Generally, harmonics are oscillations in the base power frequency. In electrical AC systems, the base frequency is typically 50 or 60 hertz (Hz) and harmonics occur in multiples of this, for example 100 Hz, 150 Hz, 200 Hz, etc. where the base frequency is 50 Hz. Harmonics occur whenever there is a disturbance of the voltage or current, e.g. if the current is interrupted or if AC current is synthesized in a converter. The problem with harmonics is that electrical devices may react differently when exposed to a different frequency than the one they are designed for, which may result in damage. This is an increasing problem in power systems as most power electronics solutions cause harmonics. The phenomenon can be reduced by the use of power filters or system design and component matching to minimize electrical harmonics.