Electric power industry consulting
Three-phase AC 50/60 Hz cable lines have magnetic fields (H) of core currents A,B,C. In normal operation, the currents A,B,C are equal to each other and have a 120° shift, so it seems that the magnetic fields A,B,C should compensate each other. However, this is not happening well, and as a result, the line has
AC 50/60 Hz power cables can be divided into two main groups:✅ single-core cables;✅ three-core cables. 1️⃣ Single-core cables, when bonding screens on both sides, have closed circuits of screens. The core currents (Ic) by their magnetic field induce AC 50/60 Hz currents in the screens (Is) – they are called circulating. Currents pass through
Today we will not talk about alcohol (“bar”), but about a conductive element called:✅ equipotential bar (bar, bus);✅ earth continuity conductor (ECC). Questions arise:1️⃣ why do we need such a bar;2️⃣ how to provide equal distances from the bar to all phases A,B,C;3️⃣ how to calculate the optimal bar material and cross section (Fb). Unfortunately,
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
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
We know that the screen’s cross-bonding is an effective way to deal with induced currents and losses in the screens of 6-500 kV cable lines (CL). The use of cross-bonding allows not only to save on losses (dozens of thousands of euros annually), but also to increase the permissible core current of the cable line,
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
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
In 110-500 kV networks with a grounded neutral, cable line lengths from 0.6 to 1.2 km are considered as “bad”. The reasons are simple – for lines more than 0.3-0.6 km, single-end screen grounding can no longer be used (due to the dangerous voltage Us induced on the screens during a single-phase short circuit external
We have to design the cable length that the customer wants. However, let’s discuss which line length would be particularly inconvenient for us and why. The answer to this question depends on the voltage class and the method of neutral grounding. Today, let’s only discuss 110-500 kV networks with a grounded neutral. For such networks,