ABB RELION REX640 Technical Manual page 846

Section 4
Protection functions
840
The protection relay does not accept a value between -0.002...+0.002
for the Start value df/dt setting.
Operate logic
This module is used for combining different protection criteria based on the frequency
and the frequency gradient measurement to achieve a more sophisticated behavior of
the function. The criteria are selected with the Operation mode setting.
Table 805: Operation modes for operation logic
Operation mode
Freq<
Freq>
df/dt
Table continues on next page
Description
The function operates independently as the
underfrequency ("Freq<") protection function.
When the measured frequency is below the set
value of the Start value Freq< setting, the module
activates the START and STR_UFRQ outputs. The
time characteristic is according to DT. When the
operation timer has reached the value set by the
Operate Tm Freq setting, the OPERATE and
OPR_UFRQ outputs are activated. If the frequency
restores before the module operates, the reset
timer is activated. If the timer reaches the value set
Reset delay Tm Freq setting, the operate
by the
timer resets and the START and STR_UFRQ
outputs are deactivated.
The function operates independently as the
overfrequency ("Freq>") protection function.
When the measured frequency exceeds the set
Start value Freq> setting, the module
value of the
activates the START and STR_OFRQ outputs. The
time characteristic is according to DT. When the
operation timer has reached the value set by the
Operate Tm Freq setting, the OPERATE and
OPR_OFRQ outputs are activated. If the frequency
restores before the module operates, the reset
timer is activated. If the timer reaches the value set
Reset delay Tm Freq setting, the operate
by the
timer resets and the START and STR_OFRQ
outputs are deactivated.
The function operates independently as the
frequency gradient ("df/dt"), rate-of-change,
protection function. When the frequency gradient
exceeds the set value of the
setting, the module activates the START and
STR_FRG outputs. The time characteristic is
according to DT. When the operation timer has
reached the value set by the
setting, the OPERATE and OPR_FRG outputs are
activated. If the frequency gradient restores before
the module operates, the reset timer is activated. If
the timer reaches the value set by the
Tm df/dt setting, the operate timer resets and the
START and STR_FRG outputs are deactivated.
1MRS759142 C
Start value df/dt
Operate Tm df/dt
Reset delay
REX640
Technical Manual