Application Notes; Setting Guidelines - GE MiCOM P40 Agile Technical Manual

Chapter 11 - Frequency Protection Functions
8.4

APPLICATION NOTES

8.4.1

SETTING GUIDELINES

A four stage, single frequency load restoration scheme is shown below. The frequency setting has been chosen
such that there is sufficient separation between the highest load shed frequency and the restoration frequency to
prevent any possible hunting. A restoration frequency setting closer to nominal frequency may be chosen if an
operating frequency of 49.3 Hz is unacceptable.
Stage Restoration Frequency Setting (Hz)
1 49.3 Hz
2 49.3 Hz
3 49.3 Hz
4 49.3 Hz
In this scheme, the time delays ensure that the most critical loads are reconnected (assuming that the higher
stages refer to more important loads). By restoring the load sequentially, system stability should normally be
maintained. These time settings are system dependent; higher or lower settings may be required depending on the
particular application.
It is possible to set up restoration schemes involving multiple frequencies. This allows faster restoration of loads,
but there is the possibility of continuous system operation at frequencies far removed from the nominal. A typical
scheme using two frequencies is illustrated below:
Restore Freq. Restoration Frequency
Stage
Setting (Hz)
1 49.5 Hz
2 49.5 Hz
3 49.0 Hz
4 49.0 Hz
Staggered time settings may be used in this scheme as well, but the time separation among the restoration of
stages will be a function of the frequency recovery pattern. Time coordinated restoration can only be guaranteed
for those stages with a common restoration frequency setting.
234
Restoration Time Delay (secs)
240 sec
180 sec
120 sec
60 sec
Restore DelayRestoration Time Delay
(S)
120 sec
60 sec
120 sec
60 sec
Holding Time Delay (secs)
20 sec
20 sec
20 sec
20 sec
Holding Time Delay (S)
20 sec
20 sec
20 sec
20 sec
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