Calculation of AC Resistance for Stranded Single-Core Power Cable Conductors

The ac resistance of power cable conductors is an important parameter for accurately estimating the ampacity of power cable and optimally designing power cable. Although international standard IEC-60287 has recommended a simplified formula for calculating the ac resistance, it is not capable of taking into account the effect of stranded conductor parameters, such as the direction and the length of lay, on the ac resistance because the stranded conductor is simplified as a solid conductor. In this paper, the method which has been used for analyzing the ac resistance of aluminum-conductor steel-reinforced overhead power lines is applied to single-core power cable conductors. Basically, the magnetic fluxes around each layer of the stranded wires are divided into circular magnetic fluxes and longitudinal magnetic fluxes, and thus each layer is equivalent to a circuit with resistor and inductor in series. Then, the ac resistance of single-core power cable conductors is calculated from the paralleled equivalent circuits representing all layers. A case study of 800 mm² single-core power cable is given to investigate the effect of the parameters of the stranded wires on the ac resistance. Results show that the ac resistance for bidirectional stranding of copper wires is a few percentage points higher than that for unidirectional stranding. Such difference will be significant in the optimization of cable design as even a slight decrease in ac resistance can save considerable copper in large-scale industrial application.