Operational Experience with Adaptive Protection and Auto-Reclosure in Indian Power Networks with High Renewable Penetration

Voltage Ride Through (LVRT) compliance create major challenges for conventional protection. Distance protection, carrier-aided tripping, auto‑reclosure, and fault‑location schemes designed for strong, synchronous‑machine‑dominated grids increasingly show misoperations under weak‑infeed conditions. This paper presents field experience from extra high voltage (EHV) transmission lines integrating renewable generation, highlighting frequent issues such as non‑operation or delayed operation of distance relays, failed carrier-assisted tripping, unsuccessful phase‑selective auto‑reclosure, LVRT miscoordination, and poor fault‑location accuracy. Disturbance records show that during single‑phase faults near the renewable terminals, inverter sources supply minimal fault current, causing impedance trajectories to miss relay zones. As a result, clearance often depends on remote‑end backup protection, reducing reliability and increasing Mean Time to Restore (MTTR). To mitigate these issues, a coordinated adaptive protection philosophy is proposed. First, the implementation of Weak Infeed Echo and Trip logic enhances carrier‑aided distance protection, enabling dependable tripping at the renewable end even under severe voltage depression and low fault current. Field validation confirms reliable phase‑selective tripping and successful auto‑reclosure from both terminals.

Given the inherent limitations of distance protection with inverter‑dominated sources, the paper further demonstrates the enhanced performance of sequence‑component‑based line differential protection. By exploiting the characteristic positive‑sequence–dominant current injection of inverters and forming weighted differential quantities, the scheme offers high sensitivity and security across varying plant capacities, high fault resistance, and weak grids. The importance of robust, time‑synchronized communication—via fibre, SDH (IEEE C37.94), or Ethernet—is emphasized as essential for dependable operation. A setting‑free, double‑ended fault‑location technique using synchronized terminal voltages and currents is also presented. Unlike traditional single‑ended methods, this approach remains accurate under inverter‑dominated fault behavior and does not rely on predefined line parameters. Field cases show fault‑location accuracy within one to two tower spans.

Comprehensive simulation studies, relay tests, and real disturbance records confirm that the proposed methods deliver faster fault clearance, dependable auto‑reclosure, improved fault‑location accuracy, and greater grid resilience. The paper concludes that adaptive, communication‑assisted protection schemes in modern numerical relays are critical for maintaining protection reliability in EHV networks with high penetration of inverter‑based renewable energy.