Disturbances in power systems due to oscillations of several kilohertz (1 .. 15 kHz) superimposed to the fundamental became more and more important in recent years. The paper discusses causes for this development such as the increased use of PWM converters (e.g. for drives or FACTS devices) or reduction in system damping together with ordinary converter load leading to an excitation of natural system frequency know as commutation oscillations. Measurement results as well as examples from several cases of disturbances investigated by the authors will be presented. The effects of these disturbances vary in a wide range such as malfunction of electronic office equipment, blown power supply units, malfunction of electronic controls or unacceptable noise.

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