Power system phase rotation and polarized protective relays

Many common protective relays used in the protection of power equipment are sensitive to phase sequence rotation of the utility supply. The authors describe a method for analyzing the relay response to the respective phase rotation and to other possible variables. They treat voltage and current phasors, maximum- and minimum-torque lines of polarized relays, and the possible effect of system power factor. It is demonstrated that phase rotation usually does not affect zero-sequence polarized relays. Attention is given to the following relays: directional power relay, IEEE protective device no. 32; directional VAR relay, IEEE protective device no. 55; directional current phase relay, IEEE protective device no. 67; and directional current ground relay, IEEE protective Device 67N