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High dU/dt transients resistant distribution transformers comprising filtering bushings

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In the article a concept of increasing the transformer withstand to voltage surges characterised by high rate of rise based on using special bushings comprising filtering chokes is presented. The concept has been implemented in new distribution transformers providing superior resistance to high dU/dt transients. The new transformers are compliant with highly demanding standard SFS2646. Streszczenie. W artykule przedstawiono koncepcję zwiększenia odporności transformatora na przepięcia o dużej stromości, polegająca na zastosowaniu w przepustach specjalnych dławików tłumiących. Koncepcja ta została wdrożona w nowych transformatorach rozdzielczych zapewniając radykalną poprawę odporności na stromość narastania napięcia dU/dt. Transformatory wyposażone w nowe przepusty spełniają wymagania normy SFS 2646. (Odporność na stromość narastania napięcia dU/dt w transformatorach mocy) Keywords: Distribution transformer, dU/dt, lightning surges, SFS 2646. Słowa kluczowe: Transformatory rozdzielcze, dU/dt, wyładowania atmosferyczne, SFS2646. Introduction Ultra steep wavefront transients characterized by a high voltage rate of rise dU/dt are extremely dangerous to electrical equipment such as transformers and motors. High dU/dt surges are superimposed on the normal phase voltages and pose significant hazard to the insulation system of the equipment, which needs to be dimensioned to withstand those temporary events. Nevertheless, according to [1], still as many as 35% of total dielectric failures in power equipment are caused by surges. The high frequency components present in the spectrum of the surge result in a highly non-uniform potential distribution, leading to local overstressing of the insulation system, as illustrated in Fig. 1, showing a simulated initial distribution of voltage with a transformer winding. Fig.1. Simulated time-evolution of voltage distribution along a transformer winding when subjected to high dU/dt transient. Due to c[...]

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