A reliable digital directional relay based on compensated voltage comparison for EHV transmission lines

A digital directional relay based on compensated voltage comparison has been implemented with a 16 bit microcontroller. The authors describe the digital implementation of the phase-angle comparators which make use of fundamental frequency components of the compensated voltages. A simple hybrid hardware structure and intelligent software routines have been developed to ensure high reliability. Using an adaptive sampling interval, the relay can maintain its overall performance even for faults that occur during power frequency disturbances. Dynamic tests on a 500 kV, 290 km transmission line analog model confirmed that the relay can provide correct operation for various faults during different operating conditions of the protected line