With reference to Fig. 1, ZPR-1A and ZPR-1B are the two
redundant protection systems for Zone 1, and ZPR-2A and
ZPR-2B are the two redundant systems for Zone 2. These
systems typically use CTs that overlap at the common breaker
to avoid any blind spots. They trip the common breaker,
circuit breaker, and other breakers defining their respective
zones of protection (CB-1 and CB-2). These breakers can be
local or remote if the protected zones are transmission lines.