Electric power industry consulting
Let us continue green posts. Today we’ll talk about how much the voltage on the equipment may differ from the voltage on the surge arrester (SA). To do this, consider a lighting wave coming from the overhead line (OHL) to switchgear. After passing the SA site, the wave decreases its magnitude to the level of
Let us continue with a series of green posts on transients and surge arresters. Today let us assume that, in three-phase network, a single-phase-to-ground fault occurs, in phase A. In this case, the 50 Hz voltage on the two undamaged phases B and C will increase compared to its normal value. Compared to normal operation,
The main characteristics of the three-phase AC network are its voltage class, frequency, and method of neutral grounding. Speaking of voltage, there are two different voltages (the designations may depend on the country):✅ Rated voltage (let it be Ur);✅ Maximum continuous operating voltage (let it be Umcov). Both voltages are the effective value of the
Let us continue the series of green posts. There is such a thing as “temporary overvoltages” (TOV), and one example of such processes is ferroresonance. Ferroresonance, like ordinary resonance, occurs in circuits containing capacitances and inductances. However, unlike resonance, with ferroresonance, it is important that the inductance does not remain constant, but changes depending on
Dear colleagues, let me please start a series of “green posts” on electromagnetic transients and protection against them. In general, I have to admit that there are too many experts in this area in the world, and it seems to me sometimes, they are ready to fight brutally for their right to exist under this
Lightning processes are statistical processes. It is hardly possible to study such processes by considering a lightning strike to the line with specific parameters (current, front) or by considering a specific lightning wave coming from the line to the switchgear. To calculate the probability, I normally use ATP/EMTP, which has been changed for the convenience
All the experience allows the author to state that the global metal-oxide surge arrester (MOA) industry is in dire need of simple MOA application methods, but, instead it, is developing endless editions of IEC 60099, adding details to an already complex document that contains dozens of MOA characteristics. At the same time, IEC 60099 does not divide
For surge arresters (SA) of 110 kV and above, special grading rings are usually used, which, in normal operation mode, make it possible to equalize the distribution of AC 50 Hz voltage along the SA height. This distribution is important because it guarantees the absence of overheating of the SA elements (varistors), eliminates the risk
The photo shows the grading ring (“screen”) that remained from the damaged 110 kV metal-oxide surge arrester (SA or MOA). I’m not going to discuss now why and where the damaged SA went (flew away or just fell down on some equipment and people’s heads). Now I would like to discuss the SA screen only.
Unfortunately, when checking the resistance of equipment to short-circuit currents, it is necessary to take into account not the time of the main protection (usually less than 0.1 seconds), but the time of backup protection (can reach 0.5-2.0 seconds). Such rules, for example, are applied all over the world when designing cable lines. This means