Limit Curves by Power System´s Transient Stability for the Inverse-Time Overcurrent Relays

This paper presents the limit curves by transient stability for the inverse-time overcurrent relays. Two cases were analyzed: (1) faults in radial lines and (2) faults in lines which are fed from both ends. A novel time-current limit curve by stability was obtained for the radial case; this curve could be compared with the inverse-time overcurrent curve of the relay. Another limit curve by stability was obtained for lines which are fed from both ends; this curve represents the combination of the maximum time-dial settings at both line ends. The nonsimultaneous clearing for lines which are fed from both ends, the dynamic evolution of the fault current, and different prefault conditions were considered in the examples.