Electric networks and the equipment serving them are built on a multi-level elemental base, the communication links inside which are provided by cables of various types. This is electrical wiring, which can perform the tasks of distribution, transmission and trunk transportation of current. Control cables occupy a special place in this segment. This is a universal channel for transporting electric currents under voltage from 380 to 1000 V, which is mainly used not for servicing power circuits, but for providing intermediate switching between power plants.
Control cable device
The product is formed by several technological layers and a core directly involved in the transfer of current. The simplest structure of such a cable can be represented as follows:
- Conductors.
- Insulation lining on the surface of the core.
- Aggregate.
- External containment.
The place of operation largely determines the requirements for the outer sheath of the wire. For example, a control shielded cable, in addition to typical mechanical protection, has insulation that protects the core from electromagnetic and electronic interference. Shielding is one of the most complex forms of external protection of the conductive circuit, representing a metal coating with certain properties for localizing electrical energy. Also, at the level of the filler and the outer shell, structural coatings can be used that protect the cable core from physical influences, moisture, fire, dust, etc. For this, a wide list of different materials is used from polyvinyl chloride with the same metal to mica tapes.
Conductors
Nevertheless, the main functional element of any cable is its core. In this case, copper or aluminum (including its copper-plated version) is used to make a conductive wire. As for the structural design, most often it is a single conductor or several thin twisted wires, providing the possibility of safe bending of the control cable. Single-type conductors are used in stationary power plants, where there is no need for bends and twists. The design with twisted wires, in turn, is involved in equipment and places of operation, where dynamic loads on the wire are provided. For example, it can be mobile electrical installations, generator units or batteries.
The material of manufacture also makes a difference in approaches to the use of wires. As already mentioned, mainly copper or aluminum is used for the conductive part. Copper products are more often used in 220 kV substations. In principle, this material is most suitable for universal use in electrical installations. Aluminum is often used because of its more affordable cost where high demands are placed on the reliability and accuracy of the system.
Basic classifications of control cable
There are several parameters by which control cables are divided. In particular, the main classifications include:
- The material of manufacture of the base wire.
- Insulation material.
- The shape of the wire.
- Section characteristics.
- Properties of the protective cover.
Special modifications include armored, dielectric and waterproof wires, designed for harsh environments with aggressive environments.
Classification by site conditions
Cables are also divided according to the conditions of use from the point of view of the external influence of mechanical loads:
- Indoors, in trenches and canals without the influence of forces contributing to the stretching. Protection is formed by winding steel tapes with an anti-corrosion coating. This is a typical control cable KVVGNG, which is used in places that do not provide strong mechanical stress, as well as a fire hazard.
- In trenches and soil without large external tensile forces. The armor layer is formed by a double steel tape with an additional outer cover made of PVC compound.
- In the soil and canals under the influence of large tensile forces. Armor is formed by steel rods coated with a zinc layer and a cover of PVC compound.
Control cable routing
Already in the process of laying, a special metal bandage with a corrugated tube is provided to protect the cable sheath. On the reverse side, the wiring is closed at the distribution terminals, electrical boxes and boxes. As a rule, wiring equipment operates at 380 kV. From power devices, a copper control cable is routed through protected channels and trays to the main consumer electrical circuit. Terminal boxes and distribution cabinets are marked with special ink indicating the characteristics of the conductive element and the outer layers of the shell.
Cable connection
Different methods are used to connect the circuit to the target equipment. Depending on the destination node, the following configurations can be used:
- The cable is led out of the trunk line with branching into two streams.
- The cable is divided into right and left sides of the electrical panel for subsequent distribution over several circuits.
- Free calculation is performed throughout the working area.
- A point connection is made via terminal clamps.
It is important not to forget that control cables are a device with a multi-level structure, therefore a special wiring tool should be used during its cutting. Be sure to use measuring instruments like a multimeter at all stages of the circuit assembly for comprehensive control of network parameters.
The influence of temperature and light on the cable
In the process of electric current flowing through the wires of the wiring, overheating or supercooling can occur, which will inevitably affect the operability of the cable and the properties of its design. Temperature factors should initially be calculated and reflected in the presence of appropriate protective qualities. For example, in conditions of low temperatures it is recommended to use plastic insulation of control cables. This will prevent cracking and breakage of the conductor in frost conditions. For example, a conventional polyethylene shell at low temperatures loses its flexibility and often bursts, losing the necessary performance.
Regarding exposure to light, exposure to the sun also harms the control cable. As an optimal protection when using outdoor wiring, armored coatings with a thin aluminum or lead cover are suitable.
Control cable maintenance
Elimination and prevention of minor defects and damage on the cable line is a prerequisite for maintaining stable operation of the electrical network. On a regular basis, maintenance personnel conduct inspection and electrical diagnostics of the route, timely changing couplings, fixing elements and protective sheath. In accordance with the schedule and routing at certain intervals, the control cable is cleaned and reconnected.
Flexible contours are checked separately at the corners and junctions. Even with an apparently integral shell, conductors can be damaged in such conductors; therefore, analysis of the internal structure by means of non-destructive testing is required. The time intervals between complex surveillance activities can vary from several months to 2-5 years.
Conclusion
Cables of this type are widespread due to their versatility in terms of the possibilities of use in a wide variety of working conditions. This is not the target means of delivering current over long distances due to the high cost and technological complexity of installation. However, for critical power supply sites, control cables are the optimal solution. The growing popularity of such wiring contributes to its environmental safety. Even in aggressive environments, the control cable does not emit substances hazardous to health and does not have a harmful effect on the environment. In terms of maintaining the protective qualities of the conductive core itself, again, much will depend on the quality of the outer insulation layers and the main metal cover at the laying site.