This thesis discusses the performance of different line voltage stability indices previously studied in literature including Lmn Index, Fast Voltage Stability Index (FVSI), Voltage Collapse Point Indicators (VCPI), and LQP Index, as well as the traditional Jacobian index based on the minimum eigenvalue of the Jacobian matrix. The indices were tested in a small 5-bus system and in a larger 39-bus system. The simulation tool used was RTDS® and the indices where computed using the control blocks components in order to monitor the values in real time. This method was chosen to have the indices values available for future control algorithm development. All the indices were found consistent with their theoretical background and the performance comparison was based on three characteristics: their accuracy, robustness to uncertainty and usable for control purposes. From the results and based on these comparison characteristics, VCPI (p) was found to have the best performance from the indices studied.