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Rethinking Grid Codes from Protection Perspective: A Case Study on Negative Sequence Directional Relay

Rapid integration of distributed generations (DGs) in the traditional grid presents new protection system challenges. These DG units are usually connected to the power network through power electronic interfaces. According to the grid code, the DG units are expected to support the grid during fault conditions. Therefore, these DG units have provisions of ancillary services like voltage ride-through (VRT) and frequency regulations. To fulfill the grid code requirements, the inverter manufacturers follow different control strategies to capture the required dynamics. Consequently, the voltage and current signatures are highly unpredictable and very much are dependent on the type of control strategy adopted. In this paper, in the first few sections, different types of control strategies for DG units are discussed under both balanced and unbalanced fault scenarios. In the later sections, detailed performance analysis of negative sequence directional relay is done in presence of these controllers and their fault behavior is studied.