Stoßüberstrom

Stoßüberstrom, also known as inrush current or surge current, refers to the temporary, significantly higher current that flows when an electrical device is first switched on. This phenomenon is particularly pronounced in devices with inductive components like motors, transformers, or solenoids. Upon initial energization, the magnetic field within these components is not yet established, and their impedance is at its lowest. This low impedance allows a large surge of current to flow until the magnetic field builds up and the impedance increases to its normal operating level.

The magnitude and duration of a stoßüberstrom depend on various factors, including the type of device, its design, and the point in the AC voltage cycle at which it is switched on. For instance, switching on an inductive load at the zero crossing of the voltage waveform will result in a lower inrush current compared to switching on at the peak. This inrush current can pose challenges for electrical system design. It can cause nuisance tripping of protective devices like circuit breakers or fuses if they are not rated to handle such transient overcurrents. Additionally, repeated exposure to high inrush currents can lead to premature wear and tear on electrical components and connections.

To mitigate the effects of stoßüberstrom, various techniques are employed. Soft starters for motors gradually increase the voltage applied to the motor, thus limiting the initial current surge. Current limiting reactors can be incorporated into circuits to resist the rapid rise in current. Proper sizing of protective devices that account for the expected inrush current is also crucial. Understanding and managing stoßüberstrom is essential for ensuring the reliable and safe operation of electrical equipment.