GE Multilin G650, Manual

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5-78 G650 Generator Protection & Control System GEK-113285A
5.5 CONTROL ELEMENTS 5 SETTINGS
5
5.5.2 UNDERFREQUENCY ELEMENT (81U)
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 5–78: 81U ELEMENT SETTINGS
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.
5.5.3 OVERFREQUENCY ELEMENT (81O)
Setpoint >Control Elements > Overfrequency
81O is an overfrequency protection element. The pickup setting can be selected from 20.00 to 65.00 Hz, with a time delay
selectable between 0 and 900 seconds. The element-reset delay is from 0.00 to 900.00 seconds.
Table 5–79: 81O ELEMENT SETTINGS
The snapshot event setting enables or disables the snapshot event generation for this element.
SETPOINT > CONTROL ELEMENTS > UNDERFREQUENCY
UNDERFREQUENCY 1 > UNDERFREQUENCY 2 > UNDERFREQUENCY 3
SETTING DESCRIPTION NAME DEFAULT VALUE STEP RANGE
Function permission Function DISABLED N/A [DISABLED – ENABLED]
Pickup level Pickup Level 49.50 0.01 Hz [20.00 : 65.00]
Trip time Trip Delay 0.00 0.01 s [0.00 : 900.00]
Reset time Reset Delay 0.00 0.01 s [0.00 : 900.00]
Minimum voltage threshold Minimum Voltage 30 1 V [30 : 500]
Snapshot event generation Snapshot Events ENABLED N/A [DISABLED – ENABLED]
SETPOINT > CONTROL ELEMENTS > OVERFREQUENCY
OVERFREQUENCY 1 > OVERFREQUENCY 2 > OVERFREQUENCY 3
SETTING DESCRIPTION NAME DEFAULT VALUE STEP RANGE
Function permission Function DISABLED N/A [DISABLED – ENABLED]
Pickup level Pickup Level 50.50 0.01 Hz [20.00 : 65.00]
Trip time Trip Delay 0.00 0.01 s [0.00 : 900.00]
Reset time Reset Delay 0.00 0.01 s [0.00 : 900.00]
Minimum voltage threshold Minimum Voltage 30 1 V [30 : 500]
Snapshot event generation Snapshot Events ENABLED N/A [DISABLED – ENABLED]