Electric power industry consulting
We often think that 6-35 kV medium-voltage (MV) networks are simpler than 110-500 kV high-voltage (HV) networks. Of course, this is not the case, and it is in MV networks that many serious problems are concentrated – among them, for example, the selection of the optimal method of neutral grounding as well as the selection
Single-core cables are used in networks of all voltage classes from 6 to 500 kV. Such cables have conductive screens (CU or AL), and these screens are often grounded on both sides. This leads to the appearance of significant longitudinal induced currents (Is) in the screens caused by the 50 Hz magnetic field of the
Sometimes it is necessary to have several cables for each phase. For example, this happens when an overhead line (OHL) and a cable line are connected in series (see photos). Or it happens when we connect a transformer of a great power to the busbars (or consumers) using a cable line. Cable connections of overhead
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
Screen cross-bonding is an important element of many 6-500 kV cable lines built with single-core XLPE-insulated cables. Therefore, special attention should be paid to the design of the cross-bonding nodes, the specifics of their installation and operation. The screens of the main 6-500 kV high-voltage cable are removed from the cable joint using special 3-6
Single-core cables with XLPE insulation are massively used in 110-500 kV networks. Solid (two-sided) grounding of the screens of such cables leads to negative consequences, and therefore, as a rule, for screens should be used:✅Single-point grounding (see diagram)✅Cross-bonding. In both schemes, voltages may occur on screens relative to the ground caused by interference from the
In 6-500 kV networks, single-core cables with XLPE insulation are widely used. Such cables have conductive screens. In such screens, if they are grounded at both ends, AC 50 Hz currents are induced in normal mode and active power losses occur. This leads to additional heating of the XLPE, a decrease in the long-term permissible
The reliability of cable lines is catastrophically dependent on the quality of installation work. Therefore, we can only be glad that there are a large number of experts all over the world who do their job accurately and precisely. Certainly, some of them may even be called as perfectionists. However, in my opinion, there is
If you are communicating with a person who puffs out his cheeks and says that he is perfectly familiar with the screens cross-bonding of single-core high voltage cables, then ask him next simple question – “What is the difference between two types of screens cross-bonding shown on schemes (a) and (b)?” There is type “123-312”
High voltage cables have an outer sheath. It is very important to ensure that sheath does not have serious damage. Otherwise, water may get into the cable, which in a few years will lead to a short-circuit of main XLPE-insulation. The sheath tests are performed by applying a DC of 10 kV between the cable