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This study presents a sub-cycle power frequency-based fault direction discrimination and fault classification algorithm for the series-compensated transmission lines. Also, it provides an accurate estimation for the fault occurrence instant which is helpful in synchronised waveforms-based pilot protective schemes. The proposed algorithm is based on capturing the initial change in the voltage and current waveforms caused by occurrence of a fault. The high-frequency components of the fault signals are first filtered out, and then the signals are sampled at a relatively low sampling rate. Unlike the conventional relative-phase-angle-based directional relays, the proposed algorithm is not affected by the current and voltage inversion phenomena due to the presence of series capacitor in the fault loop. Extensive simulation studies are performed to evaluate the proposed algorithm performance. The obtained results show that the proposed algorithm provides a simple and a very fast and reliable protection technique for power transmission lines. This algorithm also covers non-compensated transmission lines and is able to well discriminate the fault direction even if the post-fault voltage amplitude becomes too small. It is also tested using some real data recorded from a high-voltage transmission system.