The difference between high voltage cable and low voltage cable

The difference between high and low voltage cables is due to the difference in voltage and insulation capacity. These differences are to ensure the safety of electricity.



What is a high voltage cable?

High-voltage cables are collectively referred to as high-voltage cables with voltage levels ranging from 1KV to 750KV. Mainly used for transmission and voltage conversion in the power sector. It is generally used for the transformation of voltage levels in long-distance power transmission and substations. Our common voltage levels in life are all lower than 220KV. The voltage level of long-distance power transmission is ultra-high voltage, and the relevant designated personnel are responsible for it.

High-voltage cables are also divided into the following categories according to their withstand voltage levels
1. Oil-impregnated paper insulated cable: withstand voltage level is 1kv-750kv;
2. Plastic insulated cable: withstand voltage level 1kv-220kv;
3. Rubber insulated cable: withstand voltage level 1kv-138kv;
4. Gas insulated cable: withstand voltage level 220kv-500kv.

Low-voltage insulated cables are suitable for electrical equipment with a withstand voltage level of 450v/750v and below. They are widely used and classified, and are generally used for fixed laying of industrial plastic insulated cables; mobile rubber-sheathed low-voltage insulated cables; buildings are mainly used for power installation. The laying of the main circuit, the main branch circuit and the branch circuit; and the flat wires and cables used in the elevator installation.


How to distinguish between high-voltage insulated cables and low-voltage insulated cables?

 In terms of structure: the high-voltage cable has multiple layers, and the outermost layer has armor, shielding layer, insulating layer and conductor. The high-voltage can resist external damage, and it is mainly used for underground burial to prevent high-strength compression on the ground; The structure of low-voltage cables can be divided into conductors, fillers, insulating layers and protective sheaths. The function of conductors is to transmit current and is made of multi-strand copper and aluminum wires. At the same time, it is divided into single-core, double-core, three-core and four-core overhead cables  and other types.
Insulation thickness: The insulation layer of high-voltage cables is thick, and the thickness of the insulation layer is generally greater than 5MM. The insulation layer of low-voltage cables is relatively thin, and the thickness of the insulation layer is generally less than 3MM.
Uses: The purpose of high-voltage cables is to increase the stability limit, reduce line consumption, reduce project investment, save corridor laying area and improve the grid structure; low-voltage cables are used to link low-voltage power supplies and equipment, control cables, communication cables and signal cables.

Three main functions of the metal shielding layer of high-voltage cables

1. Shield the electric field

The voltage of the high-voltage cable is high, and its electric field strength is also large, and the shielding layer can effectively prevent the high-voltage cable from interfering with the outside world;

2. As a short-circuit current channel

When the high-voltage insulating layer is damaged, if there is no shielding layer, the cable will leak to the ground, causing potential safety hazards. If there is a shielding layer, the leakage current will flow to the ground through the shielding layer;

3. Capacitor current during operation

The innermost layer of the high-voltage line is the conductor, the middle is the insulating layer, and the outside is the metal sheath. The two conductors are separated by an insulating medium and can be regarded as a capacitor. The basic principle of a capacitor is two metal plates separated by an insulating medium. The alternating current will charge and discharge the capacitor, so the shield can provide the circuit for the charging and discharging of the capacitor.

In addition, we can also distinguish from the cable model, cross-sectional area, rated voltage, length and other parameters.