Protection Schemes For Inverter-Dominated Transmission Systems: First Experiences From Hardware Testbed of Hawai’I Island
The global pursuit of decarbonization requires a significant increase in the integration of distributed energy resources (DER) like wind turbines and photovoltaic power plants in the near future. This transition is reshaping the grid, transforming it into an inverter-dominant power system. However, due to the inherent characteristics of inverter-based resources (IBRs), they offer limited fault current and can distort voltage waveforms during fault events. These challenges, combined with the increased dynamics of power flow, demand a new approach to power system protection, as conventional methods may no longer be effective. We develop and validate reliable protection schemes for inverter-dominated power systems within the U.S. Department of Energy funded project Protection-Inverter Co-Design for 100% Renewable Power Systems (PICO). The project includes an application for Hawaiian Electric, involving five transmission lines in a ring configuration. Traditional protection methods currently in use include differential protection and Permissive Over-Reaching Transfer Trip (POTT) protection at the transmission level. The authors investigate whether these protection schemes remain viable under conditions of 100% IBR penetration. The protection apparatus supports complex logic configurations, incorporating a mix of line differential, POTT, distance, and overcurrent protection algorithms. The evaluation is conducted in a hardware testbed at EPRI, where real inverters inject three-phase currents through transformers into a secondary system configured with resistance and inductance parameters of the actual transmission lines of Hawai’i Island. The testing includes balanced and unbalanced faults to assess fault clearing by commercial protection relays. The paper presents the configuration of the protection system, analysis of test results, waveforms, and lessons learned from the initial series of tests.