InrushPhänomene

InrushPhänomene, also known as inrush current or switch-on surge, refers to the transient surge of current that flows when an electrical device is first connected to a power source. This phenomenon is particularly noticeable in inductive loads, such as transformers, motors, and fluorescent lamp ballasts. The primary reason for inrush is the need to establish the magnetic field within the inductive component. When power is applied, the inductance resists the rapid change in current, causing a temporary but significant increase above the steady-state operating current.

The magnitude and duration of the inrush current depend on several factors, including the inductance of the device, the impedance of the power supply, and the point in the AC voltage cycle at which the device is switched on. The worst-case scenario for inrush current occurs when the switch closes at the zero-crossing of the voltage waveform. This allows the magnetic flux in the inductor to build up from zero, potentially leading to a peak current that can be many times the normal operating current.

Inrush currents can have several implications. They can cause temporary voltage drops in the power supply, affecting other connected equipment. They can also trigger protective devices like circuit breakers and fuses, leading to nuisance tripping. In some cases, repeated or excessively high inrush currents can stress components and reduce their lifespan. Engineers often employ strategies to mitigate inrush phenomena, such as using soft-starters for motors, inrush current limiters for transformers, or carefully designed power supply sequencing.