Combined use of definite and inverse time overcurrent elements assists in transmission line ground relay coordination

In some cases the coordination of ground time overcurrent relays in transmission line protection applications can be difficult. The combined use of definite and inverse time overcurrent characteristics sometimes provides significantly improved protection speed and sensitivity. Two cases are discussed where the use of hybrid characteristics has achieved improvements. The application of hybrid characteristics is limited by difficulties in dynamic coordination. The technology to overcome the dynamic problems would appear to be technically feasible.<>