Based on an analysis of mal-operation of a relay protection in a 500 kV power system， this paper points out the problems in the coordinative setting of phase-separated pilot protection with ETL500 series power line carrier terminal. Misunderstanding of the coordinative relation between them is cleared up. According to the order priority principle of the ETL500 series power line carrier terminal， the correct connection scheme between the relay and ETL500 series power line carrier terminal is presented.