1. Context

Electrical engineers are used to observing significant transient overvoltages on their networks. These are generally caused by switching operations, lightning strikes or incidents. Their intensity and duration are generally known, and the equipment installed on the electrical network is designed to withstand them.

On the other hand, these same electrical engineers also noted that, for certain network configurations, very significant overvoltages could occur, lasting well beyond the usual transient times, jeopardizing the integrity of the equipment.

Understanding these phenomena and, above all, forecasting them - which in this respect is akin to meteorological phenomena - is a much more delicate task, but one that is essential for power network managers. Fortunately, these phenomena are fairly rare, but surges of this kind have been observed...