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In the last years, the vegetable oil for power transformers has attracted much interest from the manufacturers and users of power transformers especially due to its superior fire point and biodegradability. In this paper an experimental study regarding the properties of vegetable and mineral oils subjected to thermal stress (155 °C, 1500 h) in the presence and absence of paper is presented. During...
The insulation system of power transformers is a key topic which has to be taken into account in order to achieve an optimized design and safe longterm operation. The design of feasible insulation for high voltage direct current transformers requires the understanding of field distributions in insulating materials in both AC and DC operation because the transient stresses are dependent on both conductivities...
In this paper the results of experimental investigation on breakdown strength under AC and BIL voltage of impregnated cellulose elements in combination with oil gaps are presented. Within investigated two models three different types of breakdowns are generated: through bulk oil gap, over oil-pressboard interface (creep breakdown) and puncture breakdowns of paper insulation. In each experiment mineral...
In recent years one can observe a higher interest in alternative dielectric materials for power transformers. These are for example natural and synthetic esters or aramid fiber based solid insulation materials. In this paper moisture saturation curves of various insulation oils are presented up to a temperature of 140°C, together with the sorption isotherms of Nomex® pressboard. These lead to adjusted...
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