Electric power industry consulting
1️⃣ The current in the cable core varies throughout the day. When performing the thermal calculation of the cable line and selecting the core cross-section, the calculations traditionally include the maximum current value (Ic) of the daily load graph, not taking into account that this value is usually reached only for a limited time (say,
When designing cable lines, we use software to check ampacity, taking into account the key influencing factors:✅ cross-section of cable elements;✅ the mutual arrangement of phases and circuits;✅ screens’ bonding type;✅ laying conditions;✅ environmental parameters. It turns out that almost every software known in the cable industry calculates ampacity perfectly, and also helps with calculating
In medium voltage networks of 6-35 kV, at least the following methods of laying single-core cables in the ground are known:1️⃣ Directly in the ground;2️⃣ In the ground in a common pipe;3️⃣ In three different pipes arranged in a bundle. In 110-500 kV high voltage networks, option 2️⃣ is missing, and only options 1️⃣ and
For medium voltage (MV) line, usually, screens of single-core cables are grounded at both sides. Let us assume that we have two separate MV lines, differing in the mutual arrangement of three single-core cables:Line 1️⃣ – trefoil;Line 2️⃣ – in row. In the conditions of the example, according to the book, we get the following
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
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
Our industry has excellent international standards (IEC) and excellent software. Both provide us with high accuracy calculations. However, despite the precise methods, can we be sure of the results of the calculations? Of course not! At least because we don’t always understand which source data to use in calculations. If we do not have accurate
Numerous cable lines running next to each other are usually assembled together into so-called pipe blocks. For example, this happens in areas near the switchgear, where up to several dozen parallel lines can be located in one place. Usually, the number of pipes exceeds the number of cables that need to be laid. Such a
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
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