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Calculation of AC resistance Ro α20 R' Ys

Resistance at 20 deg C 0.03 ohm/Km Constant mass temperature coefficient at 20 °C 0 per kelvin DC resistance at 75 deg C 0.04 ohm/Km Skin effect factor 0

Xs Ks

Variable

Yp

Proximity effect factor for three single-core cables 0

Xp

0.06 1

0.06

Kp

Variable

Dc

diameter of conductor

S

distance between conductor axes

R

AC resistance of conductor

1 38 mm 58 mm Tre-foil formation 0 ohm/m

Calculation of Dielectric loss C Є Di Dc U0 tan δ Wd

capacitance per unit length relative permittivity of the insulation; external diameter of the insulation diameter of conductor Rated Voltage loss factor of the insulation Dielectric Loss

0 F/m 2.5 44.6 mm 38 mm 1.1 KV 0 0 W/m

Loss factor for Armour Armour strand dia No. of armour Total cross section of armour Rso θsc Rs R α20 s

2.5 mm 71 348.52 300 sq.mm. (Approx) is the resistance of the cable sheath or screen at 200°C ohm/m Max operating temperature 85 Deg C AC resistance of the sheath or screen at its maximum 0 ohm/Km operating temperature 1.2 times DC resistance AC resistance of conductor 0 ohm/m Constant mass temperature coefficient at 20 °C 0 per kelvin distance between conductor axes 58 mm

d X

mean diameter of the sheath 55 mm reactance per unit length of sheath or screen per unit 0 ohm/m length of cable loss factor caused by circulating currents

λ2

0.37

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 T1 T2 T3 T4 T *4 n ρTi t1 dc t2 Ds ρTis D′a t3

ratio of losses in the armouring to total losses in all conductors in that cable. thermal resistance per core between conductor and 0.08sheath K.m/W thermal resistance between sheath and armour 0.07 K.m/W thermal resistance of external serving 0.07 K.m/W thermal resistance of surrounding medium (ratio of cable K.m/W surface temperature rise above external thermal resistance in free air, adjusted for solar K.m/W radiation number of conductors in a cable thermal resistivity of insulation 3.5 K.m/W thickness of insulation between conductor and sheath 2.8 mm diameter of conductor 38 mm thickness of the inner sheath 2.04 mm external diameter of the sheath 42.08 mm thermal resistivity of inner sheath 5 K.m/W PVC external diameter of the armour 47.08 mm thickness of Outer sheath 2.04

h

heat dissipation coefficient

2.45

De' Z E g KA

external diameter of cable Table 2 IEC 60287-2-1

0.06 m 0.94 0.79 0.2 0.08 k

Δθd Δθ

a factor, having the dimensions of temperature difference, 0a to account for the dielectric lo 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