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750/760 Feeder Management Relay GE Power Management
12.8 FREQUENCY 12 S5 PROTECTION
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12.8 FREQUENCY 12.8.1 DESCRIPTION
The 750/760 can be used as the primary detecting relay in automatic load shedding schemes based on under-
frequency. The need for such a relay arises if during a system disturbance, an area becomes electrically iso-
lated from the main system and suffers a generation deficiency due to the loss of either transmission or
generation facilities. If reserve generation is not available in the area, conditions of low system frequency will
occur which may lead to a complete collapse. The 750/760 provides two underfrequency and one rate-of-
change of frequency protection elements which can automatically disconnect sufficient load to restore an
acceptable balance between load and generation.
12.8.2 UNDERFREQUENCY
There are two identical underfrequency protection elements, ANSI devices 81U-1 and 81U-2. The setpoints for
the Underfrequency 1 element are as follows. Underfrequency 2 setpoints are identical.
â– UNDERFREQUENCY 1
â– [ENTER] for more
The Underfrequency 1 setpoints path is:
\ SETPOINTS \ S5 PROTECTION \ FREQUENCY \ UNDERFREQUENCY 1
UNDERFREQUENCY 1
FUNCTION: Disabled
Range: Disabled, Trip, Alarm, Latched Alarm, Control
Select the required function.
UNDERFREQUENCY 1
RELAYS (3-7): -----
Range: Any Combination of the 3-7 AUXILIARY Relays
Select the output relays required.
UNDERFREQUENCY 1
PICKUP: 59.00 Hz
Range: 20.00 to 65.00 in steps of 0.01 Hz
Enter the level at which the underfrequency element is to pickup. For example,
if the system frequency is 60 Hz, and load shedding is required at 59.50 Hz,
enter
59.5
for this setpoint.
UNDERFREQUENCY 1
DELAY: 2.00 s
Range: 0.00 to 600.00 in steps of 0.01 s
Select the delay required.
MINIMUM OPERATING
VOLTAGE: 0.70 x VT
Range: 0.00 to 1.25 in steps of 0.01 x VT
Enter the minimum voltage required to allow the underfrequency element to
operate. Used to prevent incorrect operation before energization of the source
to the relay location, and during voltage dips.
MINIMUM OPERATING
CURRENT: 0.20 x CT
Range: 0.00 to 20.00 in steps of 0.01 x CT
Enter the minimum value of current required on any phase to allow the under-
frequency element to operate. Used to prevent underfrequency tripping during
periods of light load, when this action would have an insignificant effect on the
system.
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