ارائه یک طرح حفاظتی جدید به منظور تمایز خطای داخلی از جریان هجومی با در نظر گرفتن اشباع ترانسفورماتورهای جریان

نوع مقاله : مقاله برق

نویسندگان

دانشکده مهندسی برق و کامپیوتر، دانشگاه صنعتی نوشیروانی بابل، بابل، ایران

چکیده

حفاظت دیفرانسیل یکی از مهمترین طرحهای حفاظتی ترانسفورماتورهای قدرت میباشد. در شرایط عادی، جریان تفاضلی تقریباً صفر است، اما در هنگام وقوع خطای داخلی جریان تفاضلی افزایش می‌یابد. افزایش جریان تفاضلی می‌تواند دلایل دیگری غیر از وقوع خطای داخلی داشته باشد، لذا وجود جریان تفاضلی لزوماً نشانه رخداد خطای داخلی نیست. پدیده‌هایی مانند جریان هجومی، اشباع ترانسفورماتورهای جریان و اضافه تحریک نیز موجب ظهور جریان تفاضلی می‌گردند. بنابراین، تمایز بین جریان هجومی و خطای داخلی برای عملکرد صحیح رله دیفرانسیل ضروری است. در طرح حفاظتی ارائه شده، سیگنال جریان تفاضلی با استفاده از تبدیل فوریه گسسته تحلیل می‌شود. در مرحله اول با استفاده از این ویژگی که شدت تغییرات اندازه هارمونیک دوم جریان دیفرانسیل در خطای داخلی با اشباع ترانسفورماتور جریان، بسیار بیشتر از جریان هجومی میباشد، دو حالت ذکر شده از هم متمایز میشوند. در مرحله دوم با استفاده از این نکته که نسبت اندازه هارمونیک دوم به مولفه اصلی جریان دیفرانسیل، پس از رخداد خطای داخلی بدون اشباع ترانسفورماتور جریان، به سرعت افت میکند و تقریباً به صفر می رسد، میتوان آن را از دیگر شرایط کاری ترانسفورماتور قدرت تفکیک نمود. به منظور دستیابی به حداکثر قدرت تفکیک پذیری، شبیه سازیهای مختلفی جهت تعیین دو مقدار آستانه برای شاخصهای ذکر شده انجام شده است. نتایج به دست آمده بر روی یک ترانسفورماتور واقعی 63/230 کیلو ولت با ظرفیت 160 مگا ولت آمپر نشان میدهد که الگوریتم پیشنهادی در شرایط خطای خارجی و برق دار کردن ترانسفورماتور قدرت حتی در زمان اشباع ترانسفورماتور جریان پایدار باقی میماند.

کلیدواژه‌ها

موضوعات


عنوان مقاله [English]

A New Protective Scheme for Discrimination of Internal Fault from Inrush Currents Considering CTs Saturation

نویسندگان [English]

  • Zahra Hasanzadeh Kami
  • Ali Akbar Abdoos
Department of Electrical and Computer Engineering, Babol Noshirvani University of Technology, Babol, Iran
چکیده [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]

  • Power transformer
  • Current transformer
  • Differential protection
  • Fault current
  • Inrush current
  • Current transformer saturation
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