ALTERNATING CURRENT (AC) RESISTANCE OF HELICALLY STRANDED CONDUCTORS

The electrical resistance of helically-stranded conductors (aluminium and aluminium alloy), intended for use in distribution and transmission lines, depends on the conductor cross-section area, the conductivity of the aluminium alloy, the lay length of the aluminium layers, and the presence or absence of a steel reinforcing core. The presence of a stranded steel core both reduces the conductor resistance due to the conductivity of the galvanized steel wires and increases the resistance due to core magnetizing effects. This brochure describes a process of calculation for stranded aluminium conductors both with and without a steel reinforcing core. APPENDIX A provides a MathCad programme to determine the AC resistance of a stranded conductor for a given current. This output can be used in conjunction with the steady state model to determine the actual current flow or conductor temperature. APPENDIX B provides an alternate model for the calculation of the AC resistance On the basis of laboratory tests and theoretical studies, it has been determined, that AC resistance of stranded aluminium conductors (AAC) or all aluminium conductors (AAAC) can be calculated with acceptable accuracy by taking into consideration the conductor geometry, e.g. lay ratio, diameter of wire, current and temperature distribution of conductor. Resistance calculations with Aluminium conductor Steel reinforced (ACSR), however, can be more complex due interactions between the currents in each helically stranded layer coupled through the steel core. On the basis of results from research [5,6,7,8]* computer programs have been developed that can determine the AC resistance of ACSR very accurately (one presented here). This brochure describes the theory as well as demonstrating a programme that can be used within existing software packages that will enable rapid and accurate determination of AC resistance for helically stranded conductor types.