Single core refers to having only one conductor within an insulation layer. When the voltage exceeds 35kV, most single core cables are used, and the relationship between the wire core and the metal shielding layer can be regarded as the relationship between the coil and the iron core in the primary winding of a transformer. When a single core cable core passes current, there will be magnetic field lines crossing the aluminum or metal shielding layer, causing induced voltage at both ends.
1. In order to prevent the effect of electric force caused by short circuit, single core cables must be used with sufficient strength
(1) The supporting components are firmly fixed to withstand the electric force corresponding to the expected short-circuit current.
2. Special precautions for high-voltage AC single core cables: High voltage AC lines should use multi-core cables as much as possible. When single core cables are necessary for circuits with high operating currents, the following precautions should be taken:
(1) The cable should be unarmored or armored with non-magnetic materials. To avoid the formation of circulating currents, the metal shielding layer should only be grounded at one point.
(2) All wires in the same circuit should be placed in the same pipe, conduit or trunking, or all phase wires should be installed and fixed together with wire clamps, unless they are made of non-magnetic materials.
(3) When installing two, three, or four single core cables to form single-phase circuits, three-phase circuits, or three-phase and neutral wire circuits, the cables should be in contact with each other as much as possible. In all cases, the distance between the outer protective layers of two adjacent cables should not exceed the diameter of one cable.
(4) When a single core cable with a rated current greater than 250A must be installed near a steel cargo hold wall, the gap between the cable and the hold arm should be at least 50mm. Except for cables belonging to the same AC circuit laid in a three leaf shape.
(5) Magnetic materials should not be used between single core cables in the same group. When cables pass through steel plates, all wires in the same circuit should pass through the steel plate or stuffing box together, so that there is no magnetic material between cables, and the gap between cables and magnetic materials should not be less than 75mm. Except for cables that belong to the same communication loop and are laid in a three leaf shape.
(6) In order to ensure that the impedance of a three-phase circuit of equivalent length composed of single core cables with a conductor cross-section equal to or greater than 185mm2 is approximately equal, each phase should be swapped once at a gap of no more than 15m. Alternatively, the cable can be laid in a three leaf shape. When the cable laying length is less than 30m, the above measures do not need to be taken.
(7) When several single core cables are connected in parallel in each phase of the line, all cables should have the same path and equal cross-section. And cables belonging to the same phase should be laid alternately with cables of other phases as much as possible to avoid uneven distribution of current.