ABB RELION REX640 Technical Manual page 922

Protection functions
Freq>/< detection
The frequency detection module includes an overfrequency or underfrequency
detection based on the
In the "Freq>" mode, the measured frequency is compared to the set
Freq> . If the measured value exceeds the set value of the Start value Freq> setting,
the module reports the exceeding of the value to the operate logic module.
In the "Freq<" mode, the measured frequency is compared to the set
Freq< . If the measured value is lower than the set value of the Start value Freq<
setting, the module reports the value to the operate logic module.
df/dt detection
The frequency gradient detection module includes a detection for a positive or
negative rate-of-change (gradient) of frequency based on the set
value. The negative rate-of-change protection is selected when the set value is
negative. The positive rate-of-change protection is selected when the set value
is positive. When the frequency gradient protection is selected and the gradient
exceeds the set
value to the operate logic module.
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
mode setting.
Table 881: Operation modes for operation logic
Operation mode
Freq<
Freq>
Table continues on the next page
922
Operation mode setting.
Start value df/dt value, the module reports the exceeding of the
The protection relay does not accept a value between -0.002...+0.002 for
Start value df/dt setting.
the
Description
The function operates independently as the underfrequency
("Freq<") protection function. When the measured frequency
is below the set value of the
module activates the
time characteristic is according to DT. When the operation
timer has reached the value set by the
setting, the
If the frequency restores before the module operates, the
reset timer is activated. If the timer reaches the value set
by the
and the
The function operates independently as the overfrequency
("Freq>") protection function. When the measured frequency
exceeds the set value of the
module activates the
time characteristic is according to DT. When the operation
timer has reached the value set by the
setting, the
Start value Freq< setting, the
and
START
and
OPERATE OPR_UFRQ
Reset delay Tm Freq setting, the operate timer resets
and
START STR_UFRQ
Start value Freq> setting, the
and
START
and
OPERATE OPR_OFRQ
1MRS759142 F
Start value
Start value
Start value df/dt
Operation
outputs. The
STR_UFRQ
Operate Tm Freq
outputs are activated.
outputs are deactivated.
outputs. The
STR_OFRQ
Operate Tm Freq
outputs are activated.
REX640
Technical Manual