A non-unit adaptive pilot protection for HV transmission line interlinked with off-shore grid scale wind energy and controllable series compensator

• The relaying technique is designed for HV transmission lines integrated with all types of Series controllers and wind energy resources. • Introduces a novel and robust non-unit protection scheme utilizing the Disturbance Gradient Index (DGI) derived from negative sequence current signals for fault identification. • Enhanced fault classification using Rule-based algorithm based on Moving Variance Index (MVI) of superimposed symmetrical current components and phase angles from local and remote bus ends to correctly classify fault types. • Accurate fault location via advanced signal processing based on Park’s transformation-assisted Dual Tree Discrete Wavelet Transform (DTDWT). • Comprehensive Validation and Comparative Analysis. Conventional non-unit distance relays often malfunction when protecting transmission lines integrated with large-scale wind farms and series Flexible AC Transmission System (FACTS) controllers such as the Thyristor-Controlled Series Capacitor (TCSC). These mal-operations, commonly over-reaching and under-reaching, are primarily caused by the variable fault current behavior, low zero-sequence impedance of wind farms, and the nonlinear dynamics of Doubly Fed Induction Generator (DFIG) systems and series compensation modes. To overcome these limitations, this paper proposes a simple and robust protection scheme that performs fault detection, classification, and location estimation using synchronized measurements from both line ends. Fault detection is achieved using a Disturbance Gradient Index (DGI) derived from negative-sequence current signals. A rule-based classifier utilizes the Moving Variance Index (MVI) and phase angle features of the superimposed sequence components for fault type identification. Finally, a double-ended traveling wave-based fault location algorithm is implemented using Park’s (DQ0) transformation and Dual Tree Discrete Wavelet Transform (DTDWT). The scheme was validated using a 500-kV, 300-km two-bus transmission line model in MATLAB/Simulink under a wide range of fault types and system conditions. The proposed method achieved 100% fault detection accuracy, 98% classification accuracy, and fault location error below 1.1%, with a total decision time under 8.1 ms. Performance remained stable under high-resistance faults (up to 250 Ω) and noise levels as low as 10 dB. Comparative analysis with previous methods confirms the proposed scheme’s effectiveness, speed, and noise robustness for real-time protection of modern transmission systems.