Improvement of integrated transmission line transfer index for power system voltage stability

•A new approach for voltage stability is developed to find the weak lines.•The ITLTI index easily and fast with the Energy Management System software on-line.•ITLTI is derived for a radial transmission system and later applied to a large system.•ITILI index has a better solution for on line voltage stability evaluation.

With the increased loading of transmission lines, the voltage stability problem has become a critical issue for most power system planners and operators. Some important studies related to the voltage stability indices used in the electric power systems are first sorted. Then, a new approach for voltage stability is developed to find the weak lines in this paper. The new method is based on the practical line ABCD parameters, the power factor of receiving end, and the power angle between the sending end and the receiving end. This concept of integrated transmission line transfer index (ITLTI) is derived for a radial transmission system and later applied to a large system. However, ITILI index has a more integrated content and should be a better solution for on line voltage stability evaluation. The new ITLTI index and other existing techniques are demonstrated and compared with numerical studies by IEEE 14-bus test system, using gradually increase reactive load.