ABB Relion 611 Series, Technical Manual

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The function provides basic overfrequency, underfrequency and frequency rate-of-
change protection. Additionally, it is possible to use combined criteria to achieve even
more sophisticated protection schemes for the system.
The function contains a blocking functionality. It is possible to block function outputs,
timer or the function itself, if desired.
4.6.4 Operation principle
The function can be enabled and disabled with the Operation setting. The
corresponding parameter values are "On" and "Off".
The operation of FRPFRQ can be described using a module diagram. All the modules
in the diagram are explained in the next sections.
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 133: 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
Section 4
1MRS757454 D
Protection functions
282 611 series
Technical Manual