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
GUID-76692C3F-8B09-4C69-B598-0288CB946300 V1 EN
Figure 261: 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 IED 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.
1YHT530004D05 D Section 4
Protection functions
615 series 495
Technical Manual
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