Electric power industry consulting
It is not enough to have money to buy a good cable. It is also important to find the time and knowledge to make the necessary calculations and select the best way to lay a cable line, taking into account the screen bonding type. Today, let’s look at a simple calculation example of a double-circuit
For lines with single-core cables, there is a problem of selecting the optimal screens’ bonding type. It is especially relevant for 110-500 kV lines, where grounding of screens on both sides is almost prohibited, and 99% of lines have either grounding of screens on one side or cross-bonding of screens. In both cases, it is
In cable catalogues, in addition to the main types of cables, there are simplified recommendations on cable selection. They are given as a table with capacity currents for basic laying conditions (Ib), as well as a series of 5-8 additional tables with various correction factors (K). It is important to note that the system of
To protect the transformer from lightning surges, the metal-oxide arrester (MOA) is often placed directly at its bushings, at a distance of no more than 2-3 m. This creates an impression that the transformer will be fine. In fact, this is a false impression, and the effect on the windings depends not only on the
Three-core cables of medium voltage 6-35 kV, as a rule, are used only for small core cross-sections – up to 240 mm2 (although there are 300, 400 and more). Each of the three phases A, B, and C on top of XLPE insulation has its own individual screen, most often made of copper tape (foil)
There is one important concept in the calculations of power transmission lines – this is the equivalent depth of current in the ground (Dg). In symmetrical operating modes (normal mode and three-phase short circuit), there is no electric current in the ground, and this depth is not interesting to us. However, in any unbalanced modes
One of the weak points of cable lines is cable joints and terminations. Despite all the efforts of specialists who develop and install the joints/terminations, there are still many damages. The consequences of damage will vary depending on the location features. There are at least the following typical locations:1️⃣ Joints in the ground.2️⃣ Joints in
The materials of the outer sheath of cables usually differ depending on whether the cable is laid in the ground or above the ground (in places where oxygen is available). To avoid cable fires (for example, due to a short circuit), cables for open laying are provided with a non-flammable outer sheath. However, when laying
To design the cable line, we need to pass the following stages:✅ Evaluate the electrical strength of the cable outer sheath (jacket) and agree on what is the permissible voltage on the screen.✅ Select the grounding/bonding scheme of the screens (number of sections, cycles, etc.)✅ Perform the thermal calculation of the cable line and select
The reliability of cable lines depends on a number of factors:1️⃣ Design (including calculations);2️⃣ Production and delivery;3️⃣ Cable laying and termination/joint installation;4️⃣ Cable operation (testing, monitoring, diagnostic etc);5️⃣ Unpredictable actions of third parties. Mistakes at any of these stages can lead to serious financial losses: damage to the cable, the need to repair the damaged