This paper investigates the performance of steady-state fault calculation (SSFC) methods in power systems with a high penetration of non-synchronous generation (NSG), i.e. generation connected to the grid over fully rated converter (FRC) technologies. The chosen SSFC methods include: i) equivalent voltage source, and ii) complete (superposition). In particular, the performance of the up-to-date IEC60909 standard, which belongs to the former SSFC method, and the complete method are studied here using modified single machine-infinite bus test system including NSG utilizing FRC in DIgSILENT PowerFactory. The estimated fault currents from these methods are compared with those calculated using dynamic simulations in response to different voltage dip levels resulting from faults at different locations. This allowed us to identify issues and challenges of the existing SSFC methods planned to be applied for future networks with a high penetration of NSG utilizing FRC. Our findings are confirmed using the IEEE 9-bus test system.