CHAPTER 6: SETPOINTS S3 PROTECTION
350 FEEDER PROTECTION SYSTEM – INSTRUCTION MANUAL 6–87
Underfrequency (81U)
The relay is equipped with two Underfrequency elements per setpoint group. These
elements can be used for detecting system underfrequency conditions, and be part of an
automatic load shedding scheme. The need for such protection arises if during a system
disturbance, an area becomes electrically isolated 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 frequency will occur and
may lead to a complete collapse. The 350
provides two underfrequency elements, which
can automatically disconnect sufficient load to restore an acceptable balance between
load and generation.
The following path is available using the keypad. For instructions on how to use the
keypad, please refer to Chapter 3 - Working with the Keypad.
PATH: SETPOINTS > S3 PROTECTION > SETPOINT GROUP 1(2) > UNDER-FREQUENCY1(2)
UNDERFREQ 1(2) FUNCTION
Range: Disabled, Alarm, Latched Alarm, Trip
Default: Disabled
For details see Common setpoints
.
UNDERFREQ 1(2) PKP
Range: 40.00 to 70.00 Hz in steps of 0.01 Hz
Default: 59.00 Hz
This setting defines the Underfrequency pickup level, and it is usually set to a frequency
level considered dangerous for the stability of the system.
UNDERFREQ 1(2) DELAY
Range: 0.1 to 600.0 sec in steps of 0.1 sec
Default: 2.0 s
This setting specifies the time delay before underfrequency operation.
MIN VOLTAGE
Range: 0.00 to 1.25 x VT in steps of 0.01
Default: 0.70 x VT
The minimum operating voltage level is programmable to prevent undesired
underfrequency operation before voltage becomes available, such as on faults cleared
by downstream protection or fuses.
OUTPUT RELAY X
For details see Common setpoints
.
BLOCK 1/2/3
For details see Common setpoints
.
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