The practical effect of the enlargement law on the electrothermal life model for power-cable lines

Insulation coordination is essential for designing and testing HV cable systems properly. In transient conditions, i.e., in the presence of transient voltage surges, insulation coordination is based on the individuation of a certain maximum acceptable risk of failure under the switching and lightning overvoltages that the insulation may encounter in service, and translates into a maximum number of expected failures per year per length of line that the cable line has to match. Given the design of the cable in steady-state conditions, the number of expected failures per year and per length of cable line can be reduced by a proper design of the shield wires of overhead lines, of the grounding systems of line towers and so on, and by selecting and installing properly voltage-surge arresters when needed.