Insulation thickness determination of polymeric power cables

An analytical expression has been derived for calculating insulation wall thicknesses of single-core polymeric power cables from considerations of discharges in voids. For 10 to 30 kV cables of small conductors (16 to 50 mm²), good agreement has been obtained between the thicknesses calculated by the expression and those specified in the IEC Standard, provided that 50 μm is defined as the maximum void sizes for cables in all the voltage classes and that an additional allowance of 1.0 mm is introduced in insulation thickness for cables below 20 kV. The expression is an exponential law, which denotes that the insulation thickness of a cable depends on the product of the working voltage and the maximum void size of the cable. Thus, decreasing the maximum void size of a given cable allows an increase in the cable working voltage. Calculated results show that if the maximum size of voids decreases from 50 to 30 μm, the insulation thickness of a 15 kV cable in the current standard is adequate for use at 30 kV. Therefore, decreasing the void size is a dominant consideration in decreasing cable size, especially for higher voltage cables