ABB RER615 - Page 450

In the “Freq>” mode, the measured frequency is compared to the set Start value
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 Start value
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 Start value df/dt
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 Start value df/dt value, the module reports the exceeding of the
value to the operate logic module.
The protection relay does not accept the set value "0.00" 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 476: Operation modes for operation logic
Operation mode Description
Freq< 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
by the Reset delay Tm Freq setting, the operate timer resets
and the START and STR_UFRQ outputs are deactivated.
Freq> The function operates independently as the overfrequency
("Freq>") protection function. When the measured frequency
exceeds the set value of the Start value Freq> setting, the
module 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
by the Reset delay Tm Freq setting, the operate timer resets
and the START and STR_OFRQ outputs are deactivated.
Table continues on the next page
Protection functions 1MRS758755 C
450 REC615 & RER615
Technical Manual