Electric power industry consulting
If a short circuit occurs on the line, the line is switched off. However, what to do next depends on the type of the line:1️⃣ overhead line;2️⃣ cable line;3️⃣ mixed line, having both overhead and cable sections. 1️⃣ OVERHEAD LINEFor an overhead line, up to 60-90% of faults are associated with short-term overlaps of air
Sometimes optic fibre is embedded in power cables. Such a fibre may be located in a metal protective tube among the wires of the screen. The photo shows an example of such a cable, where 4 metal tubes are placed at once, partly to reserve each other (since fibre is very fragile). Why is an
For modern cables of 6-500 kV voltage classes, cross-linked polyethylene (XLPE) insulation is the most common. The properties of XLPE are such that if water molecules penetrate the insulation, they become a source of electric field distortion there, which contributes to the development of insulation defects called “water trees”. The appearance of water inside the
It is quite common to lay cables underground in pipes (let me please not use the word duct or conduit). There are probably three main ways to place pipes in the ground:➡️ at the bottom of a trench;➡️ in the borehole prepared by horizontal-directional drilling (HDD);➡️ in the channel prepared by puncturing the ground. The
There are many mixed lines, consisting of cable and overhead sections. Let us talk about transition towers and try to figure out how best to connect the cable screen there. Two options are possible for the screen to be grounded:1️⃣ short path – to the metal crossarm of the tower;2️⃣ long path – to the
Copper (CU) and aluminium (AL) are the two main materials for the current-carrying parts of the cable, that is, for the core and the screen. The features of AL are as follows:1️⃣ AL is up to 3-4 times cheaper than CU.2️⃣ AL is 3 times lighter in weight than CU.3️⃣ AL resistivity is 1.6 times
Let us continue the series of green posts on transients, and today let us talk about traction substations. There are at least two known options:✅ DC 3 kV (the rectifier is located at the substation, and the locomotive has only a DC motor, i.e. it is light enough).✅ AC 25 kV (the rectifier is located
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
Let me please continue a series of “green posts” on transients. One of the main reasons for installing surge arresters (SA) is to protect switchgear from lightning surges caused by lightning discharges to connected overhead lines (OHL). In a switchgear, the most valuable equipment is a power transformer, and it is next to it that
An interesting case occurred at one of the medium-voltage facilities. The 10 kV busbars were fed by a powerful 110/10 kV step-down transformer. To reduce short-circuit currents on 10 kV side, reactors were installed there between the transformer and 10 kV busbars. The transformer and reactor were connected using single-core cables (about 50 m length,