This chapter discusses electromagnetic compatibility in electrical supply systems. The ability of an electrical installation (equipment, device or system) to operate satisfactorily in its electromagnetic environment without introducing impermissible electromagnetic interference with respect to any part of this environment to which other installations also belong.

Changes in the amplitude of a voltage for a period which is longer than the period of the voltage under consideration is designated a voltage fluctuation. Such voltage fluctuations can occur once, several times, randomly or regularly. The voltage fluctuation in the form of a jump, a ramp or any quasi course is described by the value of the relative voltage change d. The chapter shows some forms of voltage fluctuations. If voltage fluctuations occur with the frequency of approximately 0.005 Hz to 35 Hz, this generally leads, according to the amplitude, to a light flicker which can be perceived by the human eye.

The increasing use of equipment and loads with a non-linear current-voltage characteristic and/or operating characteristics which are not steady over time, has led to an increase in system perturbations in electrical power supply systems of public power supply and industrial networks. In parallel with the development of suitable standards and recommendations for the definition of limits and compatibility levels, measuring procedures and instruments are being developed which enable the relevant measured quantities for system perturbations to be acquired.

For medium and low voltage networks of public and industrial electrical supply systems a survey of existing voltage harmonics and also, under certain circumstances, their change over a period of a year or development over several years is of interest. The following procedure is recommended: procurement of network data; aspects of measurement; and evaluation and assessment.