Speed of line protection - can we break free of phasor limitations?

Today's relays are predominantly based on phasors, and as such, they incur a delay associated with the full-cycle observation window required for accurate phasor estimation. Considerable improvement in speed is possible by using information in the transients of voltages and currents. We review a number of protection techniques, including directional elements, direct tripping underreaching elements, and differential elements that significantly speed up line protection.