F
BLOCK
Operate
logic
Freq>/<
detection
df/dt
detection
Blocking
logic
START
ST_FRG
ST_UFRQ
ST_OFRQ
OPERATE
OPR_FRG
OPR_UFRQ
OPR_OFRQ
dF/dt
Figure 367: Functional module diagram
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 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.
Protection functions
1MRS757644 H
702
620 series
Technical Manual
