Study of the Impact of Load Step Changes on Thermal and Voltage Stability Limits of Overhead Transmission Lines

The power handling capability of a transmission line is mainly constrained by thermal and voltage stability limits. After a change in system load (i.e. current), the transmission line reaches a new steady-state conductor temperature after a certain period of time. This paper investigates the impact of a step change in system load on the line thermal and voltage stability limits. It also proposes a methodology to determine the critical time needed to reach the line power transfer limits. For higher accuracy, the change in line current and therefore in conductor temperature, as well as the effect that a variation in conductor temperature has on line current, are taken into account. Noticeable differences were found on the transmission line's power transfer limiting factor under different levels of step change in the system load. Moreover, the impact line length has on the power transfer limiting factors with respect to a load change is also studied.