Stage Element Frequency Setting (Hz) Time Setting (Sec.)
1 Stage 5(f+t) 50.5 30
2 Stage 6(f+t) 51.0 20
The relatively long time delays are intended to provide time for the system controls to respond and will work well in
a situation wher
e 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.
E00857
Load
Load
T
o utility
Local generation
IPP generation
HV bus
MV bus
Figure 114: Power system segregation based upon frequency measurements
Chapter 11 - Frequency Protection Functions P24xM
228 P24xM-TM-EN-2.1
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