Electromagnetic interference is any electromagnetic phenomenon that can reduce the characteristics of a device, equipment or system, or have a harmful effect on living and non-living matter. These interferences are generated in various ways, but their cause is basically sudden changes in electrical quantities such as voltage and current. One of the most common examples of interference, e.g. in the power industry, is the switching operations of medium-voltage devices. Interference can spread along electrical lines and cables, or act by radiation in the form of electromagnetic waves. Undesirable consequences of these interferences are, for example, interference in the emission of radio waves or preturbations in monitoring and control systems.