ABB RELION REX640, Техническое руководство, Страница: 922 / 1960

Freq>/< detection
The frequency detection module includes an overfrequency or underfrequency
detection based on the
Operation mode setting.
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 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 881: 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.
Table continues on the next page
Protection functions 1MRS759142 F
922 REX640
Technical Manual