Transientoverspændinger

Transientoverspændinger (transient overvoltages) are brief, high-amplitude spikes in an electrical system's voltage that exceed normal operating levels, typically lasting microseconds to milliseconds and containing substantial high-frequency content. They arise in power distribution and electrical networks from switching operations, lightning strikes, faults, or the energization of long cables and transformers.

Their characteristics include peak magnitude, duration, rate of rise, and wave shape. Because of their short duration, they often propagate as traveling waves along lines and can reflect at impedance discontinuities, which can influence how they affect equipment.

Impacts of transientoverspændinger can include insulation stress or damage, nuisance tripping or malfunction of protective devices, and damage to sensitive electronics. Repeated transients can contribute to accelerated aging of insulation and components.

Mitigation methods focus on limiting peak values and controlling impulse energy. Common measures include surge arresters or metal-oxide varistors, surge protective devices at equipment interfaces, proper earthing and bonding, shielding and careful cable routing, as well as controlled switching practices (such as pre-insertion resistors or pre-charging) to reduce switching surges.

Modelling and measurement play key roles in managing transientoverspændinger. Time-domain simulations (for example with EMTP/PSCAD) help predict wave propagation and stress on insulation, while high-frequency sensors enable field measurements. Standards such as IEC 61000-4-5 and IEC 61643 provide test and immunity guidelines for devices and systems to withstand or suppress transient overvoltages.