The Geneva city utility SIG operates a large medium/low voltage distribution network with a high number of distribution transformers in place. Within the last approx. 4 years an unusual high number of transformer failed due to a premature aging. These units were all delivered between beginning of 1996 until mid 1999. Only sizes of 630 kVA and 1000 kVA were affected. Within other MV networks as well 400 kVA and 1250 kVA units failed, however a smaller number. Nondescript system failures, computer-/control system-/and process interruptions, apparatus and system destructions, explosions and fires were the reasons for 238 customer ordered measurements, network analyses and repairs in Germany, Austria, Switzerland, Italy and France throughout the years 2003 and 2004. Craftsmen's shops, doctor's cabinets, general stores, special repairshops, appartment houses in small and large cities, large offices, banking- and insurance buildings, large oil refineries, industries such as metal plastics manufacturing were affected internationally. At 157 cases systems and parts of them were destroyed. 7 cases resulted in building destructions following explosions and fire. Acc. to our knowledge the disturbances within the networks grew steadily from beginning of 1996 until the year 2000 and the increased exponentially. Within 229 cases the same cause could be determined. Concerned apparatus are capacitor bank with and without chokes, active filters, transformers, capacitors, process controls, computers, light controls, telephone switchboards, safety units (alarm and fire detectors) inverters and electronically controlled systems.
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