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Summary The existence of midpoint series flexible alternating current transmission system (FACTS) devices leads to degrade the performance of mho relay, leading in erroneous estimation of fault location, ie, overreach or underreach for wide variation in network parameters. This research article proposes a novel mho relay algorithm to improve the performance of distance relay in presence of FACTS device using phasor measurement unit (PMU). First, the complete model of transmission system employing static synchronous series compensator (SSSC) and its control strategy is described analytically, where the error introduced in measurement of impedance due to SSSC on the performance of distance relay. Second, a novel mho relay procedure is developed based on PMU to protect the first zone of double‐circuit transmission line for single line‐to‐ground (SLG) fault. The proposed work is analysed and simulated with 48‐pulse SSSC carried out with Bergeron model of transmission line using power system computer‐aided design (PSCAD) computer simulation. Finally, the simulation results represent that the suggested adaptive scheme is truthful, reliable, and secure with change in compensation level of SSSC.

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This research article proposes a powerful fractional-order PI controller to mitigate the subsynchronous oscillations in turbine-generator shaft due to subsynchronous resonance (SSR) with flexible AC transmission system devices such as static synchronous compensator (STATCOM) and unified power flow controller (UPFC). The diminution of SSR is achieved by the raising of network damping at those frequencies which are proximate to the torsional mode frequency of the turbine-generator shaft. The increase of network damping is obtained with the injection of subsynchronous frequency component of current and both current and voltage into the line. The subsynchronous component of current and voltage are derived from the measured signal of the system and further the same amount of shunt current is injected with STATCOM and simultaneous injection of current and voltage with UPFC into the transmission line to make the subsynchronous current to zero which is the prime source of turbine shaft oscillations. The insertion and proper tuning of Fractional-order PI controller in the control scheme, the subsynchronous oscillations are reduced to 92 % in case of STATCOM and 98 % in case of UPFC as compared to without controller and 14 % as compared with the results of conventional PI controller. The IEEE first benchmark model has adopted for analyze the effectiveness and speed of the proposed control scheme using MATLAB-Simulink and the corresponding results illustrates the precision and robustness of the proposed controller.