Inrush Detection Through Current Wave Shape Analysis – Advanced Transformer Protection For Power Grids With Ibrs

The increasing penetration of IBRs in the modern electrical grid helps us in achieving global decarbonization goals and makes our grid more flexible by connecting more renewable energy sources. The IBRs, however, also create new challenges for protection applications due to their unique characteristics and operational behavior. In addition to lower fault currents and impact on the frequency stability, IBRs can affect the waveform and harmonic content in the fault currents. A distorted waveform produced by IBRs during a fault event may have significant impact on the inrush stabilizing algorithm in transformer differential protection relays. These relays typically evaluate the second harmonic component to differentiate between fault and inrush currents that occur during transformer energization and overexcitation. This paper discusses the Current Waveform Analysis (CWA) algorithm introduced for transformer differential applications. CWA is able to detect the internal transformer faults after the first cycle and block conventional second harmonic inrush stabilization. To evaluate the algorithm, a modular multilevel converter with LVRT capability was modelled in MATLAB/Simulink with adequate control strategy. Test cases included external faults, internal faults at both the grid and converter sides, and turn-to-turn faults. Authors explain the CWA algorithm functionality, its logic and response to different fault events. The paper also presents several waveforms to illustrate the CWA algorithm's effectiveness.