Electric power industry
Single-core cables of medium voltage 6-35 kV often have simple grounding of the screens on both sides (“solid bonding”). As a result, the cable screens form closed contours, and the magnetic field of the core current induces currents in these contours, that is screen currents. Induced currents (Is) in the screens pass through the screens
AC 50 Hz cable lines are often referred to as reactive power sources. In idle (no-load) operating mode, any cable line by its capacitance generates reactive power, which creates difficulties:✅ for a network that is forced to consume reactive power;✅ for a cable that is heated by idle currents, especially at the beginning of the
Very often we see posts where designers and installers share beautiful photos of successfully completed projects. However, then, quietly, in private correspondence, the exploiting organizations share other photos and accompany them with words “What should we do with this?” or “How do we fix this”? In short, many “successful” projects turn out to be “UNsuccessful”
Previously, oil-soaked paper was used as insulation for medium-voltage cables of 6-20 kV classes. At the same time, there were two core designs – round-shape or sector-shape. The advantages of cables with sector cores (Design 1) are shown on the slide. Currently, cross-linked polyethylene (XLPE) is mainly used as cable insulation. Of course, the question
We know that one of the advantages of cables with solid insulation (XLPE, EPR, PVC) is that these cables have no restrictions on the height difference of the route. We can lay such cables horizontally, vertically, at an angle. Any cable arrangement is allowed, as long as the cable bending radius is not violated and
In 6-35 kV networks, single-core cables are most often arranged in a closed triangle (1), and cable screens have a small cross-section of up to 50 mm2 and a simple solid grounding. Let us figure out what happens if the cables, contrary to the project, are laid not in a closed triangle, but otherwise. Three
The method of symmetrical components is used to calculate the normal and emergency modes of the electric network. The method represents an any mode (even asymmetric) as a composition of three separate symmetrical ones:✅ Positive sequence “1”.✅ Negative sequence “2”.✅ Zero sequence “0”. To use the method, it is important that the longitudinal impedances Z1,
There are two main types of power transmission lines – overhead lines and cable lines. Traditionally, in high-voltage networks, the total length of overhead lines exceeded the total length of cable lines. Therefore, some errors in the calculations of impedances of cable lines were not able to lead to serious consequences. However, gradually, especially with
The vast majority of cable lines (CL) are double-circuit. Two circuits are needed not only to increase the transmitted power, but also for reliability reasons. If one circuit turns out to be disconnected (for testing, damage locating, repair, replacement), then the second circuit can provide power supply to consumers (to load). Two modes are possible
When designing 6-500 kV cable lines, one of the important tasks is to carry out thermal calculations and select the cable core cross-section (taking into account all influencing factors). The customer gives us the current that the cable line should pass, and we tell him which combination of cable core cross-section and screen bonding type