The future power systems are expected to operate closer to its security and stability limits mainly due to growth in variable renewable generation and the increase in load demand. In particular, voltage stability has been a major subject of discussion and concern in electric power system operation and planning worldwide. This evolution of the power system demands enhancement in ability from large synchronous generators to respond to change in demand and supply. In this contribution, a new visualization tool for online monitoring of a synchronous generator's capability is presented. In addition, the proposed tool is illustrated with a long-term voltage stability simulation carried out on a 10-bus benchmark power system. It is shown that the load models, load tap changing transformer and generator over-excitation limiter have a significant influence on voltage stability and collapse phenomena.