Application Notes; Setting Guidelines; Figure 128: Power System Segregation Based Upon Frequency Measurements - GE MiCOM P40 Agile Technical Manual

P14x
4.3

APPLICATION NOTES

4.3.1

SETTING GUIDELINES

Following changes on the network caused by faults or other operational requirements, it is possible that various
subsystems will be formed within the power network. It is likely that these subsystems will suffer from a
generation/load imbalance. The "islands" where generation exceeds the existing load will be subject to
overfrequency conditions. Severe over frequency conditions may be unacceptable to many industrial loads, since
running speeds of motors will be affected. The overfrequency element can be suitably set to sense this
contingency.
An example of two-stage overfrequency protection is shown below using stages 5 and 6 of the f+t elements.
However, settings for a real system will depend on the maximum frequency that equipment can tolerate for a
given period of time.
Stage
1 Stage 5(f+t)
2 Stage 6(f+t)
The relatively long time delays are intended to provide time for the system controls to respond and will work well in
a situation where the increase of system frequency is slow.
For situations where rapid increase of frequency is expected, the protection scheme above could be supplemented
by rate of change of frequency protection elements.
In the system shown below, the generation in the MV bus is sized according to the loads on that bus, whereas the
generators linked to the HV bus produce energy for export to utility. If the links to the grid are lost, the generation
will cause the system frequency to rise. This rate of rise could be used to isolate the MV bus from the HV system.
Load
E00857

Figure 128: Power system segregation based upon frequency measurements

Note:
This section refers to advanced frequency protection. The basic frequency protection works in a similar manner, but the
setting names and DDB signal names are different.
P14xEd1-TM-EN-1
Element
50.5
51.0
To utility
Load
Chapter 11 - Frequency Protection Functions
Frequency Setting (Hz)
IPP generation
HV bus
Local generation
Time Setting (Sec.)
30
20
MV bus
241