ABB Relion 670 series - Page 570

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.
en05000835_ansi.vsd
RESTORE
Voltage
PICKUP
PICKUP
TRIP
Pickup
&
Trip
Output
Logic
BLOCK
Frequency
100 ms
Comparator
If
[PickupFreqGrad<0
AND
df/dt < PickupFreqGrad]
OR
[PickupFreqGrad>0
AND
df/dt > PickupFreqGrad]
Then
PICKUP
Comparator
V < IntBlockLevel
Comparator
f > RestoreFreq
OR
Time integrator
Definite Time Delay
TimeDlyOperate
TimeDlyReset
TimeDlyRestore
BLKDMAGN
Rate-of-Change
of Frequency
BLOCK
BLKTRIP
BLKRESET
ANSI05000835 V1 EN
Figure 286: Schematic design of Rate-of-change frequency protection SAPFRC (81)
Section 9 1MRK505222-UUS C
Frequency protection
564
Technical reference manual