Underfrequency Element (81U) - GE F650 Instruction Manual

5 SETTINGS
Setpoint >Control Elements > Underfrequency
The steady-state frequency of a power system is a certain indicator of the existing balance between the generated power
and the load. Whenever this balance is disrupted through the loss of an important generating unit, the effect will be a
reduction in frequency. A reliable method to quickly restore the balance between load and generation is to automatically
disconnect the selected loads, based on the actual system frequency. This technique called "load-shedding" maintains
system integrity and minimizes widespread outages.
The 81U element is an underfrequency control element. The pickup setting can be selected from 20.00 to 65.00 Hz. The
element reset time delayed is selectable between 0.00 and 900 seconds, and for the element to operate it is necessary that
the voltage value is over the value set for minimum voltage threshold. This way undesired trips are prevented when the
signal for metering the frequency is not available or has a very low value.
Table 5–74: 81U ELEMENT SETTINGS
SETPOINT > CONTROL ELEMENTS > UNDERFREQUENCY
UNDERFREQUENCY 1 > UNDERFREQUENCY 2 > UNDERFREQUENCY 3
SETTING DESCRIPTION
Function permission
Pickup level
Trip time
Reset time
Minimum voltage threshold
Snapshot event generation
The snapshot event setting enables or disables the snapshot event generation for this element.
Frequency elements operate with the system frequency, this frequency is measured in the voltage channel set for the
frequency reference, in the Frequency Reference setting inside Setpoint > System Setup >General Settings.
GEK-106310AB
NAME DEFAULT VALUE
Function DISABLED
Pickup Level 49.50
Trip Delay 0.00
Reset Delay 0.00
Minimum Voltage 30
Snapshot Events ENABLED
F650 Digital Bay Controller
5.5 CONTROL ELEMENTS

5.5.2 UNDERFREQUENCY ELEMENT (81U)

STEP RANGE
N/A [DISABLED – ENABLED]
0.01 Hz [20.00 : 65.00]
0.01 s [0.00 : 900.00]
0.01 s [0.00 : 900.00]
1 V [10 : 300]
N/A [DISABLED – ENABLED]
5
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