Although the wire and cable industry is only a supporting industry, it accounts for 1/4 of the output value of China’s electrical industry. It has a wide variety of products and a wide range of applications, involving industries such as power, construction, communication, and manufacturing, and is closely related to various sectors of the national economy. In real life, people always confuse power cables with control cables, making it difficult to distinguish which is power cable and which is control cable.
KVV is a connecting line for industrial and mining enterprises, energy and transportation departments to control and protect circuits, commonly known as control cables. It is mainly used in fixed situations with high mechanical tension such as cable trenches, pipelines, and shafts, in accordance with the national standard GB9330-88.
1、 Overview of control cables
The cables connecting the control center to various systems for transmitting signals or controlling operational functions are collectively referred to as control cables. The early functions of control cables were relatively simple, including: indicator light display, instrument indication, operation of relays and switchgear, alarm interlocking system, etc. In recent years, due to the widespread application of weak current and computer networks, new functions and higher requirements have been put forward for the selection and application of control cables. This article discusses some new issues that have emerged in the selection and use of control cables in recent years, for research reference.
2、 Main series varieties of control cables
The main products of current control cables are: PVC insulated control cables, natural styrene butadiene rubber insulated control cables, and polyethylene insulated control cables. In addition, there are products with cross-linked polyethylene insulation and ethylene propylene rubber insulation. The oil immersed paper insulated lead wrapped control cables produced in the early years have been phased out.
The rated voltage of the control cable is expressed in U0/U. The national standard issued in 1998 in China stipulates that the rated voltage of plastic insulated control cables is 450/750V. Foreign countries, such as Germany, have proposed using 600/1000V products as a conventional product series for control cables. At present, China can also produce 600/1000V plastic insulated control cables. The rated voltage of rubber insulated control cables is specified as 300/500V.
The core of the control cable is copper, with a nominal cross-section of 2.5mm ² And below, 2-61 cores; 4~6mm ², 2-14 cores; 10mm ²， 2-10 cores. Control the working temperature of the cable: rubber insulation is 65 ℃, PVC insulation is 70 ℃ and 105 ℃. The control cables used in computer systems generally use products with PVC, polyethylene, cross-linked polyethylene, and fluoroplastic insulation.
3、 Measures to ensure the normal operation of control cables and prevent interference
In order to ensure that the control cable can reduce the coverage in the event of insulation breakdown, mechanical damage, or fire, the national standard GB50217-91 “Code for Design of Electric Power Engineering Cables” stipulates that two sets of systems for dual protection, including current and voltage, as well as DC power supply and trip control circuit, need to enhance reliability, and each should use its own independent control cable.
After the control cable is put into operation, there is an issue of electrical interference between different cores of the same cable and between adjacent parallel cables. The main reasons for electrical interference are:
(1) Electrostatic interference generated by the capacitive coupling between cores due to external voltage application;
(2) Electromagnetic induced interference caused by energized current. Overall, when there are high voltage and high current interference sources nearby, electrical interference is more severe. Due to the smaller distance between the cores of the same cable, the degree of interference is also much greater than that of adjacent cables laid in parallel.
