Development of Type IV WTG short circuit model and integration into commercial short circuit software

Accurately determining the contribution of short-circuit currents (SCC) from different sources is crucial for preventing protection relay mis-coordination, equipment damage, and blackouts. However, standards often provide a simplified view or lack information when it comes to inverter-based resources (IBRs). For instance, the response of conventional grid-following inverters during faults may vary considerably from expected values in standards due to factors such as terminal voltages, sequence component priority, and grid code requirements. Furthermore, recent working groups have proposed the use of look-up tables (LUTs) provided by manufacturers to represent the short-circuit current. From an original equipment manufacturer (OEM) point of view, the use of such look-up tables can be complex and also cause errors in the current estimation. To address this, a method has been proposed to provide more accurate SCC estimates during steady-state conditions using a black-box IBR current calculation component developed in collaboration between a Type IV Wind Turbine Generator (WTG) OEM and a short-circuit and relay coordination software provider. This method utilizes a steady-state phasor-based network solution and involves the use of a dynamic link library (DLL) provided by the OEM to compute and return the expected three-phase IBR injection currents, which are then used to re-compute the terminal voltages in an iterative process. Simulations in EMT domain were performed to validate the results, and the paper discusses the general possibilities and limitations of this methodology.