frequency in a power system indicates that the generated power is too low to meet the
demands of the load connected to the power grid.
The underfrequency can occur as a result of the overload of generators operating in an
isolated system. It can also occur as a result of a serious fault in the power system due
to the deficit of generation when compared to the load. This can happen due to a fault
in the grid system on the transmission lines that link two parts of the system. As a
result, the system splits into two with one part having the excess load and the other part
the corresponding deficit.
The frequency gradient is applicable in all the situations where the change of the
fundamental power system voltage frequency should be detected reliably. The
frequency gradient can be used for both increasing and decreasing the frequencies.
This function provides an output signal suitable for load shedding, generator
shedding, generator boosting, set point change in sub-transmission DC systems and
gas turbine startup. The frequency gradient is often used in combination with a low
frequency signal, especially in smaller power systems where the loss of a large
generator requires quick remedial actions to secure the power system integrity. In such
situations, the load shedding actions are required at a rather high frequency level.
However, in combination with a large negative frequency gradient, the
underfrequency protection can be used at a high setting.
4.5.1.6 Signals
Table 459: FRPFRQ Input signals
Name
Type Default Description
F SIGNAL 0 Measured frequency
dF/dt SIGNAL 0 Rate of change of frequency
BLOCK BOOLEAN 0=False Block signal for activating the blocking mode
Table 460: FRPFRQ Output signals
Name
Type Description
OPERATE BOOLEAN Operate
OPR_OFRQ BOOLEAN Operate signal for overfrequency
OPR_UFRQ BOOLEAN Operate signal for underfrequency
OPR_FRG BOOLEAN Operate signal for frequency gradient
START BOOLEAN Start
ST_OFRQ BOOLEAN Start signal for overfrequency
ST_UFRQ BOOLEAN Start signal for underfrequency
ST_FRG BOOLEAN Start signal for frequency gradient
Section 4 1MRS758755 A
Protection functions
440 REC615 and RER615
Technical Manual
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