Underfrequency (Ansi 81U) - GE G30 Instruction Manual

5.7 CONTROL ELEMENTS
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PATH: SETTINGS CONTROL ELEMENTS
 UNDERFREQUENCY 1
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5
There are six identical underfrequency elements, numbered from 1 through 6.
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 or the isolation of part of
the system from the rest of the system, the effect will be a reduction in frequency. If the control systems of the system gen-
erators do not respond fast enough, the system may collapse. A reliable method to quickly restore the balance between
load and generation is to automatically disconnect selected loads, based on the actual system frequency. This technique,
called "load-shedding", maintains system integrity and minimize widespread outages. After the frequency returns to normal,
the load may be automatically or manually restored.
The
UNDERFREQ 1 SOURCE
live phase voltage available from the selected source. If voltage is not available, the element attempts to use a phase cur-
rent. If neither voltage nor current is available, the element will not operate, as it will not measure a parameter below the
minimum voltage/current setting.
The
UNDERFREQ 1 MIN VOLT/AMP
quency element to operate. This threshold is used to prevent an incorrect operation because there is no signal to measure.
This
UNDERFREQ 1 PICKUP
if the system frequency is 60 Hz and the load shedding is required at 59.5 Hz, the setting will be 59.50 Hz.
5-224
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UNDERFREQUENCY
UNDFREQ 1 FUNCTION:
Disabled
UNDERFREQ 1 BLOCK:
MESSAGE
Off
UNDERFREQ 1 SOURCE:
MESSAGE
SRC 1
UNDERFREQ 1 MIN
MESSAGE
VOLT/AMP: 0.10 pu
UNDERFREQ 1 PICKUP:
MESSAGE
59.50 Hz
UNDERFREQ 1 PICKUP
MESSAGE
DELAY: 2.000 s
UNDERFREQ 1 RESET
MESSAGE
DELAY : 2.000 s
UNDERFREQ 1 TARGET:
MESSAGE
Self-reset
UNDERFREQ 1 EVENTS:
MESSAGE
Disabled
setting is used to select the source for the signal to be measured. The element first checks for a
setting selects the minimum per unit voltage or current level required to allow the underfre-
setting is used to select the level at which the underfrequency element is to pickup. For example,
Figure 5–104: UNDERFREQUENCY SCHEME LOGIC
G30 Generator Protection System

5.7.5 UNDERFREQUENCY (ANSI 81U)

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UNDERFREQUENCY 1(6)
Range: Disabled, Enabled
Range: FlexLogic operand
Range: SRC 1, SRC 2, SRC 3, SRC 4
Range: 0.10 to 1.25 pu in steps of 0.01
Range: 20.00 to 65.00 Hz in steps of 0.01
Range: 0.000 to 65.535 s in steps of 0.001
Range: 0.000 to 65.535 s in steps of 0.001
Range: Self-reset, Latched, Disabled
Range: Disabled, Enabled
5 SETTINGS
GE Multilin