Electric power industry consulting
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
The cable industry does not stand still and is constantly developing. New materials, new types of cables and cable products, new methods of design and calculation are emerging. However, some things in the cable industry remain unchanged from year to year – we are talking about cable drums (reels). All over the world, in the
The calculation of cable pulling forces is one of important section of the design documentation. It assumes at least the following calculations:✅ cable pulling forces (should be no more than 30 N/mm2 for a cable with an aluminium core and no more than 50 N/mm2 for a cable with a copper core);✅ pressure on the
In 6-35 kV network, suppose we have busbars ABC, with two lines, and a ground fault has occurred in phase A of a line (1). In case of isolated neutral, the ground fault current (Igf) is determined by the EMF (Ea) and the capacitances of all network to the ground, and therefore it is a