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Conductor Sizing

This document summarizes the design data and calculations for an aluminum conductor. It includes the material, number of conductors, cross-sectional area, diameter, resistance and temperature coefficients. It then calculates the continuous current rating based on thermal limits. Finally, it calculates the short-circuit current rating and verifies that the conductor cross-section is sufficient for the required 40kA, 3 second rating.

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394 views5 pages

Conductor Sizing

This document summarizes the design data and calculations for an aluminum conductor. It includes the material, number of conductors, cross-sectional area, diameter, resistance and temperature coefficients. It then calculates the continuous current rating based on thermal limits. Finally, it calculates the short-circuit current rating and verifies that the conductor cross-section is sufficient for the required 40kA, 3 second rating.

Uploaded by

zaidisofian
Copyright
© Attribution Non-Commercial (BY-NC)
We take content rights seriously. If you suspect this is your content, claim it here.
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Download as PDF, TXT or read online on Scribd
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DESIGN DATA

SYMBOL

PARAMETER VALUE Hard drawn Aluminium

UNITS mm
2

DESCRIPTION Material of Conductor No. of Conductor per Phase (feeder) Conductor cross Area Conductor Diameter

n A d Rdc c To Tc Ts r V e S' a

2 300 22.61 9.48E-05 0.00403 35 85 200 1.023 1.2 0.6 1200 0.8

mm

ohm/m Conductor DC Resistance @ 20 C / C Temperature Coefficient of Resistance C C C m/s W/m 2

Ambient Temperature Max. Conductor Operating Temperature Final Conductor Short - Circuit Temperature Skin Effect Constant Velocity of Wind Enissivity coefficient of Conductor Solar radiation intensity Solar Absorption Coefficent

CALCULATION

Continous Current Rating

The ampcity of the conductor is calculated based on thermal rating as follows: I2Rac where + Ha = Hc + Hr

I Rac Ha Hc Hr

= = = = =

Current Rating of Conductor a.c resistance at operating temperature Heat gained by solar radiation Heat loss by convection Heat loss by radiation

Resistance value Rac at conductor operating temperature

At 20 degC Rdc At 85 degC Rac = = = = = r * 1.023 * 1.023 * 1.023 * 1.17E-04 ohm/m Rdc 9.48E-05 9.48E-05 9.48E-05 * * * * 1 1 1 1.2015 + + + c 0.00403 0.2015 * * (Tc-To) 50 = 9.48E-05 W/m

Heat loss by convection (W/m) Hc = = = = = 0.387 * 0.387 * 0.387 * 0.387 * 117.04 W/m ( V* d ) 27.132 55.56 6.04858074
0.448 0.448 0.448

* * * *

(Tc - To ) (Tc - To ) 50 50

Where, v d = = Wind Velocity (m/sec) Conductor Diameter (mm)

Heat loss by radiation ( W/m ) Hr = = = = 5.70E-11 5.70E-11 5.70E-11 18.04 * * * W/m e 0.6 0.6 * * * ( Tc + 273)4 16426010896 7426832400 (To + 273 )4 8999178496 * * * pi 3.1415 3.1415 * * * d 22.61 22.61

Heat loss by absorption (W/m ) Ha = = = 1.00E-03 1.00E-03 2.17E+01 * * W/m a 0.8 * * S' 1200 * * d 22.61

Conductor Current Rating From equation I = = = Hc + Hr - Ha Rac 1.13E+02 1.17E-04 9.73E+05 986 Amp per conductor

Short - Circuit current Rating According to Annex A-9 of IEC 865-1 Rated short - time withstand current density S thr is given by: S thr = K Tkr

Where K

K20CP a20

ln

1+a20 (Tc - 20 C) 1+a20 (Ts - 20 C)

and Tkr

Rated short time

For Aluminium Conductor C P K20 a20 = = = = 910 J/kg C 3 2700 kg/m 9.48E-05 /Wmm 0.004 / C

Substituting the above values into equiation Where K = K20CP a20 = = = = = 2.33E+02 0.004 5.82E+04 5.82E+04 1.81E+04 134.62 As/mm 2 ln * ln ln 1+a20 (Ts - 20 C) 1+a20 (Tc - 20 C) 1.72 1.26 1.36508 0.31121

From equation S thr = = K Tkr 134.62

3 77.72

A/mm 2

Minimum conductor cross- area for 40kA, 3 sec. Rating Amin = = 31500 77.72 405.29 mm 2

Result For bus coupler,4 x 800mm 2 Aluminium Conductor is used, Continuous Current rating Short time current rating = = 4 x 1577.8 4 x 800 X x 77.72 = = 1,972.81 47 A kA > 2000A > 31.5kA

Hence, the current rating is sufficient

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