What is standby earth fault protection And how it is to be coordinated with transformer primary overcurrent relayin DYn11 tf?

DYn 11 is a Delta HV winding and star lv with theneutral brought out. At primary substations it is usual to have a neutral ct. The ct is a last line of defence operating a standby earth fault relay which opens the lv circuit breaker (11kV). It may have a stage 2 setting in case the lv breaker fails to open which opens the hV side. If there is no local hV breaker it may operate a fault throw switch. This device shorts one phase directly to earth forcing the protection at the remote end to operate.