Do you know the relationship between the rated voltage of the cable and the number of cores?

1. Selection conditions for 1~5-core cables for 1kV and below

(1) Single core cable

When the line is long, the working current circuit or the underwater laying, in order to avoid or reduce the intermediate joints, 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 of 1kV and below is directly grounded, the number of cable cores of the single-phase circuit, when the protective line and the neutral line share the same conductor, a 2-core cable should be used.

The DC power supply circuit should use 2-core cables.

(3) core cable

When the neutral point of the power supply of 1kV and below is directly grounded, the number of cable cores for the single-phase circuit is: when the protection line and the neutral line are independent, a 3-core cable should be used.

(4) core cable

For 4-core cables (3+1 cables) of 1kV and below, the 4th core is not only used as a protective ground, but also transmits the unbalanced current and short-circuit current of the power system. Its size is determined by the unbalanced current and short-circuit current, but generally not less than 1/2 of the phase line.

For the three-phase four-wire low-voltage power distribution system of 1kV and below, when the protection line and the neutral line share the same conductor, a 4-core cable should be used instead of a combination of a 3-core cable and a single-core cable to form a circuit, or even directly The method of using the metal sheath or armor layer of the 3-core cable as the neutral line. Otherwise, when the 3-phase current is unbalanced, it is equivalent to the running state of a single-core cable, which is likely to cause power frequency interference.

(5) core cable

Three-phase four-wire low-voltage power distribution system of 1kV or below, some electrical device distribution lines with high safety requirements, and some communication centers and automation equipment that must not only ensure electrical safety, but also require anti-interference grounding, should use The 5-core TN-C low-voltage power distribution system makes the protective wire (PE wire) and neutral wire (PN wire) independent, and the cross-sectional area of the cable core is generally 3 large and 2 small or 4 large and 1 small or 5 large.

Second, the selection of the number of medium and high voltage cable cores

For the selection of the number of cores of the 3~35kV three-phase power supply circuit cable. When the circuit or cable with large working current is laid underwater, 3 single-core cables can be used for each circuit; in addition to the above cases, 3-core cables should be used, and 3-core cables can be selected from ordinary turnkey types or 3-core cables. A single-core cable twisted construction type.

For the 110kV three-phase power supply circuit, except that 3 cores can be used when laying in lakes, underwater places such as sea water and the cable section is not large, 3 single-core cables can be used for each circuit.

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

For high-voltage AC single-phase power supply circuits such as electrified railways, 2-core cables or 2 single-core cables should be used for each circuit.

For HVDC transmission systems, single-core cables should be used; when laying underwater such as lakes and seas, coaxial 2-core cables can also be used.