Saturation Detection-Based Blocking Scheme for Transformer Differential Protection

• Published in: Energies (Basel) Vol. 7; no. 7; pp. 4571 - 4587
• Main Authors: Lee, Byung Eun, Lee, Jinsik, Won, Sung Ho, Lee, Byongjun, Crossley, Peter A, Kang, Yong Cheol
• Format: Journal Article
• Language: English
• Published: Basel MDPI AG 01.07.2014
• Subjects: Adaptive technology; Algorithms; Blocking; current differential relay; Discontinuity; Electrical engineering; Faults; harmonic blocking; Neural networks; operating time delay; Relay; Research centers; Saturation; saturation detection based blocking; Time delay; transformer protection; Transformers; Wind power
• ISSN: 1996-1073; 1996-1073
• DOI: 10.3390/en7074571

This paper describes a current differential relay for transformer protection that operates in conjunction with a core saturation detection-based blocking algorithm. The differential current for the magnetic inrush or over-excitation has a point of inflection at the start and end of each saturation period of the transformer core. At these instants, discontinuities arise in the first-difference function of the differential current. The second- and third-difference functions convert the points of inflection into pulses, the magnitudes of which are large enough to detect core saturation. The blocking signal is activated if the third-difference of the differential current is larger than the threshold and is maintained for one cycle. In addition, a method to discriminate between transformer saturation and current transformer (CT) saturation is included. The performance of the proposed blocking scheme was compared with that of a conventional harmonic blocking method. The test results indicate that the proposed scheme successfully discriminates internal faults even with CT saturation from the magnetic inrush, over-excitation, and external faults with CT saturation, and can significantly reduce the operating time delay of the relay.