The attached example shows a single generator infinite bus bar system that goes through three swings before it gets unstable.

Power Swing Blocking:

The relay is measuring the time of the impedance trajectory between entering the MHO-circle and passing the blinders. If the time is longer than a specified threshold value, it's identified to be a swing and not a fault. (Plot: "Impedance Trajectory"). If a power swing is detected, the output is blocked and the relay doesn't trip even if the impedance is inside the tripping zone (Plots: "PowerSwingBlocking Output").

Out of Step Tripping:

An out of step condition is detected, if the impedance trajectory enters from the right side and leaves the MHO circle on the left side (hence, if it doesn't swing back) (see plot "Impedance Trajectory" and "PowerSwingBlocking Output" "Tripping yout".

In the attached case the relay trips.