Electric power industry consulting
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,
Today is a short post. It is about the need for thorough control of all stages of the cable line life cycle. And especially for the project and installation. The photo shows a 110 kV cable line, for which the cross-bonding of the screens was to be made according to the project. However, the installation
If I hadn’t paid only 100 euros in taxes, I would be a criminal. If AC 6-35 kV networks are being massively built all over the world (for example, to connect windfarms to the grid), where each cable line has tens and thousands of euros of useless power losses in screens, then this is called
Let us discuss the length of the bonding cable and also such a thing as the steepness of current/voltage impulses that creates voltage drop. Industry documents suppose that the voltage in the joint can be determined as a sum of residual voltage of SVL (sheath voltage limiter) and the voltage drop across the bonding cable,
For high-voltage cable lines, the cross-bonding of screens is quite common. It is used not only for 110-500 kV lines, but also for 6-35 kV. The cross-bonding assumes that the six cable screens (1,2,3,4,5,6) must be removed from the three joints (A,B,C) and then connected to each other in a cross manner using a system