Abstract
Power transformer differential protection may confront mal-functioning in authentic discrimination between inrush and internal faults. To tackle the latter mal-functioning, a new two-stages algorithm based on phase content of the current signal of the current transformers (CTs) is put forward. The proposed algorithm is designed based on the fact that the fundamental phase angle of a fault signal ideally remains constant during the fault. However, during inrush cases, the phase angle varies. Also, during the internal fault, the phase angles of the current signals of CTs are in phase while during the external fault, the phase angles of the current signals of CTs are 180° out of phase. In the first stage, the proposed algorithm calculates the fundamental phase angles of the current signals of the CTs using sub-cycle modified recursive least squares (MRLS). Afterward, normalized mean residue (NMR) is employed to measure distance between the estimated phase angles of the CT’s currents. MRLS and NMR algorithms require limited samples (i.e. 10 and 5 samples respectively) for executing their calculations. Performance evaluation with simulated and experimental recorded current signals shows the ability of the proposed method in discrimination of the internal faults from inrush and external fault currents.
Highlights
Owning to the power transformers being strategic components and their costliness, differential protection schemes are known as the widely-employed unit protections that play an important role in decreasing the damages of the internal faults [1]
During the internal fault, the phase angles of the current signals of current transformers (CTs) are in phase while during the external fault, the phase angles of the current signals of CTs are 180◦ out of phase
During internal fault condition, during the internal fault, the phase angles of the current signals of CTs are in phase
Summary
Owning to the power transformers being strategic components and their costliness, differential protection schemes are known as the widely-employed unit protections that play an important role in decreasing the damages of the internal faults [1]. To deal with internal faults and inrush currents discrimination, several algorithms have been proposed in the literature that tried to introduce signal processing techniques to tackle the aforementioned challenges These methods consist of determining induced voltage, flux linkage, and instantaneous inductance [4,5,6,7,8], utilizing pattern recogni tion and fuzzy logic [9,10,11,12,13,14] and time–frequency analysis [15,16,17,18,19], hybrid ratio-based algorithms [20,21,22], and employing statistical and similarity indices [23,24,25,26,27]
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More From: International Journal of Electrical Power & Energy Systems
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