نوع مقاله : مقاله برق
نویسندگان
دانشکده مهندسی برق و کامپیوتر، دانشگاه صنعتی نوشیروانی بابل، بابل، ایران
چکیده
کلیدواژهها
موضوعات
عنوان مقاله [English]
نویسندگان [English]
Differential protection is one of the most important and basic protections for power transformers. In normal conditions, the differential current is almost zero, but it increases during internal faults. Since the increase in the differential current can have other reasons than the occurrence of an internal fault, the existence of a differential current is not necessarily a good sign of the internal fault occurrence. Some phenomena, such as the inrush current, saturation of current transformers, and over-excitation, also result in the appearance of the differential current. In the presented protection scheme, the differential current signal is analyzed by the discrete Fourier transform. In the first stage, based on the point that the rate of changes in the magnitude of the second harmonic of the differential current in the internal fault with current transformer saturation is much greater than the inrush current, these two events can be distinguished. In the second stage, based on the fact that the ratio of the second harmonic to the fundamental component of the differential current drops rapidly after the occurrence of internal faults without current transformer saturation and reaches almost zero, it can be easily discriminated from other conditions. Various simulations have been performed for proper threshold settings for the above-mentioned criteria to achieve maximum separability. The results obtained from simulation studies on a real 230/63 kV, 160 MVA power transformer reveal that the proposed algorithm remains stable for external faults and transformer energization conditions even during current transformer saturation.
کلیدواژهها [English]