Cable thermal resistance

QuickField simulation example

In this example we build thermal model of the high-voltage cable described in the IEC 60853-2 example F2*. Thermal resistances of the cable parts are calculated.

Problem Type
Plane-parallel problem of Heat Transfer.

Geometry

Given
Thermal resistivity of materials [K*m/W]: serving 3.5, oil/paper 5.0, soil 1. The semiconducting screens thermal conductivity is considered to be the same as that of the insulation, 5.0 K*m/W.

Task
Calculate thermal resistances** of the cable parts and compare results with the reference values*.

Solution
Thermal resistance [K*m/W] = Temperature difference [K] / Heat flux per 1 meter of cable length [W/m]
To calculate the thermal resistance we are going to specify heat losses 30 W/m in the conductor and measure the temperature drop in cable layers.

In QuickField we should specify thermal conductivity [W/K*m] of materials, that is reciprocal to the thermal resistivity. Copper conductor thermal conductivity is 380 W/K*m, lead sheath thermal conductivity is 25 W/K*m.

Results
Temperature drop conductor-sheath is (0.614+13.761+0.226) = 14.6°C, thermal resistance conductor-sheath is T1 = 14.6 / 30 = 0.487 K*m/W. Reference value* 0.488 K*m/W.

Temperature distribution along the radius of the cable.

References:
* IEC 60853-2, Calculation of the cyclic and emergency current rating of cables. Part 2: Cyclic rating of cables greater than 18/30 (36) kV and emergency ratings for cables of all voltages.
** Wikipedia, Thermal resistance.

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