Isolated ac grids are feasible solutions to energize remote communities usually based on renewables and batteries, interfaced by power electronics converters that require high reliability. The key element of such a system is the grid-forming converter witch provides voltage magnitude and frequency. This paper compares the current stresses of grid-forming converters under an isolated grid mission profile, considering three different grid configurations in terms of line voltage displacement angles: 90° (αβn-system); 120° (abn-system) and 180° (xyn-system). Besides, analytical expressions for the current stress through the semiconductors and the dc-link capacitor are proposed for each system. The lifetime analysis of the grid-forming converter indicates that the xyn-system has the lowest wear-out. Furthermore, this work highlights the influence of high-frequency components on the rms dc-link capacitor current. The xyn-system demonstrates a lower probability of capacitor failure compared to the other system, even presenting higher low-frequency. components. Finally, a sensitivity analysis shows that the grid-forming converter in xyn-system can increase its output power in 12% or reduce its heatsink volume in 25% to achieve the same wear-out B10 lifetime as the abn-system (i.e., benchmark) under nominal conditions. An experiment is conducted using a full-bridge converter to measure the power losses in the semiconductors and the case temperature of the IGBTs. The xyn converter shows 44% lower power losses, and the abn converter shows 18% lower power losses, both compared with the αβn converter.