ABB REG670 - Design

If the measured voltage level decreases below the setting of MinValFreqMeas in the
preprocessing function, both the START and the TRIP outputs are blocked.
10.3.7.4 Design
Rate-of-change frequency protection (SAPFRC) measuring element continuously
measures the frequency of the selected voltage and compares it to the setting
StartFreqGrad. 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 StartFreqGrad is essential, and controls if the function is used
for raising or lowering frequency conditions. The design of SAPFRC is schematically
described in figure
268.
IEC05000835-2-en.vsdx
RESTORE
Voltage
START
START
TRIP
Start
&
Trip
Output
Logic
BLOCK
Frequency
Comparator
If
[StartFreqGrad<0
AND
df/dt < StartFreqGrad]
OR
[StartFreqGrad>0
AND
df/dt > StartFreqGrad]
Then
START
Comparator
MinValFreqMeas
Comparator
f > RestoreFreq
OR
Time integrator
Definite Time Delay
tDelay
tReset
tRestore
BLKDMAGN
Rate-of-Change
of Frequency
BLOCK
BLKTRIP
BLKRESET
IEC05000835 V2 EN
Figure 268: Simplified logic diagram for SAPFRC
Section 10 1MRK502052-UEN B
Frequency protection
556
Technical manual