A first-principles IEC 60287 thermal-circuit solver for single-core MV/HV cable current rating \u2014 rather than looking up a rating from a manufacturer's table, it builds the actual thermal circuit (conductor\u2192sheath, sheath\u2192serving, serving\u2192ambient soil) from cable geometry and iterates to find the current that brings the conductor to its rated maximum temperature.
Standards followed
IEC 60287-1-1 (current rating equations, loss factors)IEC 60287-2-1 (thermal resistance calculation)IEC 60287-3-1 (operating conditions — reference soil temperatures/resistivities)example geometry from CIGRE Technical Brochure 880 (results not independently matched to the brochure)
What it can do
- Full thermal-circuit build-up: conductor AC resistance (temperature, skin and proximity effect corrected), dielectric loss, sheath circulating-current loss factor, and the T1/T3/T4 thermal resistances.
- Iterative solve for continuous current rating, converging the conductor temperature exactly to your specified maximum.
- Solid vs. single-point sheath bonding, with a warning on the standing-voltage implication of single-point bonding.
- Buried-in-duct or direct-buried installation methods.
Example problem
This calculator's default scenario uses the geometry of CIGRE Technical Brochure 880's Case #0-1: a 132kV copper-conductor, XLPE-insulated, aluminium-sheathed cable, buried in duct.
- Build cable geometry from conductor diameter and each layer's thickness (insulation, screens, sheath, oversheath).
- Compute capacitance and reactance from the geometry, then dielectric loss from system voltage and frequency.
- Compute the T1 (conductor-to-sheath), T3 (sheath-to-serving) and T4 (serving-to-ambient soil) thermal resistances.
- Iterate the current-rating equation, adjusting current until the resulting conductor temperature converges to the 90°C limit.
Converges in 5 iterations to about 751A, with the conductor temperature landing exactly at the 90°C limit (guaranteed by the solving method) and an 80.6°C sheath temperature. T4 uses the IEC 60287-2-1 trefoil formula plus the air gap inside a plastic duct; the duct wall is neglected, so the result is a close estimate, not the brochure’s published figure.
Want the full step-by-step version?
v1 scope: single-core, unarmoured, XLPE-insulated cable, buried in duct or direct only \u2014 free-air installation and armoured cables (with their eddy-current losses) are not yet supported.