Electrical characteristics of steel-cored aluminium conductors

The spiralling of the current in steel-cored aluminium conductors sets up an axial magnetic flux, and at power frequency this results in power loss from hysteresis in the steel core and from eddy currents. This loss increases with current and raises the a.c. resistance of the conductor; the internal inductance also increases slightly with current, owing to the variation of the complex permeability of the steel with magnetising force. Methods are given for calculating the increases of effective resistance and internal inductance with current; these require that the magnetic characteristics of the steel be known. Good agreement is obtained between measured and calculated values for conductors with one, two or three layers of aluminium wires. A method is given for calculating the effective resistance of a conductor carrying current and exposed to sunlight and wind.