Radiated interference from a high voltage impulse generator

Microelectronics are being used increasingly in the power industries and in locations which may be geometrically close to sources of interference. The main sources of interference come from the operation of switchgear which are normally accompanied by closing or opening arcs. These arcs radiate interference at high frequencies which are dependent on the type of switchgear, the most onerous of which is expected to come from SF₆ insulated systems where high dv/dt and di/dt exist. In any case, the magnitude of these fields is likely to be significantly higher than those specified in any immunity standards. As a result, the immunity level of any electrical equipment which has been certified to have satisfied the EEC Directive may not be sufficient in the environment described. Similarly, any proprietary electrical equipment which are being designed for use in the poorer industries will have to take account of the higher interference fields. In short, the microelectronics circuitry may be subjected to unusually high interference fields and appropriate measures would be required to assure that secondary and auxiliary systems are electromagnetically compatible with the primary system which includes the switchgear. Appropriate measures can only be taken if the magnitude-frequency spectra of the radiated interference are available or are predictable. At present, measured data on the magnitude-frequency spectra are very scarce as are computer programs for the prediction of pulsed radiation from large power systems. These deficiencies are being addressed by the authors and it is considered pertinent that a good understanding of the behaviour of a relatively well defined system is first achieved. The present paper therefore reports the initial results obtained from the study on a well defined SF₆ gas gap which was stressed to breakdown across the output of a high voltage impulse generator