ABB RELION 620 Series Technical Manual page 328

Section 4
Protection functions
322
Operation mode
Freq< + df/dt
Table continues on next page
Description
A consecutive operation is enabled between the
protection methods. When the measured frequency
Pickup value Freq<
is below the set value of the
setting, the frequency gradient protection is enabled.
After the frequency has dropped below the set value,
the frequency gradient is compared to the set value
Pickup value df/dt setting. When the frequency
of the
gradient exceeds the set value, the module activates
the PICKUP and PICKUP_FRG outputs. The time
characteristic is according to DT. When the operation
timer has reached the value set by the
setting, the TRIP and TRIP_FRG outputs are
activated. If the frequency gradient restores before
the module trips, the reset timer is activated. If the
timer reaches the value set by the
dt setting, the trip timer resets and the PICKUP and
PICKUP_FRG outputs are deactivated. The
TRIP_UFRQ output is not active when this operation
mode is used.
1MAC504801-IB E
Trip Tm df/dt
Reset delay Tm df/
620 series ANSI
Technical Manual