ABB Relion 670 Series Technical Reference Manual page 570

Section 9
Frequency protection
BLOCK
BLKTRIP
BLKRESET
Voltage
Rate-of-Change
of Frequency
Frequency
ANSI05000835 V1 EN
Figure 286: Schematic design of Rate-of-change frequency protection SAPFRC (81)
564
PUFreqGrad. The frequency signal is filtered to avoid transients due to power system
switchings and faults. The time integrator operates with a definite delay time. When
the frequency has returned back to the setting of RestoreFreq, the RESTORE output is
issued after the time delay tRestore, if the TRIP signal has earlier been issued. The sign
of the setting PUFreqGrad is essential, and controls if the function is used for raising
or lowering frequency conditions. The design of SAPFRC (81) is schematically
described in figure 286.
Comparator
V < IntBlockLevel
Comparator
If
[PickupFreqGrad<0
PICKUP
AND
df/dt < PickupFreqGrad]
OR
[PickupFreqGrad>0
AND
df/dt > PickupFreqGrad]
Then
PICKUP
Comparator
f > RestoreFreq
BLOCK
OR
Time integrator
Definite Time Delay
TimeDlyOperate
TimeDlyReset
TimeDlyRestore
1MRK505222-UUS C
BLKDMAGN
Pickup
&
Trip
Output
Logic
100 ms
RESTORE
en05000835_ansi.vsd
Technical reference manual
PICKUP
TRIP