4.3.1.3
Functionality
The frequency protection function 81 is used to protect network components against
abnormal frequency conditions.
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.
4.3.1.4
Operation principle
The function can be enabled and disabled with the
Operation
setting. The corresponding
parameter values are “Enable” and “Disable”.
The operation of 81 can be described using a module diagram. All the modules in the
diagram are explained in the next sections.
GUID-9BF0484B-1BC9-4C44-B64A-A2D6AB246916-ANSI V1 EN
Figure 126:
Functional module diagram
Over/under frequency 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
Pickup value Freq>
.
If the measured value exceeds the set value of the
Pickup value Freq>
setting, the module
reports the exceeding of the value to the trip logic module.
Section 4
1MRS240050-IB C
Protection functions
264
REF615R
Technical Manual
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