Moving standard deviation assisted two-terminal traveling wave based fault location estimation technique for transmission system incorporated with UPFC

Modern power systems are increasingly complex and vulnerable to disturbances, with transmission line faults being the most frequent and disruptive. Accurate fault location estimation (FLE) is essential to ensure fast system restoration and reliable operation, particularly when flexible AC transmission system (FACTS) devices such as the Unified Power Flow Controller (UPFC) are present. This paper proposes a Moving Standard Deviation (MSD) assisted two-terminal traveling wave (TW) based FLE technique for UPFC-compensated transmission lines. In the proposed approach, terminal voltage signals are transformed into aerial mode signals using Clarke’s transformation, and MSD is applied to identify peak values (PMSDs). These peaks provide estimated times of arrival waves (ETAWs), which are used to compute the fault location. The method is validated on a 500 kV three-machine system with a 100 MVA UPFC under diverse scenarios, including varying fault distances, types, resistances, inception angles, close-in and far-bus faults, UPFC operating modes, sampling frequencies, and noisy environments. Results confirm that the proposed method consistently achieves high accuracy, with percentage errors maintained below 1% even at low sampling rates (60 Hz) and under severe noise (5 dB SNR). The technique is computationally simple, robust against UPFC influences, and offers practical applicability for modern power systems.