A New Unit Protection Scheme Applied to Transmission Lines

Abstract

This paper proposes a novel unit protection scheme which combines well-known distance and differential protection principles, but in an innovative way. The algorithm calculates coefficients that lead to fault detection whenever they move towards outside a proposed restraint characteristic, which is defined as a simple circumference with center at origin. Moreover, the algorithm uses a faulted phase selection combined with an external fault detection logic and a novel harmonic restraint strategy, providing dependability for internal faults and security for external ones, even with CT saturation. To assess the proposed scheme performance, ATPDraw software was used to simulate various fault scenarios on transmission lines. Results reveals that it is more robust to fault resistance, fault distance, loading conditions, and source strength in comparison with others previously reported algorithms.

Keywords

• Unit protection
• transmission line
• for fault resistance robustness