What is the relationship between the cable voltage rating and the number of cables?

1kV and below 1 to 5 core cable selection conditions

1. Single-core cable

When the line is long and the working current is large, the circuit or the underwater laying, in order to avoid or reduce the intermediate joint, or when the single-core cable has better comprehensive technical economy than the multi-core cable, the single-core cable can be selected.

Low-voltage DC power supply circuit, single-core cable can be used when necessary.

2. Core cable

When the neutral point of the power supply is directly grounded at 1kV and below, the number of cable cores in the single-phase loop, when the protection line and the neutral line share the same conductor, the two-core cable should be used.

2-core cable is recommended for DC power supply circuit.

3. Core cable

When the neutral point of the power supply is directly grounded at 1kV or below, the number of cable cores of the single-phase loop is as follows: When the protection line and neutral line are independent, it is advisable to use 3-core cables.

4. Core cable

1kV and below 4-core cable (3+1 cable), the fourth core in addition to the protective grounding, but also to transport the power system in the imbalance current and short circuit current. Its size is determined by the unbalance current and short circuit current, but generally not less than 1/2 of the phase line.

1kV and below three-phase four-wire low-voltage distribution system, when the protection line and neutral line use the same conductor, should use 4-core cable, and shall not use 3-core cable and single-core cable combination into a primary way, or even directly use the metal sheathed or armored layer of 3-core cable as a neutral line. Otherwise, when the three-phase current is unbalanced, it is equivalent to the running state of the single-core cable, which is easy to cause power frequency interference.

5. Core cable

For the three-phase four-wire low-voltage distribution system of 1kV and below, some distribution lines of electrical devices with higher safety requirements, as well as some communication centers and automation equipment to ensure electrical safety and anti-jamming grounding, it is appropriate to use the TN-C low-voltage distribution system with 5 core wires, so that the protection line (PE line) and neutral line (PN line) are independent. The cross-sectional area of cable core is generally 3 large, 2 small or 4 large, 1 small or 5 large.

Selection of core number of medium and high voltage cable

For 3~35kV three-phase power supply circuit cable core selection. When the circuit or cable with large working current is laid under water, 3 single-core cables can be selected for each circuit; In addition to the above cases, 3-core cables should be selected. The 3-core cables can be of the common all-in-one type or of the stranded type with three single-core cables.

For 110kV three-phase power supply circuit, three single-core cables can be selected for each circuit, except that three cores can be selected when the circuit is laid in the lake, sea water and other places and the cable section is not large.

For the three-phase power supply circuit above 110kV, three single-core cables should be selected for each circuit.

For high-voltage AC single-phase power supply circuit such as electrified railway, 2-core cables should be used or 2 single-core cables should be used every time.

High voltage direct current transmission system, should choose single core cable; In the lake, sea and other underwater laying, can also choose coaxial 2-core cable.