Differential Protection for Lines Connected to Inverter-Based Resources: Problems and Solution

Inverter based renewable energy resources with controlled current output has fault characteristics different from traditional synchronous generators. In this paper, we analyze how the peculiar fault current characteristics of these sources impact percentage and alpha plane line differential protection. Inherent phase selection capability, dependability, and speed of operation of alpha plane differential is identified to be impacted mainly due to increased system non-homogeneity. Dependability of percentage differential protection is also marginally impacted particularly when the grid end is also weak. Further, a time domain energy-based current differential protection is proposed, which has advantages when compared to existing line differential protection solutions. Extensive testing, and validation using field records, demonstrates improved reliability, sensitivity, and speed of the proposed method for synchronous generator as well as IBR-connected lines.