and no output will be given. The restore functionality is only active for lowering frequency
conditions and the restore sequence is disabled if a new negative frequency gradient is detected
during the restore period, defined by the settings
RestoreFreq
and
tRestore
.
10.3.7.3 Blocking
M14970-23 v5
Rate-of-change frequency protection (SAPFRC, 81) can be partially or totally blocked, by binary
input signals or by parameter settings, where:
BLOCK: blocks all outputs
BLKTRIP: blocks the TRIP output
BLKREST: blocks the RESTORE output
If the measured voltage level decreases below the setting of
MinValFreqMeas
in the preprocessing
function, both the PICKUP and the TRIP outputs are blocked.
10.3.7.4 Design
M14970-34 v6
Rate-of-change frequency protection (SAPFRC, 81) measuring element continuously measures the
frequency of the selected voltage and compares it to the setting
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
367.
Section 10 1MRK 502 066-UUS B
Frequency protection
678
Technical manual
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