CHAPTER 5: SETTINGS CONTROL ELEMENTS
L90 LINE CURRENT DIFFERENTIAL SYSTEM – INSTRUCTION MANUAL 5-341
5
5.8.7 Overfrequency (ANSI 81O)
SETTINGS CONTROL ELEMENTS OVERFREQUENCY OVERFREQUENCY 1(4)
There are four overfrequency elements, numbered 1 through 4.
A frequency calculation for a given source is made on the input of a voltage or current channel, depending on which is
available. The channels are searched for the signal input in the following order: voltage channel A, auxiliary voltage
channel, current channel A, and ground current channel. The first available signal is used for frequency calculation.
The steady-state frequency of a power system is an indicator of the existing balance between the generated power and
the load. Whenever this balance is disrupted through the disconnection of significant load or the isolation of a part of the
system that has a surplus of generation, the effect is an increase in frequency. If the control systems of the generators do
not respond fast enough, to quickly ramp the turbine speed back to normal, the overspeed can lead to the turbine trip. The
overfrequency element can be used to control the turbine frequency ramp down at a generating location. This element
can also be used for feeder reclosing as part of the "after load shedding restoration."
The
OVERFREQ 1 SOURCE setting selects the source for the signal to be measured.
The
OVERFREQ 1 PICKUP setting selects the level at which the overfrequency element is to pickup.
Figure 5-194: Overfrequency logic
OVERFREQUENCY 1
OVERFREQ 1 FUNCTION:
Disabled
Range: Disabled, Enabled
OVERFREQ 1 BLOCK:
Off
Range: FlexLogic operand
OVERFREQ 1 SOURCE:
SRC 1
Range: SRC 1, SRC 2, SRC 3, SRC 4
OVERFREQ 1 PICKUP:
60.50 Hz
Range: 20.00 to 65.00 Hz in steps of 0.01
OVERFREQ 1 PICKUP
DELAY: 0.500 s
Range: 0.000 to 65.535 s in steps of 0.001
OVERFREQ 1 RESET
DELAY : 0.500 s
Range: 0.000 to 65.535 s in steps of 0.001
OVERFREQ 1 TARGET:
Self-reset
Range: Self-reset, Latched, Disabled
OVERFREQ 1 EVENTS:
Disabled
Range: Disabled, Enabled
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