Electric power industry consulting
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,
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,
The project usually justifies a specific screen cross-section. However, in practice, there are reasons why the actual screen cross-section may differ from the expected:1️⃣ The cable was bought from a stock (there was no time to wait since it was a line repair that was required), and as a result, a cable arrived at the
There are some things about cables:👉 cable extrusion towers are concrete and don’t look friendly;👉 cables are often black;👉 cables may be really hot;👉 cables are usually located deep underground;👉 cables can “bite” if their insulation is damaged. All this suggests that “cable is a dark force”, and Halloween is a cables’ day. However, all
If the cable insulation is damaged, the current in the cable core (Ic) and the current in the cable screen (Is) can reach the value of the network short-circuit current. One of the important steps in selecting a cable core and screen is to check their resistance to short-circuit (fault) currents, taking into account the
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