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Negative-sequence pilot protection (NSPP) is one of the most widely used protective principles for high-voltage/extra high-voltage transmission lines due to its excellent properties. Properties, such as immunity to system oscillation and the fact that it is not influenced by shunt capacitance, make it especially valuable for the protection of long-distances ultra-high voltage lines, which transfer large amounts of energy. However, negative-sequence pilot protection (NSPP) is not suitable for applications when a system operates with one phase open, which inevitably limits its overall application. To solve this problem and to achieve the selectivity and sensitivity for the NSPP algorithm, a novel algorithm for NSPP is proposed in this paper, which takes the load-phase voltage into the calculation of the negative-sequence voltage with a fault in the open-phase condition, and compensates the negative-sequence current in the open-phase operations for phase-ground faults. Simulation studies show that the proposed algorithm is able to produce excellent performance.