The Design of Electric Cable

With the rapid development of communication modernization, more and more open-line transmissions have been replaced by new transmission methods such as electric cables and power cables. And the design of electric cable is particularly important.

Selection of cable type

The following considerations should be taken into account in the selection of electric cable types:

(1) The rated voltage of the cable shall not be less than the rated voltage of the network in which it is located, and the maximum working voltage of the cable shall not exceed 15% of the rated voltage.

(2) In order to save investment, aluminium core is usually used in cables, but copper core cables are used in places where moving or vibration is severe.

(3) YJV (YJLV) series power cables without steel band armor can be used for cable tunnel (cable trench) laid at basic level without mechanical damage or mechanical external force. Otherwise, YJV22, YJLV23 (YJLV22, YJLV23) series power cables with steel band armor should be used.

(4) The direct buried cables are YJV22, YJV23 (YJLV22, YJLV23) series power cables armoured with steel strips. Where the cable is corroded, the cable should be protected and sealed through the pipe, not buried directly.

(5) In vertical or large drop locations, the cables are YJV32, YJV3, YJV42, YJV43 (YJLV32, YJLV33YJLV42, YJLV43) series power cables armoured with steel wires.

Choice of Cable Laying Mode

(1) It is advisable to use cable trench in the public network laying on both sides of the street. When the number of cables is less than 3, the investment can be saved by laying cables directly.

(2) It is advisable to lay cables to each user directly.

Arrangement of cables on brackets

According to the voltage level, the cables are arranged from top to bottom, 10kV cables are laid on the upper or middle layers, low voltage cables are laid on the middle or lower layers, the farther cables are laid in the middle of the upper or certain layers, and the nearest cables are laid on the edge of the lower or certain layers.

Cable reservation and well location

In order to prevent the cable from being scrapped because of the insufficient length of the cable caused by the damage of the intermediate joint and terminal head, the cable wells should be set up at the starting point, the end point, the intermediate joint and the easily damaged place of the cable. And the reserved panels should also be reserved when the wells are not set up. The length of the reserved panels should be 10-20m. When the cable well is together with the observation well, the observation well can be omitted.

Waterproof of cable trench

(1) In the design and construction of cable trenches on both sides of streets, waterproofing measures on the left, right and lower sides should be taken in accordance with the requirements of building engineering specifications. The upper cable trench cover should be grouted and hooked, and the cable leading out of the cable trench should be sealed at the exit.

(2) The bottom of the cable observation well is 50cm lower than the cable trench and the water collecting pit is made at the bottom of the observation well, and the pumping pit is placed in the middle (place the pump). The cable observation well cover should be waterproof.

(3) According to geographical conditions, the bottom of cable trench can be drained to one side or both sides by making a directional observation well with a drainage slope of not less than 0.5%.

(4) When the cable trench crosses with other pipes or trenches, it shall be strictly sealed and no irrelevant drainage pipes shall be allowed to be introduced into the cable trench.

(5) Cables in the cable tray should be tightly sealed outside the trenches to prevent the water sources outside the ditches from flowing into the trenches along the cables.

Fire protection of cables

(1)The cable trench shall have firewalls in the following places: where the cable enters the equipment, where the cable trench branches, where it is close to the thermal pipeline and where the cable intermediate joints are located. When the path is long, a firewall should be set up every 50-100m. The firewall can use LB expansion type fire retardant package.

(2)LDL-1 type inorganic fireproof blocking material should be brushed in the following parts of the cable: the cable in the reserved well, the cable in the observation well, the cable in the cable trench at the base of the equipment, the intermediate joint of the cable and the terminal head.

(3) LDL-2 type organic fire-proof plugging material or LGB series fire-proof partition board are used for fire-proof plugging in the following places of cables: the entrance of cables in box transformer, tap box, distribution box, etc.