Development of an adaptive differential protection scheme for transformer during current transformer saturation and over‐fluxing condition

Abstract

Despite having several modern transformer protection schemes, the protection engineer prefers the universally adopted unit-type differential protection scheme for the current transformer (CT) because of its functional flexibility. Inrush condition, external fault with current transformer saturation, over-fluxing, or the combination of these may maloperate the unit-protection schemes. In this article, all the above-mentioned situations have been addressed that mislead differential protection. A multifunctional algorithm is presented that filters the disturbance for correct relay operation. The inrush condition is carefully examined with the help of the average angle of the differential current. Moreover, an adaptive algorithm takes care of the false operation of the transformer protection scheme during an external fault with CT saturation condition. Also, the momentary over-fluxing condition is dealt with, with the help of fifth-and seventh-harmonic-based analysis of the differential current. Hence, the disturbance will be thoroughly examined and a decision signal issued accordingly to avoid unnecessary isolation of the transformer to improve system stability. The power system is simulated in PSCAD software and the algorithm is developed in MATLAB. Moreover, the proposed scheme is validated on a hardware prototype for authentication. It is found that the proposed scheme provides acceptable results and can be implemented in the real field.

Transformer differential protection scheme based on self‐adaptive biased characteristic curve and considering cross‐country faults

“…In Raichura et al, 20 a multifunctional adaptive differential protection algorithm was presented that filters the events for correct protection relay operation. The Inrush current, external fault with CT saturation, overfluxing, or the combination of these disturbances were studied that mislead differential protection.…”