Signals - ABB RELION REX640 Technical Manual

Section 4
Protection functions
4.6.1.7
844
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.

Signals

Table 807: FRPFRQ Input signals
Name Type
U3P SIGNAL
BLOCK BOOLEAN
Table 808: FRPFRQ Output signals
Name Type
OPERATE BOOLEAN
OPR_OFRQ BOOLEAN
OPR_UFRQ BOOLEAN
OPR_FRG BOOLEAN
START BOOLEAN
ST_OFRQ BOOLEAN
ST_UFRQ BOOLEAN
ST_FRG BOOLEAN
Default Description
- Three-phase voltages
0=False Block signal for activating the blocking mode
Description
Operate
Operate signal for overfrequency
Operate signal for underfrequency
Operate signal for frequency gradient
Start
Start signal for overfrequency
Start signal for underfrequency
Start signal for frequency gradient
1MRS759142 C
REX640
Technical Manual