Underfrequency - GE D90 Plus Instruction Manual

CONTROL ELEMENTS

Underfrequency

358
Indication
Autoreclose Locked Out
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 will be grey and not
operable. The local control status of a device is obtained from the autoreclose control logic.
Figure 297: Autoreclose control enabled display
Once autoreclose control is selected, the message
pushbuttons appear for the autoreclose control options.
Figure 298: Autoreclose control selected display
If tagging has been enabled, a TAG pushbutton will appear on this screen. When the TAG
pushbutton is operated, a small T is displayed 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 will be a reduction in frequency. If the control systems of the
system generators 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.
FlexLogic™ operand
AR LO
AR selected to operate
PLUS
D90 LINE DISTANCE PROTECTION SYSTEM – INSTRUCTION MANUAL
CHAPTER 7: PROTECTION
is displayed and