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AC Resistance & Dielectric Loss Calculation

This document provides calculations for determining the AC resistance and dielectric loss of an electrical cable. It includes formulas and values for parameters like resistance at different temperatures, skin effect factor, proximity effect factor, conductor diameter, insulation properties, sheath resistance, and thermal resistances. It also outlines calculations for permissible current ratings that take into account factors like the ratio of losses in the armouring, thermal resistances between cable components, conductor temperature rise limits, and ambient temperature.

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926 views9 pages

AC Resistance & Dielectric Loss Calculation

This document provides calculations for determining the AC resistance and dielectric loss of an electrical cable. It includes formulas and values for parameters like resistance at different temperatures, skin effect factor, proximity effect factor, conductor diameter, insulation properties, sheath resistance, and thermal resistances. It also outlines calculations for permissible current ratings that take into account factors like the ratio of losses in the armouring, thermal resistances between cable components, conductor temperature rise limits, and ambient temperature.

Uploaded by

swagata12345
Copyright
© Attribution Non-Commercial (BY-NC)
We take content rights seriously. If you suspect this is your content, claim it here.
Available Formats
Download as XLSX, PDF, TXT or read online on Scribd
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Calculation of AC resistance

Ro Resistance at 20 deg C 0.03 ohm/Km


α20 Constant mass temperature coefficient at 20 °C 0 per kelvin
R' DC resistance at 75 deg C 0.04 ohm/Km
Ys Skin effect factor 0

Xs 0.06
Ks Variable 1

Yp Proximity effect factor for three single-core cables


0

Xp 0.06

Kp Variable 1

Dc diameter of conductor 38 mm

S distance between conductor axes 58 mm


Tre-foil formation

R AC resistance of conductor 0 ohm/m

Calculation of Dielectric loss


C capacitance per unit length 0 F/m
Є relative permittivity of the insulation; 2.5
Di external diameter of the insulation 44.6 mm
Dc diameter of conductor 38 mm
U0 Rated Voltage 1.1 KV
tan δ loss factor of the insulation 0
Wd Dielectric Loss 0 W/m

Loss factor for Armour


Armour strand dia 2.5 mm
No. of armour 71
Total cross section of armour 348.52
300 sq.mm. (Approx)
Rso is the resistance of the cable sheath or screen at 200°Cohm/m
θsc Max operating temperature 85 Deg C
Rs AC resistance of the sheath or screen at its maximum 0 ohm/Km
operating temperature
1.2 times DC resistance
R AC resistance of conductor 0 ohm/m
α20 Constant mass temperature coefficient at 20 °C 0 per kelvin
s distance between conductor axes 58 mm
d mean diameter of the sheath 55 mm
X reactance per unit length of sheath or screen per unit
0 ohm/m
length of cable

loss factor caused by circulating currents 0.37

λ2 ratio of losses in the metal armour to total losses0.37


in all conductors in that cable

Permissible current ratings in air


Taking into account the effect of solar radiation on a cable, the permissible current rating is given

λ2 ratio of losses in the armouring to total losses in all conductors in that cable.
T1 thermal resistance per core between conductor and 0.08sheath
K.m/W
T2 thermal resistance between sheath and armour 0.07 K.m/W
T3 thermal resistance of external serving 0.07 K.m/W
T4 thermal resistance of surrounding medium (ratio of cable K.m/W
surface temperature rise above
T *4 external thermal resistance in free air, adjusted for solar
K.m/W
radiation
n number of conductors in a cable
ρTi thermal resistivity of insulation 3.5 K.m/W
t1 thickness of insulation between conductor and sheath 2.8 mm
dc diameter of conductor 38 mm
t2 thickness of the inner sheath 2.04 mm
Ds external diameter of the sheath 42.08 mm
ρTis thermal resistivity of inner sheath 5 K.m/W
PVC
D′a external diameter of the armour 47.08 mm
t3 thickness of Outer sheath 2.04

h heat dissipation coefficient 2.45


De' external diameter of cable 0.06 m
Z 0.94
E Table 2 IEC 60287-2-1 0.79
g 0.2

KA 0.08 k

Δθd a factor, having the dimensions of temperature difference,


0a to account for the dielectric lo
Δθ permissible conductor temperature rise above ambient
50 b temperature
Ambient 40 Deg C

Δθs excess of cable surface temperature above ambient temperature


IEC 60228.
Table 1 60287-1-1
R′ = Ro [1 + α20 (θ – 20)]

Table 2 60287-1-1 for round stranded Aluminium

Table 2 60287-1-1 for round stranded Aluminium

The dielectric loss should be taken into account for values of Uo equal to or greater than 36KV for X

mm. (Approx)

PVC ST2

times DC resistance

Table 1 60287-1-1
three single-core cables (in trefoil formation) with sheaths bonded at both ends

rmissible current rating is given by the formulae:

uctors in that cable.

38.24
Clipped direct to a vertical wall (De' not
greater than 0,08 m)
greater than 36KV for XLPE cable

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