

d86/d86 = 9,42

d87/d87 = 14,32

d89/d89 = 14,32

part 2 of T4= 2,410

T4 = 4,586

2.2.3.2 from IEC 287-2-1

Tc for multiple cables in duct not touching

3

4 6

7 8 9

example calculating 300 mm

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