Underfrequency - GE D90 Plus Instruction Manual

CHAPTER 7: PROTECTION

Underfrequency

PLUS
D90 LINE DISTANCE PROTECTION SYSTEM – INSTRUCTION MANUAL
Autoreclose control is available at the top-level screen by pressing the AR pushbutton. If
local control is not asserted for autoreclose, then the AR pushbutton is grey and
inoperable. The local control status of a device is obtained from the autoreclose control
logic.
Figure 301: Autoreclose control enabled display
Once autoreclose control is selected, the message
pushbuttons appear for the autoreclose control options.
Figure 302: Autoreclose control selected display
If tagging has been enabled, a TAG pushbutton appears on this screen. When the TAG
pushbutton is operated, a small T displays next to the autoreclose indication, and the on
and off operations are inhibited. When a device is tagged, the TAG pushbutton changes to
an UNTAG pushbutton.
There are two identical underfrequency elements.
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 is a reduction in frequency. If the control systems of the system
generators do not respond fast enough, the system can collapse. A reliable method to
quickly restore the balance between load and generation is to disconnect automatically
selected loads, based on the actual system frequency. This technique, called load-
shedding, maintains system integrity and minimizes widespread outages. After the
frequency returns to normal, the load can be automatically or manually restored.
Select the Settings > Protection > Control > Underfrequency menu to open the
underfrequency settings window.
CONTROL ELEMENTS
displays and
AR selected to operate
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