Turn-to-Turn Fault Detection in Power Transformers in the Presence of Inrush Current

Fallah Mollamahmod, Mahdi | 2021

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 54550 (05)
  4. University: Sharif University of Technology
  5. Department: Electrical Engineering
  6. Advisor(s): Hajipour, Ehsan
  7. Abstract:
  8. One of the most critical equipments in power grids are power transformers, which are vulnerable to damage due to the possibility of faults in its various components. A very common category of such faults is turn-to-turn fault in its winding. This fault initiates by the aging of the winding insulation with a short circuit of several adjacent loops to each other and if it is not detected quickly by the transformer protection, it will spread rapidly and can lead to irreparable failure in the transformer. Traditionally, turn-to-turn fault should be detected by mechanical pressure relays, however, due to the poor performance of these relays in the rapid detection of this type of fault, in the last decade, the task of protection against turn-to-turn fault has been assigned to the transformer protection relay. In modern commercial relays, attempts have been made to detect this fault with high speed and accuracy using algorithms based on negative differential current sequence. However, these methods do not work well in the presence of an inrush current. On the other hand, due to thermal and mechanical stresses, the inrush current itself can cause the onset of turn-to-turn fault, and therefore, the failure of turn-to-turn fault detection algorithms in the presence of inrush current will lead to the risk of inadequate protection against this fault. In this thesis, an algorithm for turn-to-turn fault detection in the presence of an inrush current is proposed. In this algorithm, turn-to-turn fault is detected by measuring the time interval when the current of all three phases of the transformer is less than a certain threshold level. Also, by examining the trend of changing the length of this time interval, the occurrence of current transformer saturation is separated from the turn-to-turn fault. In order to confirm the performance of the proposed algorithm, three-dimensional simulation of finite element of a three-phase transformer along with practical experiments on a laboratory sample transformer has been used. The results of simulations and laboratory tests confirm the performance accuracy of the proposed method
  9. Keywords:
  10. Protection ; Inrush Current ; Transformers ; Three Dimensional Modeling ; Turn to Turn Fault Detection ; Power Transformer

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