Frequency-Supervised R.o.c.o.f Logic; Application Notes; Frequency-Supervised R.o.c.o.f Example; Figure 116: Frequency-Supervised Rate Of Change Of Frequency Logic (Single Stage) - GE P24DM Technical Manual

Chapter 11 - Frequency Protection Functions
6.2

FREQUENCY-SUPERVISED R.O.C.O.F LOGIC

Frequency
V
determination
df /dt Avg .Cycles
f+df /dt 1 df/dt
Frequency
V
determination
Freq Avg.Cycles
f +df/ dt 1 freq
Stage 1
Enabled
f+df/dt 1 Status
Positive
Both
Negative
Disabled
V<B Status
Enabled
UV Block
Stg1 Block
Adv Freq Inh
Freq Not Found
Freq High
Freq Low
V00853

Figure 116: Frequency-supervised rate of change of frequency logic (single stage)

6.3

APPLICATION NOTES

6.3.1

FREQUENCY-SUPERVISED R.O.C.O.F EXAMPLE

In the load shedding scheme below, we assume that for falling frequency conditions, the system can be stabilised
at frequency f2 by shedding a stage of load. For slow rates of decay, this can be achieved using the
underfrequency protection element set at frequency f1 with a suitable time delay. However, if the generation
deficit is substantial, the frequency will rapidly decrease and it is possible that the time delay imposed by the
underfrequency protection will not allow for frequency stabilisation. In this case, the chance of system recovery
will be enhanced by disconnecting the load stage based on a measurement of rate of change of frequency and
bypassing the time delay.
232
df/dt
-1
X
Frequency
averaging
-1
X
1
1
1 1
1
& 1
&
Note: This diagram does not show all stages . Other stages follow similar principles.
P24xM
Stg 1 df /dt+t Trp
P24xM-TM-EN-2.1