For PRC-026-1, we are having consultants say that they can do it without transient studies. I am still digging through PRC-026, but I am wondering if it can be met to the standard but just not set very well. SEL has some relays that use a method they claim doesn't require a transient study but I know we don't have that option at all sites because some are mechanical. Might not be an option with the SEL relays we have.
As I understand that “zero setting” SEL OOSB the relay tracks the trajectory of the swing and differentiates between swing and fault based on the path and rate of change of the impedance. The traditional OOSB with zones and blinders and timers requires studies to determine the settings.
PRC-023 provides a characteristic to separate stable swings from unstable with the goal of avoiding trips on stable swings. I don’t believe it requires blocking on unstable swings. Without the studies you don’t know if the swings can even happen.
