Study of electromagnetic transients

A number of electrical phenomena corresponding to abrupt variations in the electrical variables of a system or a grid can be grouped together under the title of “electromagnetic transients”. Here one can include phenomena such as resonance, ferroresonance, overvoltages with various front speeds such as the transient voltages established at the terminals of a circuit breaker or those following a lightning strike, and even the impact of transformer connection currents.

These phenomena, such as ferroresonance, may be non-linear, electromagnetic phenomena being able to appear under certain conditions on electricity grids containing transformers that can be saturated (potential transformers, in particular) and capacitances (stray capacitance on the cables, compensation banks, etc.).

Any of these phenomena may cause damage to electricity grids and systems through over-currents and overvoltage (dielectric breakdown). Ferroresonance, for example, can generate large-scale overvoltage in stabilized regimes, which has the ability to destroy potential transformers.
Further, in certain cases, coordination of the isolation within the grids requires fine analysis by simulation of the main electromagnetic transients which may occur.

Capsim uses numerical simulation tools to identify and eliminate the risks of links with electromagnetic transients. When certain parameter values having an influence on the risk are not identifiable, Capsim carries out parametric studies which are able to sweep a sufficiently broad range of values to cover any risk. Additional risk limiting systems (circuit damping, lightning protection, etc.) can be sized and evaluated by simulation.

In this way, it was possible:

• to check if a structure, already in existence or part of a project, contains risks linked to electromagnetic transients
• to highlight a problematic case (for example ferroresonance) reported in such a way as to detect the influential parameters and hence propose a remedial solution