Why can't single-core cables be armored with steel tape?
A magnetic field exists around a current-carrying conductor, and the strength of the magnetic lines of force is proportional to the current flowing through it. Because steel tape is a magnetic material with high magnetic permeability, when current flows through the conductor, the magnetic lines of force flow along the tape.
Three-core cables are typically used for three-phase AC power transmission. Since the vector sum of symmetrical three-phase AC currents is zero, the magnetic lines of force generated by the current are also zero, and no induced current is generated in the steel tape. Therefore, using steel tape armor for three-core cables has no adverse effects. Single-core cables, on the other hand, can only carry a single phase of current. Obviously, when AC current flows through the cable, alternating magnetic lines of force are generated in the steel tape, and the magnetic field strength increases accordingly as the current increases.
According to the principle of electromagnetic induction, eddy currents are generated in the cable's steel tape, causing the cable to heat up. This not only increases losses but also reduces the cable's current carrying capacity. Therefore, to ensure the safe and economical operation of single-core cables, ordinary steel tape armor is not used in their manufacture.
